|3.0 ppm||Hydrogen Bromide, HBr|
|2.0 ppm||Nitric Acid, HNO3|
|1.0 mg/m3||Phosphoric Acid, H3PO4|
|1.0 mg/m3||Sulfuric Acid, H2SO4|
||A known volume of air is drawn through a silica gel tube. H2SO4, H3PO4 and other particulates are collected on the glass fiber plug while HBr and HNO3 are collected on the silica gel sorbant.
|Recommended Air Volume:
|Recommended Sampling Rate:
||0.2 liters per minute
||The glass fiber plug and the silica gel tubes are desorbed with standard eluent and analyzed by Ion Chromatography (IC).
||See Section 2.3.
|Precision and Accuracy:
|(CVA) =||0.035 for HBr|
0.037 for HNO3
0.066 for H3PO4
0.079 for H2SO4
Methods Development Team
Industrial Hygiene Chemistry Division
OSHA Salt Lake Technical Center
Sandy UT 84070-6406
This method describes the collection and analysis of airborne
acids using Ion Chromatography. The method measures the total
concentration of four airborne anions. The corresponding acids may be
collected on a single sampler and determined simultaneously. Acids
which can be collected and analyzed this way are HBr, H3PO4, HNO3, and H2SO4.
1.1. History (Ref. 9.6., Ref. 9.7., and Ref. 9.8.)
2. Working Range and Detection Limit (Ref. 9.6., Ref. 9.7., and Ref. 9.8.)
Prior to the use of this method, HBr was collected in 0.01 N NaOH,
HNO3 was collected in deionized (DI) water, H2SO4 and H3PO4 were
collected on 0.8 micron MCEF filters, and all were analyzed by IC.
1.2. Uses (Ref. 9.1.)
Hydrogen bromide is used in the manufacture of organic and
inorganic bromides and hydrobromic acid, as a reducing agent, and
as a catalyst in controlled oxidations. HBr is also used in the
alkylation of aromatic compounds, and in the isomerization of
Most nitric acid is used in fertilizer as ammonium nitrate and in
the manufacture of explosives. Nitric acid is also used in the
synthesis of a large number of industrial organic compounds.
Relatively small quantities of this acid are used for stainless
steel pickling and metal etching, and to make rocket propellants.
Most phosphoric acid is used as ammonium phosphate in fertilizer
and in the manufacture of superphosphates. Phosphoric acid is
also used in rustproofing, electropolishing, engraving,
lithographic work, coagulation of rubber latex, as an additive in
glass manufacture, and as a catalyst in the manufacture of some
Sulfuric acid is used in the fertilizer industry for the
production of superphosphates and ammonium sulfate. The chemical
industry consumes sulfuric acid in the manufacture of phosphoric
acid by the wet process. Sulfuric acid is used in the manufacture
of paper and aluminum sulfate, and is used extensively for water
purification. The petroleum industry uses sulfuric acid in the
alkylation process and in the refining of petroleum distillates
for removal of sulfur and gum-forming compounds. Other important
industrial applications consuming large amounts of sulfuric acid
include steel pickling and the manufacture of titanium pigments,
rayon, dyes, intermediates, and detergents.
1.3. Physical Properties (Ref. 9.2. and Ref. 9.3.)
Hydrogen bromide is a colorless, corrosive, nonflammable gas with
an acrid odor. HBr fumes in moist air forming clouds which have a
sour taste. Commercial grades are approximately 48% pure.
Nitric acid is a colorless liquid (depending upon purity and
freshness). The acid produces fumes in moist air and has a strong
choking odor. Long exposure to light causes nitric acid to beccme
discolored (brownish). Commercial grades are approximately 70 - 71% pure.
Phosphoric acid is a dense, colorless liquid which is toxic and is
a strong irritant to tissue.
Sulfuric acid is a dense oily liquid, colorless to dark brown
(depending on purity). Commercial grades are approximately 96%
pure. Sulfuric acid is a strong oxidant, which is toxic, a strong
irritant to tissue, very corrosive, and has a great affinity for
315 - 338°C
2.1. The working range for a 100 liter air sample is 0.08 to 3.0 ppm
for Br -, 0.10 to 3.9 ppm for NO3-, and 0.25 to 10.0 mg/m3 for
PO4-3, and SO4=. This corresponds to 2.5 to 50. ug of bromide,
nitrate, phosphate, and sulfate. The upper range can be extended
by sample dilution.
3. Precision and Accuracy
2.2. The sensitivity at 30 umho full scale is 5 ug of analyte (Br -,
NO3-, PO4-3, and SO4=) per sample per mm chart deflection (based
on a 10 mL sample volume).
2.3. The qualitative detection limits for PO4-3, Br -, NO3-, and SO4=
were calculated using the Student's T-Test. The detection limits
are as follows at a confidence level of 95%:
|| = 0.25 ug
|| = 0.20 ug
|| = 0.125 ug
|| = 0.25 ug
These detection limits were calculated based on a sample volume of
10 mL and an injection volume of 100 uL. The detection limits for
each analyte were calculated in the presence of the other three
analytes. The detection limit may be improved by using a larger
injection volume (for auto sampler only), or by using a smaller
volume than 10 mL to desorb the sample.
3.1. The average coefficient of variation (CVA) is: 0.035 for HBr,
0.037 for HNO3, 0.079 for H2SO4, and 0.066 for H3PO4.
4. Interferences (Ref. 9.6., Ref. 9.7., and Ref. 9.8.)
4.1. Large quantities of any one analyte will cause some masking of
some of the other peaks.
5. Advantages and Disadvantages
5.1. The method can be automated and is quick and accurate compared to
previous methods which involved titrations with nebulous endpoints.
6. Sampling Procedure
5.2. The sampling procedure employed uses silica gel tubes as opposed to impingers which are used in other sampling methods for acid mist. Such a sampling procedure eliminates the inherent problems of using impingers.
5.3. Unlike previous methods, nitrate and bromide particulates are not
an interference in this method since particulates can be captured on the glass fiber filter in the tubes and analyzed separately if necessary.
6.1. Apparatus - Silica gel sorbant tubes, Supelco, Inc. ORBO-53 (or equivalent silica gel tubes which have been demonstrated to show low levels of the anions of interest), personal sampling pump with calibrated flow in line with a silica gel tube to an accuracy of ±10% at the 95% confidence limit at the recommended flow rate.
7. Analytical Procedure
6.2. The silica gel tube is attached to a calibrated personal sampling
pump and the sampling tube is placed in the sampling area or
worker's breathing zone. At least 10 liters of air are drawn
through the sampling tube.
6.3. After sampling, the silica gel tube is removed from the tubing,
sealed and identified with OSHA Form 21, and shipped to the
Laboratory for analysis.
6.4. With each batch of up to 20 samples, a blank tube which has had no
air drawn through it, is submitted for analysis. The blank tube
should be from the same lot of tubes used for sampling.
6.5. It is very important that when particulate acids or salts of an
anion are known to be present in the workplace atmosphere they
should be listed as interferences.
7.1. Apparatus - Ion exchange chromatograph, equipped with electrical
conductivity detector and recorder, or integrator (an auto sampler
helps automate the analysis), 10 mL pipette, 1 mL plastic syringe
with male luer fitting, Anion Separator Column 3 × 250 mm with
Concentrator Column, Anion Suppressor Column 10 × 100 mm, and
appropriate voltietric glassware for dilutions and standard
8. Reporting Results for Compounds Determined by Ion Chromatography
7.2. Reagents - All reagents used should be ACS analyzed reagent grade
7.2.1. Deionized water with a specific conductance of 10 umho/cm
or less for preparation of eluents and other solutions
which will be used in the Ion Chromatograph.
7.3. Safety Precautions
7.2.2. Sodium Carbonate, Na2CO3.
7.2.3. Sodium Bicarbonate, NaHCO3.
7.2.4. Bromide Stock Standard (1000 ug/mL Br -). Dissolve 1.489 g
KBr and dilute to 1 liter with deionized water. Bromide
working standards are made by diluting the stcck solution
7.2.5. Nitrate Stock Standard (1000 ug/mL NO3-). Dissolve 1.3708
g NaNO3 and dilute to 1 liter with deionized water.
Nitrate working standards are made by diluting the stock solution with eluent.
7.2.6. Phosphate Stock Standard (1000 ug/mL PO4-3). Dissolve
1.495 g Na2HPO4 and dilute to 1 liter with deionized
water. Phosphate working standards are made by diluting
the stock solution with eluent.
7.2.7. Sulfate Stock Standard (1000 ug/mL SO4=). Dissolve 1.479
g of Na2SO4 into 1 liter of deionized water. Sulfate
working standards are made by diluting the stock solution
7.2.8. Standard Eluent (0.003 M CO3=/0.0024 M HCO3-). Dissolve 5
g Na2CO3 and 5 g NaHCO3 in 20 liter carboy with deionized
7.2.9. Regenerant Solution (1 N H2SO4). Dilute 111 mL of
concentrated H2SO4 to 4 liters in deionized water.
7.3.1. When using the Ion Chromatograph, the column door should
be kept closed during the analysis in case the columns
burst. To avoid this danger the pressure should be
checked at the beginning of the analysis and periodically
during the analysis. The pressure should never exceed 500
7.4. Standard Preparation
7.3.2. Care should be used when handling reagents, especially the regenerant solution (1 N H2SO4) to avoid chemical burns.
7.3.3. Care should be exercised when using laboratory glassware.
Chipped pipettes, volumetric flasks, beakers, or any
glassware with sharp edges exposed should not be used to
avoid the possibility of cuts, abrasions, and lost
7.3.4. Pipetting should never be done by mouth - a bulb should
always be used.
7.4.1. Working standards are prepared in the analytical range of
0.2 ug/mL to 50 ug/mL from dilutions of the 1000 ug/mL
stock solutions. These standard solutions should be
prepared fresh weekly.
7.5. Sample Preparation
7.4.2. If an auto sampler capable of variable volume injections
is used, a combination 50 ug/mL PO4-3, 10 ug/mL Br -, 25
ug/mL NO3-, and 50 ug/mL SO4= standard is used. This
intermediate working standard should be prepared fresh
7.5.1. The sample tube used with this analysis can be separated
into 3 parts. The first part is the glass fiber filter
plug which will collect any particulate. The second part
is a 150 mg silica gel section (section A) which collects
the acid mists. The third part is a 75 mg silica gel
section (section B) which is the backup section and will
collect any acid mists which are not collected by section
A. The second and third parts are separated by a foam
plug which is to be discarded.
7.6. Analysis (Ref. 9.4.)
7.5.2. Score the sampler with a file in front of the primary
sorbant section (section A), then break the sampler at the
score line. Transfer the glass fiber filter plug and
section A to a clean 20 mL vial. If the analysis is to be
done only for HNO3 and/or HBr, the glass fiber filter plug
can be discarded. If sulfuric and/or phosphoric acids are
requested, the glass fiber filter plug must be analyzed
separately. The glass fiber filter plug should be
analyzed separately if sulfate and/or phosphate is
requested and nitric and/or hydrobromic acids are also
7.5.3. Place silica gel section B in a separate clean 20 mL vial. Discard the urethane plug.
7.5.4. If the air volume is greater than or equal to 20 liters
pipette about 5 mL of eluent (0.003 M CO3=/0.0024 M HCO3-)
into each sample vial and cap tightly. If the air volume
is less than 20 liters, a smaller volume of eluent is
7.5.5. Place the vial in a large beaker with DI water and boil
for 10 minutes. Let cool and dilute to 10.0 mL with
eluent in a volumetric flask (if the air volume is less
than 20 liters, dilute to 5 mL in a volumetric flask).
When particulate acids are listed as interferences for
HNO3 and/or HBr, the glass fiber plug should be desorbed
separately with about 2 mL of eluent which is then diluted
to 10 mL with standard eluent. Sample solutions which are
not clear should he filtered before analysis.
7.5.6. If using an auto sampler, transfer some of the sample into
an appropriate sampling vial. The vial should be at least
half full. Label each vial with the appropriate
laboratory identification number.
7.5.7. For hand injection, use 1 mL of the eluent to flush the
0.1 mL injection loop thoroughly. When using automatic
injection try to use about a 100 uL injection volume. The
autosampler is less accurate below 100 uL.
7.6.1. For general instrument set up refer to Section 7 of the
Ion Chromatography Standard Operating Procedure.
7.6.2. The normal instrument parameters are:
Sensitivity: 30 umho full scale
Eluent: 0.003 M Na2CO3 and 0.0024 M NaHCO3
Flow Rate: 138 mL/hr approximately 30% on vernier
Concentrator Column: 3 mm I.D. × 50 mm
Anion Separator Column: 3 mm I.D. × 250 mm
Suppressor Column: 10 mm I.D. × 100 mm
Run Time: Approximately 30 minutes, depending upon
7.6.3. With the instrument set up and stabilized, place the auto
sampling vials into the sampling tray using tray positions
one through five for standards.
7.6.4. Enter the proper parameters into the auto sampler (See
Section 4 of the Ion Chromatography Standard Operating
7.6.5. Start the auto sampler and observe the first few
chromatogrms to ensure proper operation. Periodically
check the zero offset between samples to correct any
baseline drift and to ensure proper sensitivity and
retention time of the analytes.
7.6.6. Use the timer to stop the run if the auto sampler is to be
7.6.7. For hand injection, a 1 mL aliquot is taken up in a
syringe from the 20 mL vial and injected into the
injection port with the toggle switch in the load
position. After the sample is loaded, switch the toggle
to the inject position and start the integrator or push
the PIP button if a strip chart recorder is being used.
7.6.8. For both hand and auto sample injections, record the
sample number onto the chromatogram. A record of the
sample identity and instrument conditions should be kept.
7.6.9. As the analysis proceeds, check the retention times of
standards vs. samples to ensure uniformity. A typical
chromatograph of a mixed standard of Br -, NO3-, PO4-3, and
SO4=, is shown in Figure 1.
7.6.10. If interfering substances are present, establish positive
identity of the peaks by spiking known amounts of standard
solution or try to obtain better separation by changing
the eluent concentration or by reducing the flow rate.
7.7.1. Peak areas or heights of the standards are used to
construct a standard curve using the OSHA Auto Colorimetric Program.
The samples results are obtained from a plot of peak area vs. concentration.
The blank corrected sample values are then calculated
using the Auto Colorimetric Program.
7.7.2. When using the OSHA Auto Colorimetric Program, sample
numbers and volumes are entered into the calculator in the
Sample Number, Peak Area or Height, L Air Volume, mL
Solution Volume, mL Aliquot Volume.
7.7.3. Air Concentration values are calculated by the following
||(µg calculated)(mL sample vol)(GF*)(dilution factor)
(liters of air)(mL aliquot)
|GF* = Gravimetric Factor =
||1.013 for HBr
1.016 for HNO3
1.021 for H2SO4
1.032 for H3PO4
7.7.4. HNO3 and HBr are reported in ppm rather than in mg/m3. To
convert the mg/m3 values to ppm, the mg/m3 value must be
multiplied by the appropriate conversion factor.
8.1. Results are reported on the OSHA Form 91 in milligram per cubic
meter for H2SO4 and H3PO4 and in ppm for HBr and HNO3, using two
8.2. The estimated detection limit calculated by the Auto Colorimetric
Program is reported on the OSHA Form 91 when no analyte is
8.3. The presence of significant unidentifiable peaks is noted on the
OSHA Form 91.
8.4. All data processor printouts and chart recorded chromatograms are
filed in a central file according to laboratory sample
8.5. Calculations are checked by a fellow chemist before the completed
OSHA Form 91's are given to the supervisor.
9.1. Encyclopedia of Chemical Technology, Third Edition, 1981.
9.2. CRC Handbook of Chemistry & Physics, 62nd Edition, 1981-1982.
9.3. Merck Index, Tenth Edition, 1983.
9.4. OSHA Ion Chromatography Standard Operating Procedure, Prepared by
the Ion Chromatography Committee, Occupational Safety & Health
Administration Analytical Laboratory, Inorganic Division.
9.5. NIOSH Manual of Analytical Methods, Second Edition, Volume 7,
Method Number P&CAM 339 (revised), Issued on 2/15/84.
9.6. Nitric Acid in Workplace Atmospheres, Method No. ID-127, OSHA
Laboratory, Salt Lake City, UT.
9.7. Phosphoric Acid in Workplace Atmospheres, Method No. ID-111, OSHA
Laboratory, Salt Lake City, UT.
9.8. Sulfuric Acid in Workplace Atmospheres, Method No. ID-113, OSHA
Laboratory, Salt Lake City, UT.
9.9. Monitoring for Airborne Inorganic Acids, M.E. Cassinelli and D.G;
Taylor, National Institute for Occupational Safety and Health,
4676 Columbia Parkway, Cincinnati, OH, 45226.