CHLORINE AND CHLORINE DIOXIDE IN
|2% KI in an impinger|
|Recommended Air Volume:
|0.1 to 1.0 L/Min|
||Titration with 0.01 N sodium thiosulfate|
||1.0 mg/m3 for a 10 L sample|
Methods Development Team
Industrial Hygiene Chemistry
OSHA Salt Lake Technical Center
Salt Lake City, UT
1.1.1 This method describes the sampling and analysis of high
levels of chlorine and chlorine dioxide by titration with 0.01 N
1.2 Advantages and Disadvantages
1.2.1 Both chlorine and chlorine dioxide can be
1.2.2 Little instrumentation is
1.2.3 The analytical technique is not
1.2.4 The analysis suffers from many
1.2.5 This method is accurate for levels
of chlorine and chlorine dioxide above 1.0 µg/mL for a 10 L
1.2.6 The collection of oxidants can be monitored
by observing the color change of the 2% KI solution.
method gives a very precise measure of total available strength of a
solution in terms of its ability to liberate iodine from iodide.
1.2.8 Temperature and strong light affect
solution stability. Minimum ClO2 losses occur when the
determination is completed immediately at the site of sample
1.3.1 The sample is collected using an impinger or Liquid Media
Sampler (LMS) containing 2% KI.
1.3.2 The sample is then
titrated with 0.01 N sodium thiosulfate with starch as an indicator to
a colorless endpoint.
1.3.3 5 mL of 1 N sulfuric acid is
then added to the sample and the sample is again titrated with 0.01 N
sodium thiosulfate to a colorless endpoint.
concentrations of chlorine and chlorine dioxide are then
1.3.5 In a neutral solution of 2%
Cl2 + 2KI ---> I2 +
ClO2+ KI ---> KClO2 +
In an acid solution of 2%
KClO2 + 2H2SO4+ 4KI ---> KCl +
2K2SO4+ 2I2 +
- Range and Detection Limit
2.1 The detection limit is 1.0 µg/mL for a 10 L air sample. The range
is 100 µg to 50 mg.
- Precision and Accuracy
4.1 Any compounds capable of oxidizing KI to I2 will
interfere with the analysis.
5.1.1 Personal sampling pump.
5.1.2 Impinger or Liquid
5.1.3 2% KI collection solution.
5.1.4 Glass fiber
pre-filters to remove particulates.
5.2.1 Sampling is done in accordance with current
instructions contained in OSHA directives to the industrial
5.2.2 The sample is collected in a 2% KI
solution using a flow rate of 0.1 to 1 liters per minute. A glass
fiber filter should be used to remove any particulates. The net weight
collected in micrograms is then divided by the air volume in
5.2.3 Enough air must be collected to cause the clear 2% KI
solution to turn yellow or red.
5.2.4 If the samples are
to be sent to the lab for analysis, they must be protected from heat
and light. Wrap the impingers with tape, pack in ice, and ship air
- Analytical Procedure
6.1.1 50 mL Class A burette with Teflon stopcock.
6.1.2 Glass volumetric pipettes.
6.1.3 Micropipettes with tips.
6.1.4 125 mL Erlenmeyer flask.
6.1.5 Mechanical stirrer.
6.2 Reagents: All chemicals should be ACS reagent grade
equivalent, and the dilution water must be boiled in
accordance with Reference 7.1.
6.2.1 1 N Sulfuric Acid: Slowly add 28 ml H2SO4
to about 500 mL freshly boiled deionized water, stir and let
cool. Dilute to 1 L with boiled deionized water.
6.2.2 Starch indicator solution: To 5 g starch add a
little cold water and grind in a mortar to a thin paste. Pour
into 1 L of boiling distilled water, stir, and let settle overnight.
Decant the clear supernate. Preserve with 4 g zinc
6.2.3 0.1 N Sodium Thiosulfate: Dissolve 25 g
Na2S 2O3·5H2O in 1 L
freshly boiled deionized water and standardize against potassium
dichromate after at least 2 weeks storage. This initial storage is
necessary to allow oxidation of any bisulfite ion present. Add a few
mL chloroform to minimize bacterial decomposition.
0.1 N Potassium Dichromate: Dissolve 4.904 g anhydrous
K2Cr207 of primary standard quality,
in distilled water and dilute to 1 L. Store in a glass stoppered
6.2.5 0.01 N Sodium Thiosulfate titrant: Improve
the stability of 0.01 N sodium thiosulfate by diluting an aged 0.1 N
solution of sodium thiosulfate (6.2.3) with freshly boiled
deionized water. Add 4 g sodium borate and 10 mg mercuric iodide per
liter. For accurate work, standardize daily.
Potassium Iodide: Add 20 g of KI crystals to 500 mL freshly boiled
deionized water and dilute to 1 L. Store in a brown
glass-stoppered bottle and discard the solution when a yellow color
6.2.7 0.01 N Potassium Dichromate: Dilute
10 mL of the 0.1 N potassium dichromate (6.2.4.) to 1 L with deionized
6.3 Sample Preparation
6.3.1 Take a 1 to 15 mL aliquot of sample and transfer to a 125 mL
erlenmeyer flask. Add boiled deionized water to make the total
volume 30 mL. The sample aliquot size will depend on the intensity of
the color of the collecting solution.
6.4 Standard Preparation
6.4.1 Standards need not be prepared for a calibration curve for
each analysis. If standards are wanted see the chlorine dioxide
generation system described in the chlorine dioxide backup
6.5.1 Standardize the 0.01 N sodium thiosulfate (6.2.5) with the
0.01 N potassium dichromate (6.2.7) using the following procedure. To
50 mL of freshly boiled deionized water add 10 mL of the 0.01 N
potassium dichromate (6.2.7), 1 mL of concentrated sulfuric acid, and
1 g potassium iodide crystals. Allow the mixture to stand 6 minutes in
the dark before titration with the 0.01 N sodium thiosulfate
solution (6.2.5). Standardize prior to use.
Na2S2O3 = 1/mL
Record the initial volume of 0.01 N sodium thiosulfate
and titrate the sample until the yellow color almost
6.5.3 Add 0.5 mL of the starch indicator
(6.2.2). A blue color will appear.
6.5.4 Titrate with
0.01 N sodium thiosulfate until the blue color just disappears.
Record the volume of thiosulfate. This is the neutral
6.5.5 Add 5 mL of 1 N sulfuric acid. The blue
color will return and the solution should be very dark.
Titrate with 0.01 N sodium thiosulfate until the blue color just
disappears. Record the volume of thiosulfate. This is the acid
6.6.1 Subtract the initial volume of sodium thiosulfate from the
volume at the neutral endpoint. This is the volume to the neutral
endpoint. multiply this volume by the standardized normality of
the thiosulfate solution to give the number of neutral
6.6.2 Subtract the initial volume of sodium
thiosulfate from the volume at the acid endpoint. This is the
volume to the acid endpoint. Multiply this volume by the standardized
normality of the thiosulfate solution to give the number of total acid
6.6.3 From the equations in 1.3.5, it can be
seen that 1/5 of the chlorine dioxide and all of the chlorine
reacts in the neutral solution. Four fifths of the chlorine dioxide
reacts in the acid solution.
6.6.4 To calculate the
number of milligrams of chlorine dioxide use the following
6.6.5 To calculate the number of milligrams of chlorine use the
7.1 Standard Methods for the Examination of Water and
Wastewater, 15th Ed., pg 304 (1980).
Development for Sampling and Analysis of Chlorine, Chlorine
Dioxide, Bromine, and Iodine, by the Southern Research Institute for
NIOSH, project 4558-R1.
7.3 Fritz and Schenk,
Quantitative Analytical Chemistry, pg 278.
CHLORINE DIOXIDE BACKUP REPORT
1.1.1 This report describes the chlorine dioxide
generation system used to make chlorine and chlorine dioxide
1.2.1 Chlorine dioxide is produced when chlorine vapor is passed
through a concentrated aqueous solution of sodium chlorite.
2. Construction of test atmosphere generator
2.1.1 Chlorine, 99% pure.
2.1.2 Chlorine regulator,
2.1.3 250 mL impinger.
Chlorite, reagent grade.
2.1.5 Two flowmeters, accurate
to within 1 %. These flowmeters must be made of inert materials
like glass or Teflon.
2.1.6 Tubing--glass, Teflon, or
other inert materials, and tubing connectors.
mixing and sampling chamber, Teflon.
2.1.8 Separate air
source capable of providing dilution air at various temperature
2.1.9 Pure nitrogen gas with regulator.
2.2.1 The generator is designed such that any range of chlorine
dioxide can be generated from 50 to 50,000 PPM.
250 mL impinger containing 80 grams sodium chlorite in 200 mL
deionized water is used as a chlorine to chlorine dioxide conversion
2.2.3 Teflon tubing is used to connect the
chlorine tank to the chlorine flowmeter and the nitrogen tank to the
2.2.4 Teflon tubing is used
to connect the chlorine flowmeter to one leg of a "T" connector.
Tubing is also run from the nitrogen flowmeter to another leg of the
"T" connector. The third leg of the "T" will go to the chlorine
dioxide conversion chamber.
2.2.5 Connect Teflon tubing
from the output of the chlorine dioxide conversion chamber to the
output of the dilution air source.
2.2.6 The diluted
chlorine stream is then directed to the mixing and sampling manifold
using Teflon tubing.
2.2.7 For an 800 PPM chlorine
dioxide atmosphere, set the chlorine flowmeter to 17 mL/min, the
nitrogen flowmeter to 2 L/min, and the dilution air to 40
2.2.8 To prepare lower concentrations of chlorine
dioxide use a tank of 400 PPM chlorine in nitrogen instead of pure
chlorine and increase the chlorine flowmeter while cutting back on the
flow of dilution air.