|
| Method no.: |
PV2137 |
| |
|
| Control no.: |
T-PV2137-01-0403-CH |
| |
|
| OSHA PEL:
|
50 ppm (245
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) and analyzed
by GC using a flame ionization detector (FID). |
| |
|
| Recommended sampling
time and sampling rate: |
120 min at 0.2 L/min
(24 L) |
| |
|
| Reliable quantitation
limit: |
8.4 ppb (41
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 |
Uyen
Bui |
| |
|
Chromatography Team
Industrial Hygiene Chemistry
Division
OSHA Salt Lake Technical Center
Sandy UT
84070-6406
|
1.
General Discussion
1.1 Background
1.1.1 History
Cumene has a PEL of 50
ppm. OSHA desires a partially validated method or
validated method for each chemical that has a PEL. A
partially validated method was evaluated for cumene, due
to limited time and resources available. Other OSHA
validated methods collect similar compounds such as
xylene1
on coconut shell charcoal, so this medium was tried and it
worked well for cumene.
The samples were extracted
with 1 mL of carbon disulfide: N,N-dimethylformamide (99:1)
(CS2:DMF) with an extraction efficiency of
100.3%. The retention efficiency study showed no cumene
present on the back-up section of tubes that had been
spiked with 11.75 mg cumene and that had 24 L of humid air
drawn through them. The storage study showed 6% loss under
refrigerated conditions and 7% loss under ambient
conditions for samples stored for up to 14 days.
1.1.2 Toxic effects2
(This section is for information only and should not be
taken as the basis of OSHA policy.)
Cumene is a
mucous membrane, skin and eye irritant. It can cause
headaches, dermatitis and narcosis. It has a central
nervous system depressant action. It is toxic by
ingestion, inhalation and skin contact.
1.1.3
Workplace exposure2,3
Most exposures to cumene occur in the production
of acetone, phenol, acetophenone and α-methyl-styrene.
Cumene is also used as a thinner for paints and as a
constituent of some petroleum-based solvents. In 2002,
U.S. industrial capacity for cumene production was 3503
thousand metric tons.
1.1.4 Physical properties
and other descriptive information2,4
| synonyms: |
isopropyl benzene; 2-phenylpropane |
| CAS number: |
98-82-8 |
| molecular weight: |
120.19 |
| melting point: |
-96°C (-141°F) |
| appearance: |
colorless liquid |
| odor: |
sharp, penetrating, aromatic odor |
| autoignition temperature: |
424°C (795°F) |
| IMIS5: |
0780 |
| vapor density: |
4.1 |
| boiling point: |
152°C (306°F) |
| vapor pressure: |
1.33 KPa @38.3°C |
| flash point: |
39°C (102°F) (closed cup) |
| molecular formula: |
C9H12 |
| density (g/mL): |
0.864 |
| solubility: |
insoluble in water, soluble in most
organic solvents |
structural formula:
This method was evaluated according to the
OSHA SLTC "Evaluation Guidelines for Air Sampling Methods
Utilizing Chromatographic Analysis"6.
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 cumene, such that the highest
sampler loading was 10.37 μg of cumene. 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 594.3 and the SEE was
58.7. 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 0.296 µg (2.5 ppb) and 0.988 µg (8.4
ppb), respectively.
Table 1.2
Detection Limit of the Overall
Procedure for Cumene
|
mass per sample
(µg) |
area counts
(µV-s) |
|
| 0.00 |
0 |
| 1.04 |
783 |
| 2.07 |
1308 |
| 3.11 |
1968 |
| 4.15 |
2464 |
| 5.18 |
3093 |
| 6.22 |
3764 |
| 7.26 |
4350 |
| 8.29 |
4967 |
| 9.33 |
5681 |
| 10.4 |
6229 |
|
Figure 1.2.1 Plot of data to determine the
DLOP/RQL for cumene. (y = 594x + 65.3; SEE =
58.7) |
Below
is a chromatogram of cumene at the RQL. The recovery at the
RQL was 89.2%.
Figure 1.2.2 Chromatogram of the cumene
standard near the RQL. (Key: (1)
cumene) |
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
Samples are collected
using a personal sampling pump calibrated, with the sampling
device attached, to within ± 5% of the recommended flow
rate.
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 coconut shell 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
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.
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.
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.
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.
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.
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.
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 16 tubes with cumene at 0.1 to 2 times
the target concentration. These samples were stored
overnight at ambient temperature and then extracted for 30
minutes using a lab shaker, and analyzed. The mean
extraction efficiency over the studied range was 100.3%.
Table 2.4
Extraction Efficiency (%) of
Cumene |
|
level
|
sample number
|
mean
|
x
target
concn |
mg
per
sample |
1 |
2 |
3 |
4 |
|
|
| 0.1 |
0.59 |
98.3 |
100.2 |
99.9 |
99.9 |
99.6 |
| 0.5 |
2.94 |
99.9 |
99.5 |
99.3 |
100.9 |
99.9 |
| 1.0 |
5.88 |
100.7 |
99.5 |
101.7 |
100.6 |
100.6 |
| 2.0 |
11.75 |
100.7 |
100.5 |
101.2 |
101.3 |
100.9 |
|
2.5
Retention efficiency
Six charcoal tubes were spiked
with 11.75 mg (100 ppm) of cumene in the front sections,
then they had 24-L humid air (absolute humidity of 15.9 mg/L
of water, about 80% relative humidity at 22.2°C) pulled
through them at 0.2 L/min. The samples were extracted and
analyzed. The mean recovery was 98.3%. There was no analyte
found on the back-up section of any of the tubes.
Table 2.5
Retention Efficiency (%) of
Cumene |
|
section
|
sample number
|
mean
|
| |
1 |
2 |
3 |
4 |
5 |
6 |
|
|
| front of spiked tube |
97.3 |
98.3 |
98.0 |
99.5 |
97.9 |
99.1 |
98.3 |
| rear of spiked tube |
0.0 |
0.0 |
0.0 |
0.0 |
0.0 |
0.0 |
0.0 |
| total |
97.3 |
98.3 |
98.0 |
99.5 |
97.9 |
99.1 |
98.3 |
|
2.6 Sample
storage
Fifteen charcoal tubes were each spiked with
5.88 mg (50 ppm) of cumene, then they had 24 L of air, with
an absolute humidity of 15.7 milligrams of water per liter
of air (about 80% 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),
while the other six were stored at refrigerated temperature
(4°C). Three samples stored at room temperature and three
samples stored at refrigerated temperature were analyzed
after 8 days and the remaining six after 14 days. The
amounts recovered indicate good storage stability for the
time period studied.
Table 2.6
Storage Test for Cumene |
|
| time
(days) |
ambient storage recovery (%) |
refrigerated storage recovery (%) |
|
| 0 |
99.5 |
100 |
98.0 |
|
|
|
| 8 |
94.9 |
95.7 |
97.2 |
98.1 |
97.1 |
96.5 |
| 14 |
91.6 |
95.2 |
92.1 |
93.3 |
93.9 |
93.5 |
|
2.7
Recommended air volume and sampling rate
Based on
the data collected in this evaluation, 24-L air samples
should be collected at a sampling rate of 0.2 L/min for 120
minutes.
2.8 Interferences (sampling)
2.8.1 There are no known compounds which will
severely interfere with the collection of cumene.
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. For this evaluation, an Agilent 6890 GC was
used.
3.1.2 A GC column capable of separating
cumene from the extraction solvent, internal standard, and
any potential interferences. A 60-m × 0.32-mm i.d. ZB Wax
(1- 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 and an Agilent
integrator 3396 were 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 extraction 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 Cumene, reagent grade. ChemService lot
229-122C, 99.9% 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 in this
evaluation.
3.2.4 p-Cymene, reagent grade. Aldrich lot
11703TR, 99% was used in this evaluation.
3.2.5
The extraction solvent solution was carbon disulfide:
N,N-dimethylformamide (99:1)
with 0.25 μL/mL of p-cymene as
internal standard. 3.3 Standard preparation
3.3.1 Prepare standards by spiking microliter
quantities of cumene from a microliter syringe into 2-mL
vials, each containing 1 mL of the extraction solution.
For example, 6.8 μL of cumene in 1 mL CS2:DMF
is equivalent to 5.88 mg/mL. For this evaluation,
standards in the range of 0.001 to 11.75 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, and shake the vials
on a shaker for 30 minutes. 3.5 Analysis
3.5.1 Gas chromatographic conditions
GC conditions
|
| zone
temperatures: |
|
| column: |
initial
70oC, hold 2 min, program at 15°C/min to
180°C, hold 2 min |
| injector: |
225°C |
| detector: |
250°C |
| run
time: |
10.3
min |
| column gas
flow: |
3.1 mL/min
(hydrogen) |
| injection
size: |
1.0 µL
(10:1 split) |
| column: |
60-m ×
0.32‑mm i.d. capillary ZB Wax (df = 1
µm) |
| retention
times: |
2.8 min
(carbon disulfide) |
| |
8.8 min
(N,N-dimethylformamide) |
| |
7.1 min
(cumene) |
| |
8.1 min
(p-cymene) |
| Chromatogram: |
Figure
3.5.1
|
FID conditions
|
| hydrogen
flow: |
30
mL/min |
| air
flow: |
400
mL/min |
| nitrogen
makeup flow: |
25
mL/min |
Figure 3.5.1 A chromatogram of 5.88 mg/mL cumene
in the extraction solution. (Key: (1)
CS2; (2) benzene, a contaminant in
CS2; (3) cumene; (4) p-cymene; and (5)
DMF) |
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 cumene. (y = 632x -
8.10E4) | 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
cumene. | 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
=
120.19 |
4. Recommendations for Further Study
Collection, reproducibility, and other detection limit
studies need to be performed to make this a fully validated
method.
References
1. OSHA Method 1002. http://www.osha-slc.gov/index.html
(accessed 11/15/03).
2. Documentation of the Threshold Limit Values for
Chemical Substances, 7th ed., American
Conference of Governmental Industrial Hygienists Inc.,
Cincinnati, OH, 2001, vol. 1, p Cumene 1-4.
3. Chem.
Eng. News, 2003, 81 (27), p 53.
4. Lewis, R., Hazardous Chemicals Desk Reference,
3rd ed., Van Nostrand Reinhold, New York, 1993, p
357.
5. OSHA Chemical Sampling Information. http://www.osha-slc.gov/index.html
(accessed 11/15/03).
6. Burright, D.; Chan, Y.; Eide,
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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