||ID-190 (This method supersedes ID-109)
|OSHA Permissible Exposure Limits
Final Rule and
25 ppm (Time Weighted Average)
||The sampling device consists of:
1) Two glass tubes which contain
2) a middle tube which contains an
3) a personal sampling pump is used to
draw a measured volume of air through
|Recommended Sampling Rate:
|Recommended Maximum Air Volume:
||The sample is desorbed using a 1.5% triethanolamine
solution and analyzed as nitrite by ion chromatography.
0.11 ppm (6-L air sample)
0.32 ppm (6-L air sample)
|Precision and Accuracy
13.0 to 50.5 ppm
|Date (Date Revised):
||April, 1989 (May, 1991)
Commercial manufacturers and products mentioned in this method
descriptive use only and do not constitute endorsements by
Similar products from other sources can be substituted.
Branch of Inorganic Methods Development
OSHA Technical Center
This method describes the collection and analysis of airborne nitric
oxide (NO). Samples are taken in the breathing zone of workplace
personnel and analyses are performed by ion chromatography (IC).
2. Range, Detection Limit and Sensitivity
Previous methods involved oxidation of NO to nitrogen dioxide
(NO2) using a chromate compound and subsequent conversion of NO2
to nitrite using triethanolamine-impregnated molecular sieve
(TEA-IMS) sampling tubes. Common methods used a combination
sampling tube and NO was determined colorimetrically (as NO2-)
using a modified Griess-Saltzman reaction (8.1
- 8.2). This
method, like most colorimetric procedures, can have significant
A differential pulse polarographic (DPP) method (8.3) was
later developed to improve analytical sensitivity and decrease the
potential for interferences. The sensitivity of the DPP method
was more than adequate for measuring workplace concentrations of
NO; however, the nitrite ion is unstable in the pH range (pH 1-2)
used during analysis (8.4).
Method no. ID-190 uses the TEA-IMS sampling tube/chromate
oxidizer approach. Samples are analyzed by IC.
A known volume of air is drawn through the sampling device which
captures any nitrogen dioxide (NO2) in the sampled air and also
converts any NO to nitrite ion (NO2-). The sampling device
consists of three glass tubes connected in series. The front and
back tubes contain TEA-IMS, the middle or oxidizer tube contains
an inert carrier impregnated with a chromate salt. The first
TEA-IMS tube does not capture NO; this tube is only used to
capture and convert to NO2- any NO2 present in the sampled air.
The middle tube oxidizes the sampled NO to NO2. The back TEA-IMS
tube then captures and converts this NO2 to NO2-. Both TEA-IMS
samples are desorbed using an aqueous triethanolamine (TEA)
solution and analyzed as NO2- by IC. The front tube analytical
results are reported as NO2 and the back tube as NO.
The conversion mechanism of NO2 gas to NO2- has been proposed
by Gold (8.5). The following is Gold's proposal for the reaction
of equivalent amounts of NO2 and TEA in an aqueous solution:
N2O4 + (HOCH2CH2)3N -->
(HOCH2CH2)3NNO+NO3- + H2O -->
(HOCH2CH2)3NH+NO3- + HNO2
HNO2 --> H+ + NO2-
Nitrogen dioxide disproportionates to NO2- and nitrate (NO3-) in
the presence of TEA and water. The NO2- formed from the above
reaction can be analyzed via conventional analytical methods
(8.1 - 8.4,
8.7) including IC. Unfortunately NO3- is found
in the commercial TEA-IMS sorbent as a significant contaminant.
This contamination ruled out further research to also measure 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
stoichiometric factor of 0.5 is seen only when NO2 concentrations
are greater than 10 ppm (8.5,
8.9). The conversion factor
has been experimentally determined to average approximately 0.6 to
0.7 when concentrations are below 10 ppm (8.1 -
The deviation from ideal stoichiometry is believed to be due to
competing reactions; however, evidence to support a competing
mechanism has not been found (8.5).
1.3. Advantages and Disadvantages
1.3.1. This method has adequate sensitivity for determining
compliance with the OSHA Time Weighted Average (TWA)
Permissible Exposure Limit (PEL) for workplace exposures
1.4. Physical properties (8.10,
1.3.2. The sampling device can be used to simultaneously collect
NO and NO2; however, results for NO2 may not reflect
short-term exposures (see Section 5.2. for more details).
1.3.3. The analysis is simple, rapid, easily automated and is
specific for NO2-.
1.3.4. After analytical sample preparation, NO exposures (as
nitrite ion) can also be determined by colorimetric or
polarographic analytical techniques (8.1
1.3.5. 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 (DI H2O) to remove any soluble chloride salts.
1.3.6. Another disadvantage is the need for a concentration-dependent
conversion factor when calculating results.
Nitric oxide (CAS No. 10102-43-9), one of several oxides of
nitrogen, is a colorless gas. A deep blue color is usually noted
when NO is in the liquid state and a bluish-white color when solid.
Other physical characteristics of NO are:
*Nitrogen monoxide has also been used as a synonym for nitrous
||1.27 at -150.2 °C (as liquid)
||1.04 (air = 1)
||4.6 mL NO in 100 mL H2O
1.5. Some industrial sources for potential nitric oxide 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 (8.10):
arc or gas welding (esp. confined space operations)
food and textile bleaching
metal nitrosyl carbonyl production
nitric acid production
nitrogen fertilizer production
nitrosyl halide production
2NO + O2 ----> 2NO2
(K is a temperature dependent constant. At 20 °C, K = 14.8 X 109)
An experimental approximation of the NO/NO2 distribution found in
various industrial operations is shown (8.10):
|Cellulose nitrate combustion
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.
1.6. Toxicology (8.11 -
Information listed within this section is a synopsis of current
knowledge of the physiological effects of nitric oxide and is not
intended to be used as a basis for OSHA policy.
1.6.1. Nitric oxide is classified as a respiratory irritant. The
main route of exposure is inhalation; however,
physiological damage can also occur eyes or skin.
The term "silo-fillers' disease" has been used to describe exposure
to nitric as well as other nitrogen oxides. The national
population-at-risk for exposure to nitrogen oxides has been estimated by
NIOSH to be approximately 950,000 employees (National Occupational Hazard
Survey, 1972-74). When encountering either NO or
NO2 at high concentrations, both species will usually be
present. Little scientific data is available regarding
exposures to NO only. The majority of collected data
concerns exposure to NO2 since NO appears to be only
one-fifth as toxic as NO2 at low concentrations.
Symptoms immediately following NO exposure are usually mild or not
apparent. Severe symptoms may not appear up to 72 hours
1.6.2. Mild exposures to NO can result in symptoms such as:
||shortness of breath
|increased breathing rate
More severe exposures (>100 ppm) are characterized by
pulmonary edema , cyanosis, pneumonia, severe
methemoglobinemia, respiratory failure, and death.
1.6.3. The IDLH (Immediately Dangerous to Life or Health)
concentration is 100 ppm NO. The LCLo (Lethal
Concentration - Low) for inhalation by mice is 320 ppm.
1.6.4.Mechanism for toxicity:
Nitric oxide is slightly soluble in water and forms nitrous
and nitric acid. This reaction occurs with lung tissue and
produces respiratory irritation and edema. Alkali present
in the lung tissue neutralizes the nitrous and nitric acids
to nitrite and nitrate salts which are then absorbed into
the bloodstream. The end result is the formation of
nitroxy-hemoglobin complexes and methemoglobin in the
The formation of hemoglobin complexes is thought to
contribute to the toxicity of NO but is not considered to
be the sole source of the toxic reaction. The respiratory
damage from nitrous and nitric acid appears to be more
The analytical parameters and limits of this method have been previously
described (8.8). Brief descriptions are provided in Section 3 below.
3. Method Performance
This method was evaluated in the concentration range of 13.0 to
50.5 ppm. Air volumes of approximately 6 L and flow rates of about
0.025 L/min were used. Samples were collected for 240 min. Sample
results were calculated using the concentration-dependent conversion
factors mentioned in Section 7. Listed on the cover page (CVT, bias,
overall error) and below are evaluation data taken from the backup
|Qualitative detection limit1:
||0.08 µg/mL (as NO2-)
||0.11 ppm NO (6 L air volume)
|Quantitative detection limit1:
||0.23 µg/mL (as NO2-)
||0.32 ppm NO (6 L air volume)
|Sensitivity (1 to 30 µg/mL nitrite):
||239,000 area counts per
||1 µg/mL NO2-
||10,000 area counts per
||1 µg/mL NO2-
||none at levels tested3
||at least 30 days (20-25 °C)
||Detector setting = 3 microsiemens, sample loop = 50 µL (8.8)
||A model 3357 data reduction system (Hewlett-Packard, Avondale, PA)
(1 area unit = 0.25 microvolt-second) was used during first part
of evaluation. An AutoIon 400 data reduction system (Dionex,
Sunnyvale, CA) was used for later analyses.
||Collection efficiency samples were taken using a concentration of
50.5 ppm NO for 240 min, 50% RH, and 0.025 L/min. Breakthrough
tests were performed at 25 °C, 50% RH, and a flow rate of
0.025 L/min. Samples were collected at a concentration of 200 ppm
for 60, 120, 180, and 240 min.
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 that has 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, column characteristics, and/or pump flow rate.
4.4. If there is an unresolvable interference, alternate polarographic
or colorimetric methods may 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. A three tube sampling device is commercially available
(NO/NO2 sampling tubes, Cat. No. 226-40-special order,
water-washed, SKC, Eighty Four, PA) and can be used to
simultaneously sample NO2 and NO, or sample only NO2.
This device consists of three flame-sealed glass tubes:
5.2. Sampling Procedure
1) Nitrogen dioxide is collected in the first tube which
contains 400 mg TEA-IMS.
All molecular sieve used for tube packing must be washed
with DI H2O before impregnation with TEA. 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. The dimensions of the
oxidizer tube are 7-mm o.d., 5-mm i.d., and 110-mm long .
2) The second (oxidizer) tube converts NO to NO2 and
contains approximately 1 g of a chromate compound
impregnated on an inert carrier.
3) The last 400 mg TEA-IMS packed tube collects the
When the three tubes are connected in series as shown
below, NO2 and NO can be collected simultaneously. The
first TEA-IMS tube must be in place to prevent the
collection of NO2 by the second TEA-IMS tube.
|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 catalog 226-40.
5.1.2. Personal sampling pumps capable of sampling at a flow rate
of approximately 0.025 L/min are used.
5.1.3. A stopwatch and bubble tube or meter are used to calibrate
pumps. A sampling device is placed in-line during flow
5.1.4. Various lengths of Tygon tubing are used to connect the
sampling tubes and pump together.
Note: If sampling for both NO2 and NO is necessary, two separate
pumps and sampling devices should be used. The differences in
OSHA exposure limits [the NO2 PEL is a 1 ppm Short-Term Exposure
Limit (8.15). Nitric oxide is a TWA PEL.] and flow rates
dictates a need for a separate assessment of NO2. Nitric oxide is
collected at a 0.025 L/min pump flow rate. 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. Concentrations of NO2 may vary in the
workplace during a longer sampling period.
5.2.1. Calibrate the sampling pumps to a flow rate of
5.2.2. Connect the sampling device to the pump. The different
sampling schemes are listed:
a) Sampling for NO2 only: - Use a single TEA-IMS tube
5.2.3. Place the sampling tube or device in the breathing zone of the employee.
b) Sampling for both NO and NO2: The three-tube device
is used. The device must be assembled as shown above.
Label the first tube "NO2".
Label the tube following the oxidizer section "NO".
5.2.4. Collect the sample at the listed flow rates and sampling times:
a) For NO2 only: 0.200 L/min for at least 15 min (8.8) per sample.
b) For both NO and NO2: 0.025 L/min for 4 h per sample
(Note: The front ube of the three-tube device can be
submitted for NO2 analysis; however, analytical
results may not represent short-term exposures).
5.2.5. The maximum recommended air volume is 6 L per NO sample.
Take enough samples for NO to cover the workshift.
Note: One oxidizer tube per sample is sufficient for
concentration ranges of NO usually encountered in
industrial settings. A color change from orange to
blue-green will be noticeable if the oxidizer is depleted.
6.1.1. Refer to instrument and standard operating procedure (SOP)
(8.16) 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 eyewear, gloves, and labcoat when using
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 0.5 mL sample vials.
6.2.3. Laboratory automation system: Ion chromatograph
interfaced to a data reduction and control system
(AutoIon 400 or 450, Dionex).
6.2.4. Micromembrane suppressor, anion (Model AMMS-1, Dionex).
6.2.5. Separator and guard columns, anion (Model HPIC-AS4A and
6.2.6. Disposable syringes (1 mL) and 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.
6.2.7. Erlenmeyer flasks, 25-mL, or scintillation vials, 20-mL.
6.2.8. Miscellaneous volumetric glassware: Micropipettes,
volumetric flasks, graduated cylinders, and beakers.
6.2.9. 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)
sodium bicarbonate (NaHCO3)
sulfuric acid (H2SO4, concentrated 95 to 98%)
sodium nitrite (NaNO2)
6.3.3. Liquid desorber (1.5% TEA):
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 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 with DI H2O
in a 1-L volumetric flask. Prepare every three months.
6.3.7. Nitrite standard (100 µg/mL):
Dilute 10 mL of 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 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 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 6.3.
6.4.2. Pipette appropriate aliquots of standard solutions
(prepared in Section 6.3.) into 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.
6.5.1. Identify which tube is the collected NO2 sample and which
is NO. Analyze these two tubes as separate samples.
6.6. Analytical Procedure
6.5.2. Discard the oxidizer tube appropriately. This tube
contains a chromate salt and may be considered a hazardous
waste. Local regulations or restrictions should be
consulted before disposal.
6.5.3. Clean the 25-mL Erlenmeyer flasks or scintillation vials
by rinsing with DI H2O.
6.5.4. Carefully remove the glass wool plugs from the sample
tubes, making sure no sorbent is lost in the process.
Transfer each TEA-IMS section to individually labeled
25-mL Erlenmeyer flasks or scintillation vials.
6.5.5. Add 10 mL of liquid desorber to each flask containing NO
samples, shake vigorously for about 30 s. Allow the
solution to stand for at least 1 h. (Note: Add 3 mL to
NO2 samples - see reference
8.8. for further details
regarding NO2 analysis and result calculations)
6.5.6. 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 filtercap into each vial. Label the vials.
6.5.7. Load the automatic sampler with labeled samples, standards
Set up the ion chromatography and analyze the samples and standards
in accordance with the SOP (8.16). Typical operating conditions
for equipment mentioned in Section 6.2. are listed below.
||2.0 mM Na2CO3/1.0 mM NaHCO3
| Column temperature:
| Sample injection loop:
| Pump pressure:
||approximately 1,000 psi
| Flow rate:
| Run time:
| Average retention time:
||approximately 2 min
7.1. Obtain hard copies of chromatograms from a printer. A typical
chromatogram is shown in Figure 1.
7.2. Prepare a concentration-response curve by plotting the concentration
of the standards in µg/mL (or µg/sample if the same volumes are used
for samples and standards) versus peak areas or peak heights.
Calculate sample concentrations from the curve and blank correct all
7.3. The concentration of NO in each air sample is expressed in ppm and
is calculated as:
|ppm NO =
||MV × µg/mL NO2¯ ×
solution volume × conversion × GF
formula weight × air volume
|MV (Molar Volume)
||24.45 (25 °C and 760 mmHg)
||blank corrected sample result
|Conversion [NO2 (gas)/NO2-]
||varies with concentration*
|GF (Gravimetric factor NO/NO2)
|Formula Weight (NO)
*The conversion of gaseous NO2 to NO2- is concentration dependent.
The final concentration of NO should be calculated using whichever
example given below is appropriate:
Below 10 ppm NO
From 0 to 10 ppm, the average ratio has been experimentally
determined to be (8.1 -
1 µg NO2 (gas) = 0.630 µg NO2-
1 µg NO2- = 1.587 µg NO2 (gas)
Simplifying the equation and calculating the ppm NO using a 10-mL
sample volume gives:
|ppm NO =
||µg/mL NO2¯ × 10 mL × 0.843
air volume, L
Above 10 ppm NO
Above 10 ppm NO, the expected stoichiometric factor of 0.5 mole of
nitrite to 1 mole of nitrogen dioxide gas is seen (8.5,
Therefore, the following calculation should be used for sample
results above 10 ppm and a 10-mL solution volume:
|ppm NO =
||µg/mL NO2¯ × 10 mL × 1.063
air volume, L
7.4. Reporting Results
Report all results to the industrial hygienist as ppm nitric oxide.
8.1. National Institute for Occupational Safety and Health (NIOSH):
NIOSH Manual of Analytical Methods, 2nd ed., Vol. 4 (DHEW/NIOSH
Pub. No. 78-175, Method No. S321). Cincinnati, OH. 1978.
8.2. Willey, M.A., C.S. McCammon, Jr., and L.J. Doemeny: A Solid Sorbent
Personal Sampling Method for the Simultaneous Collection of
Nitrogen Dioxide and Nitric Oxide in Air. Am. Ind. Hyg. Assoc. J.
8.3. 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), 1985.
8.4. Chang, S.K., R. Kozenianskas, and G.W. Harrington: Determination of
Nitrite Ion Using Differential Pulse Polarography. Anal. Chem. 49:
8.5. Gold, A.: Stoichiometry of Nitrogen Dioxide Determination in
Triethanolamine Trapping Solution. Anal. Chem. 49:1448-50 (1977).
8.6. Blacker, J.H.: Triethanolamine for Collecting Nitrogen Dioxide in
the TLV Range. Am. Ind. Hyg. Assoc. J. 34:390 (1973).
8.7. Saltzman, B.E.: Colorimetric Microdetermination of Nitrogen Dioxide
in the Atmosphere. Anal. Chem. 26:1949 (1954).
8.8. Occupational Safety and Health Administration Technical Center:
Determination of Nitrogen Dioxide in Workplace Atmospheres (Ion
Chromatography) by J.C. Ku (USDOL/OSHA-SLTC Method No. ID-182).
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. Salt Lake City, UT.
8.10. National Institute for Occupational Safety and Health: Criteria for
a Recommended Standard...Occupational Exposure to Oxides of
Nitrogen (Nitrogen Dioxide and Nitric Oxide) (DHEW/NIOSH Pub. No.
76-149). Cincinnati, OH: NIOSH, 1976.
8.11. Braker, W. and A.L. Mossman: Matheson Gas Data Book. 5th ed.
East Rutherford, NJ: Matheson Gas Products, 1971. pp. 405-410.
8.12. Merchant, J.A. Ed.: Occupational Respiratory Diseases (DHHS/NIOSH
Pub. No. 86-102). Cincinnati, OH: NIOSH, 1986. pp. 590-594.
8.13. American Conference of Governmental Industrial Hygienists:
Documentation of the Threshold Limit Values and Biological Exposure
Indices. 5th ed. Cincinnati, OH: ACGIH, 1986. pp. 435-436.
8.14. Specialty Gas Department: Material Safety Data Sheet for Nitric
Oxide. Allentown, PA: Air Products, 1982.
8.15. "Air Contaminants; Final Rule": Federal Register 54:12 (19 Jan.
1989). pp. 2521-2523.
8.16. Occupational Safety and Health Administration Technical Center:
Standard Operating Procedure - Ion Chromatography. Salt Lake City,
UT. In progress (unpublished).
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