DIVINYLBENZENE ETHYLVINYLBENZENE STYRENE
Method no.: |
89 |
Matrix: |
Air |
Target concentration: |
50 ppm (215 mg/m3) for styrene
7.6 ppm (40 mg/m3) for ethylvinylbenzene
10 ppm (50 mg/m3) for divinylbenzene |
Procedure: |
Samples are collected by drawing air through
glass sampling tubes containing coconut shell
charcoal coated with 4-tert-butylcatechol.
Samples are desorbed with toluene and analyzed
by GC using a flame ionization detector. |
Recommended air volume and sampling rate: |
12 L at 0.05 L/min |
Reliable quantitation limit: |
100 ppb (426 µg/m3) for styrene
71 ppb (384 µg/m3) for ethylvinylbenzene
94 ppb (500 µg/m3) for divinylbenzene |
Standard error of estimate
at the target concentration: |
7.4% for styrene
|
(Section 4.7.) |
5.2% for ethylvinylbenzene
5.2% for divinylbenzene |
Status of method: |
Evaluated method. This method has been subjected to
the established evaluation procedures of the Organic Methods
Evaluation Branch. |
Date: July 1991 |
Chemist: Donald Burright |
Organic Methods Evaluation Branch
OSHA Salt Lake Technical Center
Salt Lake City, UT 84165-0200
1. General Discussion
1.1. Background
1.1.1. History
The evaluation presented here was initiated as an effort
to overcome the low and non-linear desorption efficiency
of styrene, from coconut shell charcoal, found in OSHA
Method 9, when styrene air concentrations are low (Ref.
5.1.). The development of sampling materials, such as
Carbosieve S-III and 4-tert-butylcatechol (TBC) coated
coconut shell charcoal, increased the prospects of successfully
overcoming these recovery problems. The use of
TBC-coated coconut shell charcoal coated with TBC and
toluene for desorption, ultimately provided the best results.
TBC-coated coconut shell charcoal tubes were initially used
for 1,3-butadiene in OSHA Method 56 (Ref.
5.2.).
Divinylbenzene (DVB) was included for evaluation because
preliminary tests with coconut shell charcoal sampling
tubes and carbon disulfide (CS2) desorption confirmed it
also had low desorption efficiency problems. This was anticipated
because it is structurally similar to styrene.
The collection of styrene and DVB on the same sampler was
desirable because the two chemicals are used together in
the production of some polymers.
The inclusion of DVB, for evaluation, led to the evaluation of
the procedure for ethylvinylbenzene (EVB). Although EVB has no
OSHA PEL, it is a significant and inherent contaminant of the
commonly used grades of DVB.
Technical (tech) grade DVB typically contains 42% EVB by
weight. Because the OSHA PEL for DVB applies only to the
isomers of DVB and not to the tech grade DVB. Therefore
for that reason, EVB was quantitated separately. o-DVB is
not found in tech grade DVB, because it is converted to
naphthalene during the production of DVB.
The procedure presented here successfully overcomes the
low and non-linear desorption efficiency that styrene displayed at
low sampler loadings when collected with coconut
shell charcoal and desorbed with CS2. This procedure also
improved the desorption efficiency for DVB.
1.1.2. Toxic effects (This section is for information only and
should not be taken as the basis of OSHA policy.)
Styrene is readily absorbed by the respiratory and gastrointestinal
systems, and the skin. Exposures to styrene
have caused central nervous system depression and complaints
about headache, fatigue, sleepiness, nausea, malaise,
difficulty in concentrating, and a feeling of intoxication.
Styrene vapor is an irritant to the eyes and
upper respiratory system. Liquid styrene is a skin irritant.
Studies have suggested that styrene exposure has
affected liver function. (Ref. 5.3.) The OSHA PEL for
styrene is 50 ppm (215 mg/m3) for a time weighted average
(TWA) and 100 ppm (425 mg/m3) for a short-term exposure
limit (STEL). These values are the final rule limits of
Title 29 Code of Federal Regulations. (Ref. 5.4.) The
LD50 in rats for styrene is 1220 mg/kg (Ref. 5.5.).
The toxic effects of tech grade DVB are similar to those
encountered with styrene. As with styrene, the odor can
be detected at levels below dangerous concentrations. Eye
and nasal irritation may occur at concentrations above 100
ppm. The LD50 in rats for divinylbenzene is 4640 mg/kg.
(Ref. 5.5.) The OSHA PEL for DVB is 10 ppm (50 mg/m3) for
a TWA. This is the final rule limit of Title 29 Code of
Federal Regulations. (Ref. 5.4.) There is no OSHA PEL or
ACGIH TLV for EVB. The LD50 in rats for m-ethylvinylbenzene
is
4360 mg/kg (Ref. 5.5.).
1.1.3. Workplace exposure
NIOSH estimates that at least 30 thousand workers in 1000
plants are potentially exposed in the United States on a
full-time basis to styrene. It is also estimated that
compounds containing styrene are utilized in over 20 thousand
facilities with more than 300 thousand workers potentially
exposed. In 1981, 3.3 million tons were produced
in the United States. It was estimated that in 1984, styrene
would be consumed by the production of the following
products: 62% in polystyrene, 22% in copolymers such as
styrene-acrylonitrile and acrylonitrile-butadiene-styrene,
7% in styrene-butadiene rubber, 7% in unsaturated
polyester resins, and 2% in miscellaneous uses. (Ref.
5.3.)
No estimate was found of the estimated number of workers
potentially exposed to EVB and DVB. In 1981, 3000-4000
metric tons of DVB and about 2000-3000 metric tons of EVB
was produced in the world. The largest use for DVB is as
copolymer with styrene in ion-exchange resins (Ref. 5.6.).
1.1.4. Physical properties and other descriptive information
(Ref. 5.3. for styrene and Ref. 5.6. for DVB, unless otherwise
stated)
compound: |
styrene |
tech grade DVB* |
CAS number: |
100-42-5 |
1321-74-0 |
molecular weight: |
104.15 |
130.19 |
melting point: |
-30.6°C |
-45°C |
boiling point: |
145.0°C |
195°C (calculated) |
chemical formula: |
C6H5CH=CH2 |
CH2=CHC6H4CH=CH2 |
vapor pressure: |
1.09 kPa (8.21 mmHg) |
0.12 kPa (0.9 mmHg) |
at 30°C |
|
density: |
0.9059 g/mL |
0.9162 g/mL |
at 20°C |
|
self-ignition |
|
temperature: |
490°C |
|
flash point: |
31.1°C |
74°C |
(Cleveland open cup) |
|
solubility: |
slightly soluble in water; soluble in most organic solvents |
slightly soluble in water; soluble in most organic solvents |
synonyms: |
cinnamene; cinnamenol; ethenylbenzene; vinyl benzene; phenylethylene |
DVB; vinyl styrene; divinylbenzene |
compound: |
ethylvinylbenzene |
|
CAS no.: |
28106-30-1 |
|
molecular weight: |
132.22 |
|
synonyms: |
ethyl styrene; EVB |
|
chemical formula: |
CH3CH2C6H4CH=CH2 |
* tech grade DVB used in this evaluation contained 55% DVB, 42%
EVB (CAS no. 28106-30-l), 1.5% diethylbenzene (CAS no.
25340-17-4), 1.5% naphthalene (CAS no. 91-20-3) and 1500 ppm
4-tert-butylcatechol (inhibitor) (CAS no. 98-29-3) (Ref. 5.7.)
The analyte air concentrations throughout this method are based on the
recommended sampling and analytical parameters. Air concentrations
listed in ppm and ppb are referenced to 25°C and 101.3 kPa (760 mmHg).
1.2. Limit defining parameters
1.2.1. Detection limit of the analytical procedure
The detection limits of the analytical procedure are
0.127, 0.115, and 0.151 ng per injection (1.0-µL injection
with a 40:1 split) for styrene, EVR and DVB respectively.
These are the amounts of analyte that will produce peaks
with heights that are approximately 5 times the baseline
noise or a nearby contaminant peak. (Section 4.1.)
1.2.2. Detection limit of the overall procedure
The detection limits of the overall procedure are 5.09,
4.60 and 6.02 µg per sample for styrene, EVB and DVB respectively.
These are the amounts of each analyte spiked
on the sampling device that, upon analysis, produces a
peak similar in size to that of the respective detection
limit of the analytical procedure. These detection limits
correspond to air concentrations of 100 ppb (426 µg/m3),
71 ppb (384 µg/m3), and 94 ppb (500
µg/m3) for styrene,
EVB and DVB respectively. (Section 4.2.)
1.2.3. Reliable quantitation limit
The reliable quantitation limits are 5.09, 4.60 and 6.02
µg per sample for styrene, EVB and DVB respectively.
These are the amounts of each analyte spiked on the sampling
device that, upon analysis , produces a peak similar in
size to that of the respective detection limit of the analytical
procedure and can be quantitated within the requirements
of a recovery of at least 75% and a precision
(±1.96 SD) of ±25% or better. These detection limits correspond
to air concentrations of 100 ppb (426 µg/m3), 71
ppb (384 µg/m3), and 94 ppb (500
µg/m3) for styrene, EVB
and DVB respectively. (Section 4.3.)
The reliable quantitation limit and detection limits reported in
the method are based upon optimization of the instrument for the
smallest possible amount of analyte. When the target concentration
of analyte is exceptionally higher than these limits, they
may not be attainable at the routine operating parameters.
1.2.4. Instrument response to the analyte
The instrument responses over concentration ranges representing
0.5 to 2 times the target concentration are linear.
(Section 4.4.)
1.2.5. Recovery
The recoveries of styrene, EVB and DVB from samples used
in 17-day storage tests remained above 89.7%, 91.0% and
75.0% respectively. The samples were stored in a closed
drawer at about 22°C. (Section 4.5., regression lines of
Figures 4.5.1.1., 4.5.2.1. and 4.5.3.1.)
1.2.6. Precision (analytical procedure only)
The pooled coefficients of variation obtained from replicate
determinations of analytical standards at 0.5, 1 and
2 times the target concentrations are 0.0123, 0.0052 and
0.0058 for styrene, EVB and DVB respectively. (Section
4.6.)
1.2.7. Precision (overall procedure)
The precisions at the 95% confidence level for the 17-day
ambient temperature storage tests are ±14.5%, ±10.2% and
±10.2% for styrene, EVB and DVB respectively. (Section
4.7.) These each include an additional ±5% for sampling
error.
1.2.8. Reproducibility
Six samples, liquid-spiked with styrene and tech grade DVB
and a draft copy of this procedure were given to a chemist
unassociated with this evaluation. The samples were analyzed
for styrene and EVB after 55 days of refrigerated
storage. No individual sample result for styrene and EVB
deviated from its theoretical value by more than the precision
reported in Section 1.2.7. The values for DVB were
not within established precision limits. The data could
not be reanalyzed because it was no longer available. The
test was repeated for DVB.
In the repeated test, six samples, liquid-spiked with tech
grade DVB and a draft copy of this procedure were given to
a chemist unassociated with this evaluation. The samples
were analyzed only for DVB after 1 day of ambient storage.
No individual sample result deviated from its theoretical
value by more than the precision reported in Section
1.2.7. (Sectioil 4.8.)
1.3. Advantages
1.3.1. The new sampler provides better desorption characteristics
than those of OSHA Method 9 (Ref. 5.1.). This eliminates
the need to apply a large correction for desorption at low
sampler loadings.
1.3.2. The desorption efficiency for DVB from TBC-coated coconut
shell charcoal is 81.8% with toluene as the desorbing
solvent; it was only 58.2% when desorbing with CS2.
1.3.3. The sampler may be used for other analytes as long as they
are compatible with the desorbing solvent, toluene.
1.4. Disadvantages
An extended chromatographic run time was used to remove the late
eluting TBC from the analytical column.
2. Sampling Procedure
2.1. Apparatus
2.1.1. Samples are collected using a personal sampling pump that
can be calibrated within ±5% of the recommended flow rate
with the sampling device attached.
2.1.2. Samples are collected with 4-mm i.d. × 6-mm o.d. × 7.0 cm
glass sampling tubes packed with two sections of coconut
shell charcoal that has been coated with TBC, 10% by
weight. The front section contains 110 mg and the back
section contains 55 mg of TBC-coated coconut shell charcoal.
The sections are held in place with glass wool
plugs. For this evaluation, tubes were purchased from
SKC, Inc. (catalog no. 226-73).
2.2. Reagents
No sampling reagents are required.
2.3. Technique
2.3.1. Immediately before sampling, break off the ends of the
TBC-coated coconut shell charcoal tube. All tubes should
be from the same lot.
2.3.2. Attach the sampling tube to the sampling pump with flexible
tubing. It is desirable to utilize sampling tube
holders which have a protective cover to shield the employee
from the sharp, jagged end of the sampling tube.
Position the tube so that sampled air first passes through
the 110-mg section.
2.3.3. Air being sampled should not pass through any hose or tubing
before entering the sampling tube.
2.3.4. Attach the sampler vertically with the 110-mg section
pointing downward, in the worker's breathing zone so it
does not impede work performance or safety.
2.3.5. After sampling for the appropriate time, remove the sample
and seal the tube with plastic end caps. Wrap each
sample end-to-end with a Form OSHA-21 seal.
2.3.6. 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.
2.3.7. Record sample volumes (in liters of air) for each sample,
along with any potential interferences.
2.3.8. Ship any bulk samples in a container separate from the air samples.
2.3.9. Submit the samples to the laboratory for analysis as soon
as possible after sampling. If delay is unavoidable,
store the samples at reduced temperature.
2.4. Sampler capacity
2.4.1. The sampling capacity of the front section of a TBC-coated
coconut shell charcoal sampling tube was tested by sampling
from a gas sampling bag containing an atmosphere of
99.3 ppm (423 mg/m3) of styrene at ambient temperature and
80% relative humidity. The sampling rate was 0.05 L/min.
No breakthrough was observed after sampling for 6 h at
0.05 L/min or a total of 18 L.
2.4.2. Because a stable atmosphere of EVB and DVB could not be
produced, a vapor-spiking technique had to be used to test
for sampler capacity. No EVB or DVB was found on any of
the back tubes and 92.6% of the EVB and 84.3% of the DVB
were recovered from the front tube. These values are
close to the desorption efficiencies for the compounds.
(Section 4.9.)
During the same test, styrene was found on four of the
back tubes and reached the 5% breakthrough air volume
after 14.5 L had been pulled through the tube. The recovery
of styrene from all of the tubes was 87.8%, which is
about 8.0% less than the desorption efficiency. (Section
4.9.)
2.5. Desorption efficiency
2.5.1. The average desorption efficiencies from TBC-coated coconut
shell charcoal adsorbent are 95.8%, 95.0% and 81.8%
for styrene, EVB and DVB over the range of 0.5 to 2 times
the target concentration. (Section 4.10.1.)
2.5.2. Desorbed samples remain stable for at least 24 h. (Section
4.10.2.)
2.6. Recommended air volume and sampling rate
2.6.1. For time-weighted average samples, the recommended air
volume is 12 L collected at 0.05 L/min (4-h samples).
2.6.2. For short-term exposure limit samples, the recommended air
volume is 0.75 L collected at 0.05 L/min (15-min samples).
2.6.3. When short-term exposure limit samples are required, the
reliable quantitation limit becomes larger. For example,
the reliable quantitation limits are 1.6 ppm (6.8 mg/m3),
1.1 ppm (6.1 mg/m3) and 1.5 ppm (8.0
mg/m3) for styrene,
EVB and DVB respectively when 0.75 L of air is collected.
2.7. Interferences (sampling)
2.7.1. It is not known if any compounds will severely interfere
with the collection of styrene, EVB or DVB on TBC-coated
coconut shell charcoal. In general, the presence of other
contaminant vapors in the air will reduce the capacity of
TBC-coated coconut shell charcoal to collect styrene, EVB
or DVB.
2.7.2. Suspected interferences should be reported to the laboratory
with submitted samples.
2.8. Safety precautions (sampling)
2.8.1. The sampling equipment should be attached to the worker in
such a manner that it will not interfere with work performance
or safety.
2.8.2. All safety practices that apply to the work area being
sampled should be followed.
2.8.3. Protective eyewear should be worn when breaking the ends
of the glass sampling tubes.
3. Analytical Procedure
3.1. Apparatus
3.1.1. A GC equipped with a flame ionization detector (FID). A
Hewlett-Packard 5890 Gas Chromatograph equipped with a
7673A Autosampler and an FID was used in this evaluation.
3.1.2. A GC column capable of separating styrene, EVB, DVB and
the internal standard from the desorbing solvent and any
potential interferences. A 60-m × 0.32-mm i.d. DB-5 (1.0-µm
film thickness) capillary column (J & W Scientific) was
used in this evaluation.
3.1.3. An electronic integrator or some other suitable means of
measuring detector response. A Waters 860 Networking Computer
System were used in this evaluation.
3.1.4. Two-milliliter vials with polytetrafluoroethylene-lined
caps.
3.1.5. A dispenser capable of delivering 1.0 mL of desorbing solution
is used to prepare standards and samples. If a dispenser
is not available, a 1.0-mL volumetric pipet may be
used.
3.2. Reagents
3.2.1. Styrene. Reagent grade or better should be used. The
styrene, 99+% (GOLD LABEL), used in this evaluation was
purchased from Aldrich Chemical Co. (Milwaukee, WI).
3.2.2. divinylbenzene. The divinylbenzene used in this evaluation
was purchased from Pfaltz & Bauer (Stamford, CT).
This was technical grade DVB and contained 55% m- and
p-divinylbenzene, 42% m- and p-ethylvinylbenzene and 3%
other compounds.
3.2.3. Toluene. Reagent grade or better should be used. The
toluene (b&j brand HIGH PURITY SOLVENT) used in this evaluation
was purchased from American Burdick & Jackson (Muskegon, MI).
3.2.4. Desorbing solution. The desorbing solution is prepared by
adding 250 µL of an appropriate internal standard to 1 L
of toluene. n-Hexylbenzene (reagent grade) was used in
this evaluation and was purchased from ICN (Plainview,
NY).
3.3. Standard preparation
3.3.1. Prepare concentrated stock standards of styrene, EVB and
DVB in toluene. Prepare working analytical standards by
injecting microliter amounts of concentrated stock standards
into 2-mL vials containing 1 mL of desorbing solution
delivered from the same dispenser used to desorb samples.
For example, to prepare a target level standard, inject 10
PL of a stock solution containing 254, 44.6 and 58.5 mg/mL
of styrene, EVB and DVB respectively in toluene into 1 mL
of desorbing solution.
3.3.2. Prepare a sufficient number of analytical standards to
generate a calibration curve. Ensure that the amount of
styrene, EVB and DVB found in the samples is bracketed by
the range of the standards. Prepare additional standards
if necessary.
3.4. Sample preparation
3.4.1. Remove the plastic caps from the sample tube and carefully
transfer each section of the adsorbent to separate 2-mL
vials. Discard the glass tube and glass wool plugs.
3.4.2. Add 1.0 mL of desorbing solution to each vial and immediately
seal the vials with polytetrafluoroethylene-lined
caps.
3.4.3. Shake the vials vigorously several times during the next
30 min.
3.5. Analysis
3.5.1. Analytical conditions
GC conditions |
|
|
initial |
|
temperatures: |
100°C (column)
200°C (injector)
300°C (detector) |
temp program: |
hold initial temp 1.0 min, increase temp
at 5°C/mic to 150°C, then increase temp
at 10°C/min to 280°C. |
column gas flow: |
1.2 mL/min (hydrogen) |
septum purge: |
1.5 mL/min (hydrogen) |
injection size: |
1.0 µL (40:1 split) |
column: |
60 m × 0.32-mm i.d. capillary DB-5 (l.0-µm film thickness) |
retention times: |
9.3 min (styrene)
14.1 min (m-EVB)
14.3 min (p-EVB)
14.9 min (m-DVB)
15.2 min (p-DVB)
18.2 min (n-hexylbenzene) |
|
FID conditions |
|
|
hydrogen flow: |
34 mL/min |
air flow: |
450 mL/min |
nitrogen makeup flow: |
33 mL/min |
|
chromatogram: |
Figure 3.5.1. |
3.5.2. Measure detector response using a suitable method such as
electronic integration.
3.5.3. An internal standard (ISTD) calibration method is used.
A calibration curve can be constructed by plotting micrograms
of analyte per sample versus ISTD-corrected response
of standard injections. Bracket the samples with freshly
prepared analytical standards over a range of concentrations.
Because the analytes EVB and DVB each consist of a
pair of isomers (meta and para), the peak areas of each
pair are summed to give the response for that analyte.
3.6. Interferences (analytical)
3.6.1. Any compound that produces an FID response and has a similar
retention time as the analyte or internal standard is
a potential interference. If any potential interferences
were reported, they should be considered before samples
are desorbed. Generally, chromatographic conditions can
be altered to separate an interference from the analyte.
3.6.2. Retention time on a single column is not considered proof
of chemical identity. Analysis by an alternate GC column
or confirmation by mass spectrometry are additional means
of identification.
3.7. Calculations
The analyte concentration for samples is obtained from the appropriate
calibration curve in terms of micrograms per sample, uncorrected
for desorption efficiency. The air concentration is calculated
using the following formulae. The back (55-mg) section is
analyzed primarily to determine the extent of sample saturation
during sampling. If any analyte is found on the back section, it
is added to the amount on the front section. This total amount is
then corrected by subtracting the total amount (if any) found on
the blank.
mg/m3 = |
(micrograms of analyte per sample, blank corrected) (liters of air sampled) (desorption efficiency) |
ppm = |
(mg/m3) (24.46) (molecular weight of analyte) |
where
24.46 |
= |
molar volume (liters) at 101.3 kPa (760 mmHg) and 25°C |
molecular weight = |
104.15 for styrene 132.22 for EVB 130.19 for DVB |
3.8. Safety precautions (analytical)
3.8.1. Restrict the use of all chemicals to a fume hood.
3.8.2. Avoid skin contact and inhalation of all chemicals.
3.8.3. Wear safety glasses, gloves and a lab coat at all times
while in the laboratory areas.
4. Backup Data
4.1. Detection limit of the analytical procedure
The detection limits of the analytical procedure are 0.127, 0.115,
and 0.151 ng per injection, based on a 1.0-µL injection (with a
40:1 split) of a standard containing 5.09 µg/mL of styrene, 4.60
µg/mL of EVB, and 6.02 µg/mL of DVB respectively. These amounts
produced analyte peaks with height about 5 times the height of the
baseline noise (for EVB and DVB) or a nearby contaminant peak (for
styrene). Chromatograms of the detection limits of the analytical
procedure are shown in Figures 4.1.1. and 4.1.2. Only the meta
isomers for EVB and DVB were considered for this test, the para
isomers were less than 5 times the height of the baseline noise.
4.2. Detection limit of the overall procedure
The detection limits of the overall procedure are 5.09 µg per sample
(100 ppb or 426 µg/m3) for styrene, 4.60 µg per
sample (71 ppb
or 384 µg/m3) for EVB, and 6.02 µg per sample (94
ppb or 500
µg/m3) for DVB. The injection size listed in the analytical
procedure
(1.0 µL, 40:1 split) was used in the determination of the
detection limit of the overall procedure. Six vials containing
110 mg of TBC-coated coconut shell charcoal were spiked with 5.09
µg of styrene, 4.60 µg of EVB, and 6.02 µg of DVB. The samples
were stored at ambient temperature and were desorbed about 24 h
after being spiked. Only the meta isomers for EVB and DVB were
considered for this test, the para isomers were less than 5 times
the height of the baseline noise.
Table 4.2.1. Detection Limit of the Overall Procedure for Styrene
|
sample no. |
µg spiked |
µg recovered |
|
1 |
5.09 |
4.56 |
2 |
5.09 |
4.37 |
3 |
5.09 |
4.40 |
4 |
5.09 |
4.44 |
5 |
5.09 |
4.28 |
6 |
5.09 |
4.52 |
|
Table 4.2.2. Detection Limit of the Overall Procedure for EVB
|
sample no. |
µg spiked |
µg recovered |
|
1 |
4.60 |
4.31 |
2 |
4.60 |
4.43 |
3 |
4.60 |
4.38 |
4 |
4.60 |
4.48 |
5 |
4.60 |
4.02 |
6 |
4.60 |
4.55 |
|
Table 4.2.3. Detection Limit of the Overall Procedure for DVB
|
sample no. |
µg spiked |
µg recovered |
|
1 |
6.02 |
5.17 |
2 |
6.02 |
5.48 |
3 |
6.02 |
5.00 |
4 |
6.02 |
5.55 |
5 |
6.02 |
5.00 |
6 |
6.02 |
5.19 |
|
4.3. Reliable quantitation limit data
The reliable quantitation limits are 5.09 µg per sample (100 ppb
or 426 µg/m3) for styrene, 4.60 µg per sample (71 ppb
or 384
µg/m3) for EVB, and 6.02 µg per sample (94 ppb or
500 µg/m3) for
DVB. The injection size listed in the analytical procedure (1.0
µL 40:1 split) was used in the determination of the reliable
quantitation limit. Six vials containing 110 mg of TBC-coated
coconut shell charcoal were liquid-spiked with a toluene solution
containing styrene, EVB and DVB. Because the recovery of the analytes
from the spiked samples was greater than 75% and had a precision
of ±25% or better, the detection limits of the overall procedure
and reliable quantitation limit are the same. Only the
meta isomers for EVB and DVB were considered for this test, the
para isomers were less than 5 times the height of the baseline
noise.
Table 4.3.1. Reliable Quantitation Limit for Styrene
(Based on samples and data of Table 4.2.1.)
|
percent recovered |
statistics |
|
89.6 |
|
85.9 |
|
= |
87.0 |
86.4 |
SD |
= |
2.0 |
87.2 |
Precision |
= |
(1.96)(±2.0) |
84.1 |
|
= |
±3.9 |
88.8 |
|
|
Table 4.3.2. Reliable Quantitation Limit for EVB
(Based on samples and data of Table 4.2.2.)
|
percent recovered |
statistics |
|
93.7 |
|
96.3 |
|
= |
94.8 |
95.2 |
SD |
= |
4.0 |
97.4 |
Precision |
= |
(1.96)(±4.0) |
87.4 |
|
= |
±7.8 |
98.9 |
|
|
Table 4.3.3. Reliable Quantitation Limit for DVB
(Based on samples and data of Table 4.2.3.)
|
percent recovered |
statistics |
|
85.9 |
|
91.0 |
|
= |
86.9 |
83.1 |
SD |
= |
3.9 |
92.2 |
Precision |
= |
(1.96)(±3.9) |
83.1 |
|
= |
±7.6 |
86.2 |
|
|
4.4. Instrument response to the analyte
The instrument response to styrene, EVB and DVB over the range of
0.5 to 2 times the target concentration is linear with a slope of
205, 205, and 204 (in ISTD-corrected area counts per microgram per
sample) respectively. The precision of the response to the analytes
was determined by multiple injections of standards. The
data below is presented graphically in Figures 4.4.1.-4.4.3.
Table 4.4.1. Instrument Response to Styrene
Injection Split = 40:1
|
× target concn |
0.5× |
1× |
2× |
µg/mL |
1269 |
2537 |
5074 |
|
area counts |
262250 |
531098 |
1039966 |
|
258308 |
543880 |
1027745 |
|
256228 |
532772 |
1045269 |
|
257649 |
522966 |
1043518 |
|
263441 |
532464 |
1042270 |
|
266211 |
532625 |
1056193 |
|
|
260681 |
532634 |
1042494 |
|
Table 4.4.2. Instrument Response to EVB Injection Split = 40:1
|
× target concn |
0.5× |
1× |
2× |
µg/mL |
223 |
446 |
892 |
|
area counts |
45263 |
91821 |
182599 |
|
45057 |
92287 |
182420 |
|
44978 |
91847 |
182674 |
|
45178 |
90897 |
182208 |
|
45689 |
92063 |
182221 |
|
46063 |
91570 |
183022 |
|
|
45371 |
91748 |
182524 |
|
Table 4.4.3. Instrument Response to DVB Injection Split = 40:1
|
× target concn |
0.5× |
1× |
2× |
µg/mL |
293 |
585 |
1170 |
|
area counts |
58946 |
119742 |
238241 |
|
58881 |
120439 |
238099 |
|
58688 |
119573 |
238203 |
|
58966 |
118365 |
238047 |
|
59275 |
119465 |
237883 |
|
60060 |
119505 |
238453 |
|
|
59136 |
119515 |
238154 |
|
4.5. Storage data
Storage samples for styrene were generated by sampling for 30 min
at the recommended sampling rate from a test atmosphere at 80% relative
humidity containing styrene at 8 times the target concentration.
The ability to adjust the concentration of the styrene
atmosphere was limited due to restrictions in the available equipment.
EVB and DVB storage samples were generated by drawing air
through tubes at the recommended flow rate after they had been
spiked with EVB and DVB on their glass wool plugs. Thirty-six
storage samples of each type were collected. One-half of the
tubes was stored at reduced temperature (-20°C) and the other half
was stored in a closed drawer at ambient temperature (about 22°C).
At 3-4 day intervals, three samples were selected from each of the
two storage sets and analyzed. The results are listed below and
shown graphically in Figures 4.5.1.1.-4.5.3.2.
Table 4.5.1. Storage Test of Styrene
|
storage time |
% recovery |
|
% recovery |
(days) |
(ambient) |
|
(refrigerated) |
|
0 |
96.3 |
101.0 |
92.8 |
|
96.3 |
101.0 |
92.8 |
|
85.6 |
91.2 |
92.2 |
|
85.6 |
91.2 |
92.2 |
4 |
85.1 |
89.6 |
79.2 |
|
85.9 |
92.4 |
90.6 |
7 |
89.5 |
95.0 |
96.4 |
|
95.6 |
97.5 |
94.3 |
11 |
84.4 |
94.1 |
90.0 |
|
95.4 |
93.2 |
88.1 |
14 |
92.4 |
86.7 |
81.5 |
|
96.5 |
83.9 |
97.1 |
17 |
90.1 |
95.8 |
92.8 |
|
94.2 |
96.1 |
92.7 |
|
Table 4.5.2. Storage Test of EVB
|
storage time |
% recovery |
|
% recovery |
(days) |
(ambient) |
|
(refrigerated) |
|
0 |
96.9 |
95.5 |
96.1 |
|
96.9 |
95.5 |
96.1 |
|
95.5 |
93.3 |
94.8 |
|
95.5 |
93.3 |
94.8 |
3 |
93.4 |
93.4 |
94.9 |
|
96.2 |
95.4 |
94.8 |
7 |
91.5 |
93.1 |
90.3 |
|
91.7 |
94.2 |
94.7 |
10 |
92.0 |
91.3 |
91.5 |
|
96.1 |
96.1 |
95.8 |
14 |
93.6 |
93.2 |
93.6 |
|
98.0 |
98.5 |
98.8 |
17 |
90.2 |
90.0 |
90.4 |
|
94.9 |
95.8 |
96.2 |
|
Table 4.5.3. Storage Test of DVB
|
storage time |
% recovery |
|
% recovery |
(days) |
(ambient) |
|
(refrigerated) |
|
0 |
85.5 |
83.5 |
84.2 |
|
85.5 |
83.5 |
84.2 |
|
83.5 |
82.3 |
83.9 |
|
83.5 |
82.3 |
83.9 |
3 |
80.6 |
80.7 |
81.8 |
|
82.5 |
82.3 |
82.2 |
7 |
78.6 |
78.9 |
75.5 |
|
78.6 |
81.0 |
80.5 |
10 |
77.9 |
77.0 |
77.8 |
|
82.3 |
82.3 |
83.2 |
14 |
77.2 |
76.4 |
77.5 |
|
81.5 |
82.4 |
82.2 |
17 |
75.9 |
75.3 |
76.2 |
|
81.0 |
82.8 |
81.8 |
|
4.6. Precision (analytical method)
The precision of the analytical procedure is defined as the pooled
coefficient of variation determined from replicate injections of
styrene, EVB and DVB standards at 0.5, 1 and 2 times the target
concentration. Based on the data of Tables 4.4.1.-4.4.3., the
coefficients of variation (CV) for the three levels and the pooled
coefficient of variation () were calculated and are listed below.
Table 4.6.1. Precision of the Analytical Method for Styrene
(Based on the Data of Table 4.4.1.)
|
× target concn |
0.5× |
1× |
2× |
µg/mL |
1269 |
2537 |
5074 |
|
SD1 |
3883.6 |
6667.8 |
9174.2 |
CV |
0.0149 |
0.0125 |
0.0088 |
|
= 0.0123 |
|
|
1 standard deviation is in area counts |
Table 4.6.2. Precision of the Analytical Method for EVB
(Based on the Data of Table 4.4.2.)
|
× target concn |
0.5× |
1× |
2× |
µg/mL |
223 |
446 |
892 |
|
SD1 |
420.7 |
483.5 |
310.0 |
CV |
0.0068 |
0.0058 |
0.0013 |
|
= 0.0052 |
|
|
1 standard deviation is in area counts |
Table 4.6.3. Precision of the Analytical Method for DVB
(Based on the Data of Table 4.4.3.)
|
× target concn |
0.5× |
1× |
2× |
µg/mL |
293 |
585 |
1170 |
|
SD1 |
490.8 |
670.8 |
209.0 |
CV |
0.0083 |
0.0056 |
0.0008 |
|
= 0.0052 |
|
|
1 standard deviation is in area counts |
4.7. Precision (overall procedure)
The precision of the overall procedure is determined from the
storage data. The determination of the standard error of estimate
(SEE) for a regression line plotted through the graphed storage
data allows the inclusion of storage time as one of the factors
affecting overall precision. The SEE is similar to the standard
deviation, except it is a measure of dispersion of data about a
regression line instead of about a mean. It is determined with
the following equation:
where n |
= |
total no. of data points |
k |
= |
2 for linear regression |
k |
= |
3 for quadratic regression |
Yobs |
= |
observed % recovery at a given time |
Yest |
= |
estimated % recovery from the regression line at the same given
time |
An additional 5% for pump error is added to the SEE by the addition
of variances. The precision at the 95% confidence level is
obtained by multiplying the SEE (with pump error included) by 1.96
(the z-statistic from the standard normal distribution at the 95%
confidence level). The 95% confidence intervals are drawn about
their respective regression line in the storage graph as shown in
Figure 4.5.1.1. The data for Figures 4.5.1.1., 4.5.2.1. and
4.5.3.1. were used to determine the SEEs of ±7.4%, ±5.2% and ±5.2%
and the precisions of the overall procedure of ±14.5%, ±10.2% and
±10.2% for styrene, EVB and DVB respectively.
4.8. Reproducibility data
Six samples were prepared by injecting an aliquot of a toluene
solution containing the analytes onto the glass wool plug in front
of the sorbent while air was being pulled through the tubes. More
air was drawn through the tubes to transfer the analytes to the
TBC-coated coconut shell charcoal. The samples were given to a
chemist unassociated with this study. The samples were analyzed
after being stored for 55 days at 5°C. The desorption efficiencies
were used to determine the sample results. No sample result
for styrene or EVB had a deviation greater than the precisions
of the overall procedure determined in Section 4.7., which
are ±14.5% and ±10.2% respectively.
An additional six samples were prepared for DVB in the same manner
as described above. The samples were analyzed only for DVB after
being stored for 1 day at 23°C. No sample result had a deviation
greater than the precision of the overall procedure, ±10.2%.
Table 4.8.1. Reproducibility Data for Styrene
|
µg spiked |
µg recovered |
% recovered |
% deviation |
|
2537 |
2469 |
97.3 |
-2.7 |
2537 |
2339 |
92.2 |
-7.8 |
1269 |
1154 |
90.9 |
-9.1 |
1269 |
1119 |
88.2 |
-11.8 |
3806 |
3612 |
94.9 |
-5.1 |
3836 |
3548 |
93.2 |
-6.8 |
|
Table 4.8.2. Reproducibility Data for EVB
|
µg spiked |
µg recovered |
% recovered |
% deviation |
|
446 |
435 |
97.5 |
-2.5 |
446 |
429 |
96.2 |
-3.8 |
223 |
212 |
95.1 |
-4.9 |
223 |
205 |
91.9 |
-8.1 |
669 |
645 |
96.4 |
-3.6 |
669 |
640 |
95.7 |
-4.3 |
|
Table 4.8.3. Reproducibility Data for DVB
|
µg spiked |
µg recovered |
% recovered |
% deviation |
|
277 |
287 |
103.6 |
+3.6 |
277 |
268 |
96.8 |
-3.2 |
554 |
539 |
97.3 |
-2.7 |
554 |
534 |
96.4 |
-3.6 |
831 |
813 |
97.8 |
-2.2 |
831 |
813 |
97.8 |
-2.2 |
|
4.9. Sampler capacity
Because a stable atmosphere of EVB and DVB could not be produced,
another approach had to be used to test for sampler capacity. A
tube containing 110 mg of TBC-coated coconut shell charcoal was
used as the front section for this test. The glass wool plug in
the front of the tube was pulled away from the adsorbent but left
in the tube. A new TBC-coated coconut shell charcoal tube was
attached in series downstream from the front section. While air was
flowing through the tubes at 0.05 L/min, a 5-µL spike containing
styrene, EVB and DVB in toluene was injected onto the front glass
wool plug of the front tube. This resulted in an equivalent
upstream atmospheric concentrations of 846, 149 and 195 mg/m3
for
styrene, EVB and DVB respectively, assuming a 1.5 L air volume.
This injection was repeated every 30 min for a total of 12 injections
over 6 h. Immediately before the second and subsequent injections
were performed, the back tube was removed and a new tube
installed. No EVB or DVB was found on any of the 12 back tubes
and 92.6% of the EVB and 84.3% of the DVB were recovered from the
front tube. These values are close to the desorption efficiencies
for the compounds.
Styrene was found on four of the back tubes and reached the 5%
breakthrough air volume after 14.5 L had been pulled through the
tube. Breakthrough was considered to have occurred when the
amount on the back tube contained a concentration of analyte that
was 5% (5% breakthrough) of the upstream concentration. The data
in Table 4.9. is shown graphically in Figure 4.9. The recovery of
styrene from all of the tubes was 87.8%, which is about 8.0% less
than the desorption efficiency.
Table 4.9. Styrene Breakthrough Data
|
air vol |
sample time |
downstream |
breakthrough |
(L) |
(min) |
(mg/m3) |
(%) |
|
0.75 |
15 |
0 |
0 |
2.25 |
45 |
0 |
0 |
3.75 |
75 |
0 |
0 |
5.25 |
105 |
0 |
0 |
6.75 |
135 |
0 |
0 |
8.25 |
165 |
0 |
0 |
9.75 |
195 |
0 |
0 |
11.25 |
225 |
0 |
0 |
12.75 |
255 |
3.1 |
0.2 |
14.25 |
285 |
55.1 |
4.3 |
15.75 |
315 |
117.6 |
9.3 |
17.25 |
345 |
228.1 |
18.0 |
|
4.10. Desorption efficiency and stability of desorbed samples
4.10.1. Desorption efficiency
The desorption efficiencies (DE) of styrene, EVB and DVB
were determined by liquid-spiking 110-mg portions of TBC-coated
coconut shell charcoal with the analytes at 0.5 to
2 times the target concentrations. These samples were
stored overnight at ambient temperature and then desorbed
with desorbing solution and analyzed. The average desorption
efficiency over the studied range was 95.8%, 95.0%
and 81.8% for styrene, EVB and DVB respectively.
Table 4.10.1.1. Desorption Efficiency of Styrene
|
× target concn |
0.5× |
1× |
2× |
µg/mL |
1269 |
2537 |
5074 |
|
DE, % |
94.7 |
99.5 |
92.1 |
|
95.7 |
96.0 |
94.5 |
|
95.0 |
97.7 |
95.3 |
|
95.1 |
98.3 |
93.7 |
|
95.5 |
98.4 |
94.5 |
|
95.0 |
97.6 |
94.8 |
|
95.2 |
97.9 |
94.2 |
|
Table 4.10.1.2. Desorption Efficiency of EVB
|
× target concn |
0.5× |
1× |
2× |
µg/mL |
223 |
446 |
892 |
|
DE, % |
92.8 |
96.5 |
94.2 |
|
93.6 |
94.8 |
95.5 |
|
92.5 |
95.4 |
96.5 |
|
93.9 |
96.2 |
95.8 |
|
94.8 |
95.9 |
95.8 |
|
93.6 |
95.9 |
96.4 |
|
93.5 |
95.8 |
95.7 |
|
Table 4.10.1.3. Desorption Efficiency of DVB
|
× target concn |
0.5× |
1× |
2× |
µg/mL |
293 |
585 |
1170 |
|
DE, % |
78.0 |
84.2 |
83.2 |
|
79.1 |
82.4 |
82.7 |
|
79.4 |
82.7 |
83.0 |
|
79.9 |
83.6 |
82.6 |
|
80.2 |
83.0 |
83.2 |
|
80.0 |
82.8 |
83.2 |
|
|
79.4 |
83.1 |
83.0 |
|
4.10.2. Stability of desorbed samples
The stability of desorbed samples was investigated by reanalyzing the
target concentration samples 24 h after initial analysis. The original
analysis was performed and
the vials were not recapped after injection. The samples
were reanalyzed with fresh standards. The average recovery
of the reanalysis, compared to the average recovery of
the original analysis, was 95.8% (-2.1% change), 95.0%
(-0.8% change) and 80.6% (-2.5% change) for styrene, EVB
and DVB respectively.
Table 4.10.2.1. Stability of Desorbed Samples for Styrene
|
initial recovery |
recovery after 24 h |
percent |
(percent) |
(percent) |
change |
|
99.5 |
95.1 |
-4.4 |
96.0 |
95.7 |
-0.3 |
97.7 |
96.9 |
-0.8 |
98.3 |
95.7 |
-2.6 |
98.4 |
94.4 |
-4.0 |
97.6 |
97.0 |
-0.6 |
|
Table 4.10.2.2. Stability of Desorbed Samples for EVB
|
initial recovery |
recovery after 24 h |
percent |
(percent) |
(percent) |
change |
|
96.5 |
95.3 |
-1.2 |
94.8 |
94.4 |
-0.4 |
95.4 |
95.9 |
+0.5 |
96.2 |
94.8 |
-1.4 |
95.9 |
95.0 |
-0.9 |
95.9 |
94.8 |
-1.1 |
|
Table 4.10.2.3. Stability of Desorbed Samples for DVB
|
initial recovery |
recovery after 24 h |
percent |
(percent) |
(percent) |
change |
|
84.2 |
81.1 |
-3.1 |
82.4 |
80.3 |
-2.1 |
82.7 |
80.6 |
-2.1 |
83.6 |
81.0 |
-2.5 |
83.0 |
79.6 |
-3.4 |
82.8 |
81.2 |
-1.6 |
|
Figure 3.5.1. Chromatogram of styrene, EVB and DVB at the target concentration.
Figure 4.1.1. Chromatogram of styrene at the detection limit, 0.127 ng per
injection, injection split = 40:1.
Figure 4.1.2. Chromatogram of EVB and DVB at the detection limit, 0.115
and 0.151 ng per injection respectively, injection split = 40:1.
Figure 4.4.1. Instrument response curve for styrene, slope = 235 area
counts per micrograms per sample, injection split = 40:1.
Figure 4.4.2. Instrument response curve for EVB, slope = 205 area
counts per micrograms per sample, injection split = 40:1.
Figure 4.4.3. Instrument response curve for DVB, slope = 204 area
cwnts per micrograms per sample, injection split = 40:1.
Figure 4.5.1.1. Ambient storage test for styrene.
Figure 4.5.1.2. Refrigerated storage test for styrene.
Figure 4.5.2.1. Ambient storage test for EVB.
Figure 4.5.2.2. Refrigerated storage test for EVB.
Figure 4.5.3.1. Ambient storage test for DVB.
Figure 4.5.3.2. Refrigerated storage test for DVB.
Figure 4.9. Determination of the 5% breakthrough air volume for styrene,
14.5 L at 846 mg/m3.
5. References
5.1. "OSHA Analytical Methods Manual", 2nd ed., U.S. Department of Labor,
Occupational Safety and Health Administration; OSHA Analytical
Laboratory; Salt Lake City, UT, 1990; Method 9 - Styrene; American
Conference or Government Industrial Hygienists (ACGIH); Cincinnati, OH,
Publ. No. 4542.
5.2. "OSHA Analytical Methods Manual", 2nd ed., U.S. Department of Labor,
Occupational Safety and Health Administration; OSHA Analytical
Laboratory; Salt Lake City, UT, 1990; Method 56 - 1,3-Butadiene;
American Conference of Government Industrial Hygienists
(ACGIH); Cincinnati, OH, Publ. No. 4542.
5.3. "NIOSH Criteria for a Recommended Standard: Occupational Exposure
to Styrene", U.S. Department of Health and Human Services, Public
Health Service, Center for Disease Control, National Institute for
Occupational Safety and Health, Cincinnati, OH, 1983, DHHS (NIOSH)
Publ. No. 83-119.
5.4. "Code of Federal Regulations", Title 29, 1910.1000, Table Z-l-A.
Limits for Air Contaminants, U.S. Government Printing Office,
Washington, D.C., 1990.
5.5. Lewis, P.J. et al. in "Kirk-Othmer Encyclopedia of Technology" 3rd
ed.; Grayson, M., Ed.; John Wiley & Sons, New York, 1980, Vol. 21,
pp 770-801.
5.6. Sweet, D.V., Ed., "Registry of Toxic Effects of Chemical Substances",
1985-86 ed., U.S. Department of Health and Human Services,
Government Printing Office, DHHS(NIOSH), Publication No.
87-114.
5.7. Tradenames Database on CCINFO CD-ROM disc 89-2, Canadian Centre
for Occupational Health and Safety, Hamilton, Ontario.
|