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 (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 (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.
|