BENZENE
Method no.: |
12 |
|
Matrix: |
Air and bulk material samples |
|
Target concentration: |
1 ppm (3.2 mg/m3) |
air samples |
0.1% by volume |
bulk material samples | |
|
Procedure: |
Air samples are collected on activated charcoal,
desorbed with carbon disulfide, and analyzed by gas chromatography.
Bulk samples are analyzed by liquid chromatography. |
|
Detection limits: |
Air Samples - 0.04 ppm Bulk Samples - 0.01% by
volume |
|
Recommended air volume and sampling rate: |
10 L at 0.2 L/min |
|
Standard error of estimate at the target
concentration: (Section 4.7.) |
5.4% |
|
Coefficient of variation for bulk
samples: (Section 4.4.) |
1.7% |
|
Status: |
Evaluated method. This method has been subjected to
the established evaluation procedures of the Organic Methods
Evaluation Branch. |
|
Date: September
1979 August
1980, Revised |
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 of procedure
Air samples have been analyzed at the OSHA laboratory according
to the procedure validated by NIOSH. (Ref. 5.1.) The method involves
collection of benzene vapor on charcoal, desorption with carbon
disulfide (CS2), and analysis by gas
chromatography (GC). Since this method was validated over the range
of 13 to 51.8 ppm and the emergency temporary standard is 1 ppm, it
was necessary to evaluate the method at this lower level.
The OSHA lab has normally determined the benzene content of bulks
by GC analysis. Frequently interferences from aliphatics were a
major problem in the analysis, thus the detection limit was on the
order of 0.5% by volume. This problem of interferences is eliminated
by high performance liquid chromatographic (HPLC) analysis using a
UV detector as described in this method. The benzene is analyzed at
a wavelength (i.e., 254 nm) where aliphatics will not interfere
since most have a UV cut-off less than 200 nm. Thus, the detection
limit in bulk samples is lowered to 0.01% by volume.
1.1.2. Toxic effects (Quoted from Ref. 5.2.) (This section is for
information only and should not be taken as the basis of OSHA
Policy.)
"Acute benzene exposure causes central nervous system depression;
chronic exposure results in depression of the hematopoietic system
and is said to be associated with an increased incidence of
leukemia.
Human exposure to very high concentrations, approximately 20,000
ppm, was fatal in 5 to 10 min. (Ref. 5.4.) Brief exposure to
concentrations in excess of 3000 ppm is irritating to the eyes and
respiratory tract; continued exposure may cause euphoria, nausea, a
staggering gait, and coma. (Ref. 5.5.) Inhalation of lower
concentrations (250 to 500 ppm) produces vertigo, drowsiness,
headache, and nausea. (Ref. 5.6.)
The most significant toxic effect of benzene exposure is an
insidious and often irreversible injury to the bone marrow.
Long-term exposures to low concentrations have been observed to have
an initial stimulant effect on the bone marrow, followed by aplasia
and fatty degeneration. (Ref. 5.6.) Clinically, an initial increase
followed by a decrease in the erythrocytes, leucocytes, or platelets
is observed with progression to aplastic anemia, leukopenia,
pancytopenia, and thrombocytopenia. (Ref. 5.6.) Typical symptoms may
be light-headedness, headache, nausea, loss of appetite, and
abdominal discomfort; with more severe intoxication, there may be
weakness, blurring of vision, and dyspnea on exertion. (Ref. 5.7.)
The mucous membranes and skin may appear pale; a hemorrhagic
tendency may result in petechiae, easy bruising, epistaxis, bleeding
from the gums, or menorrhagia. (Ref. 5.7.)
Clinical and epidemiologic data suggest a leukemogenic action of
benzene in humans, the leukemia tending to be acute and myeloblastic
in type, sometimes following aplastic changes in the bone marrow;
benzene may also induce chronic types of leukemia. (Ref. 5.8.) It is
important to emphasize, however, that human exposure to benzene
often involves concomitant exposure to other solvents and that
animal experiments have not supported the view that benzene is a
leukemogen. (Ref. 5.7.)
One epidemiologic study has indicated a fivefold excess of all
leukemias and a tenfold excess of myelomonocytic leukemia among
benzene-exposed workers as compared with the total U.S. white male
population. (Ref. 5.9.) Among shoemakers chronically exposed to
benzene, the annual incidence of leukemia was 13.5/100,000 while the
incidence in the general population was 6/100,000. (Ref. 5.10.) Four
cases of acute leukemia were reported in shoemakers exposed to
benzene concentrations of up to 210 ppm for 6 to 14 years; two of
the four had aplastic anemia prior to leukemia; three of the four
cases of leukemia were of the acute myeloblastic type; the fourth
patient developed thrombocythemia in the second year after an
episode of aplastic anemia, and acute monocytic leukemia developed
later. (Ref. 5.11.) In other studies, latency periods of up to 15
years following cessation of benzene exposure have been observed in
the development of acute leukemia. (Ref. 5.6.)
Among workers exposed to benzene, excessive chromosome
aberrations (stable and unstable) in the nuclei of lymphocytes have
been reported. (Ref. 5.12.)
Tests for phenol levels in urine have been used as an index of
benzene exposure; urinary phenol concentrations of 200 mg/L are
indicative of exposure to approximately 25 ppm of benzene in air.
(Ref. 5.13.)
Direct contact with the liquid may cause erythema and
vesiculation; prolonged or repeated contact has been associated with
the development of a dry, scaly dermatitis or with secondary
infections. (Ref. 5.6.)
The TLV has been chosen, not as a "safe" or "no effect" level,
but on the basis that this is the lowest level that generally can be
achieved at this time. (Ref. 5.15.) OSHA issued an emergency
temporary standard in 1977 limiting employee exposure to benzene to
1 ppm; the standard did not apply to retail automotive service
stations or to operations which use liquid mixtures containing 1 per
cent or less of benzene. (Ref. 5.6.)"
1.1.3. Operations where exposure occurs (Ref. 5.14.)
The first major industrial use of benzene was as a solvent in the
rubber industry just preceding World War I. During World War I,
benzene production was stimulated greatly by the demand for toluene
in the manufacture of explosives. The large quantities of benzene
which were produced resulted in its more widespread use as a
starting point for the manufacture of various organic compounds.
This situation led to greatly increased uses of benzene as a solvent
in the artificial leather, rubber goods, and
roto-gravure printing industries, and as a starting
material in organic syntheses.
Industries and processes using benzene include coke and gas,
chemical, printing and lithography, paint, rubber, dry cleaning,
adhesives, petroleum, and coatings. Benzene is also used extensively
in chemical laboratories as a solvent and reactant in numerous
chemical applications.
During 1967, nearly 800 million gallons of benzene were produced
in the U.S. and by 1969, this figure increased to 1,185 million
gallons with approximately 16% derived from coal. About 87% is used
chiefly as an intermediate in producing other chemicals such as
phenol, cyclohexane, and styrene. The remaining 13% is used
primarily in the manufacture of detergents and pesticides with small
amounts used in solvents and paint removal formulations. Benzene is
also found in gasoline. Gasolines in England were reported to be as
high as 6% in benzene content and an ad hoc report on European
gasolines showed that most of the gasolines tested during 1970 to
1972 were in the 5% range with some up to 16%. Benzene analysis
reported in 1972 of 37 unleaded and low-lead gasolines
from 15 companies in the U.S. showed a range from 0.3-2.0% benzene
content by volume with an average of 0.8%.
Benzene may also be a component in commercial grades of toluene,
xylene, and multi-component solvent mixtures whose
composition varies with intended usage. It is a significant
component, (i.e. 3% or more) in numerous hydrocarbon mixtures such
as the aromatic petroleum naphthas whose boiling ranges encompass
that of benzene.
Although benzene is generally used in enclosed systems wherever
possible, exposures can occur from liquid transfer operations,
equipment leakage, carry-over losses, and maintenance operations.
Exposures also occur from its use as a solvent component in small
plant open systems.
1.1.4. Size of work population that face exposure
NIOSH estimates that 2 million persons in the work force have
potential exposure to benzene. (Ref. 5.14.)
1.1.5. Physical properties (Ref. 5.2., 5.3., and 5.16.)
molecular weight: |
78.11 |
boiling point: |
80.1°C |
vapor pressure: |
75.1 mm Hg at 20°C |
color: |
clear, colorless |
odor: |
aromatic |
flash point: |
-11.1°C (closed cup) |
specific gravity: |
0.8794 (20/4°C) |
explosive limits: |
lower 1.4% (by volume in air) upper
8.0% |
vapor density: |
2.70 (relative to air) |
common names: |
Benzol; cyclohexatriene; phene; phenyl hydride;
pyrobenzol. Note: Benzin, petroleum benzin and benzine are not
benzene. However, they may contain varying amounts of
benzene. |
CAS no.: |
000071432 |
structural formula: |
![](org12str.gif) |
1.2. Detection limit, precision, sensitivity, and working range
1.2.1. The detection limit for the analytical procedure for air
samples is 1.28 ng with a coefficient of variation of 0.023 at this
level. The detection limit was determined using 1.0-µL injections.
(Section 4.1.)
The detection limit for the analytical procedure for bulk samples
is 0.88 µg with a coefficient of variation of 0.019 at this level.
The detection limit was determined using 10-µL injections. (Section
4.2.)
1.2.2. The pooled coefficient of variation of the analytical
procedure for air samples over the range of 16.04 to 64.16 µg per
sample is 0.008. This represents an air concentration range of 0.5
to 2.0 ppm based on the recommended air sample of 10 L. (Section
4.3.)
The pooled coefficient of variation of the analytical procedure
for bulk samples over the range of 0.01% to 2.0% by volume is 0.017.
(Section 4.4.)
1.2.3. The sensitivity of the analytical procedure for air
samples over a concentration range of 0.5 to 2 ppm based on the
recommended air volume is 258 area units per µg/mL. The sensitivity
is determined by the slope of the calibration curve. (Section 4.5.)
The sensitivity of the analytical procedure for bulk samples over
a concentration range of 0.01 to 2.0% benzene by volume is 4.74 ×
106 area counts per % benzene by volume.
This is determined by the slope of the calibration curve. (Section
4.6.)
The sensitivity will vary somewhat with the particular
instrumentation used in the analysis.
1.2.4. The lower limit of the estimated working range for air
samples, assuming adequate chromatographic separation and desorption
efficiency is 0.04 ppm. The upper limit of the working range is
dependent on the capacity of the activated charcoal.
The lower limit of the estimated working range for bulk samples,
assuming adequate chromatographic separation is 0.01% benzene by
volume.
1.3. Accuracy
1.3.1. The overall procedure must provide results that are ±25%
or better at the 95% confidence interval.
1.3.2. The recovery of analyte from the collection medium
(activated charcoal) must be 75% or greater.
1.3.3. The overall procedure has met the above validation
criteria. (Section 4.7.)
1.4. Advantages
1.4.1. Air samples
1.4.1.1. The sampling procedure is convenient.
1.4.1.2. The analytical procedure is quick, sensitive and
reproducible.
1.4.1.3. Reanalysis of samples is possible.
1.4.1.4. Samples are stable, even at room temperature.
1.4.1.5. It may be possible to analyze other compounds
simultaneously.
1.4.1.6. Interferences can be circumvented by proper selection
of GC parameters.
1.4.2. Bulk samples
1.4.2.1. The analytical procedure is quick, sensitive, and
reproducible.
1.4.2.2. Reanalysis of samples is possible.
1.4.2.3. Interferences can be circumvented by proper selection
of LC parameters.
1.5. Disadvantages
1.5.1. Air samples
1.5.1.1. The amount of sample that can be taken is limited by
the total milligrams the charcoal will adsorb before overloading.
1.5.1.2. The precision is limited by the reproducibility of the
pressure drop across the tubes. The pumps are usually calibrated
for one tube only.
1.5.2. Bulk samples
Samples must be free of any particulates, etc., that may clog the
capillary tubing or column in the liquid chromatograph. This may
require distilling the samples or clarifying them by filtration.
2. Sampling Procedure
2.1. Apparatus
2.1.1. A calibrated personal sampling pump whose flow can be
determined within ±5% at the recommended flow.
2.1.2. Activated charcoal tubes: Glass tube, with both ends heat
sealed, 70 mm × 6-mm o.d. × 4-mm i.d., containing
100-mg front and 50-mg backup sections of 20/40 mesh coconut-base
charcoal. SKC No. 226-01 tubes or equivalent.
2.2. Reagents
None required.
2.3. Sampling technique
2.3.1. Immediately before sampling, break open the ends of the
charcoal tube. All tubes should be from the same lot.
2.3.2. Connect the charcoal tube to the sampling pump with
flexible tubing. The short section of the charcoal tube is used as a
backup and should be positioned nearer the sampling pump.
2.3.3. The tube should be placed in a vertical position during
sampling to minimize channeling.
2.3.4. Air being sampled should not pass through any hose or
tubing before entering the charcoal tube.
2.3.5. Seal the charcoal tube with plastic caps immediately after
sampling. Wrap each tube lengthwise with official OSHA seals (Form
21).
2.3.6. With each batch of samples, submit at least one blank tube
from the same lot used for samples. This tube should be subjected to
exactly the same handling as the samples (break, seal, transport)
except that no air is drawn through it.
2.3.7. Transport the samples (and corresponding paperwork) to the
lab for analysis.
2.3.8. If bulk samples are submitted for analysis, they should be
transported in glass containers with Teflon-lined caps. These
samples must not be put in the same container used for the charcoal
tubes.
2.4. Breakthrough
2.4.1. The average breakthrough (5% breakthrough) volume from a
2.0-ppm benzene test atmosphere at about 80% relative humidity and
22°C was 86 L when sampled at 0.21 L/min.
2.4.2. The breakthrough volume could be significantly lowered if
other contaminants are present in the sample stream. This would be
the case for petroleum distillate samples, such as naphtha,
gasoline, etc.
2.5. Desorption efficiency
2.5.1. The desorption efficiency, from liquid injections onto
the front section of the tubes, averaged 99.4% from 0.5 to 2.0 ppm
for a 10-L air sample. (Section 4.8.)
2.5.2. The desorption efficiency of a particular compound may
vary from one laboratory to another and also from one lot of
charcoal to another. Thus, it is necessary to determine the
desorption efficiency for a particular lot of charcoal.
2.6. Recommended air volume and sampling rate
2.6.1. The recommended air volume is 10 L.
2.6.2. The recommended sampling rate is 0.2 L/min.
2.7. Interferences
2.7.1. It is unknown if any other compound would severely
interfere with the collection of benzene on charcoal. In general,
the presence of other solvents will decrease the breakthrough volume
for a particular solvent.
2.7.2. Suspected interferences should be listed on the sample
data sheets.
2.8. Safety precautions
2.8.1. Attach the sampling equipment on the employee so that it
does not interfere with work performance.
2.8.2. Wear safety glasses when breaking the ends of the sampling
tubes.
2.8.3. Place the sampling tube in a holder so the sharp end is
not exposed while sampling.
3. Analytical procedure
3.1. Apparatus
3.1.1. General
3.1.1.1. An electronic integrator or some other suitable
method of measuring peak areas.
3.1.1.2. Microliter syringes, 10-µL or other convenient sizes
for preparing standards, 1-µL for GC sample injections and 10-µL
for LC injections.
3.1.1.3. Volumetric flasks, 5-mL and other convenient sizes for
preparing standards and making dilutions.
3.1.2. Air samples
3.1.2.1. Gas chromatograph equipped with a flame ionization
detector.
3.1.2.2. A GC column capable of separating
CS2, benzene, an internal standard, and
any interferences. The column used for validation studies was a 10
ft × 1/8 in. stainless steel, 20% SP2100, 0.1% CW1500 on 80/100
Supelcoport. Since benzene is frequently found in petroleum
distillate type compounds, it is advisable to use a more polar
column such as TCEP, SP1000, Penta, etc., that will allow the
aliphatic compounds to elute quickly, usually before benzene. On
some samples, it may be impossible to achieve proper separations
using conventional packed columns. In these cases it is advisable
to use a capillary column to achieve better separations.
3.1.2.3. Two-milliliter vials with Teflon-lined caps.
3.1.2.4. Pipets for dispensing CS2.
The Glenco 1-mL dispenser is adequate and convenient.
3.1.3. Bulk samples
3.1.3.1. Liquid chromatograph equipped with a UV detector.
3.1.3.2. An LC column that will separate benzene from other
components in the bulk sample being analyzed. The column used for
validation studies was a Waters FBondapack
C18, 30 cm × 3.9 mm.
3.1.3.3. A clarification kit to remove any particulates in the
bulk if necessary.
3.1.3.4. A micro-distillation apparatus to distill any samples
if necessary.
3.2. Reagents
3.2.1. General
Benzene, reagent grade.
3.2.2. Air samples
3.2.2.1. Chromatographic grade carbon disulfide
(CS2) which has been treated for the
removal of trace amounts of benzene. (Sections 4.9. and 4.10.)
3.2.2.2. An internal standard, such as p-cymene, reagent grade.
3.2.2.3. Desorbing reagent, 0.05 µL internal standard/mL
CS2.
3.2.2.4. Purified GC grade helium, hydrogen, and air.
3.2.3. Bulk samples
LC grade water, methyl alcohol, and isopropyl alcohol.
3.3. Standard preparation
3.3.1. Air samples
The benzene is diluted with desorbing reagent to prepare
standards in the working range. A solution of 36.5 nL of benzene per
1 mL of desorbing reagent is equivalent to 1.00 ppm benzene in air
for a 10-L air sample desorbed with 1 mL of desorbing reagent.
3.3.2. Bulk samples
Benzene is diluted with isopropyl alcohol to prepare standards in
the working range.
3.4. Sample preparation
3.4.1. Air samples
3.4.1.1. The front and back sections of each sample are
transferred to separate 2-mL vials.
3.4.1.2. Each section is desorbed with 1.0 mL of desorbing
reagent.
3.4.1.3. The vials are sealed immediately and allowed to desorb
for 30 min with intermittent shaking.
3.4.2. Bulk samples
3.4.2.1. If necessary, the samples are distilled or clarified.
3.4.2.2. Samples are analyzed undiluted. If the benzene
concentration is out of the working range, suitable dilutions are
made with isopropyl alcohol.
3.5. Analysis
3.5.1. Air samples
3.5.1.1. Air samples were analyzed using the following GC
conditions:
flow rates (mL/min) |
|
temperatures (°C) |
helium |
30 |
|
column |
100 |
hydrogen |
30 |
|
injector |
150 |
air |
240 |
|
detector |
250 |
|
injection size - 1 µL |
|
elution time - 2.5 min |
|
chromatogram (Section 4.11.) |
|
3.5.1.2. Peak areas are measured by an integrator.
3.5.1.3. An internal standard procedure is used. The integrator
is calibrated to report results in ppm for a 10-L air sample after
correction for desorption efficiency.
3.5.2. Bulk samples
3.5.2.1. Bulk samples were analyzed using the following LC
conditions:
solvent - methyl alcohol/water, 50/50 analytical wavelength
- 254 nm injection size - 10 µL (Since a high concentration of
non-polar aliphatic compound will distort the benzene peak on high
injection volumes, the volume of 10 µL is recommended as a maximum
size. elution time - 8 min chromatograms - (Section 4.11.)
3.5.2.2. Peak areas are measured by an integrator or other
suitable means.
3.5.2.3. The integrator is calibrated to report results in %
benzene by volume. If the samples have to be diluted with
isopropyl alcohol, an appropriate factor must be applied.
3.5.2.4. If a series of bulk samples must be analyzed, in order
to save time it is advantageous to switch to pure methyl alcohol
as a solvent after the benzene has eluted to cause the later peaks
to elute faster, as in coal tar naphtha.
3.6. Interferences
3.6.1. Any compound having the same general retention time of
benzene (or the internal standard in air sample analysis) is an
interference. Possible interferences are listed on the sample data
sheets. Parameters should be chosen to circumvent any interferences.
For air samples, if a bulk is submitted with the sample set, analyze
the bulk first so a suitable column and conditions can be chosen to
select a proper internal standard before the air samples are
desorbed. If interferences are a problem at 254 nm for bulk samples,
an alternate wavelength may be chosen to possibly circumvent the
problem.
3.6.2. Retention time data on a single column is not considered
proof of chemical identity. Samples over the PEL should be confirmed
by GC/MS or other suitable means, such as GC/IR, absorbance
ratioing, etc.
3.7. Calculations
3.7.1. Air samples
Since the integrator is programmed to report results in ppm (at
25°C and 760 mm Hg) for a 10-L air sample (corrected for desorption
efficiency), the following formula is used:
ppm benzene = |
A
(0.1) (B) |
where |
A = ppm on report B = air
volume (L) |
3.7.2. Bulk samples
Since the integrator is programmed to report results in % benzene
by volume in an undiluted sample, the following formula is used:
% benzene by volume = (A)(B)
where |
A |
= |
% by volume on report |
|
B |
= |
Dilution Factor (B = 1 for undiluted
sample) |
3.8. Safety precautions
3.8.1. All work done with the solvents (preparation of
standards, desorption of samples, etc.) should be done in a hood.
3.8.2. Avoid skin contact with all of the solvents.
3.8.3. Wear safety glasses at all times.
4. Backup Data
4.1. Detection limit - air samples
The detection limit data were obtained by making 1-µL injections of
a 1.283 µg/mL standard. This standard would be equivalent to 0.040 ppm
for a 10-L air sample.
Table 4.1. Detection Limit - Air Samples
|
injection |
area counts |
injection |
area counts |
|
1 2 3 |
655.4 617.5 662.0 |
4 5 6 |
641.1 636.4 629.2 |
|
= 640.2 |
SD = 14.9 |
CV =
0.023 | |
|
4.2. Detection limit - bulk samples
The detection limit data were obtained by making 10-µL injections
of a 0.01% by volume standard.
Table 4.2. Detection Limit - Bulk Samples
|
injection |
area counts |
injection |
area counts |
|
1 2 3 |
45386 44241 43822 |
4 5 6 |
44062 44006 42724 |
|
= 44040.1 |
SD = 852.5 |
CV =
0.019 | |
|
4.3. Pooled coefficient of variation - air samples
The pooled coefficient of variation for the analytical procedure
was determined by making 1-µL replicate injections of
analytical standards. The standards were 16.04, 32.08, and 64.16
µg/mL, which are equivalent to 0.5, 1.0, and 2.0 ppm for a 10-L air
sample respectively.
Table 4.3. Pooled Coefficient of Variation - Air
Samples
|
ppm |
0.5 |
1.0 |
2.0 |
|
area counts
![mean](../mean.gif) SD CV
= 0.008 |
3996.5 4059.4 4052.0 4027.2 4046.8 4137.9
4053.3 47.2 0.0116
|
8130.2 8235.6 8307.9 8263.2 8291.1 8288.8
8254.0 62.5 0.0076
|
16481 16493 16535 16609 16552 16618
16548.3 57.1 0.0034
|
|
4.4. Pooled coefficient of variation - bulk samples
The pooled coefficient of variation for the analytical procedure
was determined by making 10-µL replicate injections of
analytical standards. The standards were 0.01, 0.02, 0.04, 0.10, 1.0,
and 2.0% benzene by volume.
Table 4.4. Pooled Coefficient of Variation - Bulk
Samples
|
|
0.01% |
0.02% |
0.04% |
0.10% |
1.0% |
2.0% |
|
area counts
![mean](../mean.gif) SD CV
= 0.017 |
45386 44241 43822 44062 44006 42724
44040.1 852.5 0.0194 |
84737 84300 83835 84381 83012 81957
83703.6 1042.2 0.0125 |
166097 170832 164160 164445 168398 173002
167822 3589.8 0.0213 |
448497 441299 443719 444842 442564 443975
444149 2459.1 0.0055 |
4395380 4590800 4593200 4642350 4646430 4646260
4585767 96839.3 0.0211 |
9339150 9484900 957580 9677060 9766240 -----
9564986 166233 0.0174 |
|
4.5. Sensitivity data - air samples
The same analytical standards as in Section 4.3. were used to
construct a calibration curve as shown in Figure 4.5.
4.6. Sensitivity data - bulk samples
The same analytical standards as in Section 4.4. were used to
construct a calibration curve as shown in Figure 4.6.
4.7. Storage data - air samples
Samples were generated at 1.03 ppm benzene at 80% relative
humidity, 22°C, and 643 mm Hg. All samples were taken for 50 min at
0.2 L/min. Six samples were analyzed immediately and fifteen samples
each were stored at refrigerated (-25°C) and ambient temperatures
(about 23°C). These samples were analyzed over a period of fifteen
days. The results are tabulated below and shown graphically in Figures
4.7.1. through 4.7.3.
Table 4.7. Storage Tests
|
storage time |
% recovery |
(days) |
(refrigerated) |
|
(ambient) |
|
0 0 2 5 9 13 15 |
97.4 97.1 95.8 93.9 93.6 94.3 96.8 |
98.7 100.6 96.4 93.7 95.5 95.3 95.8 |
98.9 100.9 95.4 92.4 94.6 93.7 94.2 |
|
97.4 97.1 95.4 92.4 95.2 91.0 92.9 |
98.7 100.6 96.6 94.3 95.6 95.0 96.3 |
98.9 100.9 96.9 94.1 96.6 94.6 95.9 |
|
4.8. Desorption data
Samples were prepared by liquid injection onto the front section of
charcoal tubes. Samples were prepared that would be equivalent to 0.5,
1.0, and 2.0 ppm for a 10-L air sample. Six samples were prepared at
each concentration.
Table 4.8. Desorption Efficiency
|
ppm |
0.5 |
1.0 |
2.0 |
|
desorption efficiency, %
![mean](../mean.gif) SD CV
= 99.4 |
99.4 99.5 99.2 99.4 99.2 99.8
99.4 0.22 0.0022 |
98.8 98.7 98.6 99.1 99.0 99.1
98.9 0.21 0.0021 |
99.5 99.7 99.8 100.0 99.7 99.9
99.8 0.18 0.0018 |
|
4.9. Benzene contamination of carbon disulfide and various bulk
materials
Various CS2 samples were analyzed by GC.
The results are tabulated below. The treated sample was treated as
explained in Section 4.10. As can be seen, it is important that the
CS2 be treated before using it for a
desorption solvent.
Table 4.9.1. Benzene Contaminant Found in
CS2
|
sample |
µg benzene/mL |
ppm equivalent (for 10-L air
sample) |
|
ALDRICH Lot 83017 BAKER Lot
720364 BAKER Lot 822351 Malinkrodt Lot WEMP Malinkrodt
Lot WDSJ Malinkrodt Lot WHGA Treated
CS2 |
4.20 1.01 1.01 1.74 5.65 2.90 ND |
0.13 0.03 0.03 0.05 0.18 0.09 -- |
|
Various bulk materials were analyzed by LC to determine their
benzene content. The results are shown in Table 4.9.2.
Table 4.9.2. Benzene Found In Various Substances
|
sample |
% benzene (v/v) |
|
Lantern Fuel Carburetor
Cleaner Regular Gasoline Premium Gasoline Unleaded
Gasoline Hexane (nanograde) Charcoal Lighter Paint
Thinner Patco Lamp Fluid Stoddard Solvent VM & P
Naphtha Naphtha Ligroine Petroleum
Ether Naphtha* VM & P Naphtha* Paint
Thinner* Cleaner* |
0.14 0.10 0.33 0.39 0.78 0.11 0.01 0.01 ND ND 0.01 ND 0.01 ND ND ND 0.01 ND |
|
* OSHA field
sample |
4.10. Removal of benzene from the CS2
desorption solvent.
The trace amounts of benzene found in CS2
must be removed before it can be used as the desorption solvent. The
pretreatment of CS2 was adapted from a paper
by Levadie and MacAskill. (Ref. 5.17.) To a round bottom flask
containing approximately 500 mL of CS2, add
10 mL of concentrated sulfuric acid and 5 drops of concentrated nitric
acid. Heat this under reflux for 2 to 3 h to totally convert the
benzene to nitrobenzene. The CS2 layer is
decanted off, dried with anhydrous sodium sulfate, and then distilled.
The CS2 is now free of benzene.
Trace amounts of benzene can also be removed from carbon disulfide
by passing it through a bed of 13× molecular sieve. This more
convenient technique was not known during the evaluation of this
method. Lab experiments indicate that 50 g of Molecular Sieve 13×
contained in a column (about 1-in. i.d.) can purify about 1 L of
benzene before it requires regeneration. It can be regenerated by
heating for at least 4 h at 400°C in a tube furnace while purging with
nitrogen.
4.11. Chromatograms
A typical chromatogram of a GC analysis of a standard is shown in
Figure 4.11.1. The analytical conditions are given in Figure 4.5.
Typical chromatograms obtained from LC analysis of bulk samples are
shown in Figures 4.11.2. and 4.11.3. The chromatograms were obtained
using the same parameters as given in Figure 4.6., except that as soon
as the benzene was eluted, the mobile phase was programmed to 100%
methanol. This caused the heavier molecules to elute faster.
Figure 4.5. Calibration curve for benzene analyzed by gas
chromatography.
Figure 4.6. Calibration curve for benzene analyzed by liquid
chromatography.
Figure 4.7.1. Refrigerated storage
samples.
Figure 4.7.2. Ambient storage samples.
Figure 4.7.3. Refrigerated versus ambient
storage.
Figure 4.11.1. Benzene standard analyzed by gas
chromatography.
Figure 4.11.2. Lantern fuel analyzed by liquid
chromatography.
Figure 4.11.3. Regular gasoline analyzed by liquid
chromatography.
5. References
5.1. U.S. Department of Health, Education, and Welfare, Public
Health Service, Center for Disease Control, NIOSH, NIOSH Manual of
Analytical Methods, Second edition, Vol. 3, S-311.
5.2. Proctor, N.H.: Chemical Hazards of the Workplace, p. 118-120,
J.B. Lipincott Company, 1978.
5.3. The Merck Index, Eighth Edition, Paul G. Stecher, Editor,
1968, page 128.
5.4. Flury, F.: Moderne gewerbliche vergiftungen in
pharmakologischtoxikologische hinsicht. Arch. Exp. Pathol.
Pharmakol., 138:65, 1928.
5.5. Gerarde, H. W.: Toxicology and Biochemistry of Aromatic
Hydrocarbons. pp. 97-108. New York: Elsevier, 1960.
5.6. Department of Labor: Occupational exposure to benzene. Federal
Register 42:22516, 1977.
5.7. Committee on Toxicology of the National Research Council:
Health Effects of Benzene--A Review. U.S. Department of
Commerce, National Technical Information Service PB-254 388. pp. 1-23.
Washington, D.C.: National Academy of Sciences, 1976.
5.8. Vigliani, E.C.: Leukemia associated with benzene exposure.
Ann. N.Y. Acad., Sci., 271:143, 1976.
5.9. Infante, P.F., Rinksy, R.A., Wagoner, J.K., and Young, R.J.:
Leukemia among workers exposed to benzene. NIOSH, April 26, 1977.
5.10. Aksoy, M., Erdem, S., and Dincol, G.: Types of leukemia in
chronic benzene poisoning: a study in thirty-four patients. Acta
Hematol., 55:65,1976.
5.11. Aksoy, M., Dincol, K., Erdem, S., and Dincol, G.: Acute
leukemia due to chronic exposure to benzene. Am. J. Med.,
52:160, 1972.
5.12. Tough, I. M., and Brown, W. M.: Chromosome aberrations and
exposure to ambient benzene. Lancet, 1:684, 1965.
5.13. Wakley, J. E., Pagnotto, L.D., and Elkins, H.B.: The
measurement of phenol in urine as an index of benzene exposure. Am.
Ind. Hyg. Assoc. J., 22:362, 1961.
5.14. National Institute for Occupational Safety and Health, U.S.
Department of Health, Education and Welfare: Criteria for a
Recommended Standard. Occupational Exposure to Benzene, (NIOSH)
Washington, D.C.: U.S. Government Printing Office, 1974.
5.15. A.C.G.I.H.: Benzene. Documentation of the TLVs for Substances
in Workroom Air. ed. 3, pp. 355-356. Cincinnati, 1976.
5.16. Manufacturing Chemists Assoc., Chemical Safety Data Sheets
D-3, 1960, Third Edition.
5.17. Levadie, B. and MacAskill, S.M., "Analysis of Organic
Solvents Taken on Charcoal Tube Samplers by a Simplified Technique,"
Anal. Chem. Vol. 48, No. 1, Jan. 1976, pp 76-78.
|