CARBON MONOXIDE IN WORKPLACE ATMOSPHERES
Method Number: |
ID-210 |
|
Matrix: |
Air |
|
OSHA Permissible Exposure Limits
Final Rule Limits: |
35 ppm Time Weighted Average (TWA)
200 ppm Ceiling (5-min sample) |
|
Transitional Limit: |
50 ppm TWA |
|
Collection Procedure: |
Each sample is collected by drawing a known volume of air into a five-layer
aluminized gas sampling bag. |
|
Recommended Air Volume: |
2 to 5 liters |
|
Recommended Sampling Rates
TWA Determination:
Ceiling Determination: |
0.01 to 0.05 L/min
1 L/min |
|
Analytical Procedure: |
A portion of the gas sample is introduced into a gas sampling loop,
injected into a gas chromatograph, and analyzed using a discharge ionization detector. |
|
Detection Limits (TWA, Ceiling)
Qualitative:
Quantitative: |
0.12 ppm
0.40 ppm |
|
Precision and Accuracy
Validation Range:
CVT(pooled):
Bias:
Overall Error: |
17.2 to 63.6 ppm
0.025
+0.058
±10.8% |
|
Special Requirements: |
Samples should be sent to the laboratory as soon as possible and analyzed
within two weeks after collection. |
|
Method Classification: |
Validated method |
|
Chemist: |
Robert G. Adler |
|
Date: |
March, 1991 |
Commercial manufacturers and products mentioned in this method are for descriptive
use only and do not constitute endorsements by USDOL-OSHA. Similar products
from other sources can be substituted.
Inorganic Methods Evaluation Branch
OSHA Salt Lake Technical Center
Salt Lake City, Utah
1. Introduction
1.1 History
The recent change in the TWA Permissible Exposure Limit (PEL) for carbon monoxide (CO)
from 50 to 35 ppm (5.1.) and the inclusion of a Ceiling of 200 ppm (5-min
sample) (5.2.) stimulated a review of the methods used for the analysis of CO in workplace
atmospheres, including both direct-reading and classical (TWA) collection
procedures. In the past, the OSHA sampling and analytical method for CO required the use
of direct-reading procedures for monitoring (5.3.). One direct-reading
procedure involved the use of CO short-term detector tubes (5.4.), and a
recent evaluation at the OSHA Salt Lake Technical Center (OSHA-SLTC) has been
carried out on several of these tubes (5.5.). Short-term detector tubes offer
only spot checks of the environment, and sampling procedures capable of determining long-term
CO concentrations are preferred. A long-term direct-reading method for
compliance determinations was performed by OSHA compliance officers using an
electrochemical detector (Ecolyzer, Energetics Science, Inc., Elmsford, NY). However, this
instrument required constant calibration, readings were subject to drift and were
difficult to assess for TWA determinations, and personal samples were difficult to take
without using gas sampling bags. It was for these reasons that the current study was
undertaken.
Previous classical methods found in the literature for the analysis of CO have
consisted of the collection of air samples in gas bags or canisters with analysis either
by infrared absorption spectrophotometry (5.6.), electrochemical means (5.7.), or gas
chromatography using a flame ionization detector (5.8.).
Gas chromatography (GC) offers many advantages for CO analysis (5.4., 5.9.); however,
because the sensitivity for CO by a flame ionization detector (FID) is extremely low, it
is necessary to react hydrogen with CO on a catalyst such as heated nickel to produce
methane before FID analysis can be performed at the levels of interest (5.5., 5.8.). This
methanization procedure introduces an additional step, since it is necessary to identify
any methane in the sample, and makes the analysis more complex. Also, the hydrogen gas
used in the conversion of CO to methane is sometimes contaminated with methane.
With the recent development of the discharge ionization detector (DID) for use with GC
analysis, it is possible to measure CO concentrations directly at very low levels (5.10.).
Helium is generally used as the sample carrier gas and as the ionized species. In the
detector, helium is passed through a chamber where a glow discharge is generated and high-energy
photons are produced. These pass through an aperture to another chamber where they ionize
the gas or vapor species in the sample stream. The resulting electrons are collected for
quantitative determination by a standard electrometer. This is the method of detection
employed in the current method.
1.2. Principle
1.2.1. A low-flow rate sampling pump is used to capture a known volume of air in a five-layer
gas sampling bag (5-L).
1.2.2. A GC fitted with a gas sampling loop and a DID is used to assess CO sample
concentrations.
1.3. Method Performance
1.3.1. Range, detection limit, and sensitivity:
- The upper analytical range used during the evaluation of this method was about 430 ppm;
the upper linear range for CO may be much larger than this concentration.
- The qualitative detection limit was 0.12 ppm for a 1-mL gas sample (size of
GC gas sampling loop). The quantitative detection limit was 0.40 ppm. If necessary, a
larger sampling loop can be used to achieve a lower limit of detection.
- The sensitivity of the analytical method [using analytical conditions stated for a
Tracor 540 GC (Tracor Instruments Austin, Inc., Austin TX) and Hewlett-Packard
3357 Laboratory Automation System, Revision 2540 (Hewlett-Packard Co.,
Avondale PA)] was taken from the slope of the linear working range curve (1.70 to 63.6 ppm
range). The sensitivity is 1,970 area units per 1 ppm. (For the HP 3357 Automation System,
1 area unit = 1 µV· s.)
1.3.2. Precision, accuracy, and stability:
- The pooled coefficient of variation for the sampling and analytical method from 17.2 to
63.6 ppm was 0.025.
- The average recovery of generated samples taken in the 17.2-63.6 ppm range
at 50% RH was 105.8%. The range of bias was -0.01 to +0.10. The Overall Error (OE) was
±10.8%.
- Precision and accuracy data were derived from generated samples and prepared standards
that were aged 4 days or less. The stability of CO in sampling bags is acceptable up to 2
weeks after sample collection.
- Stability tests indicated that significant scatter in the results and lower recoveries
tended to appear after prolonged storage. Use of new bags free of small leaks and internal
deposits may prolong sample stability. Samples should be analyzed as soon as possible to
minimize storage problems.
1.4. Advantages and Disadvantages
1.4.1. The method is specific for CO. The method is also applicable in measuring
compliance to Indoor Air Quality Standards for CO [9 ppm (8 h), 35 ppm (1 h)] (5.11.).
1.4.2. Using similar procedures, sampling and analysis for carbon dioxide (CO2)
is also possible provided the molecular sieve column is eliminated from the gas stream
during CO2 analysis.
1.4.3. Gas sampling bags are employed and may be somewhat inconvenient to use.
1.4.4. Changes in humidity do not affect sample collection.
1.4.5. The bulk of the sample is not destroyed during analysis. Other potentially toxic
gases may also be analyzed from the same sample.
1.4.6. The gas bags used as sample collection media are reusable.
1.4.7. The method requires the use of a GC equipped with a DID.
1.4.8. Analytical time required per sample is within 20 min when using the conditions
specified.
1.4.9. Gas bag samples are stable for approximately 2 weeks. Samples should be analyzed
as soon as possible.
1.5. Physical Properties of CO (5.12., 5.13.)
Molecular weight |
28.01 |
Molecular formula |
CO |
Appearance |
Colorless, odorless gas |
Explosive limits in air |
12.5 to 74.2% (v/v) |
Autoignition temperature |
651 °C |
Melting point |
-207 °C |
Boiling point |
-191.3 °C |
Specific gravity (air = 1) |
0.968 |
Density, gas* |
1.250 g/L |
Density, liquid |
0.793 |
Solubility
At 0 °C
At 25 °C |
3.54 mL/100 mL water
2.14 mL/100 mL water |
* Value indicated is at 0 °C, 101.3 kPa (760 mmHg). |
1.6. Carbon Monoxide (CAS No. 630-08-0) Prevalence and Use With the single exception of
CO2, the total yearly emissions of CO exceed all other
atmospheric pollutants combined (5.13.). Some of the potential sources for CO emission and
exposure are listed (5.13., 5.14.):
Foundries
Petroleum refineries
Fluid catalytic crackers
Fluid coking operations
Moving-bed catalytic crackers
Kraft pulp mills
Carbon black manufacturers
Steel mills
Coke ovens
Basic oxygen furnaces
Sintering operations
Formaldehyde manufacturers
Coal combustion facilities
Utility and large industrial boilers
Commercial and domestic furnaces
Fuel oil combustion operations
Power plants
Industrial, commercial, and domestic uses
Charcoal manufacturers
Meat smokehouses
Sugarcane processing operations
Motor vehicles
1.7. Toxicology
(Information contained within this section is a synopsis of present knowledge of the
physiological effects of CO and is not necessarily intended to be used as the basis for
OSHA policy.)
Carbon monoxide has over a 200-fold greater affinity for hemoglobin than has oxygen
(5.15., 5.16.). Thus, it can make hemoglobin incapable of carrying oxygen to the tissues.
Also, the presence of CO-hemoglobin interferes with the dissociation of the
remaining oxyhemoglobin, further depriving the tissues of oxygen (5.12., 5.13.).
The signs and symptoms of CO poisoning include headache, nausea, weakness, dizziness,
mental confusion, hallucinations, cyanosis, and depression of the S-T segment
of an electrocardiogram. Although most injuries in survivors of CO-poisoning
occur to the central nervous system, it is likely that myocardial ischemia is the cause
for many CO-induced deaths (5.15.).
The uptake rate of CO by blood when air containing CO is breathed increases from 3 to 6
times between rest and heavy work. The uptake rate is also influenced by oxygen partial
pressure and altitude (5.17.).
Carbon monoxide can be removed through the lungs when CO-free air is
breathed, with generally half of the CO being removed in one hour. Breathing of 100%
oxygen removes CO quickly.
Acute poisoning from brief exposure to high concentrations rarely leads to permanent
disability if recovery occurs. Chronic effects from repeated exposure to lower
concentrations have been reported. These include visual and auditory disturbances and
heart irregularities. Where poisoning has been long and severe, long-lasting
mental or nerve damage has resulted (5.12.).
The following table gives the levels of CO-hemoglobin in the blood which
tend to form at equilibrium with various concentrations of CO in the air and the clinical
effects observed. (5.18.):
Atmospheric
CO (ppm) |
COHb in
Blood (%) |
Symptoms |
|
70 |
10 |
Shortness of breath upon vigorous exertion; possible tightness across the forehead. |
|
120 |
20 |
Shortness of breath with moderate exertion; occasional headache with throbbing in the
temples. |
|
220 |
30 |
Decided headache; irritability; easily fatigued; disturbed judgment; possible
dizziness; dimness of vision. |
|
350-520 |
40-50 |
Headache; confusion; collapse; fainting upon exertion. |
|
800-1220 |
60-70 |
Unconsciousness; intermittent convulsions; respiratory failure; death if exposure is
prolonged. |
|
1950 |
80 |
Rapidly fatal. |
|
Adults (non-smokers) normally have about 1% CO-hemoglobin in the body.
Cigarette smokers generally have blood levels of 2 to 10% CO-hemoglobin
(5.17.).
In examining the CO levels in an occupational environment, consideration may also need
to be made for CO generated from tobacco smoking. These amounts may ordinarily be small,
but when added to the amounts generated by occupational activities, may aggravate
conditions from an already existing high concentration of CO (5.19., 5.20.).
1.8. Other Hazardous Properties
Carbon monoxide is flammable and is a dangerous fire and explosion risk. The flammable
limits in air range from 12 to 75% by volume (5.16.).
2. Sampling
2.1. Safety Precautions
2.1.1. Attach the sampling equipment to the worker in such a manner that it will not
interfere with work performance or safety.
2.1.2. Follow all safety practices that apply to the work area being sampled.
2.2. Equipment
Note: The gas sample taken will contact the pump and tubing during collection.
The filter (if available) of the pump should be clean and chemically inert to CO as well
as any material inside the pump that the sample comes in contact with. Pumps used to
evaluate the method were: Du Pont Model No. P-125 pumps [E. I. Du Pont de
Nemours and Co. (Inc.), Wilmington, DE] for the TWA portion, and SKC Model No. 224-30
pumps (SKC Inc., Eighty Four, PA) for the Ceiling studies. The tubing also must not affect
the CO concentration. Tygon tubing was used for method validation and therefore is
specified to be used in this procedure.
2.2.1. Use a personal sampling pump capable of delivering a flow rate of approximately
0.01 to 0.05 L/min for TWA PEL samples. Use a larger flow rate pump (1 L/min) for Ceiling
PEL measurements. Either pump must have an external inlet, an outlet port, and hose barbs.
2.2.2. Use five-layer aluminized gas sampling bags (5-L) as the collection media (the
bags can be obtained from the OSHA-SLTC or Calibrated Instruments Inc.,
Ardsley, NY).
2.2.3. Make pump, sampling media, and breathing zone connections with various lengths
of flexible Tygon tubing.
2.3. Sampling Procedure
2.3.1. Calibrate the personal sampling pumps. Since the sampling bags have a total
volume capacity of approximately 6 L, a sampling scheme for TWA PEL measurements is shown:
Flow Rate (L/min) |
Sampling Time (h) |
Sample Vol(L) |
0.015 |
4 |
3.6 |
0.022 |
4 |
5.3 |
0.035 |
2.5 |
5.3 |
0.050 |
1.5 |
4.5 |
Take as large a sample as possible (<6 L) during the time frame used for sampling. A
large flow rate (0.04-0.05 L/min) will require replacing sampling bags
throughout the day. For TWA PEL determinations, a flow rate of approximately 0.020-0.025
L/min is sufficient for a 4-h sample. For Ceiling PEL samples, calibrate the
pump to approximately 1 L/min.
2.3.2. Evacuate and check the gas sampling bags for leaks. Each sampling bag can be
evacuated and leak tested by applying a vacuum to the bag. If a vacuum is applied to a
leaky sampling bag, the bag will not fully collapse. If a vacuum pump is not available,
inflate the gas sampling bags with nitrogen (N2), let them sit
overnight, inspect for leaks, and then evacuate by hand rolling and flattening.
2.3.3. Label each sampling bag. Attach one end of a piece of flexible tubing to the
inlet hose barb of the pump, and place the other end in the breathing zone of the worker.
Use another piece of tubing to connect the metal valve sampling bib of the sampling bag to
the outlet hose barb of the pump. A graphic representation of the pump set-up
is shown:
2.3.4. For personal sampling, attach the gas sampling bag to any loose fitting clothing
on the worker's back or side with tubing clamps.
2.3.5.When ready to sample, open the gas sampling bag valve by rotating the metal valve
counter-clockwise until fully open. Attach the free end of the tubing
connected to the bag to the outlet hose barb of the pump. Turn on the pump. For Ceiling
PEL determinations, sample for 5 min; for TWA measurements, sample up to 4 h.
Note: If the employee being monitored is smoking a tobacco product during sampling, a
positive contribution of CO from the combustion of tobacco may occur for personal samples.
Ask the employee to refrain from smoking during sampling so that only the occupational
exposure is measured.
2.3.6. After sampling, rotate the valve clockwise until tight. Place an OSHA-21
seal over the metal valve. Record the total air volume taken.
2.3.7. Prepare samples and paperwork for submission to the laboratory. Do not prepare
any blank samples. Request analysis for carbon monoxide.
2.3.8. When submitting sampling bags for analysis, pack loosely and pad generously to
minimize potential damage during shipment. Submit samples to the laboratory as soon as
possible after sampling.
3. Analysis
3.1. Safety Precautions
3.1.1. Refer to instrument manuals and operating procedures for proper operation of the
instruments.
3.1.2. Observe laboratory safety regulations and practices.
3.1.3. Prepare all CO standards in a well ventilated exhaust hood. AVOID inhaling CO.
3.2. Equipment
3.2.1. Instruments:
A GC fitted with a 1-mL stainless steel gas sampling loop, sampling valve, and DID is
used. Loops other than 1 mL can also be used.
3.2.2. Standard media:
Five-layer aluminized gas sampling bags are used.
3.2.3. Columns:
A 4-foot × 1/8-inch stainless steel, 60-80 mesh, Hayesep Q column and a 12-foot
× 1/8-inch stainless steel, 60-80 mesh, molecular sieve 5A
column (in this order) are used.
3.2.4. Data reduction:
An electronic integrator is used to calculate peak areas.
3.2.5. Standard generation:
Certified CO standards can be used or standards can be prepared using any combination
of: Calibrated gas-tight syringes or calibrated rotameters, mass flow
controllers, or soap bubble flowmeters. A stopwatch is also necessary.
3.2.6. Additional accessories:
A personal sampling pump, with inlet and outlet ports and hose barbs, is used to load
the gas sampling loop (loop loading can also be manually performed by squeezing the
sampling bag).
3.3. Reagents (Gases)
3.3.1. A commercially prepared, bottled mixture of CO diluted with either air or N2
is suitable for generating gas standards. The CO concentration must be certified. If a
soap bubble flowmeter (~1 L/min) is used for standard preparation, a mixture containing
100 ppm CO is convenient. If a gas-tight calibrated syringe (~0 to 30 mL) is
used, a mixture containing 5,000 ppm is suitable.
3.3.2. Filtered, compressed, CO-free air is used for dilutions when necessary. A
convenient source of pure air is a cylinder of USP (United State Pharmacopeia) grade air.
Small amounts of CO can be removed from the air by using a catalytic filter unit
containing hopcalite to convert any CO to CO2.
3.3.3. Helium (research grade, <1 ppm impurities) is used as the carrier gas.
3.4. Standard Preparation
Prepare standards by either using a calibrated syringe or metered delivery of CO using
flow measurement. When a soap bubble flow meter is used for gas flow measurements, apply
water vapor corrections if necessary, since the gas flowing through the meter expands
somewhat upon saturation with water vapor. As an example, consider the case where dry gas
at 101.3 kPa pressure (760 mmHg) enters a flow meter and is saturated with water vapor
[vapor pressure = 2.9 kPa (22 mmHg)]. In this case the gas volume (and therefore the gas
flow rate) will be measured at (104.2/101.3 = 1.029) times the actual values. Specific
cases of whether or not to use vapor corrections are given below.
Note: Commercially prepared standards in gas cylinders, if available, can be used in
place of laboratory-prepared standards. It is recommended to use at least two
standards to prepare a concentration-response curve. One of the commercial
standards should be above the anticipated concentration of the samples.
A standard generation scheme using 100-ppm CO with metered delivery is proposed as
follows:
Standard (ppm) |
100-ppm CO Volume (L) |
Volume of Air (L) |
Blank |
0.00 |
4.00 |
10 |
0.40 |
3.60 |
17 |
0.68 |
3.32 |
35 |
1.40 |
2.60 |
70 |
2.80 |
1.20 |
100 |
4.00 |
0.00 |
Other dilution schemes with different size gas bags and gas volumes can be used. For
other concentrations of CO, use the following equation:
Where:
A = CO concentration (ppm) in the pre-diluted mixture,
B = Pre-diluted CO mixture volume (L),
C = Diluent air volume (L).
Note: % CO = ppm/10,000; i.e., if starting with a 0.50% CO
mixture, A = 5,000 ppm.
Pure CO (A = 1 × 106) can also be used for standard
preparation. Prepare standards in concentrations that bracket the sample concentrations.
Always prepare a blank standard to assure that the diluent air is not contaminated with
CO. Completely evacuate and flush the gas bags to be used for standard preparation with CO-free
air or N2. After cleaning, meter a fixed amount of CO-free air
into the bag. Add the certified CO mixture to the gas bags by either of the following two
procedures:
Note: All mixtures should be prepared within the confines of an exhaust hood.
3.4.1. Metered generations: Use a mass flow controller or calibrated rotameter to
verify and control the CO mixture delivery rate from a gas cylinder. Use a soap bubble
flowmeter before and after the standard generation to verify the CO mixture flow rate.
Meter a known volume of CO-free air. Use a stopwatch or programmed valve to
determine the volume of CO mixture delivered over time. If a soap bubble flowmeter is used
to measure both the CO gas mixture and the diluent air volumes, any vapor effect is
canceled out, and vapor corrections are not necessary.
3.4.2. Syringe injections: Use a calibrated gas-tight syringe to obtain a
known volume either from an in-line cylinder septum or from a separate gas
sampling bag filled with the concentrated CO mixture. Most gas bags have injection ports
or septa for gas syringe withdrawal or injection. Fill and flush the gas-tight
syringe with the concentrated CO mixture. After flushing, withdraw the required volume of
the CO mixture and inject into a gas bag already containing diluent air. If a
"dry" CO gas mixture is injected with a syringe into a gas bag containing air in
which the diluent air flow has been measured with a soap bubble flowmeter, the diluent air
volume must be corrected for water vapor effect.
3.5. Sample Preparation
No special preparations are necessary; however, the analyst should visually inspect the
volume of the bags upon receipt and compare with the field air volumes in order to assess
the possibility of leaks.
3.6. Sample Analysis
3.6.1. Recommended GC conditions:
Settings for a Tracor Model No. 540 GC and Model No. 706 DID are given in Appendix 1.
Other settings may apply to different GCs.
3.6.2. Sample and standard introduction:
- Connect the outlet port of the personal sampling pump to the sampling loop via inert
tubing.
- Adjust the pump to give a suitable flow rate for sample loading from the bag to the
sampling loop.
- Connect a short piece of tubing from the inlet port of the pump to the sample bag. Turn
the bag valve counterclockwise to the open position and turn on the pump.
- After the sample is loaded into the loop (which is vented to the atmosphere), turn off
the pump to allow the loop sample to return to atmospheric pressure. Wait 1 to 2 min for
pressure equalization and then open the gas sampling valve. Carrier gas flow is now
directed through the sampling loop to the column and detector.
Note: Samples and standards can be introduced into the loop without a pump by simply
squeezing a sufficient amount of sample from the bag into the loop. The sampling bag must
be released for loop sample pressure normalization before opening the gas sampling valve.
- Perform two determinations of each sample and standard.
3.6.3. Depending on column and GC flow characteristics, CO retention times are in the
range of 12 to 14 min.
3.7. Interferences
The GC determination of CO is relatively specific; however, any compound having a
similar column retention time as CO is a potential interference. Interferences can be
minimized by altering operational conditions such as oven temperature and column packings.
Using the conditions stated within this method, other common gases and vapors do not
present serious potential interferences. Carbon dioxide is adsorbed on the molecular sieve
column and does not interfere. Hydrogen, oxygen, nitrogen, methane, and carbon monoxide
will elute in the order listed (5.10.). However, the CO peak will normally appear on the
shoulder of the N2 peak for air; therefore, GC conditions should
be set so that a distinct CO peak is obtained. A chromatogram showing the elution of CO in
N2 is shown in Figure 1.
If necessary, the sample can be analyzed by GC-mass spectrometry to
confirm the presence of CO; however, since CO has nearly the same molecular weight as N2,
low resolution mass spectrometry may not distinguish the two if the peaks are not well
separated.
3.8. Calculations
3.8.1 If blank correction is necessary for the standards, subtract the blank peak area
from the standard area readings before constructing the concentration-response
curve. No blank correction is necessary for the samples.
3.8.2. Calculate CO concentrations from a least-squares regression curve.
Establish the curve with peak area or peak height versus ppm. Results are calculated in
units of ppm. No calculations using air volumes are necessary since gas phase samples are
compared directly to gas phase standards.
3.8.3. Report results to the industrial hygienist as ppm CO.
4. Backup Report
Experimental Protocol
The validation of the method consists of the following experimental protocol:
- Analysis of three sets of six spiked carbon monoxide (CO) samples having concentration
ranges of approximately 0.5, 1, and 2 × TWA PEL.
- Analysis of three sets of six dynamically generated CO samples having concentration
ranges of approximately 0.5, 1, and 2 × TWA PEL. Also, analysis of six generated samples
having a concentration close to the Ceiling PEL value.
- Determination of the storage stability of CO samples collected in gas sampling bags.
- Determination of any variation in results when sampling at low and high humidity levels.
- Determination of the qualitative and quantitative detection limits for the analysis of
CO.
- Comparison with a previous GC method used for CO determinations in which the CO was
reduced to methane and analyzed with a flame ionization detector (FID).
- Assessment of the performance of this method and conclusions.
All samples, blanks, and standards used for validation were analyzed by direct
injection into a 1-mL gas sampling valve in the GC as mentioned in the
method. A Tracor Model No. 540 GC equipped with a Model No. 706 DID was used. Integrated
peak areas were used as a measure of instrument response. Analytical parameters used
during these experiments are listed in Appendix 1. All results were statistically examined
for outliers and, when necessary for pooling results, for homogeneous variance. Possible
outliers were determined by using the American Society for Testing and Materials (ASTM)
test for outliers (5.21.). Homogeneity of the coefficients of variation was determined
using the Bartlett's test (5.22.). Overall Error (5.23.) Was calculated as: OEi = ± [|mean biasi| + 2CVi] × 100%
where i is the respective sample pool being examined.
4.1. Analysis (spiked samples)
Procedure: Three sets of spiked samples were prepared and analyzed as
follows:
4.1.1. Samples were prepared according to the following procedure:
- Gas sampling bags were flushed several times with N2. A vacuum
was then applied to completely collapse the bags.
- Air (USP grade) was used as a diluent after flowing through an Ecolyzer No. 7915 Zero
Air Filter. A known amount of air was metered into each sampling bag. Compressed air flow
rates were measured before and after each bag filling using a soap bubble flowmeter (Model
M-5, A. P. Buck, Inc., Orlando, FL). Air flow was regulated with a regulator-rotameter
system. Blank samples of the compressed air were periodically collected and analyzed along
with the samples and standards.
- A known amount of CO was injected into each sampling bag containing diluent air using a
calibrated gas syringe. A gas cylinder containing 0.50% CO in N2
(certified, Linde Div., Union Carbide Corp., Denver, Colorado) was used as the CO source.
4.1.2. Analytical standards were prepared according to the following procedure:
- Standards were prepared by dilution of 104-ppm CO in N2
(certified, Airco, Inc., Murray Hill, NJ) with USP grade air.
The CO content of the
cylinder was confirmed employing a simplified modification of a method used by Grant,
Katz, and Haines (5.24.). A known volume of the 104-ppm CO was passed through
iodine pentoxide contained in a glass tube at about 150 °C. The resulting iodine was
collected in an aqueous solution of potassium iodide. The amount of iodine formed was
determined by titration using standard thiosulfate solution with starch as the indicator
(5.25.). Two samples were collected. Carbon monoxide concentration determinations of 99.4
and 95.4 ppm (95.6% and 91.7% recovery respectively) were obtained. Previous work had
demonstrated that the results for this procedure tend to be slightly lower than expected
(5.24.). For the present work, the given concentration of 104 ppm was used.
- Known amounts of CO and air were metered into gas sampling bags as described in Section
4.1.1. above.
4.1.3. These samples and standards were analyzed within 4 days of preparation.
Results: Spiked sample recoveries (found/taken) are listed in Table 1. All
analysis data passed the ASTM outlier test. The Bartlett's test valve (13.73) was high,
most likely because the mean and standard deviation values at 1 × TWA PEL were
exceptionally better than the other levels tested.
Note: When a set of results fails the Bartlett's test, possible options are to
reject the results as being derived from significantly different sample populations, or
adopt the CV at the PEL as the "Pooled CV". In this case the CV1
(Pooled) result was used instead. This appears more conservative since CV1
(Pooled) > CV1 (TWA PEL).
The data (Table 1) indicated good precision and accuracy. The CV1
was 0.038 and the average analytical recovery was 98.1%.
4.2. Sampling and Analysis (Generated samples)
Procedure: Three sets of generated samples at 0.5, 1, and 2 × TWA PEL were
prepared and analyzed.
4.2.1. Samples were prepared according to the following procedure:
- Gas sampling bags were flushed several times with N2. A vacuum
was then applied to completely collapse the bags.
- A dynamic gas generation system was assembled as shown in Figure 2. Moisture and other
contaminants were removed from the diluent air by using a charcoal/Drierite/silica gel
filtering system. A humidity, temperature, and flow control system (Model HCS-301,
Miller-Nelson Research Inc., Monterey, CA) was used to treat the diluent air
to produce the stated RH at 25 °C. Diluent air flow was measured before and after each
experiment using a dry test meter (Model DTM-115, American Meter Co.,
Philadelphia PA). The flow control system was calibrated in-house for
temperature and humidity prior to use.
- The CO (0.5% in N2) was introduced into the flow system via a
glass mixing chamber. Gas flow rates were taken immediately before and after each
experiment using a soap bubble flowmeter (Model 823-1, Mast Development Co.,
Davenport, IA). Flow rates were controlled using a mass flow controller (Model FC-261,
Tylan Corp., Torrance, CA).
To assure continuous generation of controlled
concentrations of CO and provide an additional verification of concentrations, the flow
system was continuously monitored during each test with a direct-reading
instrument [Model 7140 (for CO), Interscan Corp., Chatsworth, CA] connected to the flow
system. Calibration of the instrument was performed with a 40-ppm calibrating
gas (certified, Alphagaz, Cambridge, MD).
4.2.2. Samples were analyzed within 2 days after preparation; standards were used
within 4 days after preparation.
4.2.3. Six samples with a CO concentration near the Ceiling PEL (200 ppm) were also
generated using the system described above. Standards were prepared by injection of CO
(0.5% in N2) using a calibrated gas syringe into a gas bag
containing a known volume of USP grade air. Samples and standards were analyzed 4 days
after preparation.
Results: Recoveries for generated samples at 0.5, 1, and 2 × TWA PEL are
listed in Table 2a. The Sampling and Analysis date showed good precision and accuracy. All
data passed the outlier test. The Bartlett's test value (9.92) was slightly higher than
the critical value (9.23), again probably due to greater precision for the TWA PEL
results. The data were pooled, since it was felt a significant amount of error would not
be introduced by pooling. The CV2 (Pooled) value is similar to
that found during the humidity studies (Section 4.4.).
Recoveries for the samples generated at the Ceiling PEL level are given in Table 2b.
These results showed excellent recovery.
The results are summarized as follows:
PEL |
Ave. Recov. (%) |
CV |
TWA |
105.8 |
0.020 |
Ceiling |
100.0 |
0.025 |
4.3. Stability Test
Procedure: A long-term evaluation of sample media stability was performed
to determine any potential problems if delays in sample analyses occur. Five-layer
aluminized gas sampling bags (5-L) containing generated samples were used to
assess CO storage stability. Samples were generated at 1 and 2 × TWA PEL and 80% RH.
Samples were analyzed at various times up to 39 days after sample collection.
Samples were also generated at 0.5 × TWA PEL and 80% RH; however, a few of the bags
used for this experiment appeared to have some leakage and technical problems occurred
during analysis.
Results: Recovery data are listed in Table 3 and graphically represented in
Figure 3 (normalized data). One result for 1 × PEL at 8 days of storage is not included
in Figure 3 since it appeared to be unrealistically high; The GC appeared to display some
instability on the day these samples were analyzed.
Previously, different types of gas sampling bags were evaluated for stability,
structural integrity, and compactness. The five-layer aluminized bag (5-L)
was considered more durable than Tedlar or Saran. The storage stability of CO using this
sampling bag was acceptable for up to two weeks. In this time frame, average sample
recoveries were within 10% of what was found at the beginning of each experiment.
Significant problems occurred when samples were analyzed after two weeks. Results
displayed significant scatter and low recoveries were noted after prolonged storage.
Storage stability was enhanced if a large gas sample (4 L or more) was taken. Thus, it is
possible that a small surface to volume ratio may contribute to storage stability. It is
also possible that storage stability may be improved if newer bags are used which are free
of small leaks and internal deposits. A preliminary study in which CO samples in new gas
bags were analyzed over a 2-week period with an Ecolyzer electrochemical
detector verified this. Recoveries averaged about 100% even after 17 days of storage.
A summary of the stability data from the GC analysis is shown below:
80% RH and 25 °C
|
1 × TWA PEL
|
|
2 × TWA PEL
|
Day |
Recovery* |
CV |
|
Day |
Recovery* |
CV |
|
1 |
100.0 |
0.023 |
|
2 |
100.0 |
0.041 |
8 |
103.5 |
0.161 |
|
15 |
89.6 |
0.108 |
21 |
80.9 |
0.135 |
|
22 |
75.9 |
0.136 |
29 |
81.9 |
0.141 |
|
32 |
79.0 |
0.211 |
39 |
79.9 |
0.176 |
|
* Normalized to 100% |
The slope of the plotted normalized 1 × PEL data is 0.00597 days¯1
and of the 2 × PEL data is 0.00781 days¯1. The
slope of the combined data for 1 and 2 × PEL, as plotted in Figure 3, is 0.00648 days¯1.
4.4. Humidity Study
Procedure: Samples were also generated at 25-28% and 80% RH
using the same equipment and conditions described in Section 4.2.
Results: The results of the gas sampling bags collected at the three RH
are presented in Tables 2 (50% RH) and 4 (25-28%, 80% RH). The RH level
displayed no apparent effect on recovery, except possibly at the 25-28% RH
level. As shown in Table 4, an analysis of variance (F test) was performed on the data to
determine any significant difference among or within the various RH groups. Variance at
each concentration level (0.5, 1, and 2 × TWA PEL) was compared across the three RH
levels (25-28%, 50%, and 80% RH). The variance among and within the different
concentration groups all gave high calculated F values. However, as is also shown in Table
4, no trends are apparent when generation recovery data are compared at different RH
levels for each concentration level, with the exception of the data at 0.5 × TWA PEL,
where increased recoveries at low humidity were indicated. The large calculated F values
appear to be mainly due to variation in sample generation and analysis. The data indicate
no apparent significant humidity effect on recovery which would require corrections. It is
known as to why the recoveries were enhanced at the 0.5 × TWA PEL, 25% RH test level.
4.5. Detection Limits
Procedure: Both qualitative and quantitative limits for the analysis of
CO by GC were calculated using the International Union of Pure and Applied Chemistry
(IUPAC) method for detection limit determinations (5.26.). The procedure used for
determining the detection limits is as follows:
4.5.1. Gas bags were prepared as described in Section 4.1.1., Step 1.
4.5.2. Blank samples were generated using the flow, humidity, and temperature control
system mentioned in Section 2.
4.5.3. Low concentration CO samples were prepared by mixing CO (0.50% in N2),
via the mixing chamber, with the treated air. Concentrations of 1.70, 2.62, 5.13, and
10.16 ppm were used.
Results: Detection limit results are listed in Table 5. The qualitative
detection limit was 0.12 ppm. The quantitative detection limit was 0.40 ppm. A 1-mL
sampling loop was used for all analyses. A larger sampling loop should allow for a lower
limit of detection; however, lower limits at this time are not necessary for workplace
determinations. Ambient air, especially around combustion sources, will probably have CO
levels comparable to or above the levels quoted as detection limits.
4.6. Comparison Methods
The results obtained in the present study were compared with those obtained during the
CO detector tube evaluation study (5.5.). For the detector tube study, the CO atmospheres
generated were sampled side-by-side using five-layer aluminized
gas sampling bags (5-L) and detector tubes. A sample of the gas from each gas
bag taken was chromatographed using a 5A Molecular Sieve column. It was then passed with H2
carrier gas through a nickel catalytic methanizer to convert the CO to methane (CH4)
before analysis with a flame ionization detector. Further details are described in
reference 5.5. Peak heights were used for sample measurement and fewer gas samples were
taken than in the present study. The results are reported in Table 6, along with a summary
of the present results for comparison purposes. The results tend to indicate that the mean
recoveries for the individual RH and concentration level determinations are less precise
in the present study. The Overall Error (Total) (OET) values obtained indicate the amount
of error is similar for either analytical technique. Either approach gives acceptable
results. The DID method is more direct, is simpler to use, and does not involve as much
auxiliary equipment as the methanizer/FID method.
4.7. Method Performance - Conclusions
The data generated during the validation of the method indicate an acceptable method
for sampling and analyzing CO. The GC-DID method offers an accurate and
precise assessment of CO exposures in the workplace. The data are summarized in Table 7.
The GC-DID CO determinations near the TWA PEL were within NIOSH and OSHA
accuracy and precision guidelines (5.22., 5.23.). The total coefficient of variation (CVT)
was 0.025, and the overall recovery was 105.8%. The data obtained in the Ceiling PEL
studies showed an average recovery of 100.0%.
Obtaining good analytical results appears to be contingent on analyzing the samples
within two weeks, and preferable as soon as possible after collection. Storage stability
appears to be enhanced if a large gas sample (4 L or more) is taken. It is also possible
that storage stability may be improved if newer bags are used which are free of small
leaks and internal deposits. Gas bag samples should be sent to the laboratory and analyzed
as soon as possible.
This method is capable of accurate and precise measurements to determine compliance
with the 35-ppm TWA PEL and 200-ppm Ceiling PEL for CO
exposures.
5. References
5.1. "Air Contaminants; Final Rule" Federal Register 29 CFR Part 1910
(19 Jan. 1989). Pp. 2332-2983.
5.2. United States Department of Labor, OSHA: "Memorandum, Updated Changes
to 29 CFR 1910.1000, Air Contaminants Standard." by Patricia Clark, Director
Designate, Directorate of Compliance Programs. United States Department of Labor, OSHA,
Washington, DC, June 1, 1990. [Memo].
5.3. Directorate of Technical Support, OSHA-DOL: Chemical Information File,
Online Database-OSHA Information System. Salt Lake City, UT: Occupational
Safety and Health Administration Salt Lake Technical Center, 1989.
5.4. Katz, M., ed.: Methods of Air Sampling and Analysis. 2nd ed., APHA
Intersociety Committee. Washington, D.C.: Publication Office, American Public Health
Association, 1977. No. 132, pp. 368-369.
5.5. Occupational Safety and Health Administration Salt Lake Technical Center: Carbon
Monoxide Detector Tubes (Short-Term) (USDOL/OSHA-SLTC PE-11).
Salt Lake City, UT: Occupational Safety and Health Administration Salt Lake Technical
Center, 1990.
5.6. National Institute for Occupational Safety and Health: NIOSH Manual of
Analytical Methods. 2nd. ed., Vol. 1 (Method No. P&CAM 112) (DHEW/NIOSH Pub. No. 77-157-A).
Cincinnati, OH: National Institute for Occupational Safety and Health, 1977.
5.7. National Institute for Occupational Safety and Health: NIOSH Manual of
Analytical Methods. 2nd. e., Vol. 4 (Method No. S340) (DHEW/NIOSH Pub. No. 78-175).
Cincinnati, OH: National Institute for Occupational Safety and Health, 1978.
5.8. Mine Safety and Health Administration: Regular Mine Gas Analysis
(MSHA Standard Method No. 1). Denver, CO: MSHA, 1979.
5.9. Guiochon, G. and C. Pommier: Gas Chromatography in Inorganics and
Organometallics. Ann Arbor, MI: Ann Arbor Science Publishers Inc., 1973. pp. 79-115.
5.10. Williams, D.M.: "Unique Applications for New Helium Glow Discharge
Ionization Detector for Gas Chromatography." Paper presented at the 1988 Pittsburgh
Conference, New Orleans, LA, February 1988.
5.11. American Society of Heating, Refrigerating and Air-Conditioning
Engineers Inc.: Ventilation for Acceptable Indoor Air Quality. ASHRAE 62-1989.
Atlanta, GA: American Society of Heating, Refrigerating and Air-Conditioning
Engineers, 1989. pp. 1-26.
5.12. Sax, N.I.: Dangerous Properties of Industrial Materials. 4th ed. New York:
Van Nostrand Reinhold Company, 1975. pp. 520-521.
5.13. National Institute for Occupational Safety and Health: Criteria for a
Recommended Standard--Occupational Exposure to Carbon Monoxide (DHEW/NIOSH Pub. HSM 73-11000).
Cincinnati, OH: National Institute for Occupational Safety and Health, 1972.
5.14. Coburn, R.F., chairman: Carbon Monoxide. Washington, DC: National
Academy of Sciences, 1977.
5.15. Proctor, N.H. and J.P. Hughes: Chemical Hazards of the Workplace.
Philadelphia, PA: J.B. Lippincott Co., 1978. pp. 151-153.
5.16. Sax, N.I. and R.J. Lewis, Sr.: Hawley's Condensed Chemical Dictionary.
11th ed. New York: Van Nostrand Reinhold Co., 1987. pp. 221-222.
5.17. American Conference of Governmental Industrial Hygienists: Documentation
of the Threshold Limit Values for Substances in Workroom Air. 3rd ed. Cincinnati, OH:
American Conference of Governmental Industrial Hygienist, 1971. pp. 41-43.
5.18. Ellenhorn, M.J., and D.G. Barceloux: Medical Toxicology. New York,
NY: Elsevier Science Publishing Co., Inc., 1988. p. 821.
5.19. Lee, H.K., T.A. McKenna, L.N. Renton, and J. Kirbride: Impact of a New
Smoking Policy on Office Air Quality. In Indoor Air Quality in Cold Climates: Hazards
and Abatement Measures, edited by D.S. Walkinshaw. Pittsburgh PA: Air Pollution
Control Association. pp. 307-322. (NIOSH-00172085).
5.20. Leaderer, B.P., W.S. Cain, R. Isseroff, and L.G. Berglung: Ventilation
Requirements in Buildings. II. Particulate Matter and Carbon Monoxide from Cigarette
Smoking. Atmospheric Environment 18, No. 1: 99-106 (1984). (NIOSH-00137853).
5.21. Mandel, J.: Accuracy and Precision, Evaluation and Interpretation of
Analytical Results, The Treatment of Outliers. In Treatise On Analytical Chemistry.
2nd ed., Vol. 1, edited by I.M. Kolthoff and P.J. Elving. New York, NY: John Wiley and
Sons, 1978. pp. 282-285.
5.22. National Institute for Occupational Safety and Health: Documentation of
the NIOSH Validation Tests by D. Taylor, R. Kupel and J. Bryant (DHEW/NIOSH Pub. No. 77-185).
Cincinnati, OH: National Institute for Occupational Safety and Health, 1977. pp. 1-12.
5.23. Occupational Safety and Health Administration Salt Lake Technical Center: OSHA
Analytical Methods Manual. Vol. III (USDOL/OSHA-SLTC Method Validation
Guidelines). Cincinnati, OH: American Conference of Governmental Industrial Hygienists
(Pub. No. ISBN: 0-936712-66-X), 1985.
5.24. Grant, G.A., M. Katz, and R.L. Haines: A Modified Iodine Pentoxide Method
for the Determination of Carbon Monoxide. Can. J. of Technol. 29: 43-51
(1951).
5.25. Skoog, D.A. and D.M. West: Analytical Chemistry: an Introduction.
4th ed. Philadelphia, PA: Saunders College Publishing, 1986. pp. 591-594.
5.26. Long, G.L. and J.D. Winefordner: Limit of Detection -- A
Closer Look at the IUPAC Definition. Anal. Chem. 55: 712A-724A (1983)
Table 1
Analysis Spiked CO Samples |
|
(OSHA TWA PEL) |
PPM
Taken |
PPM
Found |
F/T |
N |
Mean |
Std Dev |
CV |
OE |
|
(0.5 × PEL) |
17.600 |
17.741 |
1.008 |
17.600 |
16.274 |
0.925 |
17.600 |
15.691 |
0.892 |
17.600 |
17.889 |
1.016 |
17.500 |
17.326 |
0.990 |
17.500 |
15.684 |
0.896 |
|
6 |
0.954 |
0.057 |
0.060 |
16.5 |
(1 × PEL) |
35.200 |
34.619 |
0.983 |
35.200 |
34.353 |
0.976 |
35.200 |
34.523 |
0.981 |
35.300 |
34.346 |
0.973 |
35.300 |
34.080 |
0.965 |
35.500 |
34.254 |
0.965 |
|
6 |
0.974 |
0.008 |
0.008 |
4.2 |
(2 × PEL) |
70.200 |
71.064 |
1.012 |
70.000 |
67.827 |
0.969 |
69.800 |
72.870 |
1.044 |
70.000 |
73.249 |
1.046 |
70.100 |
70.539 |
1.006 |
70.000 |
70.405 |
1.006 |
|
6 |
1.014 |
0.029 |
0.028 |
7.0 |
|
F/T = Found/Taken |
OE |
= Overall Error (±%) |
|
Bias |
= -0.019 |
|
CV1 (Pooled) |
= 0.038 |
|
Overall Error (Total) |
= ±9.6% |
Table 2a
Sampling and Analysis 50% RH and 25 °C |
|
(OSHA TWA PEL) |
PPM
Taken |
PPM
Found |
F/T |
N |
Mean |
Std Dev |
CV |
OE |
|
(0.5 × PEL) |
17.200 |
18.181 |
1.057 |
17.200 |
19.160 |
1.114 |
17.200 |
18.729 |
1.089 |
17.200 |
19.082 |
1.109 |
17.200 |
18.531 |
1.077 |
17.200 |
17.570 |
1.021 |
|
6 |
1.078 |
0.035 |
0.032 |
14.2 |
(1 × PEL) |
30.800 |
34.305 |
1.114 |
30.800 |
33.635 |
1.092 |
30.800 |
33.746 |
1.096 |
30.800 |
33.884 |
1.100 |
30.800 |
34.176 |
1.110 |
30.800 |
34.019 |
1.105 |
|
6 |
1.103 |
0.008 |
0.008 |
11.8 |
(2 × PEL) |
63.600 |
62.072 |
0.976 |
63.600 |
63.479 |
0.998 |
63.600 |
63.783 |
1.003 |
63.600 |
63.860 |
1.004 |
63.600 |
63.100 |
0.992 |
63.600 |
62.426 |
0.982 |
|
6 |
0.992 |
0.012 |
0.012 |
3.1 |
|
F/T = Found/Taken |
OE |
= Overall Error (±%) |
|
Bias |
= +0.058 |
|
CV2(Pooled) |
= 0.020 |
|
CVT(Pooled) |
= 0.025 |
|
Overall Error (Total) |
= ±10.8% |
Table 2b
Ceiling PEL Study 50% RH and 25 °C |
|
PPM
Taken |
PPM
Found |
F/T |
N |
Mean |
Std Dev |
CV |
OE |
|
197.500 |
199.565 |
1.010 |
197.500 |
201.207 |
1.019 |
197.500 |
200.182 |
1.014 |
197.500 |
201.349 |
1.019 |
197.500 |
192.328 |
0.974 |
197.500 |
190.057 |
0.962 |
|
6 |
1.000 |
0.025 |
0.025 |
5.0 |
|
F/T = Found/Taken |
OE |
= Overall Error (±%) |
Table 3
Storage Stability Test |
|
1 × TWA PEL, 80% RH |
Storage |
PPM
Taken |
PPM
Found |
N |
Mean |
Std Dev |
CV |
Recov.
% |
Normalized to
100% |
|
Day 1 |
31.600 |
34.718 |
|
31.600 |
34.612 |
|
31.600 |
32.851 |
|
31.600 |
33.680 |
|
31.600 |
32.993 |
|
31.600 |
33.905 |
|
6 |
33.793 |
0.785 |
0.023 |
106.9 |
100.0 |
Day 8* |
31.600 |
43.028 |
|
31.600 |
30.716 |
|
31.600 |
36.747 |
|
31.600 |
26.702 |
|
31.600 |
36.089 |
|
31.600 |
36.484 |
|
6 |
34.961 |
5.623 |
0.161 |
110.6 |
103.5 |
Day 21 |
31.600 |
25.315 |
|
31.600 |
25.128 |
|
31.600 |
29.057 |
|
31.600 |
22.758 |
|
31.600 |
28.697 |
|
31.600 |
33.142 |
|
6 |
27.350 |
3.700 |
0.135 |
86.5 |
80.9 |
Day 29 |
31.600 |
28.268 |
|
31.600 |
27.629 |
|
31.600 |
29.594 |
|
31.600 |
20.039 |
|
31.600 |
29.396 |
|
31.600 |
31.012 |
|
6 |
27.656 |
3.910 |
0.141 |
87.5 |
81.9 |
Day 39 |
31.600 |
25.872 |
|
31.600 |
25.789 |
|
31.600 |
29.632 |
|
31.600 |
18.690 |
|
31.600 |
30.118 |
|
31.600 |
31.884 |
|
6 |
26.998 |
4.739 |
0.176 |
85.4 |
79.9 |
* |
Plot of standards showed more than the usual scatter--
GC performance was erratic. |
|
Storage Stability Test |
|
2 × TWA PEL, 80% RH |
Storage |
PPM
Taken |
PPM
Found |
N |
Mean |
Std Dev |
CV |
Recov.
% |
Normalized to
100% |
|
Day 2 |
76.200 |
68.643 |
|
76.200 |
68.459 |
|
76.200 |
69.570 |
|
76.200 |
74.060 |
|
76.200 |
74.882 |
|
76.200 |
69.094 |
|
6 |
70.785 |
2.893 |
0.041 |
92.9 |
100.0 |
Day 15 |
76.200 |
60.295 |
|
76.200 |
67.145 |
|
76.200 |
70.047 |
|
76.200 |
69.268 |
|
76.200 |
61.652 |
|
76.200 |
51.995 |
|
6 |
63.400 |
6.862 |
0.108 |
83.2 |
89.6 |
Day 22 |
76.200 |
47.042* |
|
76.200 |
55.069 |
|
76.200 |
65.320* |
|
76.200 |
55.451 |
|
76.200 |
54.587 |
|
76.200 |
44.728 |
|
6 |
53.700 |
7.288 |
0.136 |
70.5 |
75.9 |
Day 32 |
76.200 |
45.644* |
|
76.200 |
59.314 |
|
76.200 |
69.860* |
|
76.200 |
67.860 |
|
76.200 |
52.431 |
|
76.200 |
40.675 |
|
6 |
55.964 |
11.820 |
0.211 |
73.4 |
79.0 |
|
* |
Bag contents were somewhat low, indicating leakage. |
Table 4
Humidity Study 25-28% RH and 25 °C |
|
(OSHA TWA PEL) |
PPM
Taken |
PPM
Found |
F/T |
N |
Mean |
Std Dev |
CV |
OE |
|
(0.5 × PEL) |
17.700 |
21.592 |
1.220 |
17.700 |
20.188 |
1.141 |
17.700 |
19.368 |
1.094 |
17.700 |
20.083 |
1.135 |
17.700 |
20.681 |
1.168 |
17.700 |
20.840 |
1.177 |
|
6 |
1.156 |
0.043 |
0.037 |
23.0 |
(1 × PEL) |
31.100 |
30.248 |
0.973 |
31.100 |
31.445 |
1.011 |
31.100 |
31.719 |
1.020 |
31.100 |
31.081 |
0.999 |
31.100 |
32.577 |
1.048 |
31.100 |
31.972 |
1.028 |
|
6 |
1.013 |
0.026 |
0.025 |
6.4 |
(2 × PEL) |
62.900 |
60.486 |
0.962 |
62.900 |
59.319 |
0.943 |
62.900 |
55.289 |
0.879 |
62.900 |
59.345 |
0.943 |
62.900 |
61.934 |
0.985 |
62.900 |
59.764 |
0.950 |
|
6 |
0.944 |
0.035 |
0.037 |
13.1 |
|
F/T = Found/Taken |
OE |
= Overall Error (±%) |
|
Bias |
= +0.038 |
|
CV (Pooled) |
= 0.034 |
|
Overall Error (Total) |
= ±10.5% |
|
Humidity Study
80% RH and 25 °C |
|
(OSHA TWA PEL) |
PPM
Taken |
PPM
Found |
F/T |
N |
Mean |
Std Dev |
CV |
OE |
|
(0.5 × PEL) |
17.900 |
18.342 |
1.025 |
17.900 |
18.943 |
1.058 |
17.900 |
18.177 |
1.015 |
17.900 |
18.027 |
1.007 |
17.900 |
18.590 |
1.039 |
17.900 |
17.358 |
0.970 |
|
6 |
1.019 |
0.030 |
0.030 |
7.8 |
(1 × PEL) |
31.600 |
34.718 |
1.099 |
31.600 |
34.612 |
1.095 |
31.600 |
32.851 |
1.040 |
31.600 |
33.680 |
1.066 |
31.600 |
32.993 |
1.044 |
31.600 |
33.905 |
1.073 |
|
|
|
6 |
1.069 |
0.025 |
0.023 |
11.6 |
(2 × PEL) |
76.200 |
68.643 |
0.901 |
76.200 |
68.459 |
0.898 |
76.200 |
69.570 |
0.913 |
76.200 |
74.060 |
0.972 |
76.200 |
74.882 |
0.983 |
76.200 |
69.094 |
0.907 |
|
6 |
0.929 |
0.038 |
0.041 |
15.3 |
|
F/T = Found/Taken |
OE |
= Overall Error (±%) |
|
Bias |
= +0.006 |
|
CV (Pooled) |
= 0.032 |
|
Overall Error (Total) |
= ±7.0% |
|
Humidity Study
|
F Test
|
|
Recoveries %
|
Level |
F(calc) |
F(crit) |
|
RH |
25-28% |
50% |
80% |
0.5 × PEL |
21.44 |
6.36 |
|
|
115.6 |
107.8 |
101.9 |
1.0 × PEL |
27.52* |
6.36 |
|
|
101.3 |
110.3 |
106.9 |
2.0 × PEL |
7.02* |
6.36 |
|
|
94.4 |
99.2 |
92.9 |
Average |
|
103.8 |
105.8 |
100.6 |
|
* |
Large values appear to be due to variability in sample generation and not
to any significant humidity effect. |
Table 5
Determination of Qualitative and
Quantitative Detection Limits |
|
PPM
|
|
Integrated Area
|
|
Std Dev
|
Blank* |
|
1,746 |
1,601 |
1,649 |
1,769 |
1,634 |
1,630 |
|
68.8 |
1.70* |
|
5,281 |
5,254 |
5,604 |
5,659 |
5,686 |
|
|
211.6 |
2.62 |
|
7,992 |
6,602 |
8,214 |
8,032 |
8,323 |
7,342 |
|
658.2 |
5.13 |
|
10,213 |
11,142 |
10,511 |
9,054 |
10,091 |
10,066 |
|
681.9 |
10.16 |
|
19,305 |
22,274 |
18,974 |
19,903 |
18,917 |
20,201 |
|
1,256.9 |
|
* |
Manual integration was performed on chromatographic peaks
using CPLOT software (Hewlett-Packard Co., Avondale, PA, CPLOT/3350, Rev.
2509). |
|
|
|
|
IUPAC Method |
Using the equation: |
Cld = k(sd)/m |
Where: |
Cld |
= |
the smallest detectable concentration an analytical
instrument can determine at a given confidence level. |
k |
= |
3 (Qualitative detection limit, 99.86% confidence). |
|
= |
10 (Quantitative detection limit, 99.99% confidence). |
sd |
= |
standard deviation of blank readings. |
m |
= |
analytical sensitivity or slope as calculated by linear
regression. |
|
Minimum detectable signal (Qualitative detection limit): |
|
Cld = 3(68.8)/1,718.5 |
|
Cld = 0.12 ppm |
|
For k = 10(Quantitative detection limit): |
|
Cld = 0.40 ppm as a reliable detectable signal |
Table 6
Method Comparison Analysis of Gas Bags Containing CO by GC Using a
Methanizer and Flame Ionization Detector (5.5.) |
|
Test |
Samples |
Mean Recov.** |
CV |
OET%*** |
%RH |
× PEL |
N* |
|
25-30 |
0.5 |
3 |
0.944 |
0.004 |
8.2 |
|
1 |
4 |
0.937 |
0.018 |
|
2 |
3 |
0.993 |
0.028 |
50 |
0.5 |
3 |
0.933 |
0.006 |
6.0 |
|
1 |
3 |
1.028 |
0.011 |
|
2 |
6 |
0.987 |
0.028 |
80 |
0.5 |
4 |
1.013 |
0.007 |
5.3 |
|
1 |
6 |
1.000 |
0.037 |
|
2 |
6 |
0.988 |
0.017 |
Analysis of Gas Bags Containing CO by GC
in the Present Study Using a DID
|
Test |
Samples |
Mean Recov.** |
CV |
OET%*** |
%RH |
× PEL |
N* |
|
25-30 |
0.5 |
6 |
1.156 |
0.037 |
10.5 |
|
1 |
6 |
1.013 |
0.025 |
|
2 |
6 |
0.944 |
0.037 |
50 |
0.5 |
6 |
1.078 |
0.032 |
9.8 |
|
1 |
6 |
1.103 |
0.008 |
|
2 |
6 |
0.992 |
0.012 |
80 |
0.5 |
6 |
1.019 |
0.030 |
7.0 |
|
1 |
6 |
1.069 |
0.023 |
|
2 |
6 |
0.929 |
0.041 |
|
* |
These samples were collected throughout the detector tube sampling period
(5.5.). |
|
** |
Results were compared to standards prepared from 104-ppm CO
in N2. Theoretical concentrations were based on the blending of
0.50% CO in N2 with purified, humidified air during sample
generation. |
|
*** |
Note: OET% (Total Overall Error in %) is the
pooled result of all three concentrations at one RH level. |
Table 7
Precision and Accuracy Summary |
|
|
|
|
|
|
Precision: |
CV1(Pooled) = 0.038 |
|
CV2(Pooled) = 0.020 |
|
CVT(Pooled) = 0.025 |
|
|
Bartlett's Test
|
|
Level |
B(calc) |
B(crit) |
|
|
Spiked |
|
(Table 1) |
13.73 |
9.23 |
|
Generated |
|
(Tables 2 and 4) |
|
25-30% RH |
0.82 |
9.23 |
|
50% RH |
9.92 |
9.23 |
|
80% RH |
1.51 |
9.23 |
|
Recovery: |
Average recovery (Sampling and Analysis) = 105.8% |
|
Average recovery (Ceiling PEL study) = 100.0% |
Recovery and CV Ranges*
|
Mean Recovery, present GC method |
92.9 - 115.6% |
CV, present GC method |
0.008 - 0.041 |
Bias |
0.006 - 0.058 |
CV2 (Pooled) |
0.020 - 0.034 |
|
Mean Recovery, previous GC method** |
93.0 - 102.9% |
CV, previous GC method** |
0.004 - 0.037 |
|
* Range--includes different RH and concentration levels. |
** GC method--methanizer and FID analysis. |
Appendix 1
Analysis Parameters for CO Determinations |
|
|
|
|
|
Gas chromatograph |
Tracor Model No. 540 GC |
|
|
Detector |
Discharge ionization detector* |
|
|
DID power supply |
Tracor Model No. 706 |
|
|
Polarizing voltage setting |
700 |
|
|
Discharge current setting |
700 |
|
|
Electrometer settings |
|
|
Input |
10 |
|
|
Output |
2 |
|
|
GC temperature settings (°C) |
|
|
Column oven |
90 |
|
|
Valve oven |
60 |
|
|
Detector |
190* |
|
|
Flow control |
40 |
|
|
Column pressure (kPa) |
50-70 |
|
" " (psi) |
7-10 |
|
|
Time settings (min) |
|
|
Run time |
20.0 |
|
|
Pre ready |
1.0 |
|
|
On event |
0.01 |
|
|
Off event |
0.30 |
|
|
Columns (in series) |
|
|
First |
4' × 1/8" SS Hayesep Q 60-80
(Mounted in valve oven) |
|
|
Second |
12' × 1/8" SS Molecular Sieve 60-80
(Mounted in column oven) |
|
|
Helium flow rates (L/min) |
|
|
Through discharge |
0.030 |
|
|
Through columns |
0.020 |
|
|
Gas sampling loop volume (mL) |
1 |
|
Integrator |
Hewlett-Packard 3357 Laboratory
Automation System (Rev. 2540)** |
|
Recorder |
Omniscribe Model No. B5218-5 |
|
Y1 full scale setting (v) |
0.01 (TWA PEL), 0.1 (Ceiling PEL) |
|
Chart speed (in/min) |
0.05 |
|
CO peak time (min) |
12.0-14.6 |
|
* |
When the detector reaches operating temperature after
startup, helium should be allowed to flow through the detector for one day before the
discharge is started (manufacturer's recommendation). |
|
** |
Area counts for CO concentrations of <2.5 ppm were not
automatically integrated. These areas were determined by manual integration. |
Notes:
If instabilities develop in the chromatogram when the first portion of the gas sample
(i.e., O2 and N2 peaks) pass through
the DID, the GC may be programmed so that the gas flow from the columns is temporarily
vented to the outside of the GC and does not pass through the DID. This venting would
occur for about the first 8 or 10 min of the analysis, since the CO peak would normally
occur at 12 to 15 min.
An early model of the DID which was used by our laboratory for this validation was
prone to exhibit oscillatory behavior, requiring extensive down time and manufacturer
service.
Chromatogram of Elution of 104 ppm CO in N2
Figure 1
Dynamic Generation System for
Production of Carbon Monoxide Atmospheres
Figure 2
Storage Stability Study of CO in Gas Bags (1,2 × TWA PEL)
Figure 3
|