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These procedures were designed and tested for internal use by OSHA personnel. Mention of any company name or commercial product does not constitute endorsement by OSHA.
This method describes the collection and analysis of airborne nitrogen dioxide (NO2).
Samples are taken in the breathing zone of workplace personnel and analysis is performed by ion chromatography (IC).
||ID-182 (This method supersedes ID-109)
|OSHA Permissible Exposure Limits
Final Rule Limit:
1 ppm Short-Term Exposure Limit (STEL)
5 ppm Ceiling
||Each sample is collected using a sampling tube containing
triethanolamine-impregnated molecular sieve (TEA-IMS) and a calibrated sampling pump.
|Recommended Sampling Rate:
|Recommended Air Volume:
||3.0 L (0.20 L/min for 15 min)
||The sample is desorbed from the solid sorbent using a 1.5%
triethanolamine (TEA) solution. Analysis is performed as nitrite (NO2-) by ion chromatography.
0.07 ppm (3-L air sample)
0.19 ppm (3-L air sample)
|Precision and Accuracy
2.64 to 9.45 ppm
|Date (Date Revised):
||December 1987 (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.
Branch of Inorganic Methods Development
OSHA Technical Center
Sandy City, Utah
2. Range, Detection Limit and Sensitivity
Previous methods of analysis for NO2 involved collection of nitrogen dioxide in bubblers of
triethanolamine (TEA) solution or a triethanolamine-impregnated molecular sieve (TEA-IMS)
solid sorbent and TEA extraction (8.1). Nitrogen dioxide exposure was determined
colorimetrically by the Griess-Saltzman reaction (8.1
This method, like most colorimetric procedures, can have significant interferences. A differential pulse polarographic
(DPP) method (8.4) was later developed to improve sensitivity and decrease the potential for
interferences. The sensitivity of the DPP method was adequate for measuring workplace concentrations of nitrogen
dioxide; however, the nitrite ion is unstable at the pH range (pH 1-2) used during analysis
Method no. ID-182 uses the collection principle of the TEA-IMS tube.
The samples are analyzed by IC to determine NO2 exposure.
A known volume of air is drawn through a sampling tube containing TEA-IMS. Nitrogen
dioxide is trapped and converted to nitrite in the presence of TEA and water. Samples are
desorbed using an aqueous TEA solution and analyzed as nitrite. The conversion mechanism of
NO2 gas to nitrite ion has been proposed by Gold (8.6).
The following is Gold's proposal for the reaction of equivalent amounts of NO2
and TEA in an aqueous solution:
2NO2 < = > N2O4
N2O4 + (HOCH2CH2)3N -->
(HOCH2CH2)3NNO+NO3- + H2O -->
(HOCH2CH2)3NH+NO3- + HNO2
HNO2 --> H+ + NO2-
Nitrogen dioxide disproportionates to nitrite and nitrate ions in the presence of TEA. The nitrite
ion (NO2-) formed from the above reaction can be analyzed via conventional analytical methods
8.5) including IC (8.7).
The high background levels of nitrate found in commercial TEA-IMS sorbents ruled out
further research to assess this NO2-TEA disproportionation product by IC.
This reaction path requires a stoichiometric factor of 0.5 for the conversion of gaseous NO2 to
NO2-. Experiments indicate the proposed factor of 0.5 is seen only when NO2
concentrations are greater than 10 ppm (8.6,
The conversion factor has been experimentally determined to average approximately 0.6 to 0.7 when concentrations are below 10 ppm
8.6 - 8.9).
The deviation from ideal stoichiometry is believed to be due to other competing reactions; however, evidence to support this has
not been found (8.6).
1.3. Advantages and Disadvantages
1.3.1. The analysis is simple, rapid, easily automated, and specific for the nitrite ion.
1.4. Physical Properties (8.11)
1.3.2. After sample preparation, nitrogen dioxide (as nitrite ion) can also be determined by
polarographic or colorimetric analytical techniques (8.1 -
1.3.3. Nitric oxide (NO) can also be sampled when using a three-tube sampling device
(8.10). Sulfur dioxide may also be screened using the TEA-IMS sampling tube and
similar analytical conditions (8.7).
1.3.4. A disadvantage is the potential interference from large amounts of soluble chloride salts
present in commercial molecular sieve. Prior to TEA impregnation, the molecular
sieve should be washed with deionized water to remove any soluble chloride salts.
1.3.5. Another disadvantage is the need for a concentration-dependent conversion factor when
Nitrogen dioxide (CAS No. 10102-44-0), one of several oxides of nitrogen, is a reddish-brown
or dark orange gas with a formula weight of 46.01. Its dimer, nitrogen tetroxide (N2O4), is
colorless. At temperatures between -9.3 and 135 °C, NO2 and N2O4
coexist as a mixture of gases. Below -9.3 °C, a colorless solid consisting of N2O4
is formed, while above 135 °C, the gas is mainly composed of NO2. Physical characteristics of NO2 are:
||1.448 at 20 °C (liquid)
|Boiling point||21.15 °C
|Vapor pressure||96 KPa (720 mmHg) at 20 °C
|Vapor density||1.58 (air = 1)
|Other characteristics||strong oxidizer, corrosive, nonflammable
|Synonyms||dinitrogen tetroxide, nitrogen tetroxide, nitrogen peroxide, liquid dioxide
1.5. Some sources for potential nitrogen dioxide exposures are:
Nitrogen dioxide and nitric oxide usually exist together in industrial settings. Nitric oxide is
reactive in air and produces NO2 according to the following equations
arc or gas welding (esp. confined space operations)
food and textile bleaching
nitric acid production
nitrogen fertilizer production
2NO + O2 ---> 2NO2
d(NO2) / dt = K(O2)(NO)2
(K is a temperature dependent constant. At 20 °C, K = 14.8 × 109)
An experimental approximation of the NO / NO2 distribution found in various industrial
operations is shown (8.11).
|Carbon arc|| 9
|Oxyacetylene torch|| 8
|Cellulose nitrate combustion||19
The potential for exposure to both NO2 and NO should be considered because NO is easily
oxidized to NO2 and both oxides are likely to coexist in industrial settings.
Information listed within this section is a synopsis of current knowledge of the physiological
effects of nitrogen dioxide and is not intended to be used as a basis for OSHA policy.
1.6.1. Nitrogen dioxide is classified as a respiratory irritant and the route of exposure is
mainly inhalation. The term silo-fillers' disease is associated with exposure to nitrogen
dioxide as well as other nitrogen oxides.
Unlike the more soluble gases (e.g. chlorine, ammonia) that produce almost
immediate upper respiratory tract irritation, symptoms of NO2 exposure may be delayed
for up to 12 hours. The lower solubility of NO2 provides less warning and increases
the potential for physiological damage when exposures occur.
1.6.2. The symptoms from mild exposures (<50 ppm) are generalized below
|mucoid or frothy sputum production||cough
|increased breathing rate||lymphocytosis
Exposures usually result in an increased susceptibility to respiratory infections.
Changes in pulmonary function are evident when healthy subjects are exposed to 2 to 3
ppm NO2 and can occur at far lower concentrations in asthmatic subjects.
More severe exposures (>50 ppm) are characterized by pulmonary edema, cyanosis,
bronchiolitis obliterans, respiratory failure and death.
1.6.3. The LC50 (Lethal Concentration 50) for a 4-hour exposure is approximately 90 ppm
2.1. This method was evaluated over the concentration range of 2.64 to 9.45 ppm. An air volume of
3 L and a flow rate of 0.2 L/min were used. Samples were taken for 15 min. Sample results
were calculated using an average conversion relationship of:
3. Method Performance (8.8)
At NO2 concentrations above 10 ppm, the conversion factor has been shown to decrease,
approaching a value of 0.5 (8.6,
2.2. The qualitative detection limit was 0.08 µg/mL or 0.24 µg (as NO2-)
when using a 3-mL solution volume. This corresponds to 0.07 ppm NO2 for a 3-L air volume.
2.3. The quantitative detection limit was 0.23 µg/mL or 0.69 µg (as NO2-) when using a
3-mL solution volume. This corresponds to 0.19 ppm NO2 for a 3-L air volume.
A 50-L sample loop and a detector setting of 3 microsiemens were used for both detection limit determinations.
2.4. The sensitivity of the analytical method was calculated from the slope of a linear working range
curve (1 to 20 µg/mL nitrite). The sensitivity for this curve was 222,720 area units per
1 µg/mL (a Hewlett-Packard 3357 data reduction system was used, and 1 area unit = 0.25
3.1. The pooled coefficient of variation (CVT) for samples taken in the range of
2.64 to 9.45 ppm was 0.034. The method exhibited positive bias (+0.13); however, overall error is within
acceptable limits at ±19.8%.
3.2. The collection efficiency at approximately 2 times the PEL was 97.3%. Samples were collected
at a generation concentration of 9.45 ppm NO2 for 15 min. Sample generation conditions were
50% RH and 25 °C.
3.3. Breakthrough tests were performed at 30% RH and a concentration of 21 ppm. Samples were
collected for 15 min at a flow rate of 0.18 L/min. Breakthrough of NO2 into a second sorbent
tube at these parameters was 1.6% NO2. This is within an acceptable limit of <5%
3.4. Samples can be stored at ambient (20 to 25 °C) laboratory conditions for a period of at least 29
days. Storage stability results show the mean of samples analyzed after 29 days was within
±5% of the mean of samples analyzed after one day of storage. Samples were stored on a
4.1. When other compounds are known or suspected to be present in the sampled air, such
information should be transmitted to the laboratory with the sample.
4.2. Any compound having the same retention time as nitrite, when using the operating conditions
described, is an interference.
4.3 Interferences may be minimized by changing the eluent concentration, and/or pump flow rate.
4.4. If there is reason to suspect an unresolvable interference, alternate polarographic or colorimetric
methods can be used (8.1 -
4.5. Contaminant anions normally found in molecular sieve, such as NO3-,
SO42-, and PO43-, do not
interfere. Large amounts (greater than 4 to 5 µg/mL) of Cl- can interfere.
5.1.1. Personal sampling pumps capable of sampling within ±5% of the recommended flow
rate of 0.2 L/min are used.
5.2. Sampling Procedure
5.1.2. Two types of sampling tubes are commercially available (All molecular sieve used for
tube packing should be washed with deionized water before impregnation with TEA):
a. One type is a two-section tube packed with a 400-mg TEA-IMS front and a
200-mg back-up section (NO2 sampling tube,
Cat. No. 226-40-02-special order, water-washed, SKC, Eighty Four, PA).
b. The other type, a three-tube sampling device (NO/NO2 sampling tubes, Cat.
No. 226-40-special order, water-washed, SKC, Eighty Four, PA) can be used
to sample NO2 and NO simultaneously or individually. The device consists of
three flame-sealed glass tubes. Nitrogen dioxide is collected in the first tube
which contains 400 mg TEA-IMS. Two other tubes, an oxidizer tube and
another 400 mg TEA-IMS packed tube, are also included. The dimensions of
each TEA-IMS tube are 7-mm o.d., 5-mm i.d., and 70-mm long.
A 3-mm portion of silylated glass wool is placed in the front and rear of each tube.
An oxidizer tube containing approximately 1 g of a chromate compound is used to
convert NO to NO2. The dimensions of the oxidizer tube are 7-mm
o.d., 5-mm i.d., and 110-mm long. When the three tubes are connected in series as
shown below, NO2 and NO can be collected simultaneously.
|THREE-TUBE SAMPLING DEVICE
|Text Version: The first
tube in the Three-Tube Sampling Device is a nitrogen dioxide (NO2)
sampling tube (TEA-IMS Tube). The second tube in the series is an oxidizer
tube, and the third is another NO2 sampling tube that is
identical to the first tube. The three tubes are connected with short
lengths of plastic tubing (Tygon or equivalent). The three tubes should be
connected as close to one another as possible. The sampling device is
connected to the sampling pump with flexible plastic tubing. The set of
three tubes that compose the sampling device is available from SKC, Inc. as
For further information regarding sampling for NO, see reference (8.10)
5.1.3. A stopwatch and bubble tube or meter are used to calibrate pumps. A
sampling tube or device is placed in-line during flow rate calibration.
5.1.4. Various lengths of Tygon tubing are used to connect sampling tubes to pumps.
Note: If sampling for both NO2 and NO is necessary, two separate pumps and
sampling devices should be used. The differences in OSHA Final Rule PELs (NO2 is a
STEL and NO is a TWA PEL) and flow rates dictates a need for a singular assessment
of NO2. Nitric oxide is collected at a flow rate not to exceed 0.025 L/min
8.10) and a three-tube
device must be used. Nitrogen dioxide can be collected at this flow rate; however, a longer sampling
time will be necessary to collect a detectable amount of NO2 than for
a short-term measurement. Also, NO2 concentrations may vary widely
during sampling periods as long as 4 hours for NO. The three-tube sampling device
will not reflect the varying concentration. Therefore, it is recommended to sample at 0.2 L/min
for 15-min intervals using a single or two section tube for NO2.
A separate three-tube device and pump is then used for NO sampling. The front tube of the device
can be submitted for NO2 analysis; however, results from this front section may not
represent short-term exposures.
5.2.1. Calibrate the sampling pumps at either recommended flow rate listed in Section 5.2.4
5.2.2. Connect the sampling tube or device to the pump. The different sampling schemes are listed below:
a. Sampling for NO2 only: A single TEA-IMS tube taken from the
three-tube sampling device (Section
5.1.2, part b) or the two-section tube
(Section 5.1.2, part a) can be used. If the two-section tube is used, sampled air should
enter the 400 mg section first.
5.2.3. Place the sampling tube or device in the breathing zone of the employee.
Sampling for both NO and NO2: The three-tube device
(Section 5.1.2, part b) is used. Label the first tube "NO2".
The tube following the oxidizer section is labeled "NO". Also consult reference
5.2.4. Sample with pre-calibrated pumps at the listed flow rates and sampling times:
a. For NO2 only: 0.2 L/min for at least 15 min per sample.
5.2.5. The minimum recommended total air volume for collecting NO2 is 3 L.
b. For both NO and NO2: 0.025 L/min for 4 h per sample. Also consult
Nitrogen dioxide results from extended sampling times (>15 min) may not
reflect short-term exposures.
6.1.1. Refer to instrument and standard operating procedure (SOP) (8.15) manuals for proper operation.
6.1.2. Observe laboratory safety regulations and practices.
6.1.3. Sulfuric acid (H2SO4) can cause severe burns. Wear protective gloves and eyewear
when using concentrated H2SO4.
6.2.1. Ion chromatograph (Model 2010 or 4000, Dionex, Sunnyvale, CA) equipped with a conductivity detector.
6.3. Reagents - All chemicals should be at least reagent grade.
6.2.2. Automatic sampler (Model AS-1, Dionex) and sample vials (0.5 mL).
6.2.3. Data processing system: Ion chromatograph interfaced to a data reduction and control
system (AutoIon 400 or 450 System, Dionex).
6.2.5. Separator and guard columns, anion (Model HPIC-AS4A and AG4A, Dionex).
6.2.6. Micromembrane suppressor, anion (Model AMMS-1, Dionex).
6.2.7. Disposable syringes (1 mL) and pre-filters.
Note: Some syringe pre-filters are not cation- or anion-free.
Tests should be done with blank solutions first to determine suitability for the analyte being determined.
6.2.8. Erlenmeyer flasks, 25-mL, or scintillation vials, 20-mL.
6.2.9. Miscellaneous volumetric glassware: Micropipettes, volumetric flasks, graduated cylinders, and beakers.
6.2.10. Analytical balance (0.01 mg).
6.3.1. Deionized water (DI H2O) with a specific conductance of less than 10 microsiemens.
6.4. Working Standard Preparation
6.3.2. Triethanolamine [(HOCH2CH2)3N]
sodium carbonate (Na2CO3)
6.3.3. Liquid desorber (1.5% TEA):
sodium bicarbonate (NaHCO3)
sulfuric acid (H2SO4, concentrated 95 to 98%)
sodium nitrite (NaNO2)
Dissolve 15 g TEA in a 1-L volumetric flask which contains approximately 500 mL DI
H2O. Add 0.5 mL n-butanol and then dilute to volume with DI H2O.
6.3.4. Eluent (2.0 mM Na2CO3/1.0 mM NaHCO3):
Dissolve 0.848 g Na2CO3 and 0.336 g NaHCO3 in 4.0 L of DI H2O.
6.3.5. Regeneration solution (0.02 N H2SO4):
Place 1.14 mL concentrated H2SO4 into a 2-L volumetric flask which contains about
500 mL DI H2O. Dilute to volume with DI H2O.
6.3.6. Nitrite stock standard (1,000 µg/mL):
Dissolve 1.5000 g NaNO2 and dilute to the mark in a 1-L volumetric flask with DI H2O.
Prepare every 3 months.
6.3.7. Nitrite standard (100 µg/mL):
Dilute 10 mL of the 1,000 µg/mL nitrite stock standard to 100 mL with liquid desorber. Prepare monthly.
6.3.8. Nitrite standard (10 µg/mL):
Dilute 10 mL of the 100 µg/mL nitrite stock standard to 100 mL with liquid desorber. Prepare weekly.
6.3.9. Nitrite standard (1 µg/mL):
Dilute 10 mL of the 10 µg/mL nitrite stock standard to 100 mL with liquid desorber. Prepare daily.
6.4.1. Nitrite working standards (10-mL final volumes) may be prepared in the ranges specified below:
6.5. Sample Preparation
* Already prepared in Section
6.4.2. Pipette appropriate aliquots of standard solutions (prepared in Section
10-mL volumetric flasks and dilute to volume with liquid desorber.
6.4.3. Pipette a 0.5- to 0.6-mL portion of each standard solution into separate automatic
sampler vials. Place a 0.5-mL filter cap into each vial. The large exposed filter
portion of the cap should face the standard solution.
6.4.4. Prepare a reagent blank from the liquid desorber solution.
Note: For NO sample analysis and result calculations, see reference (8.10).
6.5.1. Clean the 25-mL Erlenmeyer flasks or scintillation vials by rinsing with DI H2O.
6.6. Analytical Procedure
6.5.2. Carefully remove the glass wool plugs from the sample tubes, making sure that no
sorbent is lost in the process. If the two-section tube was used for sampling, transfer
each TEA-IMS section to individual 25-mL Erlenmeyer flasks or scintillation vials.
Analyze these two sections separately. If a single section tube was used, transfer that
section to an individual 25-mL Erlenmeyer flask or scintillation vial.
6.5.3. Add 3 mL of liquid desorber to each flask or vial, shake vigorously for about 30 s and
allow the solution to settle for at least 1 h.
6.5.4. If the sample solutions contain suspended particulate, remove the particles using a
pre-filter and syringe. Fill the 0.5-mL automatic sampler vials with
sample solutions and push a 0.5-mL filtercap into each vial. Label each vial.
6.5.5. Load the automatic sampler with labeled samples, standards and blanks.
Set up the ion chromatograph and analyze the samples in accordance with the SOP
Typical operating conditions for equipment mentioned in Section
6.2 are listed below.
| Eluent:||2.0 mM Na2CO3 / 1.0 mM NaHCO3
| Column temperature:||ambient
| Sample injection loop:||50 µL
| Pump pressure:||approximately 1,000 psi
| Flow rate:||2 mL/min
| Run time:||6 min
| Average retention time:||approximately 2 min
7.1. Obtain hard copies of chromatograms from a printer. A typical chromatogram is shown in
7.2. Prepare a concentration-response curve by plotting the concentration of the standards in
µg/mL (or µg/sample if the same solution volumes are used for samples and standards) versus peak
areas or peak heights.
7.3. Blank correct the samples by subtracting the g/mL NO2-
found in the blank from the µg/mL NO2- found in the samples. If a different solution
volume was used for blanks and samples, use total micrograms NO2-
to blank correct.
7.4. Calculate the concentration of nitrogen dioxide in each air sample in ppm. A
concentration-dependent conversion factor is used. The equation is:
ppm NO2 = ||
Molar volume × µg/mL NO2- × Solution volume × Conversion
Formula weight × Air volume
| Molar volume|| = ||24.45 (25 °C and 760 mmHg)
| µg/mL NO2-|| = ||blank corrected sample result
| Formula weight (NO2)|| = ||46.01
| Conversion|| = ||varies with concentration
The conversion of gaseous NO2 to NO2- is concentration-dependent
and should be calculated
using one of the equations given below:
From 0 to 10 ppm, the average relationship has been
experimentally determined to be
8.6 - 8.9):
1 µg NO2 (gas) = 0.63 µg NO2-
1 µg NO2- = 1.587 µg NO2 (gas)
Simplifying the equation and using a 3-mL sample volume gives:
ppm nitrogen dioxide = ||
µg/mL NO2- × 3 mL × 0.843
Above 10 ppm NO2, the expected stoichiometric factor of 0.5 mole of
nitrite to 1 mole of nitrogen dioxide gas is seen (8.6,
8.9). Therefore, the following
calculation should be used for sample results above 10 ppm
and a 3-mL sample volume:
ppm nitrogen dioxide = ||
µg/mL NO2- × 3 mL 1 × 1.063
Air volume (L)
7.5. Reporting Results
Report all results to the industrial hygienist as ppm nitrogen dioxide.
8.1. National Institute for Occupational
Safety and Health:
NIOSH Manual of Analytical Methods, 2nd ed., Vol. 4
(HEW/NIOSH Pub. No. 78-175). Cincinnati, OH, 1978.
8.2. Saltzman, B.E.: Colorimetric
Microdetermination of Nitrogen Dioxide in the Atmosphere.
Anal. Chem. 26
8.3. Blacker, J.H.:
Triethanolamine for Collecting Nitrogen Dioxide in the TLV Range.
Am. Ind. Hyg. Assoc. J. 34:390
8.4. Occupational Safety and Health
Administration Analytical Laboratory:
OSHA Analytical Methods Manual (USDOL/OSHA-SLCAL
Method No. ID-109). Cincinnati, OH: American Conference of
Governmental Industrial Hygienists (Pub. No. ISBN: 0-936712-66-X),
8.5. Chang, S.K., R. Kozenianskas and G.W.
Harrington: Determination of Nitrite Ion Using Differential Pulse
Polarography. Anal. Chem.
8.6. Gold, A.: Stoichiometry of
Nitrogen Dioxide Determination in Triethanolamine Trapping Solution.
Anal. Chem. 49:1448-50 (1977).
8.7. Vinjamoori, D.V. and Chaur-Sun
Ling: Personal Monitoring Method for Nitrogen Dioxide and Sulfur Dioxide
with Solid Sorbent Sampling and Ion Chromatographic Determination.
Anal. Chem. 53:1689-1691
8.8. Occupational Safety and Health
Administration Technical Center:
Nitrogen Dioxide Backup Data Report (ID-182),
by J.C. Ku. Salt Lake City, UT. Revised 1991.
8.9. Occupational Safety and Health
Administration Technical Center:
Nitric Oxide Back-Up Report (ID-190), by
J.C. Ku (USDOL/OSHA-SLTC Method No. ID-190). Salt Lake
City, UT, Revised 1991.
8.10. Occupational Safety and Health
Administration Technical Center:
Nitric Oxide in Workplace Atmospheres, by J.C. Ku (USDOL/OSHA-SLTC
ID-190). Salt Lake City, UT. Revised 1991.
8.11. National Institute for
Occupational Safety and Health:
Criteria for a Recommended Standard...Occupational Exposure
to Oxides of Nitrogen (Nitrogen Dioxide and Nitric Oxide) (HEW/NIOSH Pub.
No. 76-149). Cincinnati, OH, 1976.
8.12. Berkow, R. and JH. Talbott, ed.:
The Merck Manual. 13th ed. Rahway, NJ: Merck, Sharp and Dohme Research
Laboratories, 1977. pp. 629-630.
8.13. Proctor, N.B. and J.P. Hughes:
Chemical Hazards of the Workplace. Philadelphia, PA: J.B. Lippincott
Company, 1978. pp. 382-383.
8.14. American Conference of
Governmental Industrial Hygienists:
Documentation of the Threshold Limit Values and Bioloical
Exposure Indices. 5th ed. Cincinnati, OH: ACGIH, 1986. pp. 435-436.
8.15. Occupational Safety and Health
Administration Technical Center:
Standard Operating Procedure-Ion
Chromatography. Salt Lake City, UT. In progress (unpublished).
Chromatogram of a 10 µg/mL Nitrate Standard in 1.5% TEA Solution