1-NITROPROPANE 2-NITROPROPANE
Method no.: |
46 |
|
Matrix: |
Air |
|
Target concentration: |
25 ppm (91 mg/m3) (OSHA PEL
for both analytes) |
|
Procedure: |
Samples are collected by drawing known volumes of air
through commercially available XAD-4 sampling tubes.
Samples are desorbed with carbon disulfide and analyzed by gas
chromatography using a flame ionization detector. |
|
Recommended air volume and sampling rate: |
4 L at 0.1 L/min |
|
Reliable quantitation limit: |
25 ppb (91 µg/m3) for both
analytes |
|
Standard errors of estimate at the target
concentration: (Section 4.4) |
1-Nitropropane, 7.2%; 2-Nitropropane,
6.2%
|
|
Special requirements: |
After samples are received at the laboratory, they
should be stored under refrigeration, until analyzed, to help
minimize migration. |
|
Status of method: |
Evaluated method. This method has been subjected to
the established evaluation procedures of the Organic Methods
Evaluation Branch. |
|
Date: January 1984 |
Chemist: Carl J.
Elskamp |
Organic Methods Evaluation Branch OSHA Analytical
Laboratory Salt Lake City, Utah
1. General Discussion
1.1. Background
1.1.1. History
In the past there were no validated sampling and analytical
procedures for determining 1-nitropropane
(1-NP) in air. Samples have been received at the OSHA
laboratory that had been collected on charcoal (coconut shell)
sampling tubes. Studies were done by the service branch to find a
suitable solvent to desorb 1-NP from charcoal. Carbon
disulfide, which is used to successfully desorb a wide range of
solvents from charcoal, desorbed less than 50% of 1 mg of
1-NP from charcoal. Attempts were made to desorb 1 mg
of 1-NP from charcoal with other commonly used
desorption solvents. The solvents tried and the desorption
efficiencies obtained were: methanol - 55 to 66%, isopropanol - 30
to 33%, 95% methylene chloride/ 5% isopropanol - 71 to 76%, 95%
carbon disulfide/ 5% isopropanol - 73%, and methylene chloride -
53%. Due to these low desorption efficiencies, solid sorbents other
than charcoal were investigated.
Since there is a validated sampling and analytical procedure for
2-NP that requires collection on Chromosorb 106 and
desorption with ethyl acetate (Ref. 5.1.), desorption efficiency
studies were done for 1-NP accordingly. Desorption
efficiencies appeared to be high (>95%), but diethylbenzene
isomers were also desorbed from the samples which proved to be
interferences using the GC column recommended in the method. The
desorbed diethylbenzene is apparently a contaminant from the
Chromosorb 106 tubes used. The isomers were not desorbed from a
blank sample, thus for this study, 1-NP had to be
present for the isomers to be desorbed with ethyl acetate. The
aforementioned validated method for 2-NP required the
Chromosorb 106 to be thermally desorbed to clean the resin before
collection of air samples. This cleanup procedure would probably rid
the resin of the interfering isomers, but it is inconvenient and
there is some question of whether thermally desorbed tubes would
always be used to collect samples, i.e. the industrial hygienist may
use the sampling tubes as received from the supplier. Thus,
alternate sampling media were considered for collection of both
1-NP and 2-NP.
Breakthrough studies were performed with XAD-4 and
XAD-7 sampling tubes (SKC West, Inc., Fullerton, CA) by sampling an
atmosphere of approximately 50 ppm 1-NP (in 80% RH air,
23°C, 656 mm Hg) at 0.2 L/min and monitoring the downstream effluent
with a total hydrocarbon analyzer. Only the front sampling section
was used in the tubes. The 5% breakthrough volumes were about 5 to
5.5 L for XAD-4 and 3 L for XAD-7, thus
XAD-4 was chosen as a possible sampler. Since a flow
rate of 0.2 L/min would allow for a maximum sampling period of less
than 20 min, breakthroughs were done at a flow of 0.1 L/min.
Breakthroughs thus determined for both 1-NP and
2-NP allow for a recommended sample volume of 4 L
collected at 0.1 L/min (40 min).
Desorption efficiencies were determined for both
1-NP and 2-NP from XAD-4
using ethyl acetate and carbon disulfide. Both solvents gave high
desorptions, but carbon disulfide was preferred since it responds
much less than ethyl acetate on a flame ionization detector, thus
lower detection limits are obtained when carbon disulfide is used.
It was found that a small amount of toluene is desorbed from samples
containing 1-NP and/or 2-NP. The desorbed
toluene is apparently a contaminant from the XAD-4
tubes used. The toluene is not desorbed from a blank
XAD-4 sample. The small amount desorbed from samples
proved to be insignificant.
The collection of 1-NP and 2-NP on
XAD-4 sampling tubes and desorption with carbon
disulfide were successfully evaluated. The only special requirement
is samples should be stored (not necessarily shipped) under
refrigeration to reduce migration of the analytes to the backup
section before analysis. After storing 1-NP samples for
15 days, there was a migration of 0.5 to 2.5% for refrigerated
samples and 11 to 15% for ambient samples. Similarly for
2-NP, migrations of 3 to 5% for refrigerated samples
and 20 to 25% for ambient samples were found.
1.1.2. Toxic effects. (The section for 1-NP is
quoted from "Occupational Health Guidelines for Chemical Hazards",
Ref. 5.2. and the section for 2-NP is taken from OSHA
Method 15 for 2-NP, Ref. 5.1. These sections are for
information only and should not be taken as the basis of OSHA
policy.)
1.1.2.1. 1-Nitropropane
"1-Nitropropane vapor is an eye irritant and in animals causes
mild respiratory irritation and severe liver damage. Rabbits died
from exposure to 5,000 ppm for 3 h, but 10,000 ppm for 1 h was not
lethal. Effects were conjunctival irritation, lacrimation, slow
respiration with some rales, muscular incoordination, ataxia, and
weakness. Autopsy of animals exposed to lethal concentrations
revealed severe fatty infiltration of the liver and moderate
kidney damage. Human volunteers exposed to over 100 ppm noted eye
irritation. There are no reports of systemic effects in humans."
1.1.2.2. 2-Nitropropane
"Exposure to concentrations of 2-nitropropane on
the order of 20 to 45 ppm are reported to cause in humans nausea,
vomiting, diarrhea, loss of appetite, and severe headaches and
concentrations of 165 to 445 ppm, nausea, dizziness, headaches,
and diarrhea. Cats which died within 17 days of exposure to 328
ppm 2-nitropropane sustained severe liver damage.
Liver damage attributed to high concentrations of
2-nitropropane in humans has been reported. Liver
cancer was found in rats exposed to 207 ppm
2-nitropropane for 6 months. This data raises the
question of carcinogenic effects in humans. While additional
studies are in progress, NIOSH believes it would be prudent to
handle 2-nitropropane as if it were a human
carcinogen."
1.1.3. Potential workplace exposure
Following are some common operations where exposure to
1-NP may occur as reported in "Occupational Health
Guidelines for Chemical Hazards" (Ref. 5.2.) and also where exposure
to 2-NP may occur as reported in OSHA method 15 (Ref.
5.1.).
1.1.3.1. 1-Nitropropane
1-Nitropropane is used:
as a thinner and solvent for cellulose compounds, lacquers,
and dopes; in vinyl resins for industrial coatings and printing
inks; in synthetic finish removers; and for oil and
spirit-soluble dyes of molded plastics.
as an extraction solvent for purification, separation,
recrystallization, and recovery for natural and synthetic
resins, tars, coating materials, fats, and oils.
a reaction medium in polymer technology, as a catalyst,
initiator, and solvent.
in organic chemical synthesis for preparation of amines,
nitrated alcohols, acids, and chloronitroparaffins.
in manufacture of explosives.
1.1.3.2. 2-Nitropropane
"Solvent systems containing 2-nitropropane are
used in coatings (e.g., vinyl, epoxy, nitrocellulose, and
chlorinated rubber), printing inks, and adhesives. Occupational
exposure to these products may occur in various industries
including industrial construction and maintenance, printing
(rotogravure and flexographic inks), highway maintenance (traffic
markings), shipbuilding and maintenance (marine coatings),
furniture, food packaging, and plastic products."
1.1.4. Physical properties (Ref. 5.3. unless otherwise noted)
|
1-NP |
2-NP |
molecular weight: |
89.09 |
89.09 |
boiling pt., 760 mm Hg: |
131.6°C |
120.3°C |
color: |
colorless |
colorless |
density (25/4°C): |
0.99 |
0.9821 |
vapor pressure, 20°C: |
7.5 mm (Ref. 5.2.) |
12.9 (Ref. 5.1.) |
flash pt., closed cup: |
34°C |
24°C |
odor: |
mild, fruity odor (Ref. 5.2.) |
|
flammable limits in air, % by volume
(lower): |
2.2 (Ref. 5.2.) |
2.6 (Ref. 5.1.) |
autoignition temp: |
420.6°C (Ref. 5.2.) |
formula: |
CH3CH2CH2NO2 |
CH3CH(NO2)CH3 |
synonyms: |
none (Ref. 5.2.) |
dimethylnitro-methane; isonitropropane;
nitroisopropane and 2-NP (Ref.
5.1.) |
1.2. Limit defining parameters (The analyte air concentrations
listed throughout this method are based on an air volume of 4 L and
solvent desorption volume of 1.0 mL. The ppb and ppm values are
referenced to an atmospheric pressure of 760 mm Hg and temperature of
25°C.)
1.2.1. Detection limit of the analytical procedure
The detection limit of the analytical procedure is 0.4 ng for
both 1-NP and 2-NP. This is the amount of
analytes which will give peaks whose heights are approximately 5
times the height of baseline noise. (Section 4.1.)
1.2.2. The detection limit of the overall procedure is 0.4 µg per
sample (25 ppb or 91 µg/m3) for both
1-NP and 2-NP. This is the amount of
analytes spiked on the sampling device which allow recoveries
approximately equivalent to the detection limits of the analytical
procedure. (Section 4.2.)
1.2.3. The reliable quantitation limit is 0.4 µg per sample (25
ppb or 91 µg/m3) for both
1-NP and 2-NP. This is the smallest amount
of analytes which can be quantitated within the requirements of
recoveries of at least 75% and a precision (1.96 SD) of ±25% or
better. (Section 4.2.)
The reliable quantitation limit and detection limits reported in
the method are based upon optimization of the instrument for the
smallest possible amount of analyte. When the target concentration of
an analyte is exceptionally higher than these limits, they may not be
attainable at the routine operating parameters.
1.2.4. Sensitivity
The sensitivities of the analytical procedure over a
concentration range representing 0.5 to 2 times the target
concentration based on the recommended air volume are 420 area
counts per µg/mL for 1-NP and 415 for
2-NP. These were determined by the slopes of the
calibration curves. (Section 4.3.) The sensitivity will vary with
the particular instrument used in the analysis.
1.2.5. Recovery
The recoveries of 1-NP and 2-NP from
samples used in 15 day storage tests remained above 87 and 91%
respectively when the samples were stored at ambient temperatures
(20-26°C) in a closed drawer. The recovery of analyte from the
collection medium after storage must be 75% or greater. (Section
4.4.)
1.2.6. Precision
The pooled coefficients of variation obtained from replicate
determinations of analytical standards at 0.5, 1, and 2 times the
target concentration are 0.009 for 1-NP and 0.013 for
2-NP. (Section 4.3.)
1.2.7. Precision (overall procedure)
The precisions at the 95% confidence level for 15-day storage
tests are ±14.1% for 1-NP and ±12.1% for
2-NP. (Section 4.4.) These limits include an additional
±5% for sampling error. The overall procedure must provide results
at the target concentration that are ±25% or better at the 95%
confidence level.
1.2.8. Reproducibility
Six samples for each analyte, collected from controlled test
atmospheres, and a draft copy of this procedure were given to a
chemist unassociated with this evaluation. The samples were analyzed
after 57 days of storage at 2°C. The average recoveries were 95.4%
and 97.6% with standard deviations of 1.2% and 2.4% for
1-NP and 2-NP respectively. (Section 4.5.)
1.3. Advantages
1.3.1. The solid sorbent tube provides a convenient method for
sampling.
1.3.2. The XAD-4 tubes do not have to be treated
before sampling.
1.3.3. The analysis is rapid, sensitive, and precise.
1.3.4. The desorption solvent is carbon disulfide, which is a
better solvent for use with a flame ionization detector than ethyl
acetate.
1.4. Disadvantages
1.4.1. This method has not been field tested.
1.4.2. The amount of sample that can be taken is limited by the
total milligrams the XAD-4 tube will adsorb before
overloading.
2. Sampling Procedure
2.1. Apparatus
2.1.1. Samples are collected by use of a personal sampling pump
that can be calibrated within ±5% of the recommended flow rate with
the sampling tube in line.
2.1.2. Samples are collected on solid sorbent sampling tubes
containing XAD-4 resin. The tubes contain two sections
of XAD-4 separated by urethane foam plugs. The front
section contains 80 mg of sorbent and the back section, 40 mg. The
sections are held in place with glass wool plugs in a glass tube 70
mm × 4-mm i.d. The glass tube is flame-sealed at both
ends. For this evaluation, SKC sorbent tubes (catalog number
226-30-11-04, lot 146) were used.
2.2. Reagents
No sampling reagents are required.
2.3. Sampling technique
2.3.1. Immediately before sampling, break open the ends of the
XAD-4 tube. All tubes should be from the same lot.
2.3.2. Connect the sampling tube to the sampling pump with
flexible tubing. Position the tube so that sampled air first passes
through the 80-mg section.
2.3.3. Air being sampled should not pass through any hose or
tubing before entering the sampling tube.
2.3.4. Place the sampling tube vertically (to avoid channeling)
in the employee's breathing zone.
2.3.5. After sampling, seal the tubes immediately with plastic
caps and wrap lengthwise with OSHA Form 21.
2.3.6. Submit at least one blank sampling tube with each sample
set. Blanks should be handled in the same manner as samples, except
no air is drawn through them.
2.3.7. Record sample volumes (in liters of air) for each sample,
along with any potential interferences.
2.3.8. Ship any bulk sample(s) in a separate container(s) from
the air samples.
2.4. Breakthrough
2.4.1. The average 5% breakthrough volume from a test atmosphere
(air at approx. 80% relative humidity) containing 52.6 ppm (191.8
mg/m3) 2-NP was determined to
be 4.8 L for three measurements. This corresponds to a sampled
amount of 0.92 mg of 2-NP. The sampling rate was
approximately 0.1 L/min and the test atmosphere was at 23°C and
654.3 mm Hg. (Section 4.6.)
2.4.2. Since it was found that the breakthrough volume was
greater (as expected) for 1-NP than 2-NP
at 0.2 L/min, only one determination for breakthrough volume was
done for 1-NP at 0.1 L/min. The 5% breakthrough volume
from an atmosphere containing 53.3 ppm (194.1
mg/m3) 1-NP was 6.0 L. This
corresponds to a sampled amount of 1.16 mg of 1-NP. The
recommended sample volume of 4 L for this combined method is based
on the breakthrough volume of 2-NP. (Section 4.6.)
2.5. Desorption efficiency
2.5.1. The average desorption efficiency of 1-NP
from spiked samples is 95.4% over the range of 0.5 to 2 times the
target concentration. (Section 4.7.)
2.5.2. The average desorption efficiency of 2-NP
from spiked samples is 96.4% over the range of 0.5 to 2 times the
target concentration. (Section 4.7.)
2.5.3. Desorption efficiencies must by determined for each lot of
XAD-4 sampling tubes.
2.6. Recommended air volume and sampling rate
2.6.1. The recommended air volume is 4 L.
2.6.2. The recommended sampling rate is 0.1 L/min.
2.7. Interferences (sampling)
2.7.1. It is not known if any compound will severely interfere
with the collection of 1-NP or 2-NP on
XAD-4. In general, the presence of any other
contaminant vapors in the air will reduce the capacity of
XAD-4 to collect 1-NP or
2-NP.
2.7.2. Suspected interferences should be reported to the
laboratory with submitted samples.
2.8. Safety precautions
2.8.1. Attach the sampling equipment to the employee so that it
will not interfere with work performance or safety.
2.8.2. Wear eye protection when breaking the ends of the
XAD-4 tubes.
2.8.3. Follow all safety procedures that apply to the work area
being sampled.
3. Analytical Procedure
3.1. Apparatus
3.1.1. A GC equipped with a flame ionization detector. For this
evaluation, a Hewlett-Packard 5840A GC was used with a
7671A Automatic Sampler.
3.1.2. A GC column capable of separating 1-NP and
2-NP from carbon disulfide and any interferences. A
10-ft × 1/8-in stainless steel column packed with 100/120
Supelcoport, coated with 20% SP-2100 and 0.1% CW1500, was used in
this evaluation.
3.1.3. An electronic integrator or some other suitable method of
measuring peak areas or heights.
3.1.4. Small vials with Teflon-lined caps capable of holding 2
mL.
3.1.5. A dispenser capable of delivering 1.0 mL to prepare
standards and samples. If a dispenser is not available, a 1-mL pipet
may be used.
3.1.6. Syringes, such as 10-µL for preparation of standards and
1-µL for injection of samples and standards into a GC.
3.1.7. Volumetric flasks and pipets to dilute the
1-NP or 2-NP.
3.2. Reagents
3.2.1. Carbon disulfide, reagent grade.
3.2.2. 1-Nitropropane and 2-nitropropane, reagent
grade (or redistilled practical grade).
3.2.3. GC grade nitrogen, air, and hydrogen.
3.3. Standard preparation
3.3.1. Analytical standards are prepared in carbon disulfide.
Dispense 1.0 mL of carbon disulfide (using the same dispenser or
pipet used for samples) into 2-mL vials. Seal the vials immediately
with Teflon-lined caps. Using a 10-µL syringe, dispense into the
sealed vials a known amount of a 1-NP or
2-NP solution prepared in carbon disulfide. Example: If
3.7 µL of a 1 to 10 dilution of 1-NP in carbon
disulfide is injected into a vial containing 1.0 mL carbon
disulfide, the vial would contain 367.6 µg (3.7 µL × 993.4 µg/mL ×
1/10) of 1-NP per sample. For a 4-L air sample, this
would be equivalent to 25.2 ppm or 91.9
mg/m3, uncorrected for desorption
efficiency.
3.3.2. Standard concentrations should bracket sample
concentrations. Thus, if samples fall out of the concentration range
of prepared standards, additional standards may have to be prepared
and analyzed to ascertain linearity of response.
3.4. Sample preparation
3.4.1. Transfer each XAD-4 section of the samples
to separate vials. The glass tube and plugs are discarded.
3.4.2. Add 1.0 mL of carbon disulfide to each vial using the same
dispenser as used for preparation of standards.
3.4.3. The vials are immediately capped and shaken periodically
for 30 min before analysis.
3.5. Analysis
GC conditions |
|
column: |
10-ft × 1/8-in SS, 20% SP-2100, 0.1% CW1500 on
100/120 Supelcoport |
injection volume: |
1 µL |
zone temperatures (°C): |
75 (column) 175 (injector) 250 (FID
detector) |
gas flows (mL/min): |
25 (nitrogen, carrier) 45 (hydrogen) 260
(air) |
retention times (min): |
2.4 (carbon disulfide) 5.7
(2-NP) 7.3 (1-NP) |
chromatograms: |
Section 4.8. |
3.6. Interferences (analytical)
3.6.1. Any compound that responds on a flame ionization detector
and has the same general retention time of the analyte is a
potential interference. Possible interferences should be reported to
the laboratory with submitted samples by the industrial hygienist.
These interferences should be considered before samples are
desorbed.
3.6.2. GC parameters (i.e. column and column temperature) may be
changed to possibly circumvent interferences.
3.6.3. Retention time on a single column is not considered proof
of chemical identity. Samples should be confirmed by GC/MS if
possible.
3.7. Calculations
The analyte concentration for samples is obtained from the
appropriate calibration curve in terms of micrograms per sample,
uncorrected for desorption efficiency. The air concentration is
calculated using the following formulae. If any analyte is found on
the backup section, it is added to the amount found on the front
section. This total amount is then corrected by subtracting the total
amount (if any) found in the blank.
mg/m3 = |
(blank corrected micrograms per
sample)
(liters of air sampled) (desorption
efficiency) |
ppm = (mg/m3)(24.46)/(89.09) =
(mg/m3)(0.2746)
where |
24.46 = molar volume (liters) at 760 mm Hg,
25°C 89.09 = molecular weight of 1- and
2-nitropropane |
3.8. Safety precautions (analytical)
3.8.1. Avoid skin contact and inhalation of all chemicals.
3.8.2. Restrict the use of all chemicals to a fume hood when
possible.
3.8.3. Wear safety glasses and a lab coat at all times while in
the lab area.
4. Backup Data
4.1. Detection limit of the analytical procedure
The recommended injection size of 1 µL was used to determine the
detection limits of the analytical procedure. The detection limit of
0.4 ng for 1-NP and 2-NP was determined by
analyzing a analytical standard containing 0.37 ng/µL
1-NP and 0.36 ng/µL 2-NP. Shown in Figure
4.1. is a chromatogram of such an injection made on a
Hewlett-Packard 5840A GC equipped with a flame ionization
detector set at an attenuation of 2-1. The
chart speed was set at 0.2 cm/min.
4.2. Detection limit of the overall procedure and reliable
quantitation limit data
Samples were prepared by injecting 368 ng of 1-NP on
six XAD-4 tubes and 363 ng of 2-NP on
another six XAD-4 tubes. The samples were later analyzed
to determine the amount recovered. Since the amounts recovered were
high and approximately equal to the detection limits of the analytical
procedure, the detection limits of the overall procedure and the
reliable quantitation limits are taken to be 0.4 µg per sample (25 ppb
or 91 µg/m3) for both 1-NP and
2-NP. The results of this study are given in Table 4.2.
Table 4.2. Detection Limits of the Overall Procedure and
Reliable Quantitation Limits Data
|
|
1-NP |
2-NP |
1-NP |
2-NP |
sample no. |
mass spiked, ng |
% recovery |
|
1 2 3 4 5 6
SD 1.96
SD |
368 368 368 368 368 368
|
363 363 363 363 363 363
|
86.4 87.4 102.4 93.7 95.1 97.9
93.8 6.1 12.0 |
92.5 94.1 98.8 98.0 98.0 96.5
96.4 2.6 5.1 |
|
4.3. Sensitivity and Precision (analytical)
The sensitivity and precision of the analytical procedure were
determined from multiple injections of analytical standards. These
data are given in Table 4.3. and shown graghically Figure 4.3.1. and
4.3.2.
Table 4.3. Sensitivity and Precision Data
|
|
1-NP |
2-NP |
|
|
|
× target conc. µg/mL |
0.5× 183.8 |
1× 367.6 |
2× 735.1 |
0.5× 181.7 |
1× 363.4 |
2× 726.8 |
|
area
counts
![mean](../mean.gif) SD CV(%)
![pooled coefficient of variation](../cv.gif) |
76240 74520 75100 74820 75280 75300
75210 585.5 0.78 |
152300 153500 152700 154400 152600 154900
153400 1058 0.69
0.009 |
306300 312000 306100 312900 306000 313900
309533 3774 1.22 |
73180 75080 74120 75280 73480 75380
74420 960 1.29 |
148800 151800 147600 152100 147900 152300
150083 2214 1.48
0.013 |
298600 305000 298800 305600 299100 306100
302200 3708 1.23 |
|
4.4. Recovery data (storage)
Storage samples were generated from test atmospheres (air at about
80% relative humidity) containing 1-NP or
2-NP near the target concentration of 25 ppm. The samples
were generated at ambient temperatures (20 to 26°C) and pressures (655
to 660 mm Hg) by drawing about 4 L of the test atmospheres through the
sampling tubes at about 0.1 L/min for 40 min. For the two sets of 36
samples each (one set per analyte), six samples were analyzed
immediately after generation, fifteen were stored in a refrigerator at
2°C and fifteen were stored in a closed drawer at ambient
temperatures. The results of recovery versus storage time are given
below in Tables 4.4.1. and 4.4.2., and shown graphically in Figures
4.4.1. and 4.4.2.
Table 4.4.1. Storage Tests for 1-Nitropropane
|
storage time |
% recovery |
(days) |
(refrigerated) |
|
(ambient) |
|
0 0 3 5 8 10 15 |
97.7 96.7 99.0 89.3 89.0 98.0 90.6 |
96.6 96.8 99.2 87.8 92.1 98.2 90.6 |
97.1 96.3 99.0 87.9 83.2 98.7 90.6 |
|
97.7 96.7 98.6 84.8 91.5 97.1 87.1 |
96.6 96.8 98.9 88.1 90.4 97.7 87.7 |
97.1 96.3 99.2 80.7 90.3 97.6 81.0 |
|
Table 4.4.2. Storage Tests for 2-Nitropropane
|
storage time |
% recovery |
(days) |
(refrigerated) |
|
(ambient) |
|
0 0 3 5 8 10 15 |
98.0 100.5 100.0 94.2 92.8 99.2 96.0 |
97.4 97.7 99.5 92.2 84.0 99.4 93.9 |
97.4 98.3 98.2 92.7 86.5 100.4 93.1 |
|
98.0 100.5 99.2 93.6 95.7 99.6 91.6 |
97.4 97.7 98.4 93.8 93.9 98.6 94.0 |
97.7 98.3 100.1 86.4 92.9 98.1 85.3 |
|
4.5. Reproducibility
Six samples for each analyte, collected from controlled test
atmospheres (80% RH, 25°C, 656 mm Hg) containing the analyte near the
target concentration, were analyzed by another chemist unassociated
with this evaluation. The samples were generated by drawing the test
atmosphere through the sampling tubes for 40 min at approximately 0.1
L/min. The samples were stored for 57 days at 2°C before being
analyzed. The results are given in Table 4.5.
Table 4.5. Reproducibility
|
|
1-NP |
2-NP |
|
|
|
sample |
µg found |
µg possible |
% found |
µg found |
µg possible |
% found |
|
1 2 3 4 5 6
SD |
333.3 394.3 350.1 363.6 402.3 |
342.8 412.3 372.8 380.3 423.7 (sample
lost) |
97.2 95.6 93.9 95.6 94.9
95.4 1.2 |
340.7 422.8 379.0 384.1 410.7 432.4 |
358.2 423.8 385.8 394.1 434.1 429.3 |
95.1 99.8 98.2 97.5 94.6 100.7
97.6 2.4 |
|
4.6. Breakthrough
The average 5% breakthrough volume of 4.8 L for 2-NP
was determined by sampling at 0.1 L/min from a test atmosphere (80%
RH, 23°C, 654 mm Hg) containing 52.6 ppm (191.8
mg/m3) of 2-NP. The sampling
tubes contained only the front section of adsorbent.
Five-percent breakthrough volumes of 4.70, 5.00, and 4.69
L were obtained from three separate determinations to give an average
of 4.8 L. This corresponds to a sampled mass of 0.92 mg. A graphical
representation of one of the tests is shown in Figure 4.6. The
atmosphere downstream from the sampling tubes was monitored by a total
hydrocarbon analyzer. A similar determination was made for
1-NP at 53.3 ppm (194.1 mg/m3).
The 5% breakthrough volume was determined to be 6.0 L.
4.7. Desorption efficiency
The desorption efficiency for each analyte was determined by
injecting known amounts of 1-NP and 2-NP
standards onto the front sections of XAD-4 sampling
tubes. The samples were analyzed the next day after storing at room
temperature in a closed drawer.
Table 4.7. Desorption Efficiency Data
|
|
1-NP |
2-NP |
|
|
|
µg ppm |
183.8 12.6 |
367.6 25.2 |
735.1 50.4 |
181.7 12.5 |
363.4 24.9 |
726.8 49.9 |
|
% desorption
![mean](../mean.gif)
![mean](../mean.gif) |
95.1 95.3 95.4 94.5 95.9 94.5
95.1 |
95.0 95.7 95.6 95.0 96.1 94.1
95.2
95.4 |
95.3 94.7 95.6 96.7 96.2 96.0
95.8 |
99.6 98.3 98.0 98.0 94.0 98.1
97.7 |
98.3 96.7 96.3 95.7 96.7 96.2
96.7
96.4 |
93.8 95.1 95.3 95.0 94.6 95.5
94.9 |
|
4.8. Chromatogram
A chromatogram of 1-NP and 2-NP is shown
in Figure 4.8. The chromatogram is from a 1-µL injection
of a standard containing 365 µg/mL each of 1-NP and
2-NP. This concentration is approximately equal to 25 ppm
each for a 4-L air sample.
Figure 4.1. Detection limit
chromatograms.
Figure 4.3.1. 1-Nitropropane calibration
curve.
Figure 4.3.2. 2-Nitropropane calibration
curve.
Figure 4.4.1. 1-Nitropropane storage
samples.
Figure 4.4.2. 2-Nitropropane storage
samples.
Figure 4.6. 2-Nitropropane breakthrough
curve.
Figure 4.8. Chromatogram of a standard.
5. References
5.1. Lee, D., 2-Nitropropane, Method 15, Organic Methods
Evaluation Branch, OSHA Analytical Laboratory, Salt Lake City, Utah,
Unpublished, September 1979.
5.2. "Occupational Health Guidelines for Chemical Hazards"
NIOSH/OSHA, January 1981, DHHS (NIOSH) Publication No. 81-123.
5.3. Windholz, M., Ed. "Merck Index", 9th ed.; Merck and Co.:
Rahway, NJ, 1979.
|