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Hexavalent Chromium
[208
KB PDF]
Related Information: Chemical Sampling -
Chromium (VI) (Hexavalent Chromium)
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Method no.: |
W4001 |
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Control no.: |
T-W4001-FV-02-0104-M |
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Target concentration: |
0.050 µg/100 cm2 |
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Procedure: |
Wipe samples are collected by using firm hand pressure to move a 37-mm
diameter polyvinyl chloride (PVC) filter, 5-µm pore size, across the surface
of interest. An alternate medium for rough surfaces is a 37-mm binderless
quartz fiber filter. Samples are digested with multiple buffered solutions.
After dilution, an aliquot of this solution is analyzed for hexavalent chromium
(Cr(VI)) by ion chromatography with postcolumn derivatization of the Cr(VI)
with 1,5-diphenyl carbazide and detected by a UV-vis detector at 540 nm. |
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Special requirements: |
In chrome plating environments, wipe samples taken on a PVC filter or an
uncoated binderless quartz fiber filter, should be placed in a vial containing
5 mL of an aqueous solution containing 10% Na2CO3 with 2% NaHCO3
immediately after sampling to eliminate the interference from the acid used
in the chrome plating process. An alternate medium which does not require
extraction in the field is a binderless quartz fiber filter coated with 1% NaOH. |
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Reliable quantitation limit: |
3 ng/sample |
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Status of method: |
Evaluated method. This method has been subjected to the established
evaluation procedures of the Methods Development Team. |
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April 2001 |
Mary E. Eide |
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Methods Development Team
Industrial Hygiene Chemistry Division
OSHA Salt Lake Technical Center
Sandy UT 84070-6407
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1. General Discussion
1.1 Background
1.1.1 History
This wipe sampling method was developed to provide a means of taking wipe samples for
hexavalent chromium (Cr(VI)). The OSHA SLTC has received wipe samples taken on a
variety of media, including PVC filters, baby wipes, paper filters such as Whatman filter,
glass fiber filter, and mixed cellulose ester filter. The Cr(VI) decomposed to trivalent
chromium (Cr(III)) on all of these media except the PVC filters. The Evaluation Guidelines
for Surface Sampling Methods(1) specifies the use of fabric wipes, whenever possible. The
cloth-like wipes which were tried, Durx 670 (polyester/cotton nonwoven fabric) and pro-Wipe
880 (polyester woven fabric), did not work because the Cr(VI) reacted with them, changing
it to Cr(III), so they could not be used for this evaluation. Wipe samples were first evaluated
by collection on PVC filters, and analyzed following the analytical procedure in OSHA
Method ID-215.(2) Because PVC filters may tear on rough surfaces, a binderless quartz fiber
filter was also evaluated and found to have good recoveries. In chrome plating processes,
there is an additional interference of the acid, which changes the Cr(VI) to
Cr(III), upon
storage. Both the samples collected on the PVC filters and the binderless quartz fiber filters
had a significant loss in a 15 day storage. This loss was eliminated by placing the samples
taken on either the PVC filters or the binderless quartz fiber filters in a vial containing 5-mL
of an aqueous solution containing 10% sodium carbonate (Na2CO3)/2% sodium bicarbonate
(NaHCO3) immediately after sampling. An alternate medium, which requires no field
extraction, binderless quartz fiber filters coated with 1% NaOH, was also evaluated for
sampling in the chrome plating environment, and found to give good recoveries.
A glass plate was first chosen for an ideal surface to check the surface sampler removal
efficiency, but Cr(VI) interacted with the glass plate changing to Cr(III). The PTFE surface
was chosen as an ideal surface for this method because of its inertness, and it gave good
recoveries for wipe sampling.
Following the procedure in OSHA Method ID-215(3), the filters, of all types, had extraction and
digestion with multiple buffers, separation by ion chromatography, with post-column
derivatization and detection by UV-vis at 540 nm. In this evaluation, the filter is digested
in an aqueous solution containing 10% sodium carbonate (Na2CO3)/2% sodium bicarbonate
(NaHCO3) and the mixture of phosphate buffer/magnesium sulfate. After dilution with DI
water, an aliquot of this solution is analyzed for Cr(VI) using an ion chromatograph equipped
with a UV-vis detector at 540 nm. A post-column derivatization of the Cr(VI) with 1,5-diphenyl carbazide is performed prior to detection. The phosphate buffer and magnesium
sulfate solutions are added to precipitate other metals, especially Fe(II), so that they do not
reduce Cr(VI) changing it to Cr(III). This was shown in the interferences studies in OSHA
Method ID-215(4). The Cr(III) is also precipitated to prevent it from oxidizing to
Cr(VI).
For analysis of samples taken in spray paint operations, it is necessary to perform a second
extraction of the filter with an aqueous solution of 5% NaOH/ 7.5% Na2CO3, with the
addition of the phosphate buffer/magnesium sulfate, to remove the Cr(VI) from the hardened
paint matrix. Again, the phosphate buffer with the magnesium sulfate is added to the
NaOH/Na2CO3 to precipitate the other metals, and prevent them from interacting with the
Cr(VI).
Samples taken in a chrome plating operation have the additional interference of the acid or
acids, which convert the Cr(VI) to Cr(III), as the samples are stored. The chrome plating
bath usually contains sulfuric acid, so a mixture of sulfuric acid and Cr(VI) in water was
prepared to emulate the chrome plating solution. The recovery on Day 15 of storage at
ambient temperature was 78.0% for PVC filters spiked with this mixture of Cr(VI) and H2SO4,
and 81.0% for refrigerated samples. Samples taken of this mixture of Cr(VI) and H2SO4 on
PVC filters, immediately placed into a vial containing a solution of 10% Na2CO3 with 2%
NaHCO3 after sampling, to neutralize the acid, and stored at ambient temperature had a
97.4% recovery on Day 15. Binderless quartz fiber filters had a loss of Cr(VI)when stored,
with an ambient recovery of 86.1% on Day 15. When the binderless quartz fiber filters were
placed immediately into a vial containing a solution of 10% Na2CO3 with 2% NaHCO3 after
sampling, the ambient recovery was 97.9% on Day 15. The method for collecting Cr(VI) air
samples in chrome plating operations used in the UK is with a binderless quartz fiber filter
coated with 1% NaOH.(5) The NaOH coating neutralizes the acid or acids, halting their
reaction with the Cr(VI). The recovery of Cr(VI) from wipe samples spiked with the mixture
of Cr(VI) and H2SO4 using the 1% NaOH coated binderless quartz fiber filters had a recovery
of 96.4% for ambient samples on Day 15. The 1% NaOH coated binderless quartz fiber
filters are digested and analyzed in the same fashion as the PVC filters. These storage
results indicate that for samples taken in chrome plating operations, the uncoated filters
should be placed into a vial containing a solution of 10% Na2CO3 with 2% NaHCO3 after
sampling, or a 1% NaOH coated binderless quartz fiber filter should be used.
1.1.2 Toxic effects (This section is for information only and should not be taken as the basis of
OSHA policy.)
Some of the water soluble salts of chromic acid, (potassium dichromate, potassium
chromate, sodium dichromate, and sodium chromate) are very corrosive and can cause
burns which can facilitate the adsorption of these compounds through the skin.(6) Cr(VI)
causes skin ulcers, blisters, burns, irritation to mucous membranes, and eye irritation.
Workers sensitized to Cr(VI) compounds experience allergic dermatitis reactions. Acute
dermal exposure can result in necrosis of the skin and underlying tissue and sloughing of
the skin.(7) Kidney damage has been reported in workers where skin absorption has
occurred. There have been reports of lung cancer in workers exposed to chrome pigments
in Germany, Norway, and the United States.(8) ACGIH has a TLV of 0.05 mg/m3 for water
soluble Cr(VI) compounds and 0.01 mg/m3 for insoluble Cr(VI) compounds and classify them
as recognized human carcinogens.(9)
ACGIH recommends BEI (Biological Exposure Indices) not exceed 10 µg/g creatinine for
the increase in urinary chromium concentrations during the workshift, obtained by comparing
a urine sample from before the shift to one at the end of the shift, and 30 µg/g creatinine for
the end of the workweek at the end of the shift. The chromium measured in urine is Cr(III),
as Cr(VI) is enzymatically reduced to Cr(III). The preshift urine sample is necessary
because Cr(III) is a nutrient necessary for humans, and it is often included in vitamin
preparations, or is taken as a supplement. Other common sources of chromium are
smoking and water supplies. The BEI is based on the difference between the two urine
samples.(10)
1.1.3 Workplace exposure(11)
Cr(VI) is primarily used in the form of chromium trioxide, and the chromates and
dichromates of sodium, potassium, ammonium, calcium, barium, zinc, strontium, and lead.
These compounds are used in photography, dyeing, electroplating, paints, as rust inhibitors,
as pigments, and as oxidizing agents in tanning.
1.1.4 Physical properties
(12) (
the physical properties listed below are for chromium trioxide, for
physical properties of the other common salts containing Cr(VI) see OSHA Method ID-215
(13))
synonyms: |
chromic acid, chromic anhydride, chromia, chromic trioxide |
CAS number: |
1333-82-0 |
molecular weight: |
100.01 |
IMIS number: |
0686(14) |
melting point: |
196ºC |
structural formula: |
CrO3 |
solubility: |
very sol in water, insol in alcohol |
appearance: |
dark purple-red crystals |
fire and explosion hazard:
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a very powerful oxidizing agent, which can cause violent reactions when
in contact with organic matter or reducing agents |
This method was evaluated according to the OSHA SLTC "Evaluation Guidelines for Surface Sampling
Methods".(15) The Guidelines define analytical parameters, specify required laboratory tests, statistical
calculations and acceptance criteria. The analyte surface concentrations throughout this method are based
on the recommended sampling and analytical parameters.
1.2 Limit defining parameters
1.2.1 Detection limit of the analytical procedure
The DLAP was calculated to be 0.09 ng. This is the lowest amount of analyte that will give
a detector response that is significantly different from the response of a reagent blank.
(Section 4.1)
1.2.2 Detection limit of the overall procedure
The detection limit of the overall procedure for PVC filters is 0.91 ng per sample, binderless
quartz fiber filters is 0.67 ng per sample, and 1% NaOH coated binderless quartz fiber filters
is 0.94 ng per sample. This is the lowest amount of Cr(VI) spiked on the wipe sampler that
will give a detector response that is significantly different from the response of wipe sampler
blanks. (Section 4.2 )
1.2.3 Reliable quantitation limit
The reliable quantitation limit for PVC filters is 3.04 ng per sample, binderless quartz fiber
filters is 2.23 ng per sample, and 1% NaOH coated binderless quartz fiber filters is 3.12 ng
per sample. This is the lowest amount of Cr(VI) spiked on the wipe sampler that will give
a detector response that is considered the lower limit for precise quantitative measurements.
(Section 4.2)
1.2.4 Recovery
The recovery of Cr(VI) from samples spiked on PVC filters used in a 15-day storage test
remained above 96.4% when the samples were stored at 22ºC. (Section 4.3)
The recovery of Cr(VI) from samples spiked on binderless quartz fiber filters used in a 15-day storage test remained above 96.4 % when the samples were stored at 22ºC. (Section
4.3)
The recovery of Cr(VI) from samples spiked with a mixture of H2SO4 and Cr(VI)(to simulate
a chrome plating operation) on PVC filters, then immediately placed into a vial containing
5 mL of an aqueous solution containing 10% Na2CO3 with 2% NaHCO3, used in a 15-day
storage test, remained above 97.9% when the samples were stored at 22°C. (Section 4.3)
The recovery of Cr(VI) from samples spiked with a mixture of H2SO4 and Cr(VI)(to simulate
a chrome plating operation) on binderless quartz fiber filters, then immediately placed into
a vial containing 5 mL of an aqueous solution containing 10% Na2CO3 with 2% NaHCO3,
used in a 15-day storage test, remained above 97.9% when the samples were stored at 22ºC. (Section 4.3)
The recovery of Cr(VI) from samples spiked with a mixture of H2SO4 and Cr(VI)(to simulate
a chrome plating operation) on 1% NaOH coated binderless quartz fiber filters used in a 15-day storage test remained above 96.4% when the samples were stored at 22ºC. (Section
4.3)
1.2.5 Surface sampler removal efficiency
The removal efficiency of filters spiked with Cr(VI) at the target concentration of 0.05
µg/100
cm2 is 96.8% for PVC, 97.7% for binderless quartz fiber filters, and 97.0% for binderless
quartz fiber filters coated with 1% NaOH . This is the percentage of Cr(VI) that was removed
from a sheet of PTFE that was spiked at the target concentration. (Section 4.4)
1.2.6 Sampling reproducibility and analytical reproducibility
Six PTFE surfaces were spiked at the target concentration. A chemist, other than the one
developing the method, conducted sampling on the PTFE surfaces, with the filters, as
described in Section 2. The test was repeated with a second chemist performing the
sampling. The samples were analyzed. For the PVC filters the first chemist was able to
achieve a removal efficiency of 96.0%, and the second chemist was able to achieve a
removal efficiency of 95.1%. (Section 4.6.1) For the binderless quartz fiber filters the first
chemist was able to achieve a removal efficiency of 95.9%, and the second chemist was
able to achieve a removal efficiency of 96.0%. (Section 4.6.3) For the 1% NaOH coated
binderless quartz fiber filters the first chemist was able to achieve a removal efficiency of
96.0%, and the second chemist was able to achieve a removal efficiency of 96.5%. (Section
4.6.5)
Six samples spiked on each of the three kinds of filters at the target concentration by liquid
injection were submitted for analysis by the OSHA Salt Lake Technical Center. The
samples on PVC filters were analyzed according to a draft copy of this procedure after 13
days of storage at 23ºC, with an average analytical result of 97.6% of theoretical (Section
4.6.2). The binderless quartz fiber filters were analyzed after 5 days of storage at
23ºC and
had an average analytical result was 96.5% of theoretical (Section 4.6.4). The 1% NaOH
coated binderless quartz fiber filters were analyzed after 9 days of storage at
23ºC, with an
average analytical result was 95.8% of theoretical (Section 4.6.6).
2. Sampling Procedure
All safety practices that apply to the work area being sampled should be followed. Sampling should be
conducted in such a manner that it will not interfere with work performance or safety. It is important to wear
gloves when handling the 1% NaOH coated binderless quartz fiber filters as the NaOH coating is very
caustic.
2.1 Apparatus
Samples are collected with 37-mm diameter polyvinyl chloride (PVC) filters 5-µm pore size (MSA
part # 625413).
On rough surfaces, samples are collected with 37-mm diameter binderless quartz fiber filters 0.45-mm thick (SKC part # 225-1809).
In chrome plating operations only, samples can be collected with 37-mm diameter 1% NaOH coated
binderless quartz fiber filters 0.45-mm thick. (Section 4.9)
The selected gloves are to be resistant to penetration of the chemical being sampled and any other
chemicals expected to be present. One pair of gloves per sample taken should be used to avoid
cross contamination of samples.
Labeled vials, 20-mL glass scintillation vials or other appropriate sized glass vial with PTFE lined
caps, one for each sample.
For samples taken in a chrome plating operation, 5 mL of an aqueous solution containing 10%
Na2CO3 with 2% NaHCO3 should be preloaded in the vials, if PVC or uncoated binderless quartz fiber
filters are used for sampling.
2.2 Reagents
For samples taken in a chrome plating operation, 5 mL of an aqueous solution containing 10%
Na2CO3 with 2% NaHCO3 should be preloaded in the vials. (Section 3.2.15)
2.3 Technique
Prepare a sufficient number of vials, each labeled with a unique number, for the projected sampling
needs.
Prepare a diagram of the area or rooms to be wipe sampled along with the locations of key surfaces.
Wear a new pair of clean gloves for each sample to prevent contamination of future samples as well
as oneself. The selected gloves are to be resistant to penetration of the chemical being sampled and
any other chemicals expected to be present. PVC gloves are suggested for sampling Cr(VI) based
on a review of a glove manufacturer's chemical resistivity and degradation information. Do not wear
powdered gloves.
Record the sample vial number and the location where the sample is taken.
Remove the filter from the carrying container with clean PTFE-coated tweezers or plastic tweezers.
Do not use metal tweezers to handle the filters as they will deposit Cr(VI) onto filters.
Depending on the purpose of the sample, it may be useful to determine the surface loading of the
contamination (e.g., in micrograms of analyte per area). For these samples, it is necessary to record
the area of the surface wiped (e.g., 100 cm2). This would not be necessary for samples taken to
simply show the presence of the contaminant.
Surfaces should not be wetted with water as the water will allow any metal interferences to interact
with the Cr(VI), thereby affecting the results.
Firm pressure should be applied when wiping. Start at the outside edge and progress toward the
center making concentric squares of decreasing size. Fold the filter with the contaminant side inward
and repeat.
Without allowing the filter to come into contact with any other surface, fold the filter with the exposed
side inward. Place the filter in a sample vial, cap and place a corresponding number at the sample
location on the diagram. Include notes with the sketch giving any further description that may prove
useful when evaluating the sample results (e.g., a description of the surface sampled, such as :
pencil, doorknob, safety glasses, lunch table, inside respirator, employee names, etc.).
PVC and binderless quartz fiber filter samples taken in a chrome plating operation should be placed
in a vial containing 5 mL of an aqueous solution containing 10% Na2CO3 with 2% NaHCO3 to stabilize
the Cr(VI) to field extract them. An alternate media only for chrome plating operations is a binderless
quartz fiber filter coated with 1% NaOH. The 1% NaOH coated binderless quartz fiber filters do not
require field extraction. Gloves must be worn when handling these NaOH coated filters as the NaOH
is very caustic.
Submit at least one blank wipe filter, treated in the same fashion, but without wiping.
Record sample location, employees names, surface area (if pertinent), work description, type of
operation, personal protective equipment, and any other necessary information, along with any
potential interferences on the OSHA-91A form.
Submit the samples to the OSHA Salt Lake Technical Center together with OSHA-91A forms as soon
as possible after sampling. Ship any bulk samples separate from the surface samples.
2.4 Extraction efficiency
It is the responsibility of each analytical laboratory to determine the extraction efficiency because the
wipe sampling media, reagents, and laboratory techniques may be different than those listed in this
evaluation and could influence the results (Section 4.5).
The mean extraction efficiency for Cr(VI) from PVC filters over the range of 0.06 to 10 times the target
concentration (3 to 500 nanograms per sample) was 96.6% for samples extracted with the first
extraction buffer (10% Na2CO3 with 2% NaHCO3) and 96.9% for samples extracted with the second
extraction buffer (5% NaOH with 7.5% Na2CO3), used for spray paint samples only.
The mean extraction efficiency for Cr(VI) from binderless quartz fiber filters over the range of 0.06 to
10 times the target concentration (3 to 500 nanograms per sample) was 97.3% for samples extracted
with the first extraction buffer (10% Na2CO3 with 2% NaHCO3) and 96.2% for samples extracted with
the second extraction buffer (5% NaOH with 7.5% Na2CO3), used for spray paint samples only.
The mean extraction efficiency for Cr(VI) from 1% NaOH coated binderless quartz fiber filters over the
range of 0.06 to 10 times the target concentration (3 to 500 nanograms per sample) was 97.3% for
samples extracted with the first extraction buffer (10% Na2CO3 with 2% NaHCO3) and 96.9% for
samples extracted with the second extraction buffer (5% NaOH with 7.5% Na2CO3), used for spray
paint samples only.
2.5 Interferences, sampling
Suspected interferences should be reported to the laboratory with submitted samples. The
interference studies were performed in OSHA Method ID-215 Cr(VI)(16).
Cr(III) is the major positive
interference and Fe(II) is the major negative interference. In chrome plating operations, the acid is
also a negative interference.
3. Analytical Procedure
Adhere to the rules set down in your Chemical Hygiene Plan
(17).
Avoid skin contact and inhalation of
all chemicals and review all appropriate MSDSs before beginning the analysis of samples.
Analyze the samples using the analytical procedure in OSHA Method ID-215 Hexavalent Chromium.
(18)
3.1 Apparatus
3.1.1 Ion chromatograph with a UV-vis detector and a postcolumn pump. A Dionex
4500i ion
chromatograph with a UV-vis detector, a pneumatic controlled postcolumn reagent delivery
system, and a reaction coil were used in this evaluation.
3.1.2 IC column and guard column which can separate Cr(VI) from any potential interferences.
A 250-mm × 4-mm i.d. Dionex IonPac AS7 column and 50-mm × 4-mm i.d. Dionex IonPac
NG1 guard column were used in this evaluation.
3.1.3 A means to integrate the chromatograms. The Dionex AI450 software, and a Millennium32
data system were used in this evaluation.
3.1.4 Automatic sampler. A Dionex model ASM-2, and sample vials, 0.5-mL, with filter caps
was used in this evaluation.
3.1.5 Volumetric flasks, pipets, and calibrated micropipets.
3.1.6 Erlenmeyer flasks, 50-mL, for sample digestion.
3.1.7 Micro-analytical balance capable of weighing at least 0.01 mg.
3.1.8 Polyethylene bottles, 1-L size or larger, for extraction solutions.
3.1.9 Scintillation vials, glass, 20-mL.
3.1.10 Hotplate temperature adjustable to 135ºC placed in an exhaust hood.
3.1.11 Equipment for eluent degassing. A vacuum pump and ultrasonic bath were used for this
evaluation.
3.1.12 Optional: Centrifuge for spinning down the precipitate in samples.
3.2 Reagents
3.2.1 Deionized water 18 Mohm. A Millipore Milli-Q system was used to prepare the water for this
evaluation.
3.2.2 Sodium carbonate (NaCO3), reagent grade. Mallinckrodt 99+% lot 7527 KHKC was used
in this evaluation.
3.2.3 Sodium bicarbonate (NaHCO3), reagent grade. Baker Analyzed Reagent 99.9% pure lot
D12721 was used in this evaluation.
3.2.4 Potassium dichromate (K2Cr2O7), reagent grade. JT Baker Reagent grade 99% lot 715426
and Acros lot A010583303 were used in this evaluation.
3.2.5 Magnesium sulfate (MgSO4), anhydrous, reagent grade. ChemPure Reagent grade 99% lot
M172KDHM was used in this evaluation.
3.2.6 Ammonium sulfate [(NH4)2SO4], reagent grade. Aldrich 99+% lot OO427TQ was used in this
evaluation.
3.2.7 Ammonium hydroxide (NH4OH) 29% solution. Baker analyzed Reagent 28.9% NH4OH lot
611248 was used in this evaluation.
3.2.8 1,5-Diphenylcarbazide (DPC) (C6H5NHNHCONHNHC6H5), reagent grade. Aldrich 99+% lot
03017AR was used in this evaluation.
3.2.9 Methyl alcohol (CH3OH), HPLC grade. Fisher Optima 99.9% lot 966306 was used in this
evaluation.
3.2.10 Sulfuric acid (H2SO4), concentrated. JT Baker Instra-analyzed 96.8% lot E24049 was used
in this evaluation.
3.2.11 Nitric acid (HNO3), concentrated (69-70%). JT Baker Instra-analyzed 69.0-70.0% lot N46048
was used in this evaluation.
3.2.12 Potassium hydrogenphosphate trihydrate (K2HPO4·3H2O), reagent grade. Aldrich 99+% lot
01525MN was used in this evaluation.
3.2.13 Potassium dihydrogenphosphate (KH2PO4), reagent grade. Aldrich 99+% lot 06327KQ was
used in this evaluation.
3.2.14 Nitric acid solution (10%): In a 1-L flask place about 500-mL deionized water, add 100 mL
concentrated nitric acid, then fill up to the mark with deionized water.
3.2.15 Buffer/extraction (BE) solution (2% NaHCO3 with 10% Na2CO3): In a 1-L flask place about
500-mL deionized water, add 20 g of NaHCO3, swirl to dissolve, then add 100 g of Na2CO3,
and bring up to the mark with deionized water. Shake to dissolve or use an ultrasonic bath.
Store in a polyethylene bottle.
3.2.16 Spray-paint extraction (SPE) solution (5% NaOH with 7.5% Na2CO3): In a 1-L flask place
about 500-mL deionized water, add 50 g of NaOH, swirl to dissolve, then add 75 g of
Na2CO3, and bring up to the mark with deionized water. Prepare the solution monthly, and
store in a polyethylene bottle.
3.2.17 Magnesium sulfate solution: In a 100-mL volumetric flask place about 50 mL deionized
water, add 9.9 g of anhydrous magnesium sulfate, mix well, and bring up to the mark with
deionized water.
3.2.18 Phosphate buffer solution (0.5 M KH2PO4 with 0.5 M K2HPO43H2O): In a 1-L flask place
about 500-mL deionized water, add 68 g of KH2PO4 and 114 g of K2HPO43H2O, swirl to
dissolve and bring up to the mark with deionized water.
3.2.19 Phosphate buffer/Mg(II) (PBM) solution: In a 100-mL beaker place 50 mL of phosphate
buffer, then add 25 mL of magnesium sulfate solution, and mix well. Prepare fresh before
each analysis, as this solution is only good for 4 hours.
3.2.20 Dilute Buffer Extraction/Phosphate buffer/Mg(II) solution (DBE/PBM solution): In a 100-mL
volumetric flask pipette 50 mL of BE solution, add 15 mL of PBM solution, bring up to the
mark with deionized water, and mix. A precipitate of magnesium hydroxide will form and
slowly precipitate out of solution. Allow the precipitation to settle for at least 60 minutes,
or place in a centrifuge at 3,200 rpm for 5-10 min. Transfer the "clear" solution to a beaker
for use in preparation of working standards. Try to avoid transfering any precipitate as it will
clog the IC.
3.2.21 Eluent [250 mM (NH4)2SO4 with 100 mM NH4OH]: In a 1-L flask place about 500 mL of
deionized water, add 6.5 mL of the 29% ammonium hydroxide, then add 33 g of ammonium
sulfate and mix well. Dilute up to the mark with deionized water. Degas the eluent before
use. In this evaluation, the eluent was degassed with vacuum while in a ultrasonic bath.
Transfer solution to the eluent container on the IC.
3.2.22 Postcolumn derivatization reagent (2.0 mM DPC in 90:10 1 N H2SO4:methyl alcohol): In a
100-mL volumetric flask place 0.5 g of DPC fill to the mark with methyl alcohol and mix well.
In a 1-L volumetric flask place about 500 mL deionized water, add 28 mL concentrated
sulfuric acid, mix well, and allow to cool to room temperature. When the sulfuric acid
solution is at room temperature, add the DPC/methanol solution, bring up to the mark with
deionized water, mix well, and allow to cool to room temperature before placing in the
postcolumn reservoir. This solution must be at room temperature for the complete reaction
between DPC and Cr(VI). This solution is stable for 3 days. For the most sensitivity, this
solution must be freshly prepared and be at room temperature.
3.3 Standard preparation
3.3.1 Wash all glassware in hot water with detergent, rinse with tap water, followed by deionized
water, 10% nitric acid solution, and finally with two rinses of deionized water. Under no
circumstance should chromic acid cleaning be used. It is best if glassware used for
the analysis of Cr(VI) is reserved for this analysis only, so that the maximum sensitivity, and
lack of outside interference can be obtained.
3.3.2 The stock standard solutions of 100 µg/mL Cr(VI) are prepared by dissolving 0.2828 g of
K2Cr2O7 or 0.3735 g of K2CrO4 in 1 L of deionized water. (Prepare solution every 3 months.)
Two separate stock solutions should be prepared, from separate sources, and used to make
the dilutions. All dilutions of the stock solutions are made with DBE/PBM solution to obtain
a working range of 0.3 to 500 ng/mL. Prepare dilutions monthly. (For example the stock
calculation is: (0.2828 g K2Cr2O7/liter) × (1000 mg/g) × (1000 g/mg) × (L/1000mL) × (MW
Cr/MW K2Cr2O7 = 51.996/294.18) × (2 moles of Cr in K2Cr2O7) = 100 g/mL Cr(VI).)
3.3.3 Bracket sample concentrations with standard concentrations. If upon analysis, sample
concentrations fall outside the range of prepared standards, prepare and analyze additional
standards to confirm instrument response, or dilute high samples with DBE/PBM solution
and reanalyze the diluted samples.
3.4 Sample preparation
3.4.1 Wash all glassware in hot water with detergent, rinse with tap water, deionized water, 10%
nitric acid solution, and finally with two rinses of deionized water. Under no circumstances
should chromic acid cleaning be used. If possible, this glassware should be reserved
for the analysis of Cr(VI) only.
3.4.2 Adjust the hotplate temperature to below the boiling point of the BE solution, near 135°C.
3.4.3 Remove the filter from the vial and place face or interior of the folds side down in a labeled
50-mL Erlenmeyer flask. Add 1.5 mL of PBM solution, swirl to wet the filter, then add 5 mL
of BE solution and mix well before proceeding to the next sample. It is important to add the
PBM solution first, as the freshly precipitated magnesium hydroxide that forms upon the
addition of the BE solution, suppresses interference from the other metal ions. This
precipitation happens immediately on mixing, so it is important that all sides of the filter be
wetted. Heat the samples on the hotplate for 60 to 90 minutes, watching carefully to prevent
the samples from boiling or evaporating to dryness. If the samples boil or evaporate to
dryness the Cr(VI) will change to Cr(III) affecting the results.
3.4.4 Allow the samples to cool to room temperature. Quantitatively transfer each solution to a
10-mL volumetric flask using deionized water, and bring up to the mark with deionized water.
Allow the samples to sit for 1 hour to allow the precipitate to settle, or centrifuge at 3200
rpm for 5 to 10 minutes. Carefully transfer the supernatant to the autosampler vial, and
make sure that none of the precipitate is transferred. The precipitate will clog the IC.
3.4.5 For wipe samples of paints, a second extraction of the filter, with a stronger base solution,
will be necessary to get the Cr(VI) out of the solidified paint. The two extractions are
prepared separately, and analyzed separately. The analytical results of this second
extraction are added to the first extraction to obtain the final result. Again add 1.5 mL of
PBM solution to the Erlenmeyer flask, followed by the SPE solution, mix well and heat on
the hotplate 60 to 90 minutes. Cool to room temperature, then quantitatively transfer the
sample to a 25-mL volumetric flask with deionized water, and bring up to the mark with
deionized water. Allow the samples to sit 1 hour to allow the precipitate to settle, or
centrifuge at 3200 rpm for 5 to 10 minutes. Carefully transfer the supernatant to an
autosampler vial.
3.5 Analysis
3.5.1 Analytical conditions
IC conditions |
|
columns: |
IonPac AS7 column, 250-mm × 4-mm i.d. and IonPac NG-1
guard column 50-mm × 4-mm i.d. at ambient temperature |
flow rate: |
0.7 mL/min |
eluent: |
250 mM (NH4)2SO4 with 100 mM NH4OH |
pump pressure: |
1000 psi |
postcolumn derivatization |
|
solution: |
0.34 mL/min of 2.0 mM DPC in 90:10 of 1 N H2SO4:methyl
alcohol |
UV detector: |
540 nm |
injection size: |
100 µl |
retention time: |
6.6 min |
output range: |
0.1 absorbance unit full scale (AUFS) |
chromatogram: |
|
Figure 3.5.1. Chromatogram of an analytical standard of 50 ng/mL Cr(VI).(1 and 2= solvent peaks, 3=carbon
dioxide from reaction of buffer and derivatizing solution, 4= Cr(VI))a
|
3.5.2 An external standard (ESTD) calibration procedure is used to prepare a calibration curve
using at least 2 stock standards, from separate sources, from which dilutions are made.
The calibration curve is prepared daily. The samples are bracketed with analytical
standards.
Figure 3.5.2. Calibration curve of Cr(VI). (Y = 96.7X + 582)
|
3.6 Interferences (analytical)
3.6.1 Any compound that produces a UV response and has a similar retention time as Cr(VI) is
a potential interference. If any potential interferences are reported, they should be
considered before samples are extracted. Generally, chromatographic conditions can be
altered to separate an interference from the analyte.
3.6.2 When necessary, the identity of an analyte peak may be confirmed with additional analytical
data. The possibility of a coeluting species which does not react with the DPC, can be
tested by injecting the sample with no postcolumn derivatizing agent being added.
3.6.3 The acid used in chrome plating operations is an interference.
3.7 Calculations
The amount of Cr(VI) per sampler is obtained from the appropriate calibration curve in terms of
nanograms per sample, uncorrected for extraction efficiency. This amount is then adjusted by subtracting the amount (if any)
found on the blank and corrected for extraction efficiency using the following formula. If samples were paint samples the results second
extraction of the filter was are also calculated with the following formula, then both results are added together.
|
where |
Ms is the mass recovered from the sampled surface (µg) |
|
M is nanograms per sample |
|
MB is the mass found on the blank (ng) |
|
EE is extraction efficiency, in decimal form |
|
CF is conversion factor of µg/1000 ng |
This amount may be expressed as µg Cr(VI) per 100 cm2 if the surface area that was sampled
was provided, by using the following formula.
|
where |
Cs is (µg) of Cr(VI) per 100 cm2 |
|
Ms is mass on the sampled surface
(µg) |
|
S is surface area sampled (cm2) |
|
100 cm2 is one hundred cubic centimeters |
The surface that was sampled may be less ideal (more porous, less smooth) than the surface that was used to evaluate the removal efficiency of the sampling media. In this circumstance, the media will remove the surface contaminant less effectively. There may be significant amounts of
contaminant remaining on the surface after sampling. Nevertheless, the amount found in the sample indicates that at least this amount of
Cr(VI) was present on the surface.
4. Backup Data
General background information about the determination of detection limits and reproducibility of the overall
procedure is found in the "Evaluation Guidelines for Surface Sampling
Methods".(19) The Guidelines
define analytical parameters, specific laboratory tests, statistical calculations and acceptance criteria.
4.1 Detection limit of the analytical procedure (DLAP)
The DLAP was calculated to be 90 picograms per injection. This is the lowest amount of analyte that will give a detector response that is
significantly different from the response of a reagent blank. The standards were prepared in equally descending amounts of 100 picograms from 1000 to 0
picograms, such that the lowest standard had a peak at least ten times the baseline noise.
Table 4.1
1500 Detection Limit of the Analytical Procedure |
|
Mass Injected (pg) |
area counts (µV-s) |
|
0 |
0 |
100 |
215 |
200 |
386 |
300 |
509 |
400 |
629 |
500 |
728 |
600 |
831 |
700 |
960 |
800 |
1169 |
900 |
1295 |
1000 |
1428 |
|
Figure 4.1. Plot of the data used to determine the DLAP (Y = 1.36X + 63).
|
4.2 Detection limit of the overall procedure (DLOP) and reliable quantitation limit
(RQL)
PVC filters
The DLOP is measured as mass per sample. Ten PVC filters were spiked with equal descending increments of
analyte, such that the highest sampler loading was 10 ng/sample. These spiked samplers, and a sample blank
were analyzed with the recommended analytical parameters, and the data obtained used to calculate the
required parameters (standard error of estimate and the slope) for the calculation of the
DLOP. Values of 131.6 and 40.0 were obtained for the slope and standard error
of estimate respectively. The DLOP was calculated to be 0.911 ng/sample.
Table 4.2.1 Detection Limit
of the Overall Procedure |
|
mass per sample (ng) |
area counts
(µV-s) |
|
0 |
0 |
1 |
209 |
2 |
379 |
3 |
498 |
4 |
615 |
5 |
710 |
6 |
806 |
7 |
938 |
8 |
1140 |
9 |
1256 |
10 |
1386 |
|
The RQL is considered the lower limit for precise quantitative measurements. It is determined from the
regression line parameters obtained for the calculation of the DLOP, providing 75% to 125% of the analyte is recovered. The RQL is
3.04 ng per sample. Recovery at this concentration is 95.1%.
Figure 4.2.1. Plot of dat to determine the DLOP/RQL for PVC filters.
(Y = 132X + 63.7)
Figure 4.2.2. Plot of the RQL. (The large peaks that are off scale are
carbon dioxide from the reaction of the buffer with derivatizing solution. 1
= Cr(VI))
|
Binderless quartz fiber filters
The DLOP for the binderless quartz fiber filters was determined by spiking ten samplers with equal descending increments of
analyte, such that the highest sampler loading was 10 ng/sample. These spiked samplers, and a sample blank were analyzed with the recommended analytical parameters, and the data obtained used to calculate the required parameters (standard error of estimate and the slope) for the calculation of the
DLOP. Values of 137.2 and 56.0 were obtained for the slope and standard error of estimate respectively. The DLOP was calculated to be 0.67
ng/sample.
The RQL is considered the lower limit for precise quantitative measurements. It is determined from the regression line parameters obtained for the calculation of the
DLOP, providing 75% to 125% of the analyte is recovered. The RQL is 2.23 ng per sample. Recovery at this concentration is 94.6%.
Table 4.2.2 Detection Limit of the Overall Procedure
Binderless Quartz Fiber Filter |
|
mass per sample (ng) |
area counts (µV-s) |
|
0 |
0 |
1 |
201 |
2 |
376 |
3 |
491 |
4 |
602 |
5 |
712 |
6 |
813 |
7 |
943 |
8 |
1144 |
9 |
1255 |
10 |
1399 |
|
Figure 4.2.3. Plot of the data used to determine the DLOP/RQL for
binderless quartz fiber filters (Y = 137X + 56).
|
1% NaOH Coated Blinderless Quartz Fiber Filters
The DLOP for the 1% NaOH coated binderless quartz fiber filters was determined by spiking ten samplers with equal descending increments of
analyte, such that the highest sampler loading was 10 ng/sample. These spiked samplers, and a sample blank were analyzed with the recommended analytical parameters, and the data obtained used to calculate the required parameters (standard error of estimate and the slope) for the calculation of the
DLOP. Values of 138 and 87.1 were obtained for the slope and standard error of estimate respectively. The DLOP was calculated to be 0.937
ng/sample.
The RQL is considered the lower limit for precise quantitative measurements. It is determined from the regression line parameters obtained for the calculation of the
DLOP, providing 75% to 125% of the analyte is recovered. The RQL is 3.12 ng per sample. Recovery at this concentration is 96.8%.
Table 4.2.3 Detection Limit of the Overall
Procedure
1% NaOH coated Binderless Quartz Fiber Filter |
|
mass per sample
(ng) |
area counts
(µV-s) |
|
0 |
0 |
1 |
245 |
2 |
408 |
3 |
534 |
4 |
667 |
5 |
786 |
6 |
897 |
7 |
1011 |
8 |
1234 |
9 |
1324 |
10 |
1439 |
|
Figure 4.2.4. Plot of the data used to determine the DLOP/RQL for 1% NaOH coated
binderless quartz fiber filters (Y = 138X + 87.1).
|
4.3 Storage tests
Cr(VI) spiked on PVC filters
Storage samples were prepared by spiking PVC filters with Cr(VI). The PVC filter was spiked with
the target concentration of Cr(VI) and allowed to dry. Twenty-one storage samples were prepared. Three samples were analyzed on the day of
preparation. Nine of the filters were stored at reduced temperature (4ºC) and the other nine were stored in a closed drawer at ambient
temperature (about 22ºC). At 5-day intervals, three samples were selected from each of the two storage sets and analyzed. Sample results
were not corrected for extraction efficiency. The recoveries at Day 15 were 96.4% at ambient and refrigerated temperature.
Table 4.3.1 Storage Test for Cr(VI) on PVC Filters |
|
time (days) |
ambient storage recovery (%) |
refrigerated storage recovery (%) |
|
0 |
98.0 |
97.8 |
97.2 |
98.0 |
97.8 |
97.2 |
5 |
96.9 |
95.9 |
96.0 |
96.7 |
97.4 |
95.6 |
10 |
95.8 |
96.9 |
96.7 |
97.1 |
98.8 |
95.1 |
15 |
97.8 |
97.6 |
94.5 |
95.2 |
96.4 |
97.3 |
|
Figure 4.3.1. Ambient storage test for Cr(VI) spiked on PVC filters.
Figure 4.3.2. Refrigerated storage test for Cr(VI) spiked on PVC filters.
|
Cr(VI) spiked on binderless quartz fiber filters.
Storage samples were prepared by spiking binderless quartz fiber filters with
Cr(VI). The binderless quartz fiber filter was spiked with the target concentration of
Cr(VI) and allowed to dry. Twenty-one storage samples were prepared. Three samples were analyzed on the day of preparation.
Nine of the filters were stored at reduced temperature (4ºC) and the other nine were stored in a closed drawer at ambient temperature
(about 22ºC). At 5-day intervals, three samples were selected from each of the two storage sets and analyzed. Sample results were not
corrected for extraction efficiency. The recoveries at Day 15 were 96.4% at ambient temperature and 96.2% at refrigerated temperature.
Table 4.3.2 Storage Test for Cr(VI) on Binderless Quartz Fiber Filters |
|
time (days) |
ambient storage recovery (%) |
refrigerated storage recovery (%) |
|
0 |
98.2 |
98.1 |
97.1 |
98.2 |
97.1 |
98.3 |
5 |
97.9 |
96.1 |
96.7 |
97.1 |
97.9 |
96.7 |
10 |
96.1 |
96.6 |
97.2 |
97.3 |
98.2 |
96.1 |
15 |
97.3 |
97.2 |
95.1 |
96.1 |
96.3 |
95.3 |
|
Figure 4.3.3. Ambient storage test for Cr(VI) spiked on binderless quartz
fiber filters.
Figure 4.3.4. Refrigerated storage test for Cr(VI) spiked on binderless quartz
fiber filters.
|
Cr(VI) and H2SO4 spiked on PVC filters
In chrome plating environments the presence of acid causes a negative interference due to reaction between the
Cr(VI) and acid to form Cr(III). Most chrome plating baths contain H2S04
so a mixture of H2S04 and
Cr(VI) was prepared in water to spike the filters with. Storage samples were prepared by spiking PVC filters with
Cr(VI) and H2S04. The PVC filter was spiked with 50 ng of
Cr(VI) and 0.5 ng H2SO4 and allowed to dry. Twenty-one storage samples were prepared. Three samples were analyzed on
the day of preparation. Nine of the filters were stored at reduced temperature (4ºC) and the other nine were stored in a closed drawer at
ambient temperature (about 22ºC). At 5-day intervals, three samples were selected from each of the two storage sets and analyzed. There
was an immediate reaction between the
Cr(VI) and the sulfuric acid, causing some of the Cr(VI) to change to Cr(III). Results were corrected for this bias.
The results show a recovery of 78.0% on day 15 for samples stored at ambient temperature, and 81.0% for
refrigerated samples.
Table 4.3.3 Storage Test for Cr(VI) and H2S04 on PVC Filters |
|
time (days) |
refrigerated storage recovery
(%) |
refrigerated storage recovery
(%) |
|
0 |
100.5 |
98.8 |
100.7 |
100.5 |
98.8 |
100.7 |
5 |
91.1 |
91.5 |
93.6 |
90.0 |
90.9 |
91.7 |
10 |
85.8 |
83.9 |
84.7 |
84.1 |
86.8 |
85.1 |
15 |
74.5 |
79.4 |
79.5 |
79.3 |
83.5 |
82.9 |
|
Figure 4.3.5. Ambient storage test for Cr(VI) and H2SO4
spiked on PVC filters.
Figure 4.3.6. Refrigerated storage test for Cr(VI) and H2SO4
spiked on PVC filters.
|
Cr(VI) and H2S04
spiked on PVC filters placed immediately in 5 mL of an aqueous solution containing 10%
Na2CO3 with 2% NaHCO3
The "Evaluation Guidelines for Surface Sampling Methods" states that a drop in recovery of greater than 10% upon storage for 15 days is a significant uncorrectable bias, and should be avoided.(20) The recoveries for the PVC filters spiked with
Cr(VI) and H2S04
on day 15 were 78.0% for ambient and 81.0% for refrigerated samples. To eliminate this negative bias from the H2S04, the PVC filters were spiked with
Cr(VI) and H2S04
and then placed into a vial containing 5 mL of an aquerous solution containing 10%
Na2CO3 with 2% NaHCO3
(BE buffer) immediately. The PVC filter was spiked with 50 ng of
Cr(VI) and 0.5 ng H2S04. Twenty-one storage samples were prepared.
Three samples were analyzed on the day of preparation. Nine of the filters were stored at reduced temperature (4ºC) and the other nine were stored in a closed drawer at ambient temperature (about 22ºC). At 5-day intervals, three samples were selected from each of the two storage sets and analyzed. There was an immediate reaction between the
Cr(VI) and the sulfuric acid, causing some of the Cr(VI) to change to Cr(III). Results were corrected for this bias.
The recoveries on day 15 were 97.4% for ambient, and 98.0% for refrigerated.
Table 4.3.4 Storage Test for Cr(VI) and
H2SO4
on PVC Filters and Placed in BE Buffer |
|
time (days) |
ambient storage recovery (%) |
refrigerated storage recovery (%) |
|
0 |
100.7 |
97.9 |
101.5 |
100.7 |
97.9 |
101.5 |
5 |
99.6 |
96.9 |
98.9 |
99.2 |
98.9 |
99.1 |
10 |
98.4 |
97.6 |
97.9 |
97.9 |
98.4 |
99.0 |
15 |
98.9 |
95.6 |
98.3 |
98.5 |
98.9 |
96.9 |
|
Figure 4.3.7. Ambient storage test for Cr(VI) and H2SO4
spiked on PVC filters and stored in 5 mL BE buffer.
Figure 4.3.8. Refrigerated storage test for Cr(VI) and H2SO4
spiked on PVC filters and stored in 5 mL BE buffer.
|
Cr(VI) and H2S04
spiked on binderless quartz fiber filters
Binderless quartz fiber filters were spiked with a mixture of H2S04
and Cr(VI) in water at concentration of 50 ng
Cr(VI) and 0.5 ng H2S04
and allowed to dry. Twenty-one storage samples were prepared. Three samples were analyzed on the day of preparation. Nine of the filters were stored at reduced temperature (4ºC) and the other nine were stored in a closed drawer at ambient temperature (about 22ºC). At 5-day intervals, three samples were selected from each of the two storage sets and analyzed. There was an immediate reaction between the
Cr(VI) and the sulfuric acid, causing some of the Cr(VI) to change to Cr(Ill). Results were corrected for this bias.
The results show a recovery of 86.1 % on day 15 for samples stored at ambient temperature, and 88.7% for refrigerated samples.
Table 4.3.5 Storage Test for Cr(VI) and H2S04
on Binderless Quartz Fiber Filters |
|
time (days) |
ambient storage recovery (%) |
refrigerated storage recovery (%) |
|
|
|
|
0 |
100.9 |
99.3 |
99.8 |
100.9 |
99.3 |
99.8 |
5 |
94.8 |
93.0 |
95.1 |
96.4 |
93.2 |
95.4 |
10 |
90.1 |
91.2 |
89.9 |
93.7 |
92.2 |
93.4 |
15 |
85.4 |
86.8 |
86.1 |
87.9 |
89.2 |
87.3 |
|
Figure 4.3.9. Ambient storage test for Cr(VI) and H2SO4
spiked on binderless quartz fiber filters.
Figure 4.3.10. Refrigerated storage test for Cr(VI) and H2SO4
spiked on binderless quartz fiber filters.
|
Cr(VI) and H2S04
spiked on binderless quartz fiber filter placed immediately in 5 mL of a solution containing 10%
Na2CO3 with 2% NaHCO3
Because the recoveries for the binderless quartz fiber filters spiked with the mixture of
Cr(VI) and H2S04
was 86.1 % on day 15 for samples stored at ambient temperature, and 88.7% for refrigerated samples, placing the filters into 5
mL of an aqueous solution containing 10% Na2CO3 with 2% NaHCO3
(BE buffer) immediately after spiking was performed. The binderless quartz fiber filter was spiked with
50 ng of
Cr(VI) and 0.5 ng H2S04. Twenty-one storage samples were prepared. Three samples were analyzed on the day of preparation. Nine of the filters were stored at reduced temperature (4ºC) and the other nine were stored in a closed drawer at ambient temperature (about 22ºC). At 5-day intervals, three samples were selected from each of the two storage sets and analyzed. There was an immediate reaction between the
Cr(VI) and the sulfuric acid, causing some of the Cr(VI) to change to
Cr(Ill). Results were corrected for this bias. The recoveries on day 15 were 97.9% for ambient and 98.4% for refrigerated
samples.
Table 4.3.6 Storage Test for Cr(VI) and H2S04
on Binderless Quartz Fiber Filters and Placed in BE Buffer |
|
time (days) |
ambient storage recovery (%) |
refrigerated storage recovery (%) |
|
0 |
100.8 |
99.9 |
99.3 |
100.8 |
99.9 |
99.3 |
5 |
96.9 |
97.9 |
98.9 |
98.8 |
97.9 |
99.3 |
10 |
98.4 |
98.5 |
97.9 |
97.9 |
98.9 |
98.5 |
15 |
98.3 |
97.5 |
97.6 |
99.1 |
98.1 |
97.9 |
|
Figure 4.3.11. Ambient storage test for Cr(VI) and H2SO4
spiked on binderless quartz fiber filters and stored in 5 mL BE buffer.
Figure 4.3.12. Refrigerated storage test for Cr(VI) and H2SO4
spiked on binderless quartz fiber filters and stored in 5 mL BE buffer.
|
Cr(VI) and H2S04
spiked on 1% NaOH coated binderless quartz fiber filter
Storage samples were prepared by spiking 1% NaOH coated binderless quartz fiber filters with
50 ng
Cr(VI) and 0.5 ng H2S04
and allowed to dry. Twenty-one storage samples were prepared. Three samples were analyzed on the day of preparation. Nine of the filters
were stored at reduced temperature (4ºC) and the other nine were stored in a closed drawer at ambient temperature (about 22ºC). At 5-day
intervals, three samples were selected from each of the two storage sets and analyzed. On Day 15 the recovery was 96.4% for samples stored
at ambient temperature and 96.1 % for samples stored at refrigerated temperature.
Table 4.3.7 Storage Test for Cr(VI) and H2SO4
on 1 % NaOH Coated binderless Quartz Fiber Filters |
|
time (days) |
ambient storage recovery
(%) |
refrigerated storage recovery
(%) |
|
0 |
100.3 |
99.2 |
99.4 |
100.3 |
99.2 |
99.4 |
5 |
97.7 |
99.6 |
100.3 |
99.5 |
97.7 |
98.1 |
10 |
98.3 |
98.4 |
98.4 |
98.6 |
95.7 |
97.9 |
15 |
94.9 |
97.4 |
96.1 |
96.4 |
95.4 |
96.1 |
|
Figure 4.3.13. Ambient storage test for Cr(VI) and H2SO4
spiked on 1% NaOH coated binderless quartz fiber filters.
Figure 4.3.14. Refrigerated storage test for Cr(VI) and H2SO4
spiked on 1% NaOH coated binderless quartz fiber filters.
|
4.4 Sampler removal efficiency
4.4.1 Removal efficiency refers to the ability of the PVC filters to absorb or otherwise capture surface
contaminants when the filter is moved across a surface under firm pressure. The surface used to
evaluate the removal efficiency was a PTFE sheet. This type of surface approaches the smooth and
non-porous characteristics of an ideal surface. The
variety of surfaces found in workplaces will likely be less than ideal, so the media will have a lower
removal efficiency. The amount of analyte found on the filter after sampling will indicate that at least that
amount was present on the surface that was sampled. Six surfaces were spiked at the target
concentration of Cr(VI), 0.05 µg/100 cm2.
Samples were collected from each surface using the technique described in Section 2.3 and analyzed. The results are shown in
Table 4.4.1.
Table 4.4.1 Sampler Removal Efficiency Data for Cr(VI)
from PTFE using PVC Filters |
|
theoretical (µg/surface) |
recovered
(µg/sample) |
recovery
(%) |
|
0.05 |
0.0490 |
98.0 |
0.05 |
0.0491 |
98.2 |
0.05 |
0.0488 |
97.6 |
0.05 |
0.0476 |
95.2 |
0.05 |
0.0479 |
95.8 |
0.05 |
0.0482 |
96.4 |
|
4.4.2 Removal efficiency of binderless quartz fiber filters was determined by placing the Cr(Vl) on a PTFE
sheet. This type of surface approaches the smooth and non-porous characteristics of an ideal surface.
The variety of surfaces found in workplaces, including theoretical recovered recovery skin, will likely be less than ideal. The media will
have a lower removal efficiency on less ideal surfaces. The amount of analyte found on the filter after sampling will indicate that at least that amount was present on the surface that was sampled. Six surfaces were spiked at the target concentration of
Cr(VI), 0.05 µg/100 cm2. Samples were collected from each surface using the technique described in Section 2.3 and analyzed.
The results are shown in Table 4.4.2.
Table 4.4.2 Sampler Removal Efficiency Data
for Cr(VI) from PTFE using
Binderless Quartz Fiber Filters |
|
theoretical (µg/surface) |
recovered
(µg/sample) |
recovery
(%) |
|
0.05 |
0.0489 |
97.8 |
0.05 |
0.0493 |
98.6 |
0.05 |
0.0492 |
98.4 |
0.05 |
0.0483 |
96.6 |
0.05 |
0.0484 |
96.8 |
0.05 |
0.0489 |
97.8 |
|
4.4.3 Removal efficiency of 1% NaOH coated binderless quartz fiber filters was
determined by placing the Cr(Vl) on a PTFE sheet. This type of surface approaches the smooth and
non-porous characteristics of an ideal surface. The variety of surfaces found in workplaces, including skin, will
likely be less than ideal. The media will have a lower removal efficiency on less ideal surfaces. The amount of analyte found on the
filter after sampling will indicate that at least that amount was present on the surface that was sampled. Six surfaces were spiked at
the target concentration of
Cr(VI), 0.05 µg/100 cm2. Samples were collected from each surface using the technique described in Section 2.3 and analyzed.
The results are shown in Table 4.4.3.
Table 4.4.3 Sampler Removal Efficiency
Data for Cr(VI) from PTFE
using NaOH Coated Binderless Quartz Fiber Filters |
|
theoretical (µg/surface) |
recovered
(µg/sample) |
recovery
(%) |
|
0.05 |
0.0487 |
97.4 |
0.05 |
0.0493 |
98.6 |
0.05 |
0.0482 |
96.4 |
0.05 |
0.0483 |
96.6 |
0.05 |
0.0475 |
95.0 |
0.05 |
0.0491 |
98.2 |
|
4.4.4 Removal efficiency shall be calculated as follows:
where |
ER is removal efficiency |
|
AR is amount of analyte recovered |
|
AS is amount of analyte spiked on the surface |
The mean removal efficiency of the six samples was 96.9% for PVC filters, 97.7% for binderless quartz fiber filters,
and 97.0% for 1% NaOH coated binderless quartz fiber filters.
4.5 Extraction efficiency
The extraction efficiencies of Cr(VI) were determined by liquid-spiking PVC filters with
Cr(VI) at concentrations ranging from the RQL (0.06) to 10 times the target concentration. These samples were stored overnight at ambient
temperature and then analyzed. The filters were either extracted and digested with the first, main extraction solution, BE, or with the
second, spray paint only, SPE solution. The mean extraction efficiency over the working range of the RQL to 10 times the target
concentration is 96.6% for samples extracted with the first (main) extraction solvent (BE) and 96.9% for samples extracted with the second
extraction solvent for paint samples
(SPE).
Table 4.5.1 Extraction Efficiency of Cr(VI)
from PVC Filters Extracted with BE |
|
level
|
sample number
|
× target concn |
ng per sample |
1 |
2 |
3 |
4 |
mean |
|
RQL |
3 |
95.4 |
96.6 |
92.7 |
95.5 |
95.1 |
0.1 |
5 |
96.4 |
96.5 |
97.9 |
95.9 |
96.7 |
1.0 |
50 |
97.8 |
97.2 |
96.7 |
97.6 |
97.3 |
10.0 |
500 |
97.4 |
97.8 |
97.0 |
96.1 |
97.1 |
|
Table 4.5.2 Extraction Efficiency of Cr(VI)
from PVC Filters Extracted with SPE |
|
level
|
sample number
|
× target concn |
ng per sample |
1 |
2 |
3 |
4 |
mean |
|
RQL |
3 |
97.8 |
95.0 |
97.3 |
95.5 |
96.4 |
0.1 |
5 |
97.5 |
97.1 |
97.6 |
96.0 |
97.1 |
1.0 |
50 |
95.9 |
97.5 |
96.3 |
96.1 |
96.5 |
10.0 |
500 |
98.0 |
96.4 |
97.1 |
97.9 |
97.4 |
|
The extraction efficiencies of Cr(VI) were determined by liquid-spiking binderless quartz fiber filters with
Cr(VI) at concentrations ranging from the RQL (0.06) to 10 times the target concentration. These samples were stored overnight at ambient
temperature and then analyzed. The filters were either extracted and digested with the first, main extraction solution, BE, or with the
second, spray paint only, SPE solution. The mean extraction efficiency over the working range of the RQL to 10 times the target
concentration is 97.3% for samples extracted with the first (main) extraction solvent (BE) and 96.2% for samples extracted with the second
extraction solvent for paint samples
(SPE).
Table 4.5.3 Extraction Efficiency of Cr(VI)
from Binderless Quartz Fiber Filters Extracted with BE |
|
level
|
sample number
|
× target concn |
ng per sample |
1 |
2 |
3 |
4 |
mean |
|
RQL |
3 |
96.3 |
95.4 |
95.9 |
96.3 |
96.0 |
0.1 |
5 |
97.2 |
96.9 |
96.8 |
97.5 |
97.1 |
1.0 |
50 |
98.4 |
97.2 |
98.2 |
97.9 |
97.9 |
10.0 |
500 |
97.9 |
98.3 |
98.1 |
98.1 |
98.1 |
|
Table 4.5.4 Extraction Efficiency of Cr(VI)
from Binderless Quartz Fiber Filters Extracted with SPE |
|
level
|
sample number
|
× target concn |
ng per sample |
1 |
2 |
3 |
4 |
mean |
|
RQL |
3 |
96.1 |
95.3 |
95.7 |
96.2 |
95.8 |
0.1 |
5 |
97.2 |
96.7 |
96.8 |
95.8 |
96.6 |
1.0 |
50 |
97.4 |
96.3 |
95.9 |
95.0 |
96.2 |
10.0 |
500 |
96.3 |
95.2 |
97.2 |
96.5 |
96.3 |
|
The extraction efficiencies of Cr(VI) were determined by liquid-spiking 1% NaOH coated binderless quartz fiber filters
with
Cr(VI) at concentrations ranging from the RQL (0.06) to 10 times the target concentration. These samples were stored overnight at ambient
temperature and then analyzed. The filters were either extracted and digested with the first, main extraction solution, BE, or with the
second, spray paint only, SPE solution. The mean extraction efficiency over the working range of the RQL to 10 times the target concentration
is 97.3% for samples extracted with the first (main) extraction solvent (BE) and 96.9% for samples extracted with the second extraction
solvent for paint samples
(SPE).
Table 4.5.5
Extraction Efficiency of Cr(VI) from 1 % NaOH
Coated Binderless Quartz Fiber Filters Extracted with BE |
|
level
|
sample number
|
× target concn |
ng per sample |
1 |
2 |
3 |
4 |
mean |
|
RQL |
3 |
97.4 |
95.3 |
97.1 |
96.2 |
96.5 |
0.1 |
5 |
96.3 |
97.1 |
96.9 |
97.4 |
96.9 |
1.0 |
50 |
98.1 |
95.9 |
98.1 |
98.2 |
97.6 |
10.0 |
500 |
97.7 |
98.1 |
97.9 |
98.3 |
98.0 |
|
Table 4.5.6
Extraction Efficiency of Cr(VI) from 1 % NaOH
Coated Binderless Quartz Fiber Filters Extracted with SPE |
|
level
|
sample number
|
× target concn |
ng per sample |
1 |
2 |
3 |
4 |
mean |
|
RQL |
3 |
96.9 |
95.9 |
96.3 |
95.4 |
96.1 |
0.1 |
5 |
98.1 |
96.8 |
97.7 |
96.4 |
97.0 |
1.0 |
50 |
97.9 |
97.5 |
96.8 |
96.5 |
97.2 |
10.0 |
500 |
96.9 |
97.2 |
97.9 |
97.5 |
97.4 |
|
4.6 Reproducibility
4.6.1 Six PTFE surfaces were spiked at the target level of 50 ng Cr(VI). A chemist, other than the one developing the method,
conducted sampling on the PTFE surfaces as described in Section 2 using PVC filters. The test was repeated with a second chemist performing
the sampling. The samples were analyzed. The first chemist was able to achieve a removal efficiency of 96.0% and the second chemist 95.1%
(Tables 4.6.1.1 and 4.6.1.2).
Table 4.6.1.1
Sampling Reproducibility Sampling
1st Chemist Samples for Cr(VI) from PTFE using PVC Filters |
|
Table 4.6.1.2
Sampling Reproducibility Sampling
2nd Chemist Samples for Cr(VI) from PTFE using PVC Filters |
|
|
|
theoretical (ng/surface) |
recovered (ng/sample) |
recovery (%) |
|
theoretical (ng/surface) |
recovered (ng/sample) |
recovery (%) |
|
|
|
50 |
48.2 |
96.4 |
|
50 |
46.5 |
93.0 |
50 |
48.7 |
97.4 |
|
50 |
47.9 |
95.8 |
50 |
48.4 |
96.8 |
|
50 |
48.6 |
97.2 |
50 |
47.2 |
94.4 |
|
50 |
48.7 |
97.4 |
50 |
48.3 |
96.6 |
|
50 |
46.9 |
93.8 |
50 |
47.2 |
94.4 |
|
50 |
46.7 |
93.4 |
|
|
|
4.6.2 Six samples were prepared by spiking PVC filters in the same manner that was used in
the preparation for the storage study. The samples were submitted to the OSHA SLTC
for analysis. The samples were analyzed after being stored for 13 days at 23ºC.
Sample results were corrected for extraction efficiency. The average recoverywas97.6%.
Table 4.6.2
Analytical Reprocibility Data for Cr(VI) using PVC Filters
|
50 |
48.1 |
96.2 |
50 |
49.2 |
98.4 |
50 |
47.9 |
95.8 |
50 |
48.6 |
97.2 |
50 |
49.1 |
98.2 |
50 |
49.8 |
99.6 |
4.6.3 Six PTFE surfaces were spiked at the target level of 50 ng
Cr(VI). A chemist, other than the one developing the method, conducted
sampling on the PTFE surfaces as described in Section 2 using binderless quartz fiber filters. The test was repeated with a second chemist
performing the sampling. The samples were analyzed. The first chemist was able to achieve a removal efficiency of 95.9% and the second
chemist 96.0% (Tables 4.6.3.1 and 4.6.3.2).
Table 4.6.3.1
Sampling Reproducibility 1st Chemist Samples for Cr(VI) from PTFE using Binderless Quartz Fiber PTFE Filters |
|
Table 4.6.3.2
Sampling Reproducibility 2nd Chemist Samples for Cr(VI) from PTFE using Binderless Quartz Fiber PTFE Filters |
|
|
|
theoretical (ng/surface) |
recovered (ng/sample) |
recovery (%) |
|
theoretical (ng/surface) |
recovered (ng/sample) |
recovery (%) |
|
|
|
50 |
47.2 |
94.4 |
|
50 |
47.5 |
95.0 |
50 |
48.9 |
97.8 |
|
50 |
48.6 |
97.2 |
50 |
47.1 |
94.2 |
|
50 |
48.3 |
96.6 |
50 |
47.5 |
95.0 |
|
50 |
48.8 |
97.6 |
50 |
48.8 |
97.6 |
|
50 |
47.1 |
94.2 |
50 |
48.4 |
96.8 |
|
50 |
47.7 |
95.4 |
|
|
|
4.6.4 Six samples were prepared by spiking binderless quartz fiber filters in the
same manner that was used in the preparation for the storage study. The samples were
submitted to the OSHA SLTC for analysis. The samples were analyzed after being
stored for 5 days at 23ºC. Sample results were corrected for extraction efficiency. The
average recovery was 96.5%.
Table 4.6.4
Analytical Reproducibility Data
for Cr(VI) using Binderless
Quartz Fiber Filters |
|
theoretical (ng/surface) |
recovered (ng/sample) |
recovery (%) |
|
50 |
47.3 |
94.6 |
50 |
48.4 |
96.8 |
50 |
47.9 |
95.8 |
50 |
48.2 |
96.4 |
50 |
48.8 |
97.6 |
50 |
48.9 |
97.8 |
|
4.6.5 Six PTFE surfaces were spiked at the target level of 50 ng
Cr(VI). A chemist, other than the one developing the method, conducted
sampling on the PTFE surfaces as described in Section 2 using 1% NaOH coated
binderless quartz fiber filters. The test was repeated with a second chemist performing the sampling. The samples were analyzed.
The first chemist was able to achieve a removal efficiency of 96.0% and the second chemist 96.5% (Tables 4.6.5.1 and 4.6.5.2).
Table 4.6.5.1
Sampling Reproducibility
1st Chemist Samples for Cr(VI) from PTFE using Binderless Quartz Fiber PTFE Filters |
|
Table 4.6.5.2
Sampling Reproducibility
2nd Chemist Samples for Cr(VI) from PTFE using Binderless Quartz Fiber PTFE Filters |
|
|
|
theoretical (ng/surface) |
recovered (ng/sample) |
recovery (%) |
|
theoretical (ng/surface) |
recovered (ng/sample) |
recovery (%) |
|
|
|
50 |
47.9 |
95.8 |
|
50 |
48.9 |
97.8 |
50 |
47.8 |
95.6 |
|
50 |
47.2 |
94.4 |
50 |
48.2 |
96.4 |
|
50 |
47.7 |
95.4 |
50 |
48.7 |
97.4 |
|
50 |
48.8 |
97.6 |
50 |
47.9 |
95.8 |
|
50 |
48.9 |
97.8 |
50 |
47.5 |
95.0 |
|
50 |
47.9 |
95.8 |
|
|
|
4.6.6 Six samples were prepared by spiking 1% NaOH coated binderless quartz fiber filters in
the same manner that was used in the preparation for the storage study. The
samples were submitted to the OSHA SLTC theoretical recovered recovery for analysis. The samples were analyzed after being stored
for 9 days at 23ºC. Sample
results were corrected for extraction efficiency. The average recovery was 95.8%.
Table 4.6.6 Analytical Reproducibility Data
for Cr(VI) on NaOH Coated Binderless Quartz Fiber Filters |
|
theoretical (ng/surface) |
recovered (ng/sample) |
recovery (%) |
|
50 |
47.4 |
94.8 |
50 |
48.2 |
96.4 |
50 |
48.8 |
97.6 |
50 |
47.1 |
94.2 |
50 |
47.6 |
95.2 |
50 |
48.4 |
96.8 |
|
4.7 Interferences (sampling)
Suspected interferences should be reported to the laboratory with submitted samples. The interference studies
were performed in Method ID-215 Hexavalent Chromium, and should be consulted for specific information about the metal species of
interest(21). The major
positive interference is
Cr(III), which can be oxidized to Cr(VI). The major negative interference is
Fe(II), which can reduce the Cr(VI) to Cr(III). Other reducing metal species can also change
Cr(VI) to Cr(III).
In chrome plating operations the acid is a negative interference, and samples taken on PVC or uncoated binderless quartz fiber filters must
be placed into a vial containing a solution of 10%
Na2CO3 with 2% NaHCO3, or the 1% NaOH coated binderless quartz fiber filters should be used.
4.8 Confirmation
The presence of Cr(VI) can be confirmed by a second column analysis using a different column packing,
ICP-mass spec, or by reanalyzing the samples without the addition of the postcolumn derivatizing solution. To confirm the sample without
the addition of the post column derivatizing solution, a solution of 90:10 0.1 N H2S04:methyl alcohol is substituted
for the derivatizing solution, and the sample is rerun under the same conditions it was first analyzed under. If a peak appears at the
same retention time as the hexavalent chromium, it is an interference, but conversely, if no peak appears, the original peak was all
hexavalent chromium.
4.9 Preparation of the 1% NaOH coated binderless quartz fiber filters
The 1% NaOH coated binderless quartz fiber filters are prepared by placing binderless quartz fiber filters in a single layer in a shallow
pan containing 1 N NaOH overnight. They were removed and placed on a PTFE sheet to dry for four hours. Twelve dry filters were placed into
a sealed jar and stored for up to 60 days, and another twelve dry filters were placed into a jar, a stream of nitrogen was blown into the
jar for 1 minute to blanket the filters, and then sealed and stored for up to 67 days. The filters were analyzed by acid titration after
29 and 67 days to determine the available hydroxide ion. The filters stored under nitrogen stored the best, with recoveries of 95.6% for
29 days and 90.8% for 67 days. Filters stored with air were barely acceptable for 29 days, 84.0% recovery, but those stored for 67 days
lost too much of the hydroxide ion, 65.6% recovery. These results indicate that the filters should be used within a month of preparation,
unless they are stored under nitrogen, then they can be stored two months.
Table 4.9
Storage of 1% NaOH coated Binderless Quartz Fiber Filter |
|
filter storage
|
sample number
|
type of gas over filters |
days stored |
1 |
2 |
3 |
4 |
mean |
|
air |
30 |
83.2 |
85.4 |
84.9 |
82.8 |
84.0 |
air |
60 |
63.0 |
68.6 |
64.5 |
66.3 |
65.6 |
nitrogen |
30 |
95.4 |
96.6 |
94.9 |
95.4 |
95.6 |
nitrogen |
60 |
90.2 |
90.9 |
90.6 |
91.4 |
90.8 |
|
1 Lawrence R. Evaluation Guidelines for Surface Sampling Methods;
OSHA Salt Lake Technical Center, U.S. Department of Labor: Salt Lake City,
UT, 2001, unpublished.
2 Ku, J., Eide, M.,
Hexavalent Chromium In Workplace Atmospheres, (accessed May 2000).
3 Ku, J., Eide, M.,
Hexavalent Chromium In Workplace Atmospheres, (accessed May 2000).
4 Ku, J., Eide, M.,
Hexavalent Chromium In Workplace Atmospheres, (accessed May 2000).
5 Foster, R., Usher, J., and Howe, A. Hexavalent Chromium in Chromium
Plating Mists, 1998, MDHS method 52/3, Health and Safety Executive,
Sheffield UK.
6 Toxicological Profile for Chromium (update), draft for public
comment, U.S. Department of Health and Human Services, Public Health
Service, Agency for Toxic Sunstances and Disease Registry, 1998, p 97.
7 Toxicological Profile for Chromium (update), draft for public
comment, U.S. Department of Health and Human Services, Public Health
Service, Agency for Toxic Sunstances and Disease Registry, 1998, p 105.
8 Documentation of the Threshold Limit Values and Biological
Exposure Indices, 6th ed,; American Conference of Governmental
Industrial Hygienists, Inc.: Cincinnati, OH, 1991, Vol II, p.313.
9 Documentation of the Threshold Limit Values and Biological
Exposure Indices, Supplement to the Sixth Edition, American Conference
of Governmental Industrial Hygienists, Inc.: Cincinnati, OH, 1996, p
Supplement :Chromium - 1.
10 Documentation of the Threshold Limit Values and Biological
Exposure Indices, 6th ed,; American Conference of Governmental
Industrial Hygienists, Inc.: Cincinnati, OH, 1991, Vol.III, p BEI-69.
11 Documentation of the Threshold Limit Values and Biological
Exposure Indices, 6th ed,; American Conference of Governmental
Industrial Hygienists, Inc.: Cincinnati, OH, 1991 Vol. 1, pp 312-315.
12 Budavari, S., The Merck Index, 12th ed., Merck & Co.
Inc.: Whitehouse Station, NJ, 1996, p 375.
13 Ku, J., Eide, M.,
Hexavalent Chromium In Workplace Atmospheres, (accessed May 2000).
14 OSHA Computerized Information System Database, Chemical Sampling
Information, http://www.osha.gov, (accessed May 2000).
15 Lawrence R. Evaluation Guidelines for Surface Sampling Methods;
OSHA Salt Lake Technical Center, U.S. Department of Labor: Salt Lake City,
UT, 2001, unpublished.
16 Ku, J., Eide, M.,
Hexavalent Chromium In Workplace Atmospheres,
(accessed May 2000).
17 Occupational Exposure to Chemicals in Laboratories. Code of Federal
Regulations, Part 1910.1450, Title 29, 1998; www.osha.gov,
standards, 5/12/2000.
18 Ku, J., Eide, M.,
Hexavalent Chromium In Workplace Atmospheres,
(accessed May 2000).
19 Lawrence R. Evaluation Guidelines for Surface Sampling Methods;
OSHA Salt Lake Technical Center, U.S. Department of Labor: Salt Lake City,
UT, 2001, unpublished.
20 Lawrence R. Evaluation Guidelines for Surface Sampling Methods;
OSHA Salt Lake Technical Center, U.S. Department of Labor: Salt Lake City,
UT, 2001, unpublished.
21 Ku, J., Eide, M.,
Hexavalent Chromium In Workplace Atmospheres,
(accessed May 2000).
|
|
| |