ASTM D2914-15(2022)

Standard Test Methods for Sulfur Dioxide Content of the Atmosphere (West-Gaeke Method)

SIGNIFICANCE AND USE
5.1 Sulfur dioxide is a major air pollutant, commonly formed by the combustion of sulfur-bearing fuels. The Environmental Protection Agency (EPA) has set primary and secondary air quality standards (7) that are designed to protect the public health and welfare.  
5.2 The Occupational Safety and Health Administration (OSHA) has promulgated exposure limits for sulfur dioxide in workplace atmospheres (8).  
5.3 These methods have been found satisfactory for measuring sulfur dioxide in ambient and workplace atmospheres over the ranges pertinent in 5.1 and 5.2.  
5.4 Method A has been designed to correspond to the EPA-Designated Reference Method (7) for the determination of sulfur dioxide.
SCOPE
1.1 These test methods cover the bubbler collection and colorimetric determination of sulfur dioxide (SO2) in the ambient or workplace atmosphere.  
1.2 These test methods are applicable for determining SO2 over the range from approximately 25 μg/m3 (0.01 ppm(v)) to 1000 μg/m3 (0.4 ppm(v)), corresponding to a solution concentration of 0.03 μg SO2/mL to 1.3 μg SO2/mL. Beer's law is followed through the working analytical range from 0.02 μg SO2/mL to 1.4 μg SO2/mL.  
1.3 The lower limit of detection is 0.075 μg SO2/mL (1),2 representing an air concentration of 25 μg SO2/m3 (0.01 ppm(v)) in a 30-min sample, or 13 μg SO2/m3 (0.005 ppm(v)) in a 24-h sample.  
1.4 These test methods incorporate sampling for periods between 30 min and 24 h.  
1.5 These test methods describe the determination of the collected (impinged) samples. A Method A and a Method B are described.  
1.6 Method A is preferred over Method B, as it gives the higher sensitivity, but it has a higher blank. Manual Method B is pH-dependent, but is more suitable with spectrometers having a spectral band width greater than 20 nm.
Note 1: These test methods are applicable at concentrations below 25 μg/m3 by sampling larger volumes of air if the absorption efficiency of the particular system is first determined, as described in Annex A4.
Note 2: Concentrations higher than 1000 μg/m3 can be determined by using smaller gas volumes, larger collection volumes, or by suitable dilution of the collected sample with absorbing solution prior to analysis.  
1.7 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.8 Warning—Mercury has been designated by many regulatory agencies as a hazardous material that can cause serious medical issues. Mercury, or its vapor, has been demonstrated to be hazardous to health and corrosive to materials. Caution should be taken when handling mercury and mercury containing products. See the applicable product Safety Data Sheet (SDS) for additional information. Users should be aware that selling mercury and/or mercury containing products into your state or country may be prohibited by law.  
1.9 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. For specific precautionary statements, see 8.3.1, Section 9, and A3.1.3.  
1.10 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 28-Feb-2022
• ICS: 13.040.20 - Ambient atmospheres
• Technical Committee: D22 - Air Quality
• Drafting Committee: D22.03 - Ambient Atmospheres and Source Emissions

Relations

• Refers: ASTM D1356-20a - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-Sep-2020
• Refers: ASTM D1356-20 - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 15-Mar-2020
• Refers: ASTM D1357-95(2019) - Standard Practice for Planning the Sampling of the Ambient Atmosphere
• Effective Date: 01-Aug-2019
• Refers: ASTM D3631-99(2017) - Standard Test Methods for Measuring Surface Atmospheric Pressure
• Effective Date: 01-Mar-2017
• Refers: ASTM D1356-15a - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 15-Oct-2015
• Refers: ASTM D1356-15 - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-Jul-2015
• Refers: ASTM D1356-14b - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-Dec-2014
• Refers: ASTM D1356-14a - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-May-2014
• Refers: ASTM D1356-14 - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 15-Jan-2014
• Refers: ASTM E1-13 - Standard Specification for ASTM Liquid-in-Glass Thermometers
• Effective Date: 01-May-2013
• Refers: ASTM D3631-99(2011) - Standard Test Methods for Measuring Surface Atmospheric Pressure
• Effective Date: 01-Oct-2011
• Refers: ASTM D1357-95(2011) - Standard Practice for Planning the Sampling of the Ambient Atmosphere
• Effective Date: 01-Oct-2011
• Refers: ASTM E2251-11 - Standard Specification for Liquid-in-Glass ASTM Thermometers with Low-Hazard Precision Liquids
• Effective Date: 01-May-2011
• Refers: ASTM E2251-10 - Standard Specification for Liquid-in-Glass ASTM Thermometers with Low-Hazard Precision Liquids
• Effective Date: 01-Nov-2010
• Refers: ASTM D1356-05(2010) - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-Apr-2010

Overview

ASTM D2914-15(2022): Standard Test Methods for Sulfur Dioxide Content of the Atmosphere (West-Gaeke Method) establishes reliable procedures for detecting and quantifying sulfur dioxide (SO₂) in ambient or workplace air. Developed by ASTM, this international standard details the bubbler collection and colorimetric measurement of SO₂, accommodating detection from as low as 25 μg/m³ (0.01 ppm) up to 1000 μg/m³ (0.4 ppm). The West-Gaeke method remains widely accepted for compliance with air quality regulations and industrial hygiene protocols.

Key Topics

• Sulfur Dioxide as a Pollutant: SO₂ is recognized as a significant air pollutant arising primarily from combustion of sulfur-containing fuels. Its measurement is crucial for environmental protection and occupational safety.
• Regulatory Alignment: The methods conform to Environmental Protection Agency (EPA) reference methods for ambient air quality and support OSHA requirements for workplace exposures.
• Dual Methods (A and B):
  • Method A: Offers higher sensitivity and aligns with EPA reference methods but may have a higher background blank.
  • Method B: Is pH-dependent and suitable for optical spectrometers with broader spectral bandwidths.
• Range and Sensitivity: The test can reliably measure SO₂ concentrations from 25 to 1000 μg/m³, with the detection limit as low as 0.075 μg/mL in solution.
• Sampling Flexibility: Enables sampling over time periods from 30 minutes to 24 hours, supporting both short- and long-term monitoring needs.
• Safety Considerations: Use of mercury compounds mandates stringent safety and environmental precautions in line with regulatory requirements.

Applications

The West-Gaeke Method described in ASTM D2914-15(2022) is essential for several practical applications:

• Ambient Air Monitoring: Used by environmental agencies to measure sulfur dioxide near industrial sources and urban areas, helping ensure compliance with air quality standards.
• Workplace Exposure Assessment: Utilized by industrial hygienists to monitor worker exposure in locations where sulfur dioxide may be present, ensuring adherence to OSHA exposure limits.
• Regulatory Compliance: Both federal and state authorities reference this standard for enforcing public health and environmental welfare through air quality monitoring programs.
• Industrial Emission Studies: Applied in power plants, refineries, and manufacturing facilities to evaluate emission controls and abatement strategies for sulfur dioxide.
• Laboratory Analysis: Employed in analytical laboratories for validation and calibration of other SO₂ detection methods.

Related Standards

To supplement and ensure the accurate implementation of ASTM D2914-15(2022), several related standards and practices are commonly referenced:

• ASTM D1193 - Specification for Reagent Water: Defines requirements for water purity, critical for analytical procedures.
• ASTM D1356 - Terminology Relating to Sampling and Analysis of Atmospheres: Provides key definitions.
• ASTM D1357 - Practice for Planning the Sampling of the Ambient Atmosphere.
• ASTM D3195 - Practice for Rotameter Calibration.
• ASTM D3609 - Calibration Techniques Using Permeation Tubes.
• ASTM D3631 - Test Methods for Measuring Surface Atmospheric Pressure.
• EPA 40 CFR Part 58 - Probe and Monitoring Path Siting Criteria from Ambient Air Quality Monitoring.
• Additional guidance from OSHA and EPA for sample collection, handling, and health risk management.

Practical Value

Implementing ASTM D2914-15(2022) ensures accurate, consistent, and regulatory-compliant measurement of sulfur dioxide in the atmosphere. Its adherence to international standardization principles, flexibility in sampling duration, sensitivity to low concentrations, and cross-compatibility with regulatory reference methods make it indispensable for environmental laboratories, regulatory agencies, and industrial workplaces concerned with air quality and health impacts of SO₂ exposure.

Keywords: ASTM D2914-15, sulfur dioxide measurement, West-Gaeke method, air quality testing, SO₂ analysis, environmental compliance, occupational exposure, air sampling standards, EPA reference method.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D2914 − 15 (Reapproved 2022)
Standard Test Methods for
Sulfur Dioxide Content of the Atmosphere (West-Gaeke
Method)
This standard is issued under the fixed designation D2914; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope 1.8 Warning—Mercury has been designated by many regu-
latory agencies as a hazardous material that can cause serious
1.1 These test methods cover the bubbler collection and
medical issues. Mercury, or its vapor, has been demonstrated to
colorimetric determination of sulfur dioxide (SO)inthe
be hazardous to health and corrosive to materials. Caution
ambient or workplace atmosphere.
should be taken when handling mercury and mercury contain-
1.2 These test methods are applicable for determining SO
ing products. See the applicable product Safety Data Sheet
over the range from approximately 25 µg/m (0.01 ppm(v)) to
(SDS) for additional information. Users should be aware that
1000 µg/m (0.4 ppm(v)), corresponding to a solution concen-
selling mercury and/or mercury containing products into your
tration of 0.03 µgSO /mL to 1.3 µgSO /mL. Beer’s law is
2 2
state or country may be prohibited by law.
followed through the working analytical range from 0.02 µg
1.9 This standard does not purport to address all of the
SO /mL to 1.4 µgSO /mL.
2 2
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
1.3 The lower limit of detection is 0.075 µgSO /mL (1),
representing an air concentration of 25 µgSO /m priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
(0.01ppm(v)) in a 30-min sample, or 13 µgSO /m (0.005
ppm(v)) in a 24-h sample. Forspecificprecautionarystatements,see8.3.1,Section9,and
A3.1.3.
1.4 These test methods incorporate sampling for periods
1.10 This international standard was developed in accor-
between 30 min and 24 h.
dance with internationally recognized principles on standard-
1.5 These test methods describe the determination of the
ization established in the Decision on Principles for the
collected(impinged)samples.AMethodAandaMethodBare
Development of International Standards, Guides and Recom-
described.
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
1.6 Method A is preferred over Method B, as it gives the
higher sensitivity, but it has a higher blank. Manual Method B
2. Referenced Documents
is pH-dependent, but is more suitable with spectrometers
2.1 ASTM Standards:
having a spectral band width greater than 20 nm.
D1193Specification for Reagent Water
NOTE 1—These test methods are applicable at concentrations below
D1356Terminology Relating to Sampling and Analysis of
25 µg/m by sampling larger volumes of air if the absorption efficiency of
Atmospheres
the particular system is first determined, as described in Annex A4.
NOTE 2—Concentrations higher than 1000 µg/m can be determined by D1357Practice for Planning the Sampling of the Ambient
using smaller gas volumes, larger collection volumes, or by suitable
Atmosphere
dilution of the collected sample with absorbing solution prior to analysis.
D1914PracticeforConversionUnitsandFactorsRelatingto
1.7 The values stated in SI units are to be regarded as
Sampling and Analysis of Atmospheres
standard. No other units of measurement are included in this
D3195Practice for Rotameter Calibration
standard.
D3609Practice for Calibration Techniques Using Perme-
ation Tubes
D3631Test Methods for Measuring Surface Atmospheric
These test methods are under the jurisdiction ofASTM Committee D22 on Air
Quality and are the direct responsibility of Subcommittee D22.03 on Ambient
Pressure
Atmospheres and Source Emissions.
Current edition approved March 1, 2022. Published April 2022. Originally
approved in 1970. Last previous edition approved in 2015 as D2914–15. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
DOI:10.1520/D2914-15R22. contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
The boldface numbers in parentheses refer to a list of references at the end of Standards volume information, refer to the standard’s Document Summary page on
this standard. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D2914 − 15 (2022)
E1Specification for ASTM Liquid-in-Glass Thermometers heavy metals by EDTA and phosphoric acid (4, 5). At least
E275PracticeforDescribingandMeasuringPerformanceof 60 µg of Fe(III), 10 µg of Mn(II), and 10 µg of Cr(III), 10 µg
Ultraviolet and Visible Spectrophotometers ofCu(II)and22 µgofV(V)in10mLofabsorbingreagentcan
E2251Specification for Liquid-in-Glass ASTM Thermom- be tolerated in the procedure. No significant interference was
eters with Low-Hazard Precision Liquids found with 2.3 µgofNH (9).
2.2 Other Standards:
40 CFR Part 58 Probe and Monitoring Path Siting Criteria 7. Apparatus
from Ambient Air Quality Monitoring, Appendix E
7.1 For Sampling:
7.1.1 Absorber, Short–Term Sampling—An all-glass midget
3. Terminology
impinger having a solution capacity of 30 mL and a stem
3.1 For definitions of terms used in this method, refer to
clearance of 4 6 1 mm from the bottom of the vessel is used
Terminology D1356.
for sampling periods of 30 min and 1 h (or any period
considerably less than 24 h).
4. Summary of Test Methods
7.1.2 Absorber, 24-h Sampling—A glass or polypropylene
4.1 Sulfur dioxide (SO ) is absorbed by aspirating a mea-
tube 32 mm in diameter and 164 mm long with a polypropyl-
sured air sample through a tetrachloromercurate (TCM)
enetwo-portcap(rubberstoppersareunacceptablebecausethe
solution, resulting in the formation of a dichlorosulfonatomer-
absorbing reagent can react with the stopper to yield errone-
curate complex (2, 3). Ethylenediaminetetraacetic acid diso-
ously high SO concentrations, and cause high and variable
dium salt (EDTA) is added to this solution to complex heavy
blank values). Insert a glass impinger stem, 6 mm inside
metals that interfere with this method (4).
diameter and 158 mm long, into one port of the absorber cap.
Dichlorosulfonatomercurate, once formed, is stable to strong
Taper the tip of the stem to a small diameter orifice (0.4 6
oxidants(forexample,ozoneandoxidesofnitrogen) (2).After
0.1mm)suchthataNo.79jeweler’sdrillbitwillpassthrough
the absorption is completed, any ozone in the solution is
the opening but a No. 78 drill bit will not. Clearance from the
allowed to decay (5). The liquid is treated first with a solution
bottomoftheabsorbertothetipofthestemshallbe6 62mm.
of sulfamic acid to destroy the nitrite anion formed from the
Perform the orifice test before use to verify the orifice size.
absorption of oxides of nitrogen present in the atmosphere (6).
Permanentlymarkthe50mLvolumelevelontheabsorber.See
It is treated next with solutions of formaldehyde and specially
Fig. 1.
purified acid-bleached pararosaniline containing phosphoric
7.1.3 Air Sample Probe—A sample probe meeting the re-
acid(H PO )tocontrolpH.Pararosaniline,formaldehyde,and
3 4
quirements of Section 7 of 40 CFR Part 58, Appendix E,
the bisulfite anion react to form the intensely colored pararo-
(TFE-fluorocarbon, polypropylene, or glass with a residence
saniline methyl sulfonic acid which behaves as a two-color pH
time less than 20 sec), used to transport ambient air to the
indicator (2). The pH of the final solution is adjusted to the
sampling train location. Design or orient the end of the probe
desired value by the addition of prescribed amounts of 3 N
to preclude the sampling of precipitation, large particles, etc.
H PO to the pararosaniline reagent (5).
3 4
7.1.4 Moisture Trap—Glass or polypropylene trap as shown
5. Significance and Use
in Fig. 1, placed between the absorber tube and flow control
device to prevent entrained liquid from reaching the flow
5.1 Sulfur dioxide is a major air pollutant, commonly
control device. Pack the tube with coconut charcoal and glass
formed by the combustion of sulfur-bearing fuels. The Envi-
wool or with indicating silica gel. Charcoal is preferred when
ronmental Protection Agency (EPA) has set primary and
collecting long-term samples (1 h or more) if flow changes are
secondary air quality standards (7) that are designed to protect
routinely encountered.
the public health and welfare.
7.1.5 Cap Seals—Seal the absorber and moisture trap caps
5.2 The Occupational Safety and Health Administration
securely to prevent leaks during use, by using heat-shrink
(OSHA) has promulgated exposure limits for sulfur dioxide in
material to prevent the caps coming loose during sampling,
workplace atmospheres (8).
shipment, or storage.
5.3 These methods have been found satisfactory for mea-
7.1.6 Filter,membrane,of0.8to2.0 µmporosity,withfilter
suring sulfur dioxide in ambient and workplace atmospheres
holder, to protect the flow controller from particles during
over the ranges pertinent in 5.1 and 5.2.
long-term sampling. This item is optional for short-term
5.4 Method A has been designed to correspond to the sampling.
EPA-Designated Reference Method (7) for the determination
7.1.7 Pump,equippedwithvacuumgauge,capableofmain-
of sulfur dioxide.
taining a vacuum greater than 70 kPa (0.7 atm) at the specified
flow rate across the flow control device.
6. Interferences
7.1.8 Flow Control and Measurement Devices:
6.1 The interferences of oxides of nitrogen are eliminated
7.1.8.1 Flow Control Device—A calibrated rotameter and
by sulfamic acid (5, 6), of ozone by time delay (5), and of
needle valve combination capable of maintaining and measur-
ing air flow to within 62 percent is suitable for short-term
sampling but shall not be used for long-term sampling. A
Available from U.S. Government Publishing Office (GPO), 732 N. Capitol St.,
NW, Washington, DC 20401, http://www.gpo.gov. critical orifice can be used for regulating flow rate for both
D2914 − 15 (2022)
FIG. 1 Sampling System
long-term and short-term sampling. Use a 22-gauge hypoder- of the 15 6 10°C range to minimize losses during this period.
mic needle 25 mm long as a critical orifice (10) to yield a flow Thermoelectric coolers specifically designed for this tempera-
rate of approximately 1 L/min for a 30-min sampling period. ture control are available commercially and normally operate
When sampling for 1 h, use a 23-gauge hypodermic needle in the range of 5 to 15°C. Small refrigerators can be modified
16mm in length to provide a flow rate of approximately to provide the required temperature control; however, insulate
0.5L⁄min. Provide a flow control for a 24-h sample by a the inlet lines from the lower temperatures to prevent conden-
27-gauge hypodermic needle critical orifice that is 9.5 mm in sationwhensamplingunderhumidconditions.Asmallheating
lengthsothattheflowrateisintherangeof0.18to0.22L/min. pad may be necessary when sampling at low temperatures
7.1.8.2 Flow Measurement Device—Calibrated as specified (<7°C) to prevent the absorbing solution from freezing (11).
in 11.1.1, and used to measure sample flow rate at the
7.1.12 Sampling Train Container—A light-proof box to
monitoring site.
shield the absorbing solution from light during and after
7.1.9 Thermometer—ASTMThermometer33C,meetingthe
sampling.
requirementsofSpecificationE1willmeettherequirementsof
7.1.13 Timer—To initiate and to stop sampling for the 24-h
most applications in this method. A comparable precision
sampling period. This is not a required piece of equipment;
low-hazard liquid thermometer, ASTM Thermometer S33C,
however, without the timer it will be necessary to manually
meeting the requirements of Specification E2251, may also be
startandstopthesampling.Anelapsedtimemetermayalsobe
used.
used to determine the sampling period.
7.1.10 Barograph or Barometer, capable of measuring at-
7.1.14 The arrangement of the component parts for sam-
mospheric pressure to 60.5 kPa (5 torr). (See Test Methods
pling is shown in Fig. 1.
D3631.)
7.2 Shipping:
7.1.11 Temperature Control Device—To maintain the tem-
perature of the absorbing solution during sampling at 15 6 7.2.1 Shipping Container—To maintain a temperature of 5
10°C.Maintainthetemperatureofthecollectedsampleat5 6 6 5°C while transporting the sample from the collection site
5°C,assoonaspossiblefollowingsamplinganduntilanalysis. totheanalyticallaboratory.Icecoolersorrefrigeratedshipping
Where an extended period of time may elapse before the containers have been found to be satisfactory. The use of
collected sample can be moved to the lower storage eutectic cold packs instead of ice will give a more stable
temperature, use a collection temperature near the lower limit temperature control.
D2914 − 15 (2022)
7.3 Analysis: and 6.0 g KCl in distilled water and dilute to volume with
7.3.1 Spectrophotometer or Colorimeter—The instrument distilled water in a 1000–mL volumetric flask. The pH of this
shall be suitable for measurement of color at 548 nm for reagentshouldbebetween3.0and5.0 (5).CheckthepHofthe
MethodAor575nmforMethodB.ForMethodA,aneffective absorbingsolutionbyusingpHindicatingpaperorapHmeter.
spectralbandwidthoflessthan15nmisrequiredsincereagent If the pH of the solution is not between 3.0 and 5.0, dispose of
blank problems may otherwise result. Verify the wavelength the solution in accordance with the disposal technique de-
calibration of the spectrophotometer in accordance with Prac- scribed in AnnexA3.The absorbing reagent is normally stable
tice E275 upon initial receipt of the instrument and after each for 6 months. If a precipitate forms, dispose of the reagent in
160 h or normal use or every 6 months, whichever occurs first, accordancewithAnnexA3.(Warning—Mercuricchlorideand
using a standard wavelength filter traceable to the National TCM are very poisonous, particularly when concentrated.
Institute of Standards and Technology. Avoid contact with skin and especially, with eyes. Avoid
7.3.2 Spectrophotometer Cells—A set of 1-cm path length generating or breathing dust. Keep away from food. Wash
cells suitable for use in the visible region. If the cells are hands after use. Do not ingest.)
unmatched, determine the matching correction factor in accor- 8.3.1.1 Ethylenediaminetetraacetic acid disodium salt
dance with 11.2. (EDTA).
7.3.3 Temperature Control Device—Conduct the color de-
8.3.1.2 Mercuric chloride, HgCl
2.
velopmentstepsduringanalysisinanenvironmentthatisinthe
8.3.1.3 Potassium chloride, KCl.
range of 20 to 30°C and controlled to 61°C. Perform both
8.3.2 Acetate Buffer (1 M)—Dissolve in a 100 mLvolumet-
calibration and sample analysis under identical conditions
ric flask, 13.61 g of sodium acetate trihydrate (NaC H O ·
2 5 2
(within 1°C). Adequate temperature control may be obtained
3H O) in 50 mL of water. Add 5.7 mL of glacial acetic acid
by means of constant temperature baths, water baths with
(CH COOH) and dilute to 100 mL. The pH should be 4.74.
manual temperature control, or temperature controlled rooms.
8.3.3 1-Butanol—Certain batches of 1-butanol contain oxi-
7.3.4 TCM Waste Receptacle—A glass waste receptacle for
dants that create a sulfur dioxide (SO ) demand. Check by
the storage of spent TCM solution. Store the vessel stoppered
shaking 20 mL of 1-butanol with 5 mL of 15% potassium
in a hood at all times.
iodide (KI) solution. If a yellow color appears in the alcohol
phase, redistill the 1-butanol from silver oxide.
8. Reagents and Materials
8.3.4 Formaldehyde (0.2%)—Dilute 5 mL of 36 to 38%
formaldehyde (HCHO) to 1 L. Prepare this solution daily.
8.1 Purity of Reagents—Reagent grade chemicals shall be
8.3.5 Hydrochloric Acid (1 N)—Slowly and while stirring,
used in all tests.All reagents shall conform to the specification
add 86 mL of concentrated hydrochloric acid to 500 mL of
of the Committee on Analytical Reagents of the American
Chemical Society, where such specifications are available. distilled water. Allow to cool and dilute to 1000 mL with
distilled water. This is stable for one year.
Other grades may be used, provided it is first ascertained that
the reagent is of sufficiently high purity to permit its use 8.3.6 Pararosaniline, Stock Solution (PRA), 0.2 %—
Dissolve 0.2 g of pararosaniline in 100 mLof water.The stock
without lessening the accuracy of the determination.
pararosaniline solution shall meet the following specifications:
8.2 Purity of Water—Unlessotherwiseindicated,watershall
8.3.6.1 The solution shall have a wavelength of maximum
be Type II distilled water in accordance with Specification
absorbance at 540 nm for MethodAor at 575 mn for Method
D1193. Water shall be free of oxidants.
B, in a buffered solution of 0.01 M sodium acetate-acetic acid.
8.2.1 Verify the purity of the distilled water as follows:
8.3.6.2 The absorbance of the reagent blank, which is
8.2.1.1 Place 0.20 mL of potassium permanganate solution
temperature-sensitive (0.015 absorbance units/°C) shall not
(0.316 g/L), 500 mL of distilled water, and 1 mL of concen-
exceed 0.170 absorbance units at 22°C with a 10-mm optical
trated sulfuric acid in a chemically resistant glass bottle,
path length where the blank is prepared as specified and at the
stopper the bottle, and allow to stand.
specified concentration of the stock pararosaniline solution.
8.2.1.2 If the permanganate color (pink) does not disappear
completelyafteraperiodof1hatroomtemperature,thewater
NOTE 3—This specification is applicable only in the case of MethodA.
is suitable for use.
8.3.6.3 The calibration curve (AnnexA2) shall have a slope
8.2.1.3 If the permanganate color does disappear, the water
of 0.030 6 0.002 absorbance units/µgSO , at the same optical
can be purified by redistilling with one crystal each of barium
path length, when the sulfite solution is properly standardized.
hydroxide and potassium permanganate in an all glass still.
NOTE 4—This specification is applicable only in the case of MethodA.
8.3 Sampling Reagents:
8.3.6.4 A specially purified (99 to 100% pure) solution
8.3.1 Absorbing Reagent (0.04 M potassium tetrachloro-
whichmeetstheabovespecificationsiscommerciallyavailable
mercurate [TCM])—Dissolve 10.86 g HgCl , 0.066 g EDTA,
in the required 0.20% solution.
8.3.6.5 Alternatively,thedyemaybepurifiedasindicatedin
Annex A1.
ACS Reagent Chemicals, Specifications and Procedures for Reagents and
Standard-Grade Reference Materials, American Chemical Society, Washington,
8.3.7 Pararosaniline Reagent:
DC. For suggestions on the testing of reagents not listed by theAmerican Chemical
8.3.7.1 Pipet 1.0 mL of stock pararosaniline solution into a
Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset,
100mLvolumetricflask,anddilutetovolume.Pipet5.0mLof
U.K., and the United States Pharmacopeia and National Formulary, U.S. Pharma-
copeial Convention, Inc. (USPC), Rockville, MD. that solution into a 50 mL volumetric flask. Add 5.0 mL of
D2914 − 15 (2022)
acetate buffer solution, and dilute to the mark. After 1 h, a little water and add the paste slowly to 200 mL of boiling
determinetheabsorbanceat540nmforMethodAorat575mn water. Boil until clear; cool and transfer to a glass-stoppered
for Method B, with a spectrophotometer having a spectral bottle.
bandwidth of less than 11 µm, using 1-cm optical path length.
8.4.5 Sodium Thiosulfate, Stock Solution (0.1 N)—Dissolve
Determine the assay of PRA as follows:
24.82 g of sodium thiosulfate (Na S O ·5 H O) in freshly
2 2 3 2
boiled,cooledwater,add0.1gofsodiumcarbonate(Na CO ),
A 321.3 2 3
M 5 (1)
and dilute to 1 L.Allow the solution to stand for a day before
W
standardizing.
where:
8.4.5.1 Tostandardize,accuratelypipet50mLofpotassium
M = %PRA in sample,
iodate solution into a 500 mL iodine flask and add 2.0 g of
A = absorbance of solutions,
potassium iodide and 10 mLof 1 N HCI. Stopper the flask and
W = the mass in g of the PRA dye used in the assay to
allowtostandfor5min.Titratethesolutionwithstocksodium
prepare50mLofstocksolution(thatis,0.1gofdye
thisulfate solution to a pale yellow color. Add 5 mL of starch
was used to prepare 50 mL of the solution in the
solution and titrate until the blue color just disappears. Repeat
purification procedure described in Annex A1) (see
this procedure three times.
Note 5), and
8.4.5.2 Calculate the normality of the sodium thiosulfate
21.3 = constant to convert absorbance to mass.
solution as follows:
NOTE5—Whencommercialconcentrateisused,usethestatedpurityto
compute w. For example, if the stated purity is 98%, W will be 0.098 g. 3
W 310 30.1
N 5 (2)
s
V 335.67
8.3.7.2 Pararosaniline Reagent for Method A—Toa1L
flask, add 80 mL of stock PRA, plus 0.8 mL of stock for each
where:
percent the stock assays below 100%. Add 100 mL of 3 M
N = normality of the sodium thiosulfate solution,
s
phosphoric acid and dilute to volume. This is stable for 9
V = volume of thiosulfate solution taken, mL,
months when stored at 25°C or below.
W = mass, g, of the KIO ,
8.3.7.3 Pararosaniline Reagent for Method B—Toa1L
10 = conversion factor, mL to L,
flask, add 80 mL of stock PRA, plus 0.8 mL of stock for each
0.1 = dilution factor, and
35.67 = gram equivalent weight of KIO .
percent the stock assays below 100%. Add 800 mL of 3 M
phosphoric acid and dilute to volume. This is stable for 9
Average the normality found from the three determinations.
months when stored away from light at 25°C or below.
8.4.6 Sodium Thiosulfate, Working Solution (0.01 N)—
8.3.8 Phosphoric Acid (3.0 M)—Dilute 205 mL of concen-
Dilute 100 mL of stock sodium thiosulfate solution into a
trated phosphoric acid (H PO , sp gr 1.69) to 1 L by pouring
3 4
1000mL volumetric flask and dilute to volume with freshly
the acid into 700 mL of water while stirring, then dilute to
boiled, cooled, distilled water. Calculate the normality of the
volume. This is stable for one year.
working sodium thiosulfate titrant (NT) as follows:
8.3.9 Potassium Hydroxide Solution (6 N)—Dissolve
N 5 N x0.100 (3)
T s
33.67g of potassium hydroxide (KOH) in 100 mL of water.
8.3.10 Potassium Iodate Solution—Accurately weigh to the 8.4.7 Sulfite Solution, Standard—Dissolve 0.4 g of sodium
nearest0.1mg,1.5g(recordweight)ofprimarystandardgrade sulfite (Na SO ) or 0.3 g of sodium metabisulfite (Na S O)in
2 3 2 2 5
potassium iodate, KIO , that has been previously dried at 500mLofrecentlyboiledandcooledwater(preferablydoubly
180°Cforatleast3handcooledinadessicator.Dissolve,then distilled deaerated water). This solution contains from 320 to
dilute to volume in a 500 mL volumetric flask with distilled 400 µg/mL as SO . The actual concentration in the standard
water. solutionisdeterminedbyaddingaknownexcessofiodineand
back titrating with sodium thiosulfate that has been standard-
8.3.11 Sulfamic Acid (0.6%)—Dissolve 0.6 g of sulfamic
ized against the potassium iodate solution (primary standard).
acid (NH SO H) in 100 mL of water. Prepare fresh daily.
2 3
As sulfite solution is unstable, prepare fresh daily.
8.4 Calibration Reagents:
8.4.7.1 To back-titrate, pipet 50 mL of the 0.01 N iodine
8.4.1 Iodine Solution, Stock (0.1 N)—Dissolve 12.7 g of
solution into each of two 500 mL iodine flasks (A and B). To
resublimed iodine (I ) and 40 g of potassium iodide (KI) in
flask A (blank) add 25 mL distilled water, and to flask B
25mL of water, and dilute to 1 L in a volumetric flask.
(sample) pipet 25 mL sulfite solution. Stopper the flasks and
8.4.2 Iodine Solution, Working (0.01 N)—Dilute 50 mL of
allow to stand for 5 min. Prepare the working sulfite-TCM
stock iodine solution (0.1 N) to 500 mL in a volumetric flask.
solution immediately prior to adding the iodine solution to the
8.4.3 Potassium Iodate Solution—Accurately weigh to the flasks. Using the standardized 0.01 N thiosulfate titrant, titrate
nearest0.1mg,1.5g(recordweight)ofprimarystandardgrade
thesolutionineachflasktoapaleyellowcolor.Thenadd5mL
potassium iodate (KIO ) that has been previously dried at starch solution and continue the titration until the blue color
180°Cforatleast3handcooledinadessicator.Dissolve,then
just disappears.
dilute to volume in a 500 mL volumetric flask with distilled
8.4.7.2 Working Sulfite-TCM Solution—Pipet 5 mL of the
water.
standard sulfite solution into a 250 mL volumetric flask and
8.4.4 Starch Indicator Solution—Triturate 0.4 g of soluble dilute to volume with 0.04 M TCM. Calculate the concentra-
starch and 2 mg of mercuric iodide (HgI ) (preservative) with tion of sulfur dioxide in the working solution as follows:
D2914 − 15 (2022)
A 2 B NT 32000 to the inlet of the absorber. For 24 h samples, determine the
~ !~ !~ !
C 5 30.02 (4)
TCM/SO
25 standard flow rate at the time the absorber is placed in the
sampling train and again when the absorber is removed from
where:
the train for shipment to the analytical laboratory with a
C = equivalent concentration of SO in solution,
TCM/SO 2
2 calibrated flow measuring device connected to the inlet of the
µg/mL,
samplingtrain.Determinetheflowratewithallcomponentsof
A = volume of thiosulfate titrant required for the
the sampling system in operation (for example, the absorber
blank, mL,
temperaturecontrollerandanysampleboxheatersmustalsobe
B = volume of thiosulfate titrant required for the
operating). Use Eq 5 to determine the standard flow rate when
sample, mL,
a calibrated positive displacement meter is used as the flow
NT = normality of the thiosulfate titrant, from Eq 3,
measuring device. Other types of calibrated flow measuring
32 000 = milliequivalent weight for SO , µg,
devices may also be used to determine the flow rate at the
25 = volume of standard sulfite solution, mL, and
sampling site provided that the user applies any appropriate
0.02 = dilution factor.
corrections to devices for which output is dependent on
This solution is stable for 30 days if kept at 5°C (12).
temperature or pressure.
Prepare fresh daily if not kept at 5°C.
P 1 2 RH P
~ ! 298.16
a H O
8.4.7.3 Dilute Working Sulfite-TCM Solution—Prepare a
Q 5 Q 3 3 (5)
std act
P T 1273.16
dilute working sulfite-TCM solution by diluting 10 mL of the
std meter
working sulfite-TCM solution to 100 mLwithTCM absorbing
where:
reagent.
Q = flow rate at standard conditions, std L/min (25°C
std
8.4.8 Sulfur Dioxide Permeation Tube—Permeation devices
and 101.3 kPa,
may be prepared or purchased and in both cases shall be
Q = flow rate at monitoring site conditions, L/min,
act
traceable either to a National Institute of Standards and
P = barometric pressure at monitoring site conditions,
b
Technology (NIST) Standard Reference Material (SRM 1625,
kPa,
SRM 1626, SRM 1627) or to an NBS/EPA-approved commer-
RH = fractional relative humidity of the air being
cially available Certified Reference Material (CRM). See Ref
measured,
(13) for a description of CRM’s and a list of CRM sources.A
P = vaporpressureofwateratthetemperatureoftheair
H O
recommendedprotocolforcertifyingapermeationdevicetoan
in the flow or volume standard, in the same units as
NIST SRM or CRM is given in Practice D3609. Device
P , (for wet volume standards only, that is, bubble
b
permeation rates of 0.2 to 0.4 µg/min, inert gas flows of about
flowmeter or wet test meter; for dry standards, that
50 mL/min, and dilution air flow rates from 1.1 to 15 L/min
is, dry test meter, P =0),
H O
conveniently yield standard atmospheres in the range of 25 to
P = standardbarometricpressure,inthesameunitsasP
std b
600 µgSO /m (0.010 to 0.230 ppm(v)).
(101.3 kPa), and
T = temperature of the air in the flow or volume
meter
9. Precautions
standard, °C (for example, bubble flowmeter).
9.1 Safety Precautions:
If a barometer is not available, the following equation may
9.1.1 Mercury Compounds—The absorbing solution con-
be used to determine the barometric pressure:
tains mercury salts. Precautions to its use are shown in 8.3.1.
P 5101.3 2.01 H kP (6)
~ !
b a
9.2 Sampling and Transporting Precaution—Maintain the
where:
temperature of the impinging solution below 25°C during
sampling, transporting to the laboratory, and storage prior to
H = sampling site elevation above sea level in meters.
analysis, to avoid loss of SO . Do not expose to light.
10.4 If the initial flow rate (Q) differs from the flow rate of
i
thecriticalorificeortheflowrateindicatedbytheflowmeterin
10. Sampling
the sampling train (Q ) by more than 5 percent as determined
c
10.1 See Practice D1357 for general sampling guidelines.
by Eq 7, check for leaks and redetermine Q.
i
10.2 Sampling procedures are described for short-term (30
Q 2 Q
i c
min) and for long-term (24 h) sampling. Select different % Diff 5 3100 (7)
Q
c
combinations of sampling rate and time to meet special needs,
Invalidate the sample if the difference between the initial
but adjust sample volumes and air flow rates so that the
(Q) and final (Q) flow rates is more than 5 percent as
linearity is maintained between absorbance and concentration
i f
determined by Eq 8:
over the dynamic range.
Q 2 Q
10.3 See 12.1 for detailed sampling procedures.
i f
% Diff 5 3100 (8)
Q
10.3.1 Determination of Flow Rate at Sampling Site—For
f
short-term samples, determine the standard flow rate at the
11. Calibration and Standardization
sampling site at the initiation and completion of sample
collection with a calibrated flow measuring device connected 11.1 Sampling:
D2914 − 15 (2022)
11.1.1 Flowmeter or Hypodermic Needle—Calibrate the nationwithallcomponentsofthesamplingsysteminoperation
flowmeter in accordance with Practice D3195.
...