|
| Method no.: |
PV2138 |
| |
|
| Control no.: |
T-PV2138-01-0403-CH |
| |
|
| OSHA PEL: |
500 ppm (2350
mg/m3) |
| |
|
| Procedure: |
Samples are collected
by drawing a known volume of air through glass sampling tubes
containing coconut-shell charcoal. Samples are extracted with
1 mL of a solution of carbon disulfide: N,N-dimethylformamide (99:1) with 0.25
µL/mL p-cymene internal standard,
and analyzed by GC using a flame ionization detector
(FID). |
| |
|
| Recommended sampling
time and sampling rate: |
80 min at 0.05 L/min
(4.0 L) |
| |
|
| Reliable quantitation
limit: |
200 ppb (933
µg/m3) |
| |
|
| Status of method: |
Partially evaluated
method. This method has been subjected to established
evaluation procedures of the Methods Development Team and is
presented for information and trial use. |
| |
|
| |
|
| March 2004 |
Anna
Tang |
| |
|
Chromatography Team
Industrial Hygiene Chemistry
Division
OSHA Salt Lake Technical Center
Sandy, UT
84070-6424
|
1. General
Discussion
1.1 Background
1.1.1 History
OSHA Method 48 for Petroleum Distillates validated
collection of a boiling fraction that contained n-octane
on coconut shell charcoal1.
NIOSH Method 1500 for sampling and analysis of n-octane
requires sample collection on coconut shell charcoal,
extraction with carbon disulfide, and analysis by gas
chromatography with FID detection2.
These two methods were used as a guide for selection of
parameters for this partially-validated method for
n-octane. Storage stability was not assessed in the NIOSH
work. This work was done to confirm the NIOSH evaluation
results using the OSHA partially-validated methods
evaluation protocol and to perform a storage stability
test. Samples in this method are collected with coconut
shell charcoal, extracted with 1 mL of carbon disulfide:
N,N-dimethylformamide (99:1
CS2:DMF) and analyzed by GC/FID. The
extraction, storage, and retention efficiency studies
showed good recoveries.
1.1.2 Toxic effects
(This section is for information only and should not be
taken as the basis of OSHA policy.)3,4
n-Octane is a mucous membrane, eye, and nose
irritant. High concentrations can cause drowsiness,
dermatitis, and narcosis. It is toxic by ingestion,
inhalation, and skin contact.
1.1.3 Workplace
Exposure3
n-Octane has been used as a solvent, in organic
synthesis, and in azeotropic distillations. The octanes
are present in gasoline and petroleum solvents such as
VM&P naphtha.
1.1.4 Physical
properties and other descriptive information3,5
| CAS number: |
111-65-9 |
IMIS6: |
1957 |
| molecular weight: |
114.23 |
vapor density: |
3.86 |
| melting point: |
-56.8°C |
boiling point: |
127°C |
| appearance: |
colorless liquid |
vapor pressure: |
1.4 kPa @20°C |
| odor: |
gasoline |
flash point: |
22°C (72°F) (open cup) |
| solubility: |
soluble in ethyl ether, ethyl alcohol and
benzene |
molecular formula: |
CH3(CH2)6CH3 |
| synonyms: |
normal octane |
density: |
0.7028
g/mL |
structural formula:
This method was evaluated according to the
OSHA SLTC "Evaluation Guidelines for Air Sampling Methods
Utilizing Chromatographic Analysis"7.
The Guidelines define analytical parameters, specify required
laboratory tests, statistical calculations, and acceptance
criteria. The analyte air concentrations throughout this
method are based on the recommended sampling and analytical
parameters.
1.2 Detection limit
of the overall procedure (DLOP) and reliable quantitation
limit (RQL)
The DLOP is measured as mass per sample
and expressed as equivalent air concentration, based on the
recommended sampling parameters. Ten samplers were spiked
with equally descending increments of analyte, such that the
highest sampler loading was 3.5 µg of n-octane. This is the
amount spiked on a sampler that would produce a peak about
10 times the response for a sample blank. These spiked
samplers were analyzed with the recommended analytical
parameters, and the data obtained used to calculate the
required parameters (standard error of estimate (SEE) and
slope) for the calculation of the DLOP. The slope was 232.4
and the SEE was 86.2. The RQL is considered the lower limit
for precise quantitative measurements. It is determined from
the regression line parameters obtained for the calculation
of the DLOP, providing 75% to 125% of the analyte is
recovered. The DLOP and RQL were 1.11 µg (59.5 ppb) and 3.71
µg (198.9 ppb), respectively. The recovery at the RQL was
93.8%.
Table 1.2
Detection Limit of the Overall
Procedure
for n-Octane
|
mass per
sample
(µg) |
area
counts
(µV-s) |
|
| 0.00 |
0 |
| 0.35 |
282 |
| 0.70 |
355 |
| 1.05 |
385 |
| 1.40 |
483 |
| 1.75 |
571 |
| 2.10 |
811 |
| 2.44 |
689 |
| 2.79 |
773 |
| 3.14 |
791 |
| 3.49 |
937 |
|
Figure 1.2.1. Plot of data to determine
the DLOP/RQL for n-octane. (y=232.41x + 146.58; SEE =
86.2) |
Below is a chromatogram of
the RQL level.
Figure 1.2.2. Chromatogram of the
n-octane peak in a standard. (Key: (1)
n-octane) |
2. Sampling
Procedure
All safety practices that apply to the work
area being sampled should be followed. The sampling equipment
should be attached to the worker in such a manner that it will
not interfere with work performance or safety.
2.1 Apparatus
2.1.1 Samples are
collected using a personal sampling pump calibrated, with
the sampling device attached, to within ±5% of the
recommended flow rate.
2.1.2 Samples are
collected with 7-cm × 4-mm i.d. × 7-mm o.d. glass sampling
tubes packed with two sections (100/50 mg) of charcoal.
The sections are held in place with foam plugs and with a
glass wool plug at the front. For this evaluation,
commercially prepared sampling tubes were purchased from
SKC, Inc. (catalog no. 226-01, lot 2000).
2.2 Reagents
None required.
2.3 Technique
2.3.1 Immediately
before sampling break off the ends of the flame-sealed
tube to provide an opening approximately half the internal
diameter of the tube. Wear eye protection when breaking
the tube. Use tube holders to minimize the hazard of
broken glass. All tubes should be from the same lot.
2.3.2 The smaller
section of the adsorbent tube is used as a back-up and is
positioned nearest the sampling pump. Attach the tube
holder to the sampling pump so that the adsorbent tube is
in an approximately vertical position with the inlet
facing down during sampling. Position the sampling pump,
tube holder, and tubing so they do not impede work
performance or safety.
2.3.3 Draw the air to
be sampled directly into the inlet of the tube holder. The
air being sampled is not to be passed through any hose or
tubing before entering the sampling tube.
2.3.4 After sampling
for the appropriate time, remove the adsorbent tube and
seal it with plastic end caps. Seal each sample end-to-end
with an OSHA-21 form as soon as possible.
2.3.5 Submit at least
one blank sample with each set of samples. Handle the
blank sample in the same manner as the other samples
except draw no air through it.
2.3.6 Record sample
air volumes (liters), sampling time (minutes), and
sampling rate (L/min) for each sample, along with any
potential interferences on the OSHA-91A form.
2.3.7 Submit the
samples to the laboratory for analysis as soon as possible
after sampling. If delay is unavoidable, store the samples
at refrigerator temperature. Ship any bulk samples
separate from the air samples.
2.4 Extraction
efficiency
The extraction efficiency was determined
by spiking front sections of sampling tubes with n-octane at
0.1 to 2 times the target concentration based on 4-L air
samples. These samples were stored overnight at ambient
temperature and then extracted for 30 minutes with shaking,
and analyzed. The mean extraction efficiency over the
studied range was 101.9%.
Table 2.4
Extraction Efficiency (%) of
n-Octane
|
| Level |
|
|
|
|
|
x
target
concn |
mg
per
sample |
1 |
2 |
3 |
4 |
mean |
|
| 0.1 |
0.91 |
95.4 |
98.0 |
99.9 |
99.8 |
98.3 |
| 0.5 |
4.89 |
109.4 |
108.1 |
107.9 |
109.5 |
108.7 |
| 1.0 |
9.08 |
99.5 |
100.2 |
100.2 |
101.1 |
100.3 |
| 2.0 |
18.86 |
100.1 |
100.6 |
100.4 |
100.4 |
100.4 |
|
2.5 Retention
efficiency
Eighteen charcoal sampling tubes were
each spiked with 18.86 mg of n-octane on the front sections.
This mass of n-octane is approximately equivalent to 2 times
the OSHA PEL, based on a 4-L air volume. The test was
performed by pulling humid air (absolute humidity 15.7
milligrams of water per liter of air, about 78% relative
humidity at 23°C) through the tubes at approximately
0.05-L/min for increasing times. Pairs of samples were
removed at approximately 0.5-L increments between 2 and 6-L
and analyzed. The analytical results of the tube front and
back charcoal sections were compared to detect breakthrough.
These results show that the recommended air volume of 4-L,
sampled at 0.05-L/min, provides an adequate safety margin
against sampler saturation. The average of each pair of
samples is presented for the air volumes shown in table
2.5.
Table 2.5
Retention Efficiency (%) of
n-Octane
|
| L of air |
6.09 |
5.59 |
5.15 |
4.57 |
4.03 |
3.56 |
3.07 |
2.52 |
2.04 |
|
| section A |
104 |
105 |
110 |
107 |
107 |
109 |
105 |
106 |
105 |
| section B |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
|
2.6 Sample
storage
Fifteen charcoal tubes were each spiked with
9.08 mg (500 ppm) of n-octane, then they had 4-L of air,
with an absolute humidity of 15.7 milligrams of water per
liter of air (about 78% relative humidity at 23°C), drawn
through them. Three samples were analyzed immediately, and
the rest were sealed. Six were stored at room temperature
(23°C), and the other six were stored at refrigerated
temperature (4°C). The amounts recovered indicate good
storage stability for the time period studied.
Table 2.6
Storage Test for n-Octane
|
| time
(days) |
ambient storage
recovery (%) |
refrigerated storage
recovery (%) |
|
| 0 |
97.5 |
97.0 |
96.1 |
|
|
|
| 7 |
94.9 |
96.3 |
94.1 |
98.0 |
92.7 |
96.5 |
| 14 |
100.5 |
100.7 |
101.3 |
100.1 |
101.3 |
101.1 |
|
2.7 Recommended
air volume and sampling rate
Based on the data
collected in this evaluation, 4-L air samples should be
collected at a sampling rate of 0.05 L/min for 80
minutes.
2.8 Interferences
(sampling)
2.8.1 There are
no known compounds which will severely interfere with the
collection of n-octane.
2.8.2 Suspected
interferences should be reported to the laboratory with
submitted samples. 3. Analytical
Procedure
Adhere to the rules set down in your
Chemical Hygiene Plan. Avoid skin contact and inhalation of
all chemicals and review all appropriate MSDSs.
3.1 Apparatus
3.1.1 A gas
chromatograph equipped with an FID detector. An Agilent
6890 Plus Gas Chromatograph equipped with a 7683 Injector
was used in this evaluation.
3.1.2 A GC column
capable of separating n-octane from the extraction
solvent, internal standard, and any potential
interferences. A 60-m × 0.32-mm i.d. DB-1 J & W
(5.0-µm df) capillary column was used in this evaluation.
3.1.3 An electronic
integrator or some other suitable means of measuring peak
areas. A Waters Millennium32 Data System was used in this
evaluation.
3.1.4 Glass vials
with poly(tetrafluoroethylene)-lined caps. For this
evaluation 2-mL vials were used.
3.1.5 A dispenser
capable of delivering 1.0 mL of desorbing solvent to
prepare standards and samples. If a dispenser is not
available, a 1.0-mL volumetric pipet may be used.
3.1.6 Volumetric
flasks – 10-mL and other convenient sizes for preparing
standards.
3.1.7 Calibrated
10-µL or 20-µL syringe for preparing standards.
3.1.8 A mechanical
shaker. An Eberbach mechanical shaker was used in this
evaluation.
3.2 Reagents
3.2.1 n-Octane,
reagent grade. ChemService lot FJ8667, 99% was used in
this evaluation.
3.2.2 Carbon
disulfide, reagent grade. EM Science lot 40298103, 99.9%
was used in this evaluation.
3.2.3 N,N-dimethylformamide, reagent grade.
Sigma-Aldrich lot 01340AB, 99.8% was used this evaluation.
3.2.4 p-Cymene, reagent grade. Aldrich lot
306PZ, 99% was used in this evaluation.
3.2.5 The extraction
solvent solution was carbon disulfide: N,N-dimethylformamide (99:1) with
0.25µL/mL of p-cymene as
internal standard.
3.3 Standard
preparation
3.3.1 Prepare
standards by spiking microliter quantities of n-octane
from a microliter syringe into 2-mL vials, each containing
1 mL of the desorbing solution. For example, 13 µL of
n-octane in 1 mL CS2:DMF is equivalent to 9.14
mg/mL. For this evaluation, standards in the range of
0.0003 to 18.9 mg/mL were used. A check standard from a
second source should be prepared to check the calibration.
3.3.2 Bracket sample
concentrations with standard concentrations. If upon
analysis, sample concentrations fall outside the range of
prepared standards, prepare and analyze additional
standards to confirm instrument response, or dilute high
samples with extraction solvent and reanalyze the diluted
samples.
3.4 Sample
preparation
3.4.1 Remove the
plastic end caps from the sample tubes and carefully
transfer each adsorbent section to separate 2-mL vials.
Discard the glass tube, urethane foam plug and glass wool
plug.
3.4.2 Add 1.0
mL of extraction solvent to each vial using the same
dispenser as used for preparation of standards.
3.4.3 Immediately
seal the vials with poly(tetrafluoroethylene)-lined caps.
3.4.4 Shake the vials
on a shaker for 30 minutes.
3.5 Analysis
3.5.1 Gas
chromatographic conditions
GC
conditions
|
|
| Temperature: |
|
| column: |
initial 50°C, hold 3
min, program at 8°C/min to 185 °C, hold 5 min |
| injector: |
225°C |
| detector: |
250°C |
| run time: |
24.6 min |
| column gas flow: |
2.5 mL/min
(hydrogen) |
| septum purge: |
1.9 mL/min
(hydrogen) |
| injection size: |
1.0 µL (10:1
split) |
| column: |
60-m × 0.32 mm i.d.
capillary DB-1 (df = 5.0 µm) |
| retention
times: |
8.3 min (carbon
disulfide)
14.6 min (N,N-dimethylformamide)
16.1
min (n-octane)
22.0 min (p-cymene) |
| Chromatogram: |
Figure 3.5.1. |
| |
|
FID conditions
|
|
| hydrogen flow: |
35 mL/min |
| air flow: |
450 mL/min |
nitrogen
makeup
flow: |
35
mL/min |
Figure 3.5.1. A chromatogram of 9136
µg/mL n-octane in 99:1 CS2/DMF with 0.25µL/mL
p-cymene
internal
standard. (Key: (1) CS2; (2) DMF; (3)
n-octane; and (4) p-cymene) |
3.5.2 Peak
areas are measured by an integrator or other suitable
means.
3.5.3 An
internal standard (ISTD) calibration method is used. A
calibration curve can be constructed by plotting response
of standard injections versus micrograms of analyte per
sample. Bracket the samples with freshly prepared
analytical standards over the range of concentrations.
Figure 3.5.3. Calibration curve of
n-octane. (y = 482x – 3.73E4) |
3.6 Interferences
(analytical)
3.6.1 Any
compound that produces a GC response and has a similar
retention time as the analyte is a potential interference.
If any potential interferences were reported, they should
be considered before samples are extracted. Generally,
chromatographic conditions can be altered to separate an
interference from the analyte.
3.6.2 When necessary,
the identity or purity of an analyte peak may be confirmed
by GC-mass spectrometry.
Figure 3.6.2. Mass spectrum of
n-octane. |
3.7 Calculations
The amount of analyte per sampler is obtained from
the appropriate calibration curve in terms of micrograms per
sample, uncorrected for extraction efficiency. This total
amount is then corrected by subtracting the total amount (if
any) found on the blank. The air concentration is calculated
using the following formulas.
| where: |
CM is concentration by
weight (mg/m3) |
| M is micrograms per sample |
| V is liters of air sampled |
| EE is extraction
efficiency, in decimal
form |
| where: |
CV is concentration by
volume (ppm) |
| VM is molar volume at
25°C and 1 atm = 24.46 |
| CM is concentration by
weight |
| Mr is molecular weight
=
114.23 |
4. Recommendations
for Further Study
Collection, reproducibility, and
other detection limit studies need to be performed to make
this a validated method.
References
1.
OSHA Method 48 http://www.osha-slc.gov/
(accessed 11/11/03).
2. NIOSH Method 1500 http://www.osha-slc.gov/pls/oshaweb/owaredirect.html?p_url=http://www.cdc.gov/niosh/homepage.html
(accessed 11/11/03).
3. Documentation of the Threshold
Limit Values and Biological Exposure Indices, 7th
ed., American Conference of Governmental Industrial Hygienists
Inc., Cinncinnati, OH, 2001, Vol. 2.
4. O’ Neil, M.,
The Merck Index, 13th ed. Merck & Co Inc., Whitehouse
Station, NJ, 2001, p. 6775.
5. Lewis, R., Sr., Hawley’s
Condensed Chemical Dictionary, 14th ed., John Willy &
Sons, Inc. NY, 2001, p. 812.
6. OSHA Chemical Sampling
Information, http://www.osha-slc.gov/
(accessed 11/11/03).
7. Burright, D.; Chan, Y.; Edie,
M.; Elskamp, C.; Hendricks, W.; Rose, M.C. Evaluation
Guidelines for Air Sampling Methods Utilizing Chromatographic
Analysis; OSHA Salt Lake Technical Center, U.S. Department of
Labor, Salt Lake City, UT, 1999.
| |
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