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| Method no.: |
PV2130 |
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| Control no.: |
T-PV2130-01-0401-M |
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| Target Concentration: |
0.5 mg/m3 (AIHA Workplace
Environmental Exposure Level (WEEL)) |
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| Procedure: |
Samples are collected by drawing a known volume
of air through glass sampling tubes containing Chromosorb 106. Samples are extracted with a solution of 99:1
carbon disulfide: N,N-dimethylformamide and analyzed by gas
chromatography using a flame ionization detector (GC/FID). |
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| Sampling rate: |
240 min at 0.2 L/min (48 L) |
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| Reliable quantitation limit: |
18.5 µg/m3 |
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| 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. |
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| January 2004 |
Mary E. Eide |
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|
Methods Development Team
Industrial Hygiene Chemistry Division
OSHA Salt Lake Technical
Center
Sandy UT 84070-6406 |
1. General Discussion
1.1 Background
1.1.1 History
Air samples collected on Chromosorb 106 tubes were
received at OSHA Salt Lake Technical Center (OSHA SLTC) requesting analysis for
benzophenone. In a previous study, samples collected on OVS-7 tubes requesting
benzophenone analysis were received at OSHA SLTC, but the extraction study
showed a recovery of 81.7% when extracted with methyl alcohol. These samples
were analyzed by gas chromatography with a flame ionization detector (GC-FID).1
That instrumentation was used in this study. The XAD-7 of the OVS-7 tubes is a
polar medium, while the Chromosorb 106 is a nonpolar collection media. Carbon
disulfide was first tried as the extraction solvent for the Chromosorb 106.
While the extraction efficiency for dry tubes was 97.6%, the spiked tubes that
had humid air pulled them had a loss of benzophenone in the extracted solution
after the samples sat on the autosampler for more than two hours after shaking.
Next a solution of 99:1 carbon disulfide:N,N-dimethylformamide (DMF), was tried and found to give good extraction (98.4% recovery)
with no loss as the samples waited on the autosampler to be analyzed. The
retention efficiency was 98.6% and the storage stability recovery of 98.0% on
Day 14 of ambient storage.
1.1.2 Toxic effects (This section is for information
only and should not be taken as the basis of OSHA policy).2,3,4
Benzophenone is a naturally occurring compound used in flavorings and perfumes.
The FDA allows 0.5 ppm in non-alcoholic beverages, 1.70 ppm in candy, and
0.09-0.3% in perfumes, but recommends that the least amount possible for the
effect desired be used in formulations, due to its toxicity. At higher
concentrations, benzophenone is a contact irritant affecting eyes, skin, and
respiratory system. Benzophenone is moderately toxic by ingestion.
1.1.3 Workplace exposure5,6
Benzophenone is used as a fixative for heavy perfumes in soaps, detergents, and
room deodorizers. It is used as a flavoring agent, ultraviolet absorber in inks
and coatings, and as a polymerization inhibitor for styrene. It is used in the
manufacture of antihistamines, hypnotics, and insecticides.
1.1.4 Physical properties and other descriptive information7
|
synonyms: |
benzoylbenzene |
diphenylmethanone |
diphenyl Ketone |
a-oxodiphenyl methane |
phenyl ketone |
|
CAS number: |
119-61-9 |
molecular weight: |
182.22 |
|
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|
melting point: |
48.5 °C |
boiling point: |
305 °C |
|
|
appearance:
|
white solid |
molecular formula: |
C13H10O |
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|
odor: |
rose or geranium-like |
flash point: |
144°C (291 °F) (cc) |
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solubility: |
insoluble in water, soluble in
organics such as alcohol, ether, chloroform |
|
IMIS8: |
B505 |
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Structural Formula:
This method was evaluated according to the OSHA SLTC "Evaluation Guidelines
for Air Sampling Methods Utilizing Chromatographic Analysis".9
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 12.6 µg of benzophenone. This is the amount spiked on a
sampler that would produce a peak at least 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 and slope) for the calculation of the DLOP. The
slope was 1528 and the SEE was 136. 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 0.27 µg (5.63 µg/m3)
and 0.89 µg (18.5 µg/m3) respectively. The recovery at the RQL was
95.7%.
Table 1.2
Detection Limit of the Overall Procedure for Benzophenone
|
|
mass per sample (µg) |
area counts (µV-s) |
|
|
0.00 |
0 |
|
1.26 |
2148 |
|
2.52 |
3654 |
|
3.78 |
5789 |
|
5.04 |
7664 |
|
6.30 |
6910 |
|
7.56 |
11506 |
|
8.82 |
13680 |
|
10.1 |
15348 |
|
11.3 |
17168 |
|
12.6 |
19379 |
|
 |
 |
|
Figure 1.2.1
Plot of data to determine the DLOP/RQL for benozophenone. (y=1528x+5.33) |
Figure 1.2.2
Chromatogram of the RQL level of benzophenone. (Key: (1) benzophenone) |
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 x 4-mm i.d. x 7-mm o.d. glass sampling tubes
packed with two sections (100/50 mg) of Chromosorb 106. The sections are held in
place and separated with a glass wool plug and two urethane foam plugs. For this
evaluation, commercially prepared sampling tubes were purchased from SKC, Inc.
(catalog no. 226-110 lot 2573).
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 ends. 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
sampler 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 front sections of Chromosorb 106
tubes with
benzophenone at 0.1 to 2 times the target concentration. These samples were
stored overnight at ambient temperature and then extracted with 1 mL of
extracting solvent for 30 minutes on a shaker, and analyzed by GC-FID. The mean
extraction efficiency over the studied range was 98.4%. The wet extraction
efficiency was determined at 1 times the target concentration by liquid spiking
the analyte onto Chromsorb 106 tubes which had 48-L humid air (absolute humidity
of 15.9 mg/L of water, about 80% relative humidity at 22.2 °C) drawn through
them immediately before spiking. The mean recovery for the wet samples was
98.5%.
Table 2.4
Extraction Efficiency (%) of Benzophenone
|
level
|
sample number
|
x target
concn |
µg per
Sample |
1 |
2 |
3 |
4 |
5 |
6 |
mean |
|
|
0.1 |
2.42 |
99.4 |
99.1 |
97.0 |
98.5 |
97.9 |
99.1 |
98.5 |
|
0.5 |
12.1 |
99.8 |
99.5 |
97.7 |
98.7 |
97.6 |
98.4 |
98.6 |
|
1.0 |
24.2 |
98.6 |
97.6 |
98.5 |
97.9 |
98.8 |
98.5 |
98.3 |
|
1.5 |
36.3 |
98.2 |
98.0 |
97.5 |
99.0 |
97.2 |
98.8 |
98.1 |
|
2.0 |
48.4 |
98.9 |
98.5 |
98.7 |
98.5 |
98.9 |
98.6 |
98.7 |
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|
1.0 (wet) |
24.2 |
97.9 |
98.9 |
98.1 |
99.0 |
97.9 |
98.9 |
98.5 |
|
2.5 Retention efficiency
Six Chromosorb 106 tubes were spiked with 48.4 µg (1.01
mg/m3) of benzophenone and allowed to equilibrate for 6 h. The tubes
had 48-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 98.6%. There was no analyte found
on the backup section of any of the tubes.
Table 2.5
Extraction Efficiency (%) of Benzophenone
sample number
|
| section |
1 |
2 |
3 |
4 |
5 |
6 |
mean |
|
| front |
98.7 |
97.6 |
99.0 |
99.2 |
98.8 |
98.4 |
98.6 |
| rear |
0.0 |
0.0 |
0.0 |
0.0 |
0.0 |
0.0 |
0.0 |
| total |
98.7 |
97.6 |
99.0 |
99.2 |
98.8 |
98.4 |
98.6 |
|
2.6 Sample storage
Fifteen Chromosorb 106 tubes were each spiked with 24.2 µg (0.50 mg/m3)
of benzophenone. They were allowed to equilibrate for 6 h, then 48 L of air,
with an absolute humidity of 15.7 milligrams of water per liter of air (about
80% relative humidity at 22.2 ° C), was drawn through them. Three samples were
analyzed immediately. Six of the remaining samples were sealed and stored at
room temperature. The other six samples were sealed and stored in the
refrigerator. Three samples from each storage condition were removed after 7
days and analyzed. The remaining three samples of each storage condition were
analyzed after 14 days of storage. The amounts recovered indicate good storage
stability for the time period studied.
Table 2.6
Storage Test for Benzophenone
|
time
(days) |
ambient storage
recovery (%) |
refrigerated storage
recovery (%) |
|
| 0 |
97.9 98.1 99.0 |
|
| 7 |
98.4 98.1 98.8 |
99.2 98.0 98.9 |
| 14 |
97.5 98.3 98.2 |
97.7 98.6 98.3 |
|
2.7 Recommended air volume and sampling rate
Based on the data collected in
this evaluation, 48-L air samples should be collected at a sampling rate of 0.2
L/min for 240 minutes.
2.8 Inferences (sampling)
There is no known compound
which will severely interfere with the collection of benzophenone. 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. For this evaluation, an Agilent 6890 Gas
Chromatograph equipped with a 7683 Injector was used.
3.1.2
A GC column capable of
separating benzophenone from the extraction solvent, internal standard and any
potential interferences. A 60-m x 0.32-mm i.d. capillary DB-1 with a 1.0-µm df (J&W Scientific, Folsom, CA) was used in the 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
extracting 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 syringe for preparing
standards.
3.1.8
Shaker or rotator to agitate samples during
extraction. An Eberbach shaker was used
in this evaluation.
3.2
Reagents
3.2.1
Benzophenone, Reagent grade. Aldrich 99% (lot 09710TA) was used in this evaluation.
3.2.2
Carbon disulfide, Reagent grade. Omni-Solv® 99.99% (lot 43279343) was used for
this evaluation.
3.2.3 p-Cymene, Reagent grade.
Aldrich 99% (lot 11703TR) was used in this evaluation.
3.2.4 N,N-Dimethylformamide,
anhydrous. Aldrich
99.8% (lot 04643LA) was used in this evaluation.
3.2.5
The extraction solvent was a solution of 99:1 carbon disulfide:DMF
with 0.25 µL/mL p-cymene internal standard.
3.2.6
GC grade nitrogen, air, and hydrogen.
3.3 Standard preparation
Prepare working analytical
standards by weighing microgram amounts of benzophenone into
volumetric flasks and diluting up to the mark with the extraction solvent. Weigh out at least two stock standards. Make
dilutions of these stock standards with the extraction solvent to bracket the
samples. If sample concentrations are higher than the
concentration range of prepared standards, either analyze higher standards, or
dilute the sample. The higher standards
should be at least as high in concentration as the highest sample. Diluted samples should be prepared with
extracting solvent to obtain a concentration within the existing standard
range. The concentration range of
standards used in this study was from 1 to 48.4 µg/mL.
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 chromatograph conditions.
|
GC conditions
|
|
| temperatures: |
|
| column: |
50°C,
hold 1 min, ramp at 10°C/min to 170°C,
hold 21 min |
| injector: |
250°C |
| detector: |
250°C |
| run time: |
34 min |
| column gas flow: |
3.2 mL/min (hydrogen) |
| septum purge: |
1.9 mL/min (hydrogen) |
| injection size: |
1.0 µL (10:1 split) |
| column: |
60-m x 0.32-mm i.d. capillary DB-1(1.0-µm df) |
retention times:
|
4.0 min (carbon disulfide); 7.0 min (DMF); 11.8
min (p-cymene); 31.0 min (benzophenone) |
FID conditions
|
|
| hydrogen flow: |
30 mL/min |
| air flow: |
400 mL/min |
| makeup flow: |
25 mL/min |
| (nitrogen) |
|
 |
|
Figure 3.5.1
A chromatogram of 48.8 µg/mL benzophenone in 99:1 carbon disulfide: DMF with
0.25 µg/mL p-cymene internal standard. Key: (1)
carbon disulfide; (2) benzene contaminant in the carbon disulfide; (3) DMF;
(4) p-cymene; (5) contaminant in solvent; (6)
benzophenone |
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 ISTD-corrected response of standard injections versus
micrograms of analyte per sample. Bracket the samples with freshly prepared analytical standards over a
range of concentrations.
|
|
Figure 3.5.3
Calibration curve of benzophenone (y=894x + 113) |
3.6
Interferences (analytical)
Any compound that produces
a GC response and has a similar retention time as the analyte is a potential
interference. If any potential interference
were reported, they should be considered before samples are extracted. Generally, chromatographic conditions can be
altered to separate interference from the analyte.
When necessary, the identity or purity of an
analyte peak may be confirmed by mass spectrometry or by another analytical
procedure. The mass spectrum in Figure 3.6
was from the NIST spectral library.
|
|
Figure 3.6
The mass spectrum of benzopehone |
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 formula.
| 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 |
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. Eide, M., Collection and Analysis of Benzophene from OVS-7 Tubes, 1993, unpublished.
2. Lewis, R., Ed., Sax's Dangerous Properties of Industrial Materials, 10th ed.,
John Wiley & Sons, New York, 2000, p 390.
3. National Toxicology Program, ntp-server.niehs.nih.gov, (accessed 12/18/03).
4. Material Safety Data Sheet: Benzophenone, Aldrich Chemical Co., Milwaukee,
WI, Dec. 2003.
5. Lewis, R., ED., Hawley's Condensed Chemical Dictionary, 14th ed., John Wiley
& Sons, New York, 2001, p 126.
6. O'Neil, M., The Merck Index, 13th ed., Merck & Co., Whitehouse Station, NJ
2001, p 188.
7. Lewis, R., ED., Hawley's Condensed Chemical Dictionary, 14th ed., John Wiley
& Sons, New York, 2001, p 126.
8. OSHA Chemical sampling information. www.osha.gov (accessed 12/17/03).
9. 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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