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CHLORINE IN WORKPLACE ATMOSPHERES |
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Method Number: |
ID-101 |
|
Matrix: |
Air |
|
OSHA Permissible Exposure Limits:
Final Rule Limits |
1 ppm Chlorine (Short-Term Exposure
Limit) 0.5 ppm Chlorine (Time Weighted Average) |
|
Transitional Limit |
1 ppm Chlorine (Ceiling) |
|
Collection Device: |
A calibrated personal sampling pump is used to draw a known
volume of air through a midget fritted glass bubbler containing a
0.1% sulfamic acid solution. |
|
Recommended Sampling Rate: |
1 L/min |
|
Recommended Air Volumes Short-Term
Exposure Limit: Time Weighted Average: |
15 L 240 L |
|
Analytical Procedure: |
An aliquot of the sulfamic acid solution is added to a buffered
potassium iodide solution. Any chlorine contained in the first
solution oxidizes the potassium iodide to iodine which is then
measured with a residual chlorine ion specific electrode. |
|
Detection Limit: Qualitative |
0.014 ppm (15-L air sample) |
|
Quantitative |
0.14 ppm (15-L air sample) |
|
Precision and Accuracy: Validation
Level: |
0.56 to 2 ppm (15-L air sample) |
|
CVT |
0.03 |
|
Bias |
-0.006 |
|
Overall Error |
±6.6% |
|
Classification: |
Validated Method |
|
Chemists: |
Steven Edwards, James Ku |
|
Date (Date Revised): |
1982 (May, 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.
Division of Physical Measurements and Inorganic
Analyses OSHA Technical Center Salt Lake City, Utah
1. Introduction
This method describes the collection and analysis of airborne chlorine
in the workplace. It is applicable for both Short-Term (STEL)
and Time Weighted Average (TWA) exposure evaluations.
1.1 History
Chlorine was previously determined using o-tolidine
(8.1). The previous OSHA sampling method for chlorine was
to capture it in a dilute o-tolidine/hydrochloric acid
solution and then analyze the sample using a colorimetric procedure.
This method was used as a field test to immediately determine
atmospheric chlorine concentrations. Due to problems associated with
interferences, instability, and hazards associated with the collecting
media, this method is no longer used by OSHA. Another method which
utilized the ability of chlorine to bleach an acidic
methyl-orange solution had been reported (8.2); however,
without any modifications the method was too sensitive for
concentrations pertinent to industrial hygiene applications. Sample
instability and significant interferences were also noted.
A method was developed by OSHA during the early 1980s which
collected chlorine in a sulfamic acid solution and samples were
analyzed using an ion specific electrode technique. The sulfamic acid
collection and residual chlorine ion specific electrode (RCE) analysis
has been evaluated (8.3) and has shown an acceptable level of
precision and accuracy for the determination of chlorine in workplace
atmospheres. Another evaluation by an independent laboratory has also
been conducted (8.4).
1.2 Principle
The sampling method is based on a previous report of chlorine
collection in sulfamic acid solutions (8.5). The analytical method is
based on iodometric measurements of chlorine using a RCE. An iodide
and a buffer reagent are added to the sulfamic
acid-chlorine sample and the iodide reacts completely
with the chlorine to form iodine:
Cl2 + 2I- » ----->
2Cl- + I2
The iodine concentration formed after the reaction is indirectly
measured by the RCE and is equal to the chlorine concentration before
reaction. This reaction takes place in an acetic acid/sodium acetate
buffer. This buffer provides the optimal pH range for the reaction
(8.6).
1.3 Advantages and Disadvantages
1.3.1 This method has adequate sensitivity for measuring
workplace concentrations of chlorine contained in the atmosphere.
1.3.2 No sample elution or desorption is required because the
sample is collected in a liquid medium.
1.3.3 Collected samples are stable for at least 30 days before
analysis.
1.3.4 The analytical equipment is inexpensive.
1.3.5 One disadvantage of this method is the use of a liquid in
midget fritted glass bubblers (MFGB) to collect samples. Spillage or
breakage can occur if precautions are not taken.
1.4 Properties (8.2, 8.7)
Chlorine (CAS No. 7782-50-5) is a
greenish-yellow gas with an irritating odor. Some
physical properties of chlorine are:
Atomic Number |
17 |
Atomic Symbol |
Cl |
Molecular Weight (Cl2) |
70.91 |
Boiling Point |
-33.6°C |
Density |
13.546 g/mL (20°C) |
Vapor Pressure |
670.8 kPa (6.62 atm) at 20°C |
Color (gas) |
yellow-green |
Flammability |
nonflammable |
Solubility (H2O) |
2.26 L of chlorine will dissolve in 1 L of H2O
at 20°C |
Chlorine reacts readily with metals, and by substitution or
addition with a wide variety of organic compounds.
1.5 Uses
Chlorine is used primarily as a bleaching agent or for chlorination
of various organic compounds. Some industrial operations which have
the potential for chlorine exposures are (8.2):
Aerosol propellant makers |
Iron detinners |
Alkali salt makers |
Iron dezinkers |
Aluminum purifiers |
Laundry workers |
Benzene hexachloride makers |
Methyl chloride makers |
Bleachers |
Paper bleachers |
Bleaching powder makers |
Petroleum refinery workers |
Bromine makers |
Phosgene makers |
Broommakers |
Photographic workers |
Carpetmakers |
Pulp bleachers |
Chemical synthesizers |
Rayon makers |
Calcium chloride makers |
Refrigerant makers |
Chlorinated solvent makers |
Rubber makers |
Chlorinated hydrocarbon makers |
Sewage treaters |
Chlorine workers |
Silver extractors |
Colormakers |
Sodium hydroxide makers |
Disinfectant makers |
Submarine workers |
Dyemakers |
Sugar refiners |
Ethylene glycol makers |
Sulfur chloride makers |
Ethylene oxide makers |
Swimming pool maintenance workers |
Flour bleachers |
Tetraethyl lead makers |
Fluorocarbon makers |
Textile bleachers |
Gasoline additive workers |
Tin recovery workers |
Gold extractors |
Vinyl chloride makers |
Inkmakers |
Vinylidene chloride makers |
Insecticide makers |
Water treaters |
Iodine makers |
Zinc chloride makers |
2. Working Range and Detection Limits
2.1 Using the iodide reagent as directed in the analytical
procedure for chlorine, a linear response up to 20 µg/mL chlorine can
be produced when the electrode potential versus log (Cl2)
concentration is plotted (8.6). To bring large concentrations (>20
µg/mL) into the linear working range, these samples can be diluted
with 0.1% sulfamic acid solution before any aliquots are reacted with
the iodide/buffer reagents.
2.2 Qualitative and quantitative detection limits of 0.01 and 0.1
µg/mL, were estimated during validation studies and calculates to 0.25
and 2.5 µg per sample, respectively.
3. Method Performance (8.3)
Validation studies conducted over the concentration range of 0.56 to 2
ppm (15-L air volume) gave an overall pooled coefficient of
variation of 0.03, a bias of -0.006, and an overall error of ±6.6%.
Overall error was calculated using the equation:
OEi = ± [ |mean biasi
| + 2CVi] × 100%
where i is the respective sample pool being examined.
4. Interferences
Strong oxidizing agents including iodate, bromine, cupric ion, and
manganese dioxide have been reported to interfere during analysis (8.6).
These agents may react with the KI and produce a positive interference.
It has also been reported that silver and mercuric ion concentrations
above 10 to 20 µg/mL in the sampled solution will also interfere with the
analysis (8.6) by poisoning the RCE. However, concentrations of this
magnitude may be unlikely when sampling for chlorine in the workplace.
Reduced sulfur-containing compounds (i.e., methyl mercaptan, dimethyl
sulfide, dimethyl disulfide) and sulfur dioxide have been reported as
negative interferences (8.4). These compounds apparently inhibit the
recovery of chlorine from the sulfamic acid solution.
Particulate (i.e., hypochlorites, trichloroisocyanuric acid) which may
break down to free chlorine in the sulfamic acid solution are a positive
interference. Particulate may be excluded from the sulfamic acid solution
by using a Teflon prefilter during sampling.
5. Sampling
5.1 Equipment
Note: |
If the workplace air being sampled is suspected
of containing particulate (i.e., sodium hypochlorite,
trichloroisocyanuric acid) which may liberate free chlorine in
the collection solution, a prefilter as mentioned in Section
5.1.7 should be used. |
5.1.1 Collection solution, 0.1% sulfamic acid: Dissolve 1.0 g
sulfamic acid in deionized water and dilute to the mark in a
1-L volumetric flask.
5.1.2 Personal sampling pumps capable of sampling within ±5% of
the recommended flow rate of 1 L/min are used.
5.1.3 Midget fritted glass bubblers (MFGBs) (25-mL,
part no. 7532, Ace Glass Co., Vineland, NJ).
5.1.4 Shipping vials: Scintillation vials, 20-mL,
part no. 74515 or 58515, (Kimble, Div. of
Owens-Illinois Inc., Toledo, OH) with polypropylene or
Teflon cap liners. Tin or other metal cap liners should not be used.
5.1.5 A stopwatch and bubble tube or meter are used to calibrate
pumps.
5.1.6 Various lengths of PVC tubing are used to connect bubblers
to the pumps.
5.1.7 If any particulate may present an interference, a prefilter
is attached to each bubbler such that sampled air enters the
prefilter first. The prefilter should consist of:
- Carbon-filled polypropylene cassette, 25-mm
diameter, (part no. 300075, Nucleopore Corp., Pleasanton, CA).
- Filter for particulate collection, PTFE, 0.45 µm pore size,
25-mm diameter (part no. 130620, Nucleopore).
- Porous plastic support pad, (part no. 220600, Nucleopore).
Assemble the prefilter such that sampled air enters the PTFE
filter first and the plastic support pad faces the MFGB.
5.2 Sampling Procedure
5.2.1 Calibrate the sampling pump with a MFGB containing about
10 mL of 0.1% sulfamic acid solution in-line. Also
calibrate with a prefilter if necessary.
5.2.2 Place 10 to 15 mL of 0.1% sulfamic acid solution in an
MFGB. Connect the MFGB (and prefilter if necessary) to a calibrated
sampling pump. If a prefilter is necessary, use a minimum amount of
tubing to connect the MFGB and prefilter together. Place the
sampling device in the breathing zone of the employee.
5.2.3 Sample at a flow rate of 1 L/min. For STEL determinations,
a minimum sampling time of 15 min is recommended.
5.2.4 For measurements of TWA exposures, sample up to 240 min.
Take enough samples to cover the shift worked.
5.2.5 Transfer the collection solution into a 20-mL glass
scintillation vial. Rinse the bubbler with 2 to 3 mL of fresh
sulfamic acid solution and transfer the rinsings into the sample
vial. Place the Teflon-lined cap tightly on each vial
and seal with vinyl or waterproof tape around the caps to prevent
leakage during shipment. Attach an OSHA 21 seal lengthwise around
each vial.
5.2.6 Prepare a blank solution by taking 10 to 15 mL of the
sulfamic acid solution not used for collection and transfer to a
20-mL glass vial. Seal the vial as mentioned in Section
5.2.5.
5.2.7 If a prefilter was used, the filter can be submitted for
analysis of available chlorine. Immediately after sampling, remove
each filter from it's cassette and place in individual vials
containing about 5 mL of fresh 0.1% sulfamic acid solution. Also
prepare a blank filter/sulfamic acid solution and then seal all
vials as mentioned in Section 5.2.5.
5.2.8 Request chlorine analysis on the OSHA 91A form. If
prefilters are submitted, request the filters are analyzed for total
available chlorine using OSHA stopgap method ID-101-SG.
5.2.9 Ship the samples to the laboratory using appropriate
packing materials to prevent breakage.
6. Analysis
6.1 Safety Precautions
6.1.1 Care must be exercised when handling glacial acetic acid.
Gloves and face protection should be used. The area where the acid
is diluted should be well ventilated (NOTE: Do not vent acetic acid
into hoods designated for perchloric acid use). Inhalation of acetic
acid vapors should be avoided. The glacial acetic acid should be
added to the aqueous solution, thus avoiding any splattering which
can occur when water is added to a concentrated acid. If any acid
contacts the eyes, skin, or clothes, flush the area immediately with
copious amounts of cold water and then seek medical attention.
6.1.2 Care should be exercised when using laboratory glassware.
Chipped pipettes, volumetric flasks, beakers, or any glassware with
sharp edges exposed should not be used.
6.1.3 Pipetting is always done using a pipetting bulb, never by
mouth.
6.2 Equipment
6.2.1 Residual chlorine electrode (Model 97-70, Orion Research
Inc., Cambridge, MA).
6.2.2 Millivolt meter, capable of relative mV or concentration
readings (Model EA 940 Expandable Ionanalyzer, Orion Research Inc.).
6.2.3 Laboratory glassware including Class A volumetric flasks,
pipettes, beakers, graduated cylinders, etc.
6.2.4 Beakers, disposable plastic.
6.2.5 Analytical balance (0.01 mg).
6.3 Reagents - All reagents used should be reagent grade or better.
6.3.1 Deionized water (DI H20).
6.3.2 Sulfamic acid solution, 0.1%: Dissolve 1.0 g sulfamic acid
(NH2SO3H) in DI H2O2 and
dilute to 1 L.
6.3.3 Potassium iodide (KI), 0.5 M: Dissolve 20.75 g KI in DI
H2O and dilute to 250 mL. The solution should be prepared
daily.
6.3.4 Buffer reagent, 6.4 M acetic acid/1.8 M sodium acetate:
Dissolve 37.1 g sodium acetate in 100 mL of DI H2O. Add
92 mL of glacial acetic acid and dilute the solution to 250 mL using
DI H2O. This buffer is acidic, having a pH of about 4.7.
Prepare monthly.
6.3.5 Stock Solution: Dissolve 0.500 g potassium iodate in DI
H2O and dilute to 500 mL in a volumetric flask. This
solution is equivalent to 1,000 µg/mL chlorine. Prepare every 6
months.
6.4 Standard Preparation
6.4.1 Dilute the 1,000 µg/mL stock solution (prepared in Section
6.3.5) with 0.1% sulfamic acid using dilutions to make 100-, 10-,
and 5.0-µg/mL standard solutions.
6.4.2 Working standards are prepared by diluting aliquots
of the 100-, 10-, and 5.0-µg/mL standard solutions to
the analytical range of 0.2 to 20 µg/mL. A dilution scheme is shown
below (also see note in Section 6.5.3):
|
Working standard (µg/mL) |
Standard Solution Aliquot (mL) |
Standard
Solution Concentration (µg/mL) |
Final Volume (mL) |
|
0.2 |
2.0 |
5.0 |
50 |
0.6 |
3.0 |
10 |
50 |
1.0 |
5.0 |
10 |
50 |
10.0 |
5.0 |
100 |
50 |
20.0 |
10.0 |
100 |
50 |
|
Prepare the working standards the same day the analysis is
performed. Use the following procedure for preparation:
- An aliquot of the indicated standard solution (either 100-,
10-, or 5.0-µg/mL) is placed into a
50-mL volumetric flask.
- Add 0.5 mL buffer reagent to the volumetric flask.
- Add 0.5 mL KI to the volumetric flask and swirl to mix the
reagents; allow the solution to react for at least 2 min before
proceeding.
- Dilute the working standard to volume (50 mL) with 0.1%
sulfamic acid solution. Mix thoroughly by inverting the flask
several times. Store in a dark environment until the analysis is
performed.
6.5 Sample Preparation
Note: |
If prefilters are submitted for analysis, they should be
analyzed for total available chlorine using OSHA stopgap method
ID-101-SG. |
6.5.1 Collected liquid samples are stable for at least 30 days.
Special precautions are not necessary during storage. Analyze
samples the same day they are prepared for analysis.
6.5.2 Measure and record each sample volume received.
6.5.3 Place an aliquot of each sample solution into a separate
50-mL volumetric flask. It is recommended to take the majority of
the solution for those air samples having less than 60-L air volumes
(i.e., STEL or ceiling samples).
If necessary, a duplicate analysis can be conducted using the
remaining aliquot; however, sensitivity may be significantly
decreased.
Note: |
A "dilution" effect has been noted in the
literature (8.8.) and may result in a net decrease of analyte
formed after reaction with KI. This effect is apparently
caused by differences in pH of the sample or µ. µs and samples
should be matrix matched using 0.1% sulfamic acid. The volume
of the aliquot taken may also alter the pH (for further
information see reference 8.8). A significant "dilution"
effect was not noted when µs and samples were prepared and
diluted with 0.1% sulfamic acid, and the aliquot volumes were
kept below 15 mL (8.9). |
6.5.4 React each aliquot with KI and prepare for analysis using
the following steps:
- Add 0.5 mL buffer reagent to the volumetric flask.
- Add 0.5 mL KI to the volumetric flask and swirl to mix; allow
the solution to react for at least 2 min before proceeding.
- Dilute the sample to volume (50 mL) using 0.1% sulfamic acid
solution. Mix thoroughly by inverting the flask several times.
Store in a dark environment until the analysis is performed.
6.6 Analytical Procedure
6.6.1 Set up the millivolt meter according to the µ Operating
Procedure (8.10.) or manufacturers' guidelines.
6.6.2 Place the electrode into a disposable plastic beaker
containing 1.0-µg/mL solution. Allow the electrode to
stabilize (approximately 3 min) and then record the mV reading.
Remove the electrode from the standard solution, rinse with DI
H2O, and blot dry. Place the electrode into a
10-µg/mL solution and record the mV reading. The
difference between the 1.0- and 10-µg/mL should be
approximately 29 mV.
6.6.3 Analyze the standards and samples according to the SOP
(8.10). Take a fresh aliquot from the volumetric flasks and prepare
as mentioned in Section 6.4. each time a standard is analyzed. Using
a relative reading of 0 mV for the 1 µg/mL and equipment mentioned
in Section 6.2, typical standard readings and differences in mV
values are shown below:
|
Std, µg/mL |
mV Reading |
|
20.00 |
35.00 |
10.00 |
29.00 |
1.00 |
0.00 |
0.50 |
-11.00 |
0.20 |
-20.00 |
|
Note: |
For the 1 µg/mL standard, a relative mV setting
of zero was used. Absolute readings may be
different. |
6.6.4 Always rinse the residual chlorine electrode with DI
H2O and blot dry with a clean dry tissue before placing
it in the next solution to be analyzed.
6.6.5 Analyze a standard in the concentration range of the
samples after every fourth or fifth sample and at the end of the
analysis. If a sample reading indicates the concentration is greater
than the largest standard, dilute the unreacted sample to
bring the concentration within the analytical range:
- take an aliquot from the remaining unreacted sample,
- dilute with sulfamic acid, and
- follow the procedure described in Section 6.5.4.
Do not dilute any reacted samples into the analytical range.
7. Calculations
7.1 Determine the total µg/mL chlorine content of each sample and
blank using a concentration-response regression curve if
readings were measured in concentration units. If mV readings were
taken, plot the log (concentration) versus the mV readings and
determine µg/mL chlorine for each sample and blank.
7.2 The total µg chlorine for each sample or blank is calculated
as:
µg Chlorine = |
µg/mL Chlorine × (sample
volume, mL) × 50 mL
(aliquot taken, mL) |
where: µg/mL Chlorine = From curve (Section
7.1)
7.3 Each sample is blank-corrected and the air concentration is
calculated to determine chlorine exposure using the following
equation:
ppm Chlorine = |
MV × (µg sample - µg blank)
molecular volume × air volume, L |
where: |
MV (Molar Volume) |
= 24.45 (25°C and 760 mmHg) |
Molecular Weight (Cl2) |
= 70.91 |
7.4 Reporting Results
Results are reported to the industrial hygienist as ppm chlorine.
8. References
8.1 American Public Health Association, American Water Works
Association, Water Pollution Control Federation: Standard
Methods for the Examination of Water and Wastewater. 13th ed.,
Washington, D.C.: American Public Health Association, 1971.
8.2 National Institute for Occupational Safety and Health:
Criteria for a Recommended Standard -- Occupational Exposure to
Chlorine (DHEW/NIOSH Pub. No. 76-170). Cincinnati,
OH: National Institute for Occupational Safety and Health, 1976.
8.3 Occupational Safety and Health Administration Technical
Center: Chlorine in Workplace Atmospheres - Backup Report
(ID-101) by J. Ku. Salt Lake City, UT. Revised 1991.
8.4 National Council of the Paper Industry for Air and Stream
Improvement, Inc.: A Laboratory Evaluation of the Sulfamic
Acid-Iodometric Method for Determining Chlorine in Pulp Bleaching Area
Workplace Atmospheres (Special Report No. 82-02). New
York: NCASI, March 1982.
8.5 Takeuari, J. et al.: Measurement of Chlorine in the
Atmosphere. Osen Kenkyu (Air Pollution Research) 9(2):
210 (1974).
8.6 Orion Research, Inc.: Residual Chlorine Electrode,
Model 9970 Instruction Manual. Cambridge, MA: Orion Research,
Inc., 1976.
8.7 Fassett, D.W., ed.: Patty's Industrial Hygiene and
Toxicology. 2nd rev. ed., Vol. 2. New York: John Wiley and Sons,
1963.
8.8 Rando, R.J., and Y.Y. Hammad: A Diffusive Sampler for
Gaseous Chlorine Utilizing an Aqueous Sulfamic Acid Collection Medium
and Specific Ion Electrode Analysis. Appl. Occup. Environ. Hyg.
5(10): 700-706 (1990).
8.9 Occupational Safety and Health Administration Technical
Center: Dilution Effect Study by J. Ku. Salt Lake City, UT.
1991 (unpublished).
8.10 Occupational Safety and Health Administration Technical
Center: Standard Operating Procedure - Ion Specific
Electrodes. Salt Lake City, UT. In progress (unpublished).
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