METHOD 327.0 DETERMINATION OF CHLORINE DIOXIDE AND CHLORITE ION
IN DRINKING WATER USING LISSAMINE GREEN B AND
HORSERADISH PEROXIDASE WITH DETECTION BY
VISIBLE SPECTROPHOTOMETRY
EPA 815-B-03-001
Revision 1.0
July 2003
Teri A. Dattilio and Barry V. Pepich, Shaw Environmental, Inc.
David J. Munch and Patricia S. Fair, US EPA, Office of Ground Water and
Drinking Water
Zsolt Kortvelyesi and Gilbert Gordon, Miami University
TECHNICAL SUPPORT CENTER
OFFICE OF GROUND WATER AND DRINKING WATER
U. S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
327.0-1
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METHOD 327.0
DETERMINATION OF CHLORINE DIOXIDE AND CHLORITE ION IN DRINKING WATER
USING LISSAMINE GREEN B AND HORSERADISH PEROXIDASE WITH DETECTION
BY VISIBLE SPECTROPHOTOMETRY
1. SCOPE AND APPLICATION
1.1 This is a spectrophotometric method for the analysis of chlorine dioxide and chlorite* in
finished drinking waters. It is primarily intended to be used at drinking water utilities in
conjunction with daily monitoring requirements.
1.2 The experimentally determined Detection Limits (DLs) for chlorine dioxide and chlorite
are provided in Section 17, Table 1. The DL is defined as the statistically calculated
minimum concentration that can be measured with 99% confidence that the reported
value is greater than zero.(1) Detection Limits are technique and instrument dependent.
The DL differs from, and is lower than, the Minimum Reporting Level (MRL)
(Sect. 3.10). Method performance was demonstrated over a combined concentration
range of 0.2 mg/L to 2.2 mg/L. Precision and accuracy data are presented in Section 17,
Tables 1-3.
1.3 Chlorine dioxide is a volatile, reactive gas. Care was taken during method development
to minimize steps that could result in the loss of chlorine dioxide during analysis.
Analyst technique can affect method precision and accuracy.
2. SUMMARY OF METHOD
2.1 A drinking water sample is collected headspace-free in a 16-mL amber glass vial. A
second sample is collected and sparged with an inert gas to remove all traces of chlorine
dioxide and then transferred to a second 16-mL amber vial. A third vial is filled with
reagent water. A 1.0-mL aliquot of water is removed from each vial, and a 1.0-mL
aliquot of a concentrated citric acid buffer containing glycine is added. The samples are
capped and gently mixed, and then a second 1.0-mL aliquot is removed and a 1.0-mL
aliquot of a Lissamine Green B (LGB)/Horseradish Peroxidase (HRP) reagent is added.
The HRP catalyzes the conversion of chlorite to chlorine dioxide.(2>3) Chlorine dioxide
rapidly oxidizes the LGB, reducing its absorption in the red region of the visible spectrum
in proportion to the chlorine dioxide concentration/4'5) A visible spectrophotometer is
used to measure the absorbance of the reagent water blank and sample absorbance at
633 nm, which is the absorbance maximum for LGB in the citric acid/glycine buffer. The
absorbance difference between the reagent water blank and the samples is used to
calculate the concentrations of chlorine dioxide, using an external standard calibration
*Throughout this document chlorite ion (C1O2 ) is referred to as 'chlorite' for simplicity,
even though the use of 'chlorite ion' is more accurate.
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curve, determined using chlorite standards. The unsparged sample is used to determine
the total chlorite and chlorine dioxide concentration and the sparged sample is used to
determine the chlorite concentration. The chlorine dioxide concentration is the difference
between these two values.
3. DEFINITIONS
3.1 ANALYSIS BATCH - A set of samples that is processed and analyzed together and
includes no more than 10 Field Samples. An analysis batch must also include at least one
Method Blank and all required QC samples. The Method Blanks and QC samples do not
contribute to the maximum Field Sample total of 10.
3.2 CALIBRATION STANDARD (CAL) - A solution prepared from the primary dilution
standard solution and/or stock standard solution. The CAL solutions are used to calibrate
the instrument response with respect to analyte concentration.
3.3 CONTINUING CALIBRATION CHECK (CCC) - A calibration standard containing the
method analyte(s), which is analyzed periodically to verify the accuracy of the existing
calibration for those analytes.
3.4 DETECTION LIMIT (DL) - The minimum concentration of an analyte that can be
identified, measured, and reported with 99% confidence that the analyte concentration is
greater than zero. This is a statistical determination of precision (Sect. 9.2.3), and
accurate quantitation is not expected at this level.(1)
3.5 FIELD DUPLICATES (FD1 and FD2) - Two separate samples collected at the same
time and place under identical circumstances and treated exactly the same throughout
field and laboratory procedures. Analyses of FD1 and FD2 give a measure of the
precision associated with sample collection and storage, as well as laboratory procedures.
3.6 LABORATORY FORTIFIED SAMPLE MATRIX (LFSM) - An aliquot of an envi-
ronmental sample to which known quantities of the method analytes are added in the
laboratory. The LFSM is analyzed exactly like a sample, and its purpose is to determine
whether the sample matrix contributes bias to the analytical results. The background
concentrations of the analytes in the sample matrix must be determined in a separate
aliquot and the measured values in the LFSM corrected for background concentrations.
3.7 LABORATORY FORTIFIED SAMPLE MATRIX DUPLICATE (LFSMD) - A second
aliquot of the field sample used to prepare the LFSMD, fortified, processed and analyzed
identically. The LFSMD is used instead of the Field Duplicate to access method
precision when the occurrence of target analytes is low.
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3.8 MATERIAL SAFETY DATA SHEET (MSDS) - Written information provided by
vendors concerning a chemical's toxicity, health hazards, physical properties, fire, and
reactivity data, including storage, spill, and handling precautions.
3.9 METHOD BLANK (MB) - An aliquot of reagent water that is free from all method
analytes and is processed and analyzed with the samples in the analysis batch. The
absorbance value of the MB is used to calculate the absorbance change caused by the
reaction of chlorine dioxide with LGB.
3.10 MINIMUM REPORTING LEVEL (MRL) - The minimum concentration that can be
reported as a quantitated value for a target analyte in a sample following analysis. This
concentration can be no lower than the concentration of the lowest continuing calibration
standard for that analyte and can be used only if acceptable quality control criteria for this
standard are met.
3.11 PRIMARY DILUTION STANDARD (PDS) SOLUTION - A solution containing the
analytes prepared in the laboratory from stock standard solutions and diluted as needed to
prepare calibration solutions and other needed analyte solutions.
3.12 REAGENT WATER - A high-purity water, typically either distilled or deionized, that is
free from organic and inorganic contaminants and all method analytes.
3.13 STOCK STANDARD SOLUTION (SSS) - A concentrated solution containing one or
more method analytes prepared in the laboratory using assayed reference materials or
purchased from a reputable commercial source.
4. INTERFERENCES
4.1 Free available chlorine reacts with LGB to discolor the solution. Glycine reacts with the
free available chlorine to form chloroaminoacetic acid, thereby eliminating the potential
for this type of interference.
4.2 Laboratory glassware can potentially exhibit a demand for chlorine dioxide.(5) While this
was not observed during method development, it could bias the analytical results and lead
to poor accuracy and/or precision. This potential problem can be avoided if sample
collection vials are cleaned and reused as described in Section 8.1.2.
4.3 Chlorite concentrations are calculated after the samples are sparged to remove chlorine
dioxide. Samples that are not efficiently sparged to remove the chlorine dioxide will
yield chlorite values that are higher than the true value.
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5. SAFETY
5.1 The toxicity or carcinogenicity of each reagent used in this method has not been precisely
identified; each chemical compound should be treated as a potential health hazard, and
exposure to these chemicals should be minimized. The laboratory is responsible for
maintaining a current awareness file of OSHA regulations regarding the safe handling of
the chemicals specified in this method. A reference file of MSDSs should also be made
available to all personnel involved in the chemical analysis. Additional references to
laboratory safety are available.(6~8)
5.2 This method does not require the preparation of chlorine dioxide standards, which could
have inhalation hazards. It also does not require the preparation of chlorite standards
from a recrystallized solid standard, which can have an explosion hazard. Because of the
significant potential dangers associated with these materials, they are not recommended
for use in conjunction with this method. The chlorite standard cited in Section 7.3.1 does
not pose an explosion hazard.
6. EQUIPMENT AND SUPPLIES
6.1 VISIBLE SPECTROPHOTOMETER - A single- or double-beam spectrophotometer that
uses a monochromator to make accurate absorbance measurements at discrete
wavelengths (Agilent Model 8453 or equivalent) equipped with a standard, rectangular
1-cm path length cell is recommended. The spectrophotometer must have a linear
response and acceptable photometric accuracy up to an absorbance value (A) of 1.6.
6.1.1 Nondispersive spectrophotometers (e.g., filter-based, light emitting diode-based,
etc.) with alternate cuvette shapes and pathlengths are allowed as long as they
meet the method QC requirements. These devices must have filters with
transmission maximum near 633 nm and must have a linear response and
acceptable photometric accuracy up to an absorbance value of 1.6.
6.1.2 Longer pathlength cells may be used for applications that require lower DLs;
however, the concentration of the Buffered LGB Stock Solution (Sect. 7.2.4)
must be adjusted accordingly. Shorter pathlengths are not recommended.
6.2 CUVETTES - A matched set of 1-cm glass cuvettes with polytetrafluoroethylene (PTFE)
stoppers (Fisher Cat. #: 22200-350 or equivalent). Alternate path lengths and/or cell
shapes are allowed as long as the method QC criteria are met.
6.3 ANALYTICAL BALANCE - Used to accurately weigh analytical standard materials
(±0.1 mg sensitivity).
6.4 TOP LOADING BALANCE - Used to accurately weigh reagents (±10 mg sensitivity).
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6.5 WEIGHING BOATS - Plastic, disposable - used to weigh reagents.
6.6 WEIGHING FUNNEL - Used to weigh and transfer LGB and HRP (Fisher Cat. #:
19958-3 or equivalent).
6.7 PIPETTES - Use 0.5-mL and 1.0-mL Class A, volumetric pipettes (Fisher Cat. #: 13-
651-11 or equivalent) and/or variable volume single channel pipettes with disposable
plastic tips.
6.7.1 Use a variable volume, single channel pipette (Brinkman Eppendorf Research
Pro Pipette, Fisher Cat. #:21-378-84 or equivalent) with a volume of 500 to
5000 |jL to deliver volumes of 1.0 mL or larger.
6.7.2 Use a variable volume, single channel pipette (Brinkman Eppendorf Research
Pro Pipette, Fisher Cat. #:21-378-83 or equivalent) with a volume of 50 to
1000 |jL to deliver volumes less than 1.0 mL.
6.8 VIALS - 16-mL amber glass vials with PTFE-lined screw caps (Fisher Cat. #: 03-391-8E
or equivalent) used to collect samples.
6.9 ERLENMEYER FLASKS - 500 mL and 250 mL glass, used to prepare reagents.
6.10 BOTTLES - Amber glass bottles with PTFE-lined screw caps or opaque, high-density
polyethylene (HDPE) bottles of various sizes to store reagents and standards.
6.11 BEAKERS - 100 mL (Fisher CatJ: 02-540H or equivalent), used to collect and sparge
samples for chlorite analyses.
6.12 VOLUMETRIC FLASKS - Class A, of varying sizes.
6.13 SPARGING APPARATUS - A cylinder of nitrogen or helium equipped with a regulator
that is attached to an appropriate length of Tygon tubing and a disposable, Pasteur
pipette. Glass gas-dispersion tubes with fritted cylinders or disks may also be used as
long as they are rinsed between uses.
7. REAGENTS AND STANDARDS
7.1 INTENDED USE OF REAGENTS AND STANDARD SOLUTIONS - Sections 7.2 and
7.3 describe reagents, solvents and standards that are compatible with a 1-cm rectangular
cuvette. In this configuration, and with these reagents, this method has a linear range of
0.2 - 2.2 mg/L total chlorite and chlorine dioxide. If longer pathlength cells are used to
obtain concentration data at lower levels, the Buffered LGB Stock Solution (Sect. 7.2.4)
must be adjusted accordingly.
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7.2 REAGENTS AND SOLVENTS - Reagent grade or better chemicals should be used.
Unless otherwise indicated, all reagents should conform to the specifications of the
Committee on Analytical Reagents of the American Chemical Society(9), where such
specifications are available. Other grades may be used, provided it is first determined
that the reagent is of sufficiently high purity to permit its use without lessening the
quality of the determination.
7.2.1 REAGENT WATER - Purified water (typically either deionized or distilled)
which does not contain any chlorine dioxide or chlorite or compounds that
absorb light at 633 nm. The absorbance of the reagent water at 633 nm for a
1-cm pathlength (against a cuvette containing air) should be 5 milli-absorbance
units (mA) or less.
7.2.2 CONCENTRATED CITRIC ACID/GLYCINE BUFFER - Add 9.0 g of
trisodium citrate dihydrate (C6O7H5Na3»2H2O) (Sigma Cat. #: C3434 or
equivalent), 5.0 g disodium hydrogencitrate sesquihydrate (C6O7H6Na2»1.5H2O)
(Sigma Cat. #: 35908-4 or equivalent) and 1.0 g glycine (Sigma Cat. #: G7162
or equivalent) to a 250-mL Erlenmeyer flask. Add 125 mL of reagent water and
mix thoroughly. Add one drop of chloroform (or about 50 jiL) (Aldrich HPLC
Grade, Cat. #: 36,692-7 or equivalent) and store this solution at < 6 °C.
7.2.2.1 Care must be taken to ensure that all crystalline material is completely
dissolved either by using a stir bar or by swirling the contents of the
flask manually for several minutes.
7.2.2.2 The pH of the concentrated buffer stock solution should be confirmed
with a pH electrode to be in the pH range of 6.0 - 6.2 upon dilution by
adding a 1.0-mL aliquot of the buffer to 15 mL of reagent water. The
pH of the concentrated stock solution may be adjusted, if necessary, by
adding small amounts of the C6O7H6Na2»1.5H2O to lower the pH value
or C6O7H5Na3»2H2O to increase the pH value.
7.2.2.3 Chloroform acts as an antimicrobial agent. If the buffer solution turns
cloudy, which is indicative of microbial growth, it must be discarded.
7.2.3 LISSAMINE GREEN B (LGB) CONCENTRATED STOCK SOLUTION IN
REAGENT WATER - Accurately weigh 240 mg of LGB (Aldrich CatJ:
19958-3 or equivalent) in a glass weighing funnel (Sect. 6.6). Transfer the LGB
to a 250-mL wide neck volumetric flask with reagent water and dilute to the
mark using reagent water. Add a small PTFE stirbar and allow the solution to
stir overnight. Transfer the solution to a 500-mL amber glass bottle which has a
PTFE-lined cap and store this solution at < 6 °C. If stored properly, this
solution should be stable for 2 months.
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7.2.3.1 The minimum acceptable purity for the LGB solid is 70%. Higher
purity is recommended. Although Aldrich specifies that their LGB has
a minimum purity of 60%, the lot of LGB used in this work was 73%
pure according to the manufacturer. This information can be obtained
from Aldrich by contacting a technical service representative.
7.2.3.2 Confirm that the LGB solid is at least 70% pure as follows. Add 6 mL
of the Concentrated Citric Acid/Glycine Buffer (Sect. 7.2.2) to a
100-mL volumetric flask. Fill the flask about half full with reagent
water and then add a 1.0-mL aliquot of the LGB Concentrated Stock
Solution. Fill the flask to the mark with reagent water and mix
thoroughly. Allow the flask to equilibrate at room temperature for 15 -
20 minutes, and then mix again. Transfer an aliquot of this solution to
a cuvette with a 1-cm pathlength. The absorbance of this solution
must be > 0.99.
7.2.4 BUFFERED LGB STOCK SOLUTION - Prepare a dilution of the LGB
Concentrated Stock Solution in the Concentrated Citric Acid/Glycine Buffer.
The concentration of this solution should be confirmed prior to mixing it
with the Horseradish Peroxidase (HRP) Stock Solution to prepare the
Combined LGB/HRP Reagent (Sect. 7.2.6). This step will eliminate waste
of the HRP enzyme, which is the most expensive reagent in the method.
The procedure below is used to determine that the Buffered LGB Stock Solution
has been prepared at the appropriate concentration so that when it is used in the
procedure it will yield a Method Blank absorbance in the required absorbance
range of 1.5 ± 0.1.
7.2.4.1 For LGB with a purity of 73%, transfer 40 mL of the LGB
Concentrated Stock Solution (Sect. 7.2.3) to a wide neck 100-mL
volumetric flask. Add 6 mL of the Concentrated Citric Acid/Glycine
Buffer (Sect. 7.2.2), dilute to the mark with reagent water, and mix
thoroughly. For LGB that has lower purity, the volume of the
Concentrated Stock Solution can be estimated using the equation
LGS-
where VLGB is the volume of the LGB Concentrated Stock Solution
required, and PLGB is the purity of the LGB (obtained from the
manufacturer) expressed as a whole number.
7.2.4.2 Confirm that the Buffered LGB Stock Solution concentration is in the
correct range as follows. Fill a 16-mL vial with reagent water, remove
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1 .0 mL of the water and add 1.0 mL of the of the Concentrated Citric
Acid/Glycine Buffer (Sect. 7.2.2). Cap the vial and shake. Remove
0.5 mL of the buffered reagent water and add 0.5 mL of the Buffered
LGB Stock Solution. Recap the vial and mix the contents thoroughly
by shaking. Transfer an aliquot of this solution to a 1-cm cuvette and
determine the absorbance at 633 nm. The absorbance of this solution
at 633 nm must be in the range of 1 .5 ± 0. 1 . If not, the Buffered LGB
Stock Solution should be reprepared from the LGB Concentrated
Stock Solution. The appropriate volume of the LGB Concentrated
Stock Solution can be calculated using the equation
where Vreq is the volume of the LGB Concentrated Stock Solution that
is required to prepare the new solution, Vadded is the volume of the LGB
Concentrated Stock Solution originally added (40 mL in Sect. 7.2.4.1),
andAmeas is the measured absorbance.
7.2.4.3 If the analyst is using the method to determine concentrations
< 0.2 mg/L, a longer pathlength cuvette is required. The Buffered
LGB Stock Solution concentration must be adjusted accordingly so
that the absorbance in the longer pathlength cuvette, when checked as
described in Section 7.2.4.2, is in the absorbance range of 1.5 ± 0.1.
To calculate the amount of LGB Concentrated Stock Solution required
for the solution, simply divide the recommended volume in Section
7.2.4.1 by the pathlength.
7.2.4.4 This stock solution is used to prepare the Combined LGB/HRP
Reagent and is not preserved with chloroform. This solution should
not be kept or stored for more than one day.
7.2.5 BUFFERED HORSERADISH PEROXIDASE (HRP) STOCK SOLUTION -
Weigh out 60 - 70 mg of Type II HRP (Sigma Cat. #: P6782 or equivalent)
using a glass weighing funnel (Sect. 6.6) and an analytical balance. Transfer the
HRP to a wide-neck, 50-mL volumetric flask by washing it from the funnel with
reagent water. The HRP is a lyophalized powder that can be lost during transfer
if care is not taken to minimize air currents. Carefully rinse the walls of the
funnel with reagent water to ensure complete transfer. Add 6 mL of the
Concentrated Citric Acid/Glycine Buffer (Sect. 7.2.2) and then dilute the flask
contents to the mark with reagent water and mix thoroughly.
7.2.5.1 The HRP must have a minimum activity of 150 units per mg of solid
using the purpurogallin method. (10) The Type II HRP sold by Sigma
meets this criterion. According to Sigma, their HRP is stable for up to
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1 year if stored as a solid at < -20 °C.(11) Other sources of HRP may
also be suitable, but they have not been evaluated.
7.2.5.2 This stock solution is used to prepare the Combined LGB/HRP
Reagent and is not preserved with chloroform, and therefore should
not be kept or stored for more than one day.
7.2.6 COMBINED LGB/HRP REAGENT - Confirm the concentration of the
Buffered LGB Stock Solution according to Section 7.2.4.2 prior to performing
this step. This will prevent wasting the Buffered HRP Stock Solution, which is
the most expensive reagent in this method. Combine 50 mL of the Buffered
LGB Stock Solution (Sect. 7.2.4) with the entire volume of Buffered HRP Stock
Solution (Sect. 7.2.5) in an amber glass bottle with a PTFE-lined cap. Do not
rinse the 50-mL volumetric flask containing the Buffered HRP Stock Solution
to transfer the remaining droplets as quantitative transfer of this reagent is not
necessary. The volume of the combined reagent is sufficient for
approximately 100 tests (e.g., blanks, samples, calibrations, etc.). Add one drop
of chloroform (or about 50 jiL). This solution may be used for 14 days if stored
at < 6 °C.
7.2.7 HELIUM OR NITROGEN (> 99.995%) - UHP Grade or purer, used to sparge
samples to remove chlorine dioxide.
7.3 STANDARD SOLUTIONS - Because chlorite is converted to chlorine dioxide using the
HRP reagent, this method uses chlorite standards to calibrate for both chlorine dioxide
and chlorite (Sect. 2.1). Chlorite standard solutions may be prepared from certified,
commercially available solutions or from solid compounds. Preparation of chlorite
standards from a recrystallized solid of high purity (95%+) is not recommended as this
form of chlorite can pose an explosion hazard. Solution concentrations listed in this
section were used to develop this method and are included as an example. Even though
stability times for standard solutions are suggested in the following sections,
laboratories should use standard QC practices to determine when Standard
Solutions described in this section should be replaced.
7.3.1 CHLORITE STOCK STANDARD SOLUTION (1000 mg/L) - Certified
chlorite standard solutions are commercially available (Absolute Standards, Cat.
#54106 or equivalent). Commercial standards should be stored at < 6 °C in an
amber glass bottle or high density polyethylene (HOPE) container to prolong
standard life. If stored properly, this solution should be stable for 6 months.
7.3.2 CHLORITE PRIMARY DILUTION STANDARD (PDS) (10 mg/L) - This
solution is used to prepare Calibration Standards and Continuing Calibration
Check Standards. Partially fill a 500-mL volumetric flask with reagent water.
Add 5.0 mL of the Chlorite Stock Standard Solution (Sect. 7.3.1) using a pipette
and fill the flask to the mark using reagent water. Invert and shake the flask
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several times to ensure that the solution is completely mixed and then transfer
the flask contents to an amber bottle with a PTFE-lined cap or an HDPE
container. This solution should be stored at < 6 °C. If stored properly, this
solution should be stable for 3 months.
7.3.3 CALIBRATION STANDARDS - At least three Calibration Standards are
required to establish an initial calibration curve. Five Calibration Standards are
recommended. The concentration of the Calibration Standards must span the
intended reporting range. An example of the dilutions that were used to prepare
the standards used in the development of this method is included in the table
below. All Calibration Standards are to be prepared from the Chlorite Primary
Dilution Standard (Sect. 7.3.2) using Class A volumetric or variable-volume
pipettes and volumetric flasks. Transfer an appropriate aliquot of the Chlorite
PDS (10 mg/L) (Sect. 7.3.2) to the appropriate flask and dilute to the mark with
reagent water. Mix the contents of the flask thoroughly and transfer to an amber
glass bottle or opaque plastic container. These solutions should be stored at
< 6 °C. If stored properly, these solutions should be stable for 3 months.
Chlorite PDS
Volume
(mL)
10
25
50
75
100
Final
Volume
(mL)
500
500
500
500
500
Calibration
Std. Cone.
(mg/L)
0.20
0.50
1.00
1.50
2.00
7.3.4 CONTINUING CALIBRATION CHECK (CCC) STANDARDS - Calibration
Standards prepared above may also be used as CCC Standards.
7.3.5 LFSM FORTIFICATION SOLUTION (100 mg/L) - This solution is used to
fortify Field Samples for the Laboratory Fortified Sample Matrix requirement
(Sect. 9.5). Partially fill a 100-mL volumetric flask with reagent water. Add
10.0 mL of the Chlorite Stock Standard Solution (Sect. 7.3.1) using a pipette,
and then fill the flask to the mark using reagent water. Invert and shake the
flask several times to ensure the solution is completely mixed and then transfer
the contents of the flask to an amber bottle with a PTFE-lined cap or an HDPE
container. This solution should be stored at <6 °C. If stored properly, this
solution should be stable for 3 months.
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8. SAMPLE COLLECTION. PRESERVATION. AND STORAGE
8.1 SAMPLE VIAL PREPARATION
8.1.1 VIAL SELECTION - The procedure and reagent concentrations were
developed using the vials listed in Section 6.8. The manufacturer lists the
volume of these vials to be 16 mL. The procedure used to select appropriate
vials is described below. If alternate vials are used that have an average volume
that differs from 16 mL by more than 10%, reagent concentrations and volumes
must be adjusted accordingly.
8.1.1.1 Select an appropriate number of vials based on anticipated sample load
requirements. Vials that do not have appropriate volumes will be
rejected during this process, so begin the selection process with 10-
15% more vials than needed. Vials may be reused after cleaning.
Method development was conducted with approximately 30 vials.
8.1.1.2 Label and cap each 16-mL vial and determine the tare weight with the
PTFE-lined cap. Fill the vial with water and recap. Dry the external
walls of the vial and confirm that there is no headspace by inverting
the vial and looking for an air bubble. Weigh the full vial and record
the water weight. Convert the water weight to volume of the vial by
assuming 1.0 g of water is equal to 1.0 mL.
8.1.1.3 Determine the average volume for the vials tested, and select the vials
that are closest in volume. Discard any vial that has a volume that is
greater than 1% above or below the average value. During
development of this method, the average volume was 16.4 mL and
vials were accepted that were in the volume range of 16.4 ±0.1 (or
within 0.63%). Approximately 10% of the vials were rejected.
8.1.2 VIAL CLEANING - Vials may be reused. Prior to reuse they should be
thoroughly cleaned with soap and water and rinsed several times with reagent
water. Vials (without caps) can be dried in an oven at 140 °C. Reusing vials
may help avoid any potential for bias associated with chlorine dioxide
demand of the glassware (Sect. 4.2).
8.2 SAMPLE COLLECTION
8.2.1 Prior to sample collection, remove the aerator (if present) to minimize loss of
chlorine dioxide during sample collection. Open the tap and allow the system to
flush until the water temperature has stabilized (usually 3-5 minutes). Reduce
the tap flow just before collecting the samples.
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8.2.2 Two aliquots must be collected at each sampling point if both chlorine dioxide
and chlorite are to be determined. Both aliquots require sample processing to
halt the continued formation and/or reproportionation of the method analytes.
Two pipette tips (or pipettes) will be required for this procedure. Tips can be
used repeatedly to perform the same functions with each Field Sample. This is
not expected to cause significant contamination due to carryover. However,
care should be taken to ensure that fluid is not retained in (or on) the pipette tip
prior to performing the next transfer. These pipette tips (or pipettes) are given
numbers for clarity. The pipette tips are summarized in the table below with
their function. These tips may be saved for use in Section 11.
Pipette Tip #
1
2
Used to
Remove sample and remove buffered sample
Transfer citric acid/glycine buffer
8.2.3 FIELD SAMPLE COLLECTION TO DETERMINE CHLORINE DIOXIDE
AND CHLORITE - Fill the 16-mL vial completely so that no headspace
remains after capping the vial. This is most easily done by slightly overfilling
the vial. Invert the capped vial to ensure that the vial does not contain an air
bubble (or headspace). Recollect the sample if a bubble is noted. Remove a
1.0-mL aliquot of the Field Sample from the vial using pipette tip 1 and add a
1.0-mL aliquot of the Concentrated Citric Acid/Glycine Buffer (Sect. 7.2.2)
using pipette tip 2. Free available chlorine is removed in this step. Gently mix
the vial by inverting it three times. Clearly label the sample. This aliquot will
be used to determine the total chlorine dioxide and chlorite concentration.
Note: When removing the 1.0-mL aliquot from the vial, carefully place the
pipette tip into the vial in such a way that the sample does not overflow out of
the vial. As sample is withdrawn into the pipette, the tip should be gently
lowered so that it is always below the surface of the sample.
8.2.4 FIELD SAMPLE COLLECTION TO DETERMINE CHLORITE - Collect a
second aliquot (approximately 40 mL) in an open container with a large surface
area such as a 100-mL beaker. Containers like bottles are not efficiently
sparged even over long times and should not be used. This aliquot will be used
to determine the chlorite concentration and must be sparged immediately after
collection Field Samples that are not completely sparged will yield chlorite
concentrations that are high.
8.2.4.1 Sparge the sample using a constant flow of nitrogen or helium gas
until the chlorine dioxide is removed. This can be accomplished using
327.0-13
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a lecture bottle or gas cylinder with a regulator equipped with a
suitable length of Tygon tubing attached to a Pasteur pipette or a gas-
dispersion tube with a fritted cylinder or disk (Sect. 6.13). A new
pipette should be used for each sample. Glass gas-dispersion tubes
should be rinsed thoroughly between samples.
8.2.4.1.1 Sparging a sample contained in a beaker with nitrogen at a
flow rate of 250 mL/minute for 15 minutes using a Pasteur
pipette removed over 97% of the chlorine dioxide.
8.2.4.1.2 Laboratories should confirm that their procedure used to
sparge chlorine dioxide from Field Samples is sufficient by
analyzing a sample known to contain high levels of
chlorine dioxide ( > 2 mg/L) and evaluating its removal at
various sparge times.
8.2.4.2 Transfer an aliquot of the sparged Field Sample to a 16-mL vial.
Invert the capped vial to ensure that it is completely filled. If an air
bubble is noted, uncap the vial and add additional sparged sample as
necessary. Remove a 1.0-mL aliquot of the sparged Field Sample
from the vial using pipette tip 1 and add a 1.0-mL aliquot of the
Concentrated Citric Acid/Glycine Buffer (Sect. 7.2.2) using pipette tip
2. This step removes any free available chlorine from the sample.
Gently mix the vial by inverting it three times.
8.2.5 QC SAMPLES - Field Duplicates require collection of an extra 16-mL vial as
per Section 8.2.3 and an additional sparged sample as per Section 8.2.4. A
portion of the Field Sample sparged in Section 8.2.4 should be used for the
Laboratory Fortified Sample Matrix.
8.3 SAMPLE STORAGE - Field Samples and Field Duplicates should be analyzed as soon
as possible. Samples may be held for up to 4 hours if collected properly and stored in a
cooler at < 10 °C.
9. QUALITY CONTROL
9.1 Each laboratory using this method is required to operate a Quality Control (QC) program.
The requirements of this program consist of an Initial Demonstration of Capability (IDC),
and subsequent analysis in each analysis batch of a Continuing Calibration Check
Standard (CCC). A Laboratory Fortified Sample Matrix (LFSM) and a Field Duplicate
Sample are recommended weekly. This section details the specific requirements for each
QC parameter. The QC criteria discussed in the following sections are summarized in
Section 17, Tables 5 and 6. These criteria are considered the minimum acceptable QC
327.0-14
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criteria, and laboratories are encouraged to institute additional QC practices to meet their
specific needs.
9.2 INITIAL DEMONSTRATION OF CAPABILITY (IDC) - Requirements for the Initial
Demonstration of Capability are described in the following sections. The full IDC must
be conducted prior to the analysis of any Field Samples each time a new analyst uses the
method. Sections 9.2.1 and 9.2.2 must be repeated each time a new LGB Concentrated
Stock Solution (Sect. 7.2.3) is prepared. An acceptable Initial Calibration (Sect. 10.2)
must be conducted prior to performing the IDC.
9.2.1 INITIAL DEMONSTRATION OF ACCURACY - Process and analyze five
highest-level Calibration Standards and five reagent water Method Blanks
through the procedure described in Section 11.2. Calculate the chlorite
concentration for each Calibration Standard as described in Section 12. The
average concentration for the five replicates must be ± 30% of the fortified
value.
9.2.2 INITIAL DEMONSTRATION OF PRECISION - Using the same set of
replicate data generated for Section 9.2.1, calculate the standard deviation and
relative standard deviation (RSD) of the replicate values. The RSD is calculated
using the equation
S
RSD = -= x 100%
X
where
S is the standard deviation for the replicate values,
and X is the average value for the replicates.
The RSD of the results of the replicate analyses must be less than 20%.
9.2.3 DETECTION LIMIT (DL) DETERMINATION - Prepare and analyze at least
seven replicate CCCs at a chlorite concentration estimated to be near the DL
using the procedure described in Section 11.2 for total chlorite and chlorine
dioxide. For a 1-cm pathlength, the CCCs must be fortified with chlorite in the
concentration range of 0.20 to 0.35 mg/L or at a concentration no more than 3-
to 5-times the calculated DL. Calculate the DL using the equation
DL =
where
t(n-1, i -« = o.99)ls the Student's t value for the 99% confidence level with
n-1 degrees of freedom,
n is the number of replicates,
and S is the standard deviation of replicate analyses.
327.0-15
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Selected t values can be found in the table below.
Number of Replicates
Student's t value
7
3.143
8
2.998
9
2.896
10
2.821
11
2.764
9.2.3.1 The DL for this method is a function of pathlength and analyte
concentration. Longer pathlengths will result in improved sensitivity
and should decrease the DLs for chlorine dioxide and chlorite. DLs
for a 1-cm pathlength calculated by fortifying reagent water with
chlorite in the concentration range of 0.20 to 0.35 mg/L should be <
0.25 mg/L.
9.2.3.2 Detection Limit is a statistical determination of precision only.(1) If the
DL replicates are fortified at a low enough concentration, they may
result in a calculated DL that is higher than the fortified concentration.
Therefore no precision and accuracy are specified for the DL.
9.3 CONTINUING CALIBRATION CHECK (CCC) STANDARDS - A mid-level CCC is
prepared as described in Section 7.3.4 and analyzed with each analysis batch or each day
samples are analyzed. For a 1-cm pathlength, this CCC should have a chlorite
concentration near 1.0 mg/L. The calculated chlorite concentration for the CCC
(Sect.12.5) must be ± 30% of the expected value. If this criterion is not met, the Field
Sample(s) should be re-collected and reanalyzed after establishing acceptable CCC
recovery (Sect. 10.3.2).
9.4 FIELD DUPLICATE (FD) - A Field Duplicate is recommended weekly for both chlorine
dioxide and chlorite. Calculate the relative percent difference (RPD) between the Field
Sample (FD1) and the Field Duplicate (FD2) as shown below. The RPD for samples
with concentrations greater than the lowest calibration standard should not exceed 30%.
The RPD at concentrations at or near the lowest calibration standard (at or below 0.30
mg/L for a 1-cm pathlength) should not exceed 50%.
RPD =
\FDl - FD2\
(FDl + FD2)/2
x 100%
If the RPD for the Field Sample and the Field Duplicate falls outside the designated
range, and the laboratory performance for that analyte meets the QC performance
criterion in the CCC, the recovery is judged to be matrix biased. The result for that
analyte in the Field Sample is labeled "suspect/matrix" to inform the data user that the
results are suspect due to matrix effects.
327.0-16
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9.5 LABORATORY FORTIFIED SAMPLE MATRIX (LFSM) - A Laboratory Fortified
Sample Matrix is recommended weekly.
9.5.1 Collect a Field Sample for the LFSM as described in Section 8.2.4 and process
it as described in Section 11.4. Fortify the Field Sample using the LFSM
Fortification Solution (Sect. 7.3.5) with a chlorite concentration that is greater
than the expected concentration based on historical levels, being careful not to
exceed the upper limit of the initial calibration curve. This should be done in a
manner that does not increase the sample volume by more than 1%.
9.5.2 Calculate the recovery (R) for each analyte using the equation
(A- B)
R= -x 100%
C
where A is the measured concentration in the fortified sample, B is the measured
concentration in the unfortified sample, and C is the fortification concentration.
9.5.3 Recoveries from samples fortified at or above their native concentration should
range between 70 and 130% unless the samples were fortified at low levels
(e.g., total concentrations at or below 0.30 mg/L) where 50 to 150% recoveries
are acceptable. If the accuracy of the LFSM falls outside the designated range,
and the laboratory performance for chlorite is shown to be in control (e.g., the
QC criterion for the CCC was met), the recovery is judged to be matrix biased.
The result for that analyte in the unfortified sample is labeled "suspect/matrix"
to inform the data user that the results are suspect due to matrix effects.
10. CALIBRATION
10.1 An acceptable initial calibration must be established before Field or QC Samples are
analyzed. After initial calibration is successful, a Continuing Calibration Check (CCC) is
required during each analysis batch or each day samples are analyzed.
10.2 INITIAL CALIBRATION - An initial calibration curve must be generated prior to
conducting the IDC and prior to analyzing any Field Samples. An initial calibration is
also required after preparing new Combined LGB/HRP Reagent as described in Section
7.2.6 (at least every 2 weeks). An initial calibration curve is established by plotting the
absorbance differences (A A) between the Method Blank and a number of Calibration
Standards versus chlorite concentrations in the Calibration Standards. Studies conducted
during method development indicated that calibration curves generated for chlorite and
chlorine dioxide using the Combined LGB/HRP Reagent (Sect. 7.2.6) were similar
enough to allow the calibration for both analytes using chlorite. This procedure is
described below.
327.0-17
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10.2.1 Prepare at least three Chlorite Calibration Standards that span the intended
reporting range as described in Section 7.3.3. Five Calibration Standards are
recommended.
10.2.1.1 The high-level calibration standard should not exceed a concentration
of 2.2 mg/L. At higher concentrations, the response becomes
nonlinear.
10.2.2 Fill a 16-mL sample vial with each Calibration Standard and process each vial
along with at least one Method Blank (MB) according to the procedure outlined
in Section 11.2. Two MBs are recommended.
10.2.3 Calculate AA at 633 nm between the MB and each Calibration Standard. If two
MBs are used, use the average MB absorbance value for this calculation.
10.2.4 Plot A A for each calibration standard as a function of chlorite concentration (or
chlorine dioxide concentration, since chlorite is converted to chlorine dioxide
prior to reacting with LGB). This is a procedural calibration technique, where
the calibration standards are processed identically to the Field and QC Samples.
This eliminates the need to adjust the Calibration Standard concentrations to
account for dilutions made during the procedure.
10.2.5 Fit the data using a linear regression and determine the slope and y intercept
using the equation
AA = Slope[ClO2-] + Int.
where AA is the absorbance difference between the blank and the sample,
[C1CV] is the chlorite concentration in mg/L, and Slope and Int. are the slope
and y intercept for the linear fit, respectively.
10.2.6 The r2 value for the linear fit should be 0.98 or better. Use the equation for the
line to calculate chlorine dioxide and/or chlorite concentration.
10.2.7 Check the Initial Calibration by calculating the concentrations of the Calibration
Standards that were used to create the calibration curve. Use the linear
regression fit formula for the calculation. Each calculated concentration, except
the calculated concentration for the lowest Calibration Standard, should
calculate to be 70-130% of its expected value. The lowest Calibration Standard
should calculate to be 50-150% of its expected value. Laboratories that have
difficulty achieving these criteria will have trouble meeting the QC
requirements summarized in Section 9.
10.3 CONTINUING CALIBRATION CHECK (CCC) - A Continuing Calibration Check is
required with each Analysis Batch or each day samples are analyzed. This QC sample is
327.0-18
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processed with the Method Blank(s) and Field Sample(s) in the Analysis Batch to ensure
that the data collected in the Analysis Batch are valid.
10.3.1 Process a CCC in an identical manner to the Field Samples as described in
Section 11.2. The CCC concentration should be near the mid-point of the initial
calibration range. Calibration Standards used to prepare the initial calibration
curve may be used for this purpose. For a 1-cm pathlength, the CCC should
have a chlorite concentration at or near 1.0 mg/L.
10.3.2 Calculate the CCC concentration using the initial calibration curve generated
above (Sect. 10.2) as described in Section 12. The CCC response must be in the
range of ± 30% of the expected value. If this criterion is not met, then all data
for the Field Samples in the Analysis Batch are invalid. Remedial action should
be taken which could require establishing a new initial calibration and may
require the preparation of new reagents (the HRP and LGB solutions have the
shortest shelf lives). Field Samples should be re-collected and reanalyzed after
re-establishing acceptable QC performance.
11. PROCEDURE
11.1 As noted in Section 2.1, this procedure involves a two-step process for the determination
of chlorine dioxide and chlorite in drinking waters. The first step, described in Section
11.2, uses the Combined LGB/HRP Reagent to convert chlorite to chlorine dioxide to
measure the total concentration of both analytes. This procedure is used to process Field
Samples, Field Duplicates, and CCCs. In the second step, described in Section 11.3,
samples are sparged to remove the chlorine dioxide, and are then analyzed to determine
the chlorite concentration. Chlorite is not removed during sparging. This procedure is
used to process Field Samples and Field Duplicates. (The chlorine dioxide concentration
is calculated by subtracting the chlorite concentration determined in the second step from
the total concentration determined in the first step.) Section 11.4 describes the processing
of LFSMs, which require a slight modification to the procedure described in Section 11.3.
11.1.1 This is a headspace-free procedure. Care taken to minimize headspace will help
the analyst to achieve the QC performance criteria summarized in Section 9.
11.2 TOTAL CHLORINE DIOXIDE AND CHLORITE PROCEDURE USED TO PROCESS
FIELD SAMPLES, FIELD DUPLICATES AND CCCs
11.2.1 The unsparged samples collected in the 16-mL vials are prepared and analyzed
using the procedure described in this section. If samples have been stored (Sect.
8.3), they should be allowed to equilibrate to room temperature.
327.0-19
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11.2.2 Fill a 16-mL vial with reagent water and label it as the Method Blank. One MB
is required in each Analysis Batch (< 10 Field Samples). Two MBs are
recommended.
11.2.3 Fill a 16-mL vial with a CCC solution prepared according to the procedure
described in Section 7.3.4.
11.2.4 This procedure requires three separate pipette tips (or pipettes). Each tip will be
used repeatedly to perform the same function with each Field and QC sample.
This is not expected to cause significant contamination due to carryover.
However, care should be taken to ensure that fluid is not retained in (or on) the
pipette tip prior to performing the next transfer. These pipette tips (or pipettes)
are given numbers for clarity. The pipette tips are summarized in the table
below with their function.
Pipette Tip #
1
2
O
Used to
Remove sample and remove buffered sample
Transfer citric acid/glycine buffer
Transfer HRP/LGB mixed reagent
11.2.5 Remove a 1.0-mL aliquot from the CCC and MBs using pipette tip 1. Add a
1.0-mL aliquot of the Concentrated Citric Acid/Glycine Buffer (Sect. 7.2.2) to
the CCC and MBs using pipette tip 2.
Note: Field Samples and Field Duplicates are buffered with the Concentrated
Citric Acid/Glycine Buffer at the time of collection to remove the free available
chlorine.
11.2.6 Cap the CCC and MB vials and gently mix their contents by inverting them
three times. This step buffers the samples to a uniform pH.
11.2.7 Process all Field Samples, Field Duplicates, CCCs and MBs at the same time
through the remainder of the procedure described in this section. Be careful not
to agitate the samples any more than necessary. Uncap the vial and remove an
additional 1.0-mL aliquot using pipette tip 1. Immediately add 1.0-mL of the
Combined LGB/HRP Reagent (Sect. 7.2.6) using pipette tip 3. Cap and mix the
contents of the vial thoroughly.
11.2.8 Check the vial for headspace by inverting it and looking for an air bubble. If the
vial contains air bubbles, the sample must be re-collected (or reprepared in the
case of a CCC or MB).
327.0-20
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11.2.9 Allow the samples to react at room temperature for at least 20 minutes, but
preferably not longer than 40 minutes. Loss of color during this period is
normal and is a result of the reaction between LGB and chlorine dioxide.
11.2.10 Thoroughly mix the contents of each vial and then transfer an aliquot to a 1-cm
cuvette. The cuvette should first be rinsed with reagent water or an aliquot of the
sample. Wipe the outside of the cuvette to remove water droplets and/or finger
prints. Use the same cuvette, to measure the visible absorbance at 633 nm for
the MB(s), Field Sample(s), Field Duplicate (if processed), and CCC
minimizing the time between measurements.
11.3 CHLORITE PROCEDURE USED TO PROCESS FIELD SAMPLES AND FIELD
DUPLICATES
11.3.1 This procedure may be used as a stand-alone procedure for the determination of
chlorite or in conjunction with the procedure in Section 11.2 for the
determination of chlorine dioxide as well. The sparged samples are analyzed
using the procedure described in this section.
11.3.2 Collect, sparge, and preserve each FS or FD to remove chlorine dioxide and free
available chlorine as described in Section 8.2.4.
11.3.3 If samples have been stored (Sect. 8.3), they should be allowed to equilibrate to
room temperature.
11.3.4 Process the Field Samples and Field Duplicates through all steps described in
Sections 11.2.7 through 11.2.10.
11.4 PROCESSING LABORATORY FORTIFIED SAMPLE MATRICES (LFSMs)
11.4.1 This procedure is used for the processing of Laboratory Fortified Sample
Matrices.
11.4.2 Collect, sparge, and preserve an FS as described in Section 8.2.4. The sparged
sample should be poured into two 16-mL vials. One vial is analyzed for chlorite
using the procedure described in Section 11.3 and the other vial is fortified and
analyzed according to the procedure described below.
11.4.3 Fortify the Field Sample with the LFSM Fortification Solution (Sect. 7.3.5) that
is greater than the expected chlorite concentration based on historical
information This will require a fourth pipette tip that must not be used for
other purposes. Small amounts of the LFSM Fortification Solution can
contaminate other Field or QC samples from carryover because this
solution is highly concentrated.
327.0-21
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1 1.4.3.1 Be careful not to exceed the upper concentration of the initial
calibration curve when calculating the fortification level. Fortification
levels should be in the range of 1 - 2 times the native level so that the
chlorite concentration will be within the linear range of the initial
calibration curve.
1 1.4.3.2 As an example, to fortify a Field Sample in a 16.4-mL vial with
1.0 mg/L of chlorite, one would need to add 0.0164 mg (1.0 mg/L x
0.0164 L). This would require a 164-|iL aliquot of the LFSM
Fortification Solution ( 0.0164 mg/0.100 mg/mL = 0.164 mL or
164
11.4.3.3 If small volumes of the LFSM Fortification Solution are used (1% of
the vial volume or less), this aliquot can be delivered without first
removing a same-size aliquot to make room for reagents. If this
technique is used the analyst must be careful to insert the pipette tip
beneath the surface of the vial during delivery of the aliquot and to
check the pipette tip after delivery of the aliquot to ensure that the
entire volume has been delivered. Cap the vial once the fortification is
complete and mix thoroughly.
1 1 .4.4 Process the LFSM according to the steps described in Sections 1 1 .2.7 through
11.2.10.
12. DATA ANALYSIS AND CALCULATION
12.1 Chlorine dioxide and chlorite concentrations are calculated using an initial calibration
curve that is generated using chlorite standards. Slopes for both analytes are similar and,
therefore, no conversion factor is required in order to calculate the chlorine dioxide
concentrations.
12.2 Generate an initial calibration curve according to Section 10.2 by processing at least
three, but preferably five, initial calibration standards through the entire procedure
outlined in Section 10.2.
12.3 Establish an Initial Calibration curve as described in Section 10.2. Plot AA against the
undiluted concentration of the calibration standards.
12.3.1 Samples processed according to the method generated initial calibration curves
with slopes in the range of 0.33 - 0.38. Different vial volumes and/or reagent
volumes will cause the slopes to differ from this value.
12.4 C1O2 AND C1O2 CALCULATION: Determine the absorbance difference for each Field
and QC Sample processed according to Section 11.2, and calculate the total chlorine
327.0-22
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dioxide and chlorite concentration using the slope and intercept determined in Section
10.2. If more than one MB is prepared and analyzed in the Analysis Batch, use the
average MB absorbance when determining the absorbance difference for each sample.
12.5 C1CV CALCULATION: Determine the absorbance difference for each Field and QC
Sample processed according to Sections 11.3 and 11.4, and calculate the chlorite
concentration using the slope and intercept determined in Section 10.2. If more than one
MB is prepared and analyzed in the Analysis Batch, use the average MB absorbance
when determining the absorbance difference for each sample.
12.6 C1O2 CALCULATION: Calculate the chlorine dioxide concentration for each Field and
QC sample by subtracting the chlorite concentration (Sect. 12.5) from the total chlorite
plus chlorine dioxide concentration (Sect. 12.4).
12.7 Quantitate only those values for which the combined chlorine dioxide and chlorite
concentration falls within the concentration range defined by the lowest and highest
initial calibration standards.
12.7.1 Pathlength and reagent concentrations were carefully optimized during method
development. Analyte concentrations above 2.2 mg/L are in a concentration
range that is not linear if the reagent concentrations specified in this method for
a 1-cm pathlength are used. For this reason, analysts must not extrapolate
beyond the calibration range nor should the initial calibration range be extended
beyond this concentration.
12.7.2 Field Samples that exceed this concentration (2.2 mg/L) should be re-collected
and carefully diluted by a factor of 2 being careful to minimize unnecessary
sample agitation that will result in the loss of chlorine dioxide.
12.7.3 Analytical results obtained from dilutions should be considered estimated
values.
12.8 Analyte concentrations are reported in mg/L usually to two significant figures.
13. METHOD PERFORMANCE
13.1 PRECISION, ACCURACY, AND DETECTION LIMITS - Detection Limits for chlorite
and chlorine dioxide are presented in Section 17, Table 1 together with method precision
and accuracy in reagent water. Single laboratory precision and accuracy are presented in
Table 2 for a chlorinated surface water and in Table 3 for a chlorinated ground water.
13.2 SAMPLE STORAGE STABILITY STUDIES - A storage stability study was conducted
by fortifying 0.8 mg/L of chlorine dioxide and 1.0 mg/L of chlorite into a chlorinated
drinking water sample and analyzing at 0, 2, and 4 hours after storage at 10 °C. The data
327.0-23
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in Table 4 illustrate that chlorite concentrations are stable over a 4-hour time period when
glycine is present to eliminate the free available chlorine residual.
14. POLLUTION PREVENTION
14.1 For information about pollution prevention that may be applicable to laboratory
operations, consult "Less is Better: Laboratory Chemical Management for Waste
Reduction" available from the American Chemical Society's Department of Government
Relations and Science Policy, 1155 16th Street NW, Washington, D.C., 20036.
15. WASTE MANAGEMENT
15.1 The analytical procedures described in this method generate relatively small amounts of
waste since only small amounts of reagents and solvents are used. The matrices of
concern are finished drinking water. However, the Agency requires that laboratory waste
management practices be conducted consistent with all applicable rules and regulations,
and that laboratories protect the air, water, and land by minimizing and controlling all
releases from fume hoods and bench operations. Also, compliance is required with any
sewage discharge permits and regulations, particularly the hazardous waste identification
rules and land disposal restrictions. For further information on waste management,
consult "The Waste Management Manual for Laboratory Personnel" also available from
the American Chemical Society at the address in Section 14.1.
16. REFERENCES
1. Glaser, J.A.; Foerst, D.L.; McKee, G.D.; Quave, S.A.; Budde, W.L. "Trace Analyses for
Wastewaters," Environ. Sci. Technol. 1981, 15, 1426-1435.
2. Hollenberg, P. F.; Rand-Meir, T.; Hager, L. P. "The Reaction of Chlorite with
Horseradish Peroxidase and Chloroperoxidase," J. Biol. Chem.1914, 249, 5816-5825.
3. Hewson, W. D.; Hager, L. P. "Mechanism of the Chlorination Reaction Catalyzed by
Horseradish Peroxidase with Chlorite," J. Biol. Chem.1979, 254, 3175-3181.
4. Chiswell,B.; O'Hallaran,K.R. "Use of Lissamine Green B as a Spectrophotometric
Reagent for the Determination of Low Residuals of Chlorine Dioxide" The Analyst, 1991,
116,657-661.
5. Hoffman, R.; Andrews, R.C.;Ye, Q. "Comparison of Spectrophotometric Methods for
Measuring Chlorine Dioxide in Drinking Water," Environmental Technology, 1998, 19,
761-773.
327.0-24
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6. "OSHA Safety and Health Standards, General Industry," (29CFR1910). Occupational
Safety and Health Administration, OSHA 2206, (Revised, Jan. 1976).
7. "Carcinogens-Working with Carcinogens," Publication No. 77-206, Department of
Health, Education, and Welfare, Public Health Service, Center for Disease Control,
National Institute of Occupational Safety and Health, Atlanta, Georgia, August 1977.
8. "Safety In Academic Chemistry Laboratories," 3rd Edition, American Chemical Society
Publication, Committee on Chemical Safety, Washington, D.C., 1979.
9. "Reagent Chemicals," Sixth Edition, American Chemical Society Specifications, Official
from Jan. 1, 1982, American Chemical Society, S, Washington, D. C., 1981.
10. Peroxidase description, Sigma catalog 2002-2003, page 1635 and references contained
therein.
11. Personal communication with Technical Representative at Sigma (1-800-521-8956).
327.0-25
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17. TABLES. DIAGRAMS. FLOWCHARTS. AND VALIDATION DATA
TABLE 1: PRECISION AND ACCURACY AND DETECTION LIMITS FOR CHLORINE
DIOXIDE AND CHLORITE IN REAGENT WATER
Fortification
Concentration
C1O2
(mg/L)
0.25
0.25
not
fortified
1.0
1.0
C1O2
(mg/L)
not
fortified
0.95
0.26
0.26
0.94
Chlorite
Recovery
(%)
112
118
not
fortified
103
98.5
RSD
(%)
12
8.5
not
fortified
2.9
3.2
DLa
(mg/L)
0.11
0.078
not
calculated
not
calculated
not
calculated
Chlorine Dioxide
Recovery
(%)
not
fortified
116
102
124
111
RSD
(%)
not
fortified
3.6
5.1
16
4.8
DLa
(mg/L)
not
fortified
not
calculated
0.042
0.16
not
calculated
aBased on seven replicates analyzed over one day. Detection Limits were calculated as follows:
DL — ^>Xt(n.ij.a=o.99)
where
t(n-u-a = o 99) = Student's t value for the 99% confidence level with n-1
degrees of freedom
n = number of replicates, and
S = standard deviation of replicate analyses.
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TABLE 2: PRECISION AND ACCURACY FOR CHLORITE AND CHLORINE DIOXIDE
IN A CHLORINATED SURFACE WATER3
Fortification Level
C1O2
(mg/L)
1.0
not fortified
1.0
2.0
not fortified
C1O2
(mg/L)
not fortified
0.82
0.82
not fortified
1.94
Chlorite
Recovery
(%)
107
not fortified
109
105
not fortified
RSD
(%)
4.2
not fortified
3.7
1.4
not fortified
Chlorine Dioxide
Recovery
(%)
not fortified
100
91.3
not fortified
96.9
RSD
(%)
not fortified
1.9
8.9
not fortified
1.0
aThe drinking water used in these studies had a free available chlorine concentration of 0.9 mg/L.
327.0-27
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TABLE 3: PRECISION AND ACCURACY FOR CHLORITE AND CHLORINE DIOXIDE
IN A CHLORINATED GROUND WATER3
Fortification Level
C1O2
(mg/L)
1.0
not fortified
1.0
2.0
not fortified
C1O2
(mg/L)
not fortified
0.90
0.90
not fortified
2.0
Chlorite
Recovery
(%)
110
not fortified
107
100
not fortified
RSD
(%)
4.4
not fortified
1.6
2.7
not fortified
Chlorine Dioxide
Recovery
(%)
not fortified
92.0
93.8
not fortified
110
RSD
(%)
not fortified
3.3
3.0
not fortified
1.7
aThe drinking water used in these studies had a free available chlorine concentration of
0.8 mg/L and a hardness of 325 mg/L (CaCO3).
327.0-28
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TABLE 4: STORAGE STABILITY FOR CHLORITE AND CHLORINE DIOXIDE IN A
CHLORINATED SURFACE WATER SAMPLE3
Holding
Time
(Hours)
0
2
4
Chlorite Fortified
at 1.0 mg/L
Recovery
(%)
83.3
100
99.3
RSD
(%)
2.5
6.6
2.4
Chlorine Dioxide and
Chlorite Fortified at a Total
Concentration of 1.8 mg/Lb
Recovery
(%)
97.3
98.1
98.1
RSD
(%)
1.4
1.4
2.8
a The drinking water used in these studies had a free available chlorine concentration of 0.9 mg/L.
b Chlorine dioxide and chlorite were fortified into the chlorinated drinking water sample using
concentrated standards just prior to preserving the samples so that the concentrations in the
surface water were 0.80 and 1.0 mg/L, respectively.
327.0-29
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TABLE 5: INITIAL DEMONSTRATION OF CAPABILITY (IDC) REQUIREMENTS
Method
Reference
Requirement
Specification and
Frequency
Acceptance Criteria
Section
9.2.1
Initial Demonstration
of Accuracy
Prior to the analysis of any
Field Samples by a new
analyst and each time a new
LGB Concentrated Stock
Solution is prepared, process
five highest-level calibration
standards. Calculate the
average concentration for
five standards.
Mean concentration must be
within ± 30% of the fortified
value.
Section
9.2.2
Initial Demonstration
of Precision
Using the same data from
Section 9.2.1, calculate the
RSD.
RSD must be < 20%.
Section
9.2.3
Detection Limit
Determination
Prior to the analysis of any
Field Samples by a new
analyst, prepare and analyze
a minimum of seven
replicate CCCs fortified at a
chlorite concentration of
0.20 - 0.35 mg/L if using the
1-cm pathlength procedure.
Calculate the DL using the
equation in Section 9.2.3.
DL should be < 0.25 mg/L
when using the 1-cm
pathlength procedure.
327.0-30
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TABLE 6: QUALITY CONTROL REQUIREMENTS (SUMMARY)
Method
Reference
Requirement
Specification and Frequency
Acceptance Criteria
Section 8.:
Sample
Storage
Analyze samples as soon as
possible. Samples may be stored at
< 10°C for up to 4 hours
Sample results are valid only if
samples are analyzed within
holding time.
Section
10.2
Initial
Calibration
Calibrate with at least three
calibration standards prior to the
IDC and each time a new
Combined LGB/HRP Reagent is
prepared.
Five calibration standards are
recommended.
Highest level for the 1-cm
pathlength procedure must not
exceed 2.2 mg/L.
When each calibration standard
is calculated as an unknown
using the calibration curve, the
result should be 70-130% of the
expected value for all except
the lowest standard, which
should be 50-150% of the
expected value.
Sections
9.3 and
10.3
Continuing
Calibration
Check (CCC)
Verify initial calibration by
analyzing a mid-level CCC each
day samples are analyzed.
The CCC should be at or near 1.0
mg/L for the 1-cm pathlength
procedure.
The calculated chlorite
concentration must be ± 30% of
the expected value.
Section 9.4
Field
Duplicate (FD)
An FD is recommended weekly.
Calculate RPD according to
Section 9.4.
RPD should not exceed 30%
for concentrations above the
low-level calibration standard.
RPD should not exceed 50%
for concentrations at or near the
low-level calibration standard
(at or below 0.3 mg/L for the 1-
cm pathlength procedure).
Section 9.5
Laboratory
Fortified
Sample Matrix
(LFSM)
An LFSM is recommended weekly.
Calculate Recovery according to
Section 9.5.
Recovery should be 70 - 130%
except for samples fortified at
low levels (total concentrations
at or below 0.3 mg/L for the 1-
cm pathlength procedure),
where the Recovery should be
50- 150%.
327.0-31
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