1,3-BUTADIENE
Method no.: |
56 |
|
Matrix: |
Air |
|
Target concentration: |
1 ppm (2.21 mg/m3) |
|
Procedure: |
Air samples are collected by drawing known volumes of
air through sampling tubes containing charcoal adsorbent which has
been coated with 4-tert-butylcatechol. The samples are desorbed with
carbon disulfide and then analyzed by gas chromatography using a
flame ionization detector. |
|
Recommended air volume and sampling rate: |
3 L at 0.05 L/min |
|
Detection limit of the overall procedure: |
90 ppb (200
µg/m3) |
|
Reliable quantitation limit: |
155 ppb (343 µg/m3) |
|
Standard error of estimate at the target
concentration: (Section 4.6.1.) |
6.5%
|
|
Special requirements: |
The sampling tubes must be obtained from the Salt
Lake City Analytical Laboratory. Collected samples should be stored
in a freezer. |
|
Status of method: |
Evaluated method. This method has been subjected to
the established evaluation procedures of the Organic Methods
Evaluation Branch. |
|
Date: December 1985 |
Chemist: Warren
Hendricks |
Organic Methods Evaluation Branch OSHA Analytical
Laboratory Salt Lake City, Utah
1. General Discussion
1.1. Background
1.1.1. History
This work was undertaken to develop a sampling and analytical
procedure for 1,3-butadiene at 1 ppm. The 1 ppm target
concentration was selected in anticipation of a possible reduction
in the current OSHA PEL of 1000 ppm. NIOSH has recently recommended
that 1,3-butadiene be treated as a potential
occupational carcinogen, teratogen and as a reproduction hazard.
(Ref. 5.1.)
The current method recommended by OSHA for collecting
1,3-butadiene uses activated coconut shell charcoal as
the sampling medium (Ref. 5.2.). This method was found to be
inadequate for use at low 1,3-butadiene levels because
of sample instability (Sections 4.5.2. and 4.6.2.).
The stability of collected samples has been significantly
improved through the use of a specially cleaned charcoal which is
coated with 4-tert-butylcatechol (TBC). TBC is a polymerization
inhibitor for 1,3-butadiene (Ref. 5.3.).
1.1.2. Toxic effects (This section is for information only and
should not be taken as the basis of OSHA policy).
Symptoms of human exposure to 1,3-butadiene include
irritation of the eyes, nose and throat. It can also cause coughing,
drowsiness and fatigue. Dermatitis and frost-bite can result from
skin exposure to liquid 1,3-butadiene. (Ref. 5.1.)
NIOSH recommends that 1,3-butadiene be handled in
the workplace as a potential occupational carcinogen. This
recommendation is based on two inhalation studies that resulted in
cancers at multiple sites in rats and in mice. 1,3-Butadiene has
also demonstrated mutagenic activity in the presence of a liver
microsomal activating system. It has also been reported to have
adverse teratogenic and reproductive effects. (Ref. 5.1.)
1.1.3. Potential workplace exposure
In 1984, 2.53 billion pounds of rubber grade butadiene were
produced. This amount was only 3.7% less than the average yearly
amount produced during the past decade of 1974-1984. In
1984, butadiene ranked 36th of the top 50 chemicals produced in the
United States. (Ref. 5.4.) About 80% of the
1,3-butadiene produced in the United States is a
by-product of the manufacture of ethylene. The
remaining 20% is produced by the dehydrogenation of n-butene and
n-butane. (Ref. 5.1.)
About 90% of the annual production of 1,3-butadiene
is used to manufacture styrene-butadiene rubber and
polybutadiene rubber. Other uses include: polychloroprene rubber,
acrylonitrile-butadiene-styrene resins, nylon intermediates,
styrene-butadiene latexes, butadiene polymers, thermoplastic
elastomers, nitrile resins, methyl
methacrylate-butadiene-styrene resins and chemical
intermediates. (Ref. 5.1.)
A NIOSH survey, that was conducted from 1972 to 1974, estimated
that approximately 65,000 workers were potentially exposed to
1,3-butadiene. About 70% of this total was employed in
chemical and chemical products occupations. Another 25% of the total
was employed in work places which included: rubber and rubber
products industries miscellaneous business services and
miscellaneous manufacturing industries. (Ref. 5.1.)
1.1.4. Physical properties (Ref. 5.1.)
CAS no.: |
106-99-0 |
molecular weight: |
54.09 |
appearance: |
colorless gas |
boiling point: |
-4.41°C (760 mm Hg) |
freezing point: |
-108.9°C |
vapor pressure: |
2 atm at 15.3°C 5 atm at 47.0°C |
explosive limits: |
2 to 11.5% (by volume in air) |
odor threshold: |
1.3 ppm |
structural formula: |
H2C:CHCH:CH2 |
synonyms: |
biethylene; bivinyl; butadiene; divinyl;
buta-1,3-diene; alpha-gamabutadiene;
erythrene; NCI-C50602; pyrrolylene;
vinylethylene. |
1.2. Limit defining parameters (The analyte air concentrations
listed throughout this method are based on an air volume of 3 L and a
desorption volume of 1 mL. Air concentrations listed in ppm are
referenced to 25°C and 760 mm Hg.)
1.2.1. Detection limit of the analytical procedure
The detection limit of the analytical procedure was 304 pg per
injection. This was the amount of 1,3-butadiene which
gave a measurable response relative to the interferences present in
a standard. (Section 4.1.)
1.2.2. Detection limit of the overall procedure
The detection limit of the overall procedure was 0.60 µg per
sample (90 ppb or 200 µg/m3). This amount
was determined graphically. It was the amount of analyte which, when
spiked on the sampling device, would allow recovery approximately
equivalent to the detection limit of the analytical procedure.
(Section 4.1.2.)
1.2.3. Reliable quantitation limit
The reliable quantitation limit was 1.03 µg per sample (155 ppb
or 343 µg/m3). This was the smallest
amount of analyte which could be quantitated within the limits of a
recovery of at least 75% and a precision (±1.96 SD) of ±25% or
better. (Section 4.2.)
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
an analyte is exceptionally higher than these limits, they may not be
attainable at the routine operating parameters.
1.2.4. Sensitivity
The sensitivity of the analytical procedure over a concentration
range representing 0.6 to 2 times the target concentration, based on
the recommended air volume, was 387 area units per µg/mL. This value
was determined from the slope of the calibration curve. (Section
4.3.) The sensitivity may vary with the particular instrument used
in the analysis.
1.2.5. Recovery
The recovery of 1,3-butadiene from samples used in
storage tests remained above 77% when the samples were stored at
ambient temperature for 17 days, and above 94% when the samples were
stored at refrigerated temperature for 18 days. These values were
determined from regression lines which were calculated from the
storage data. (Section 4.6.) The recovery of the analyte from the
collection device must be at least 75% following storage.
1.2.6. Precision (analytical method only)
The pooled coefficient of variation obtained from replicate
determinations of analytical standards over the range of 0.6 to 2
times the target concentration was 0.011. (Section 4.3.)
1.2.7. Precision (overall procedure)
The precision at the 95% confidence level for the refrigerated
temperature storage test was ±12.7%. (Section 4.6.1.) This value
includes an additional ±5% for sampling error. The overall procedure
must provide results at the target concentrations that are ±25% at
the 95% confidence level.
1.2.8. Reproducibility
Samples collected from a controlled test atmosphere and a draft
copy of this procedure were given to a chemist unassociated with
this evaluation. The average recovery was 97.2% and the standard
deviation was 6.2%. (Section 4.7.)
1.3. Advantages
1.3.1. The sampling and analytical procedure permits
determination of 1,3-butadiene at low levels.
1.3.2. Samples are relatively stable following storage at ambient
temperature for 17 days.
1.4. Disadvantage
The recommended sampling tubes must be obtained from the Salt Lake
City Analytical Laboratory.
2. Sampling Procedure
2.1. Apparatus
2.1.1. Samples are collected by use of a personal sampling pump
that can be calibrated to within ±5% of the recommended 0.05 L/min
sampling rate with the sampling tube in line.
2.1.2. Samples are collected with laboratory prepared sampling
tubes. The sampling tube is constructed of silane-treated glass and
is about 5-cm long. The i.d. is 4 mm and the o.d. is 6 mm. One end
of the tube is tapered so that a glass wool end plug will hold the
contents of the tube in place during sampling. The opening in the
tapered end of the sampling tube is at least one-half the i.d. of
the tube (2 mm). The other end of the sampling tube is open to its
full 4-mm i.d. to facilitate packing of the tube. Both ends of the
tube are fire-polished for safety. The tube is packed with 2
sections of pretreated charcoal which has been coated with TBC. The
tube is packed with a 50-mg backup section, located nearest the
tapered end, and with a 100-mg sampling section of
charcoal. The two sections of coated adsorbent are separated and
retained with small plugs of silanized glass wool. Following
packing, the sampling tubes are sealed with two 7/32-in. o.d.
plastic end caps. Instructions for the pretreatment and coating of
the charcoal are presented in Section 4.8. of this method.
2.2. Reagents
None required
2.3. Technique
2.3.1. Properly label the sampling tube before sampling and then
remove the plastic end caps.
2.3.2. Attach the sampling tube to the pump using a section of
flexible plastic tubing such that the large front section of the
sampling tube is exposed directly to the atmosphere. Do not place
any tubing ahead of the sampling tube. The sampling tube should be
attached in the worker's breathing zone in a vertical manner such
that it does not impede work performance.
2.3.3. After sampling for the appropriate time, remove the
sampling tube from the pump and then seal the tube with plastic end
caps. Wrap the tube lengthwise with an official OSHA seal (Form 21).
2.3.4. Include at least one blank for each sampling set. The
blank should be handled in the same manner as the samples with the
exception that air is not drawn through it.
2.3.5. List any potential interferences on the sample data sheet.
2.3.6. The samples require no special shipping precautions under
normal conditions. The samples should be refrigerated if they are to
be exposed to higher than normal ambient temperatures. If the
samples are to be stored before they are shipped to the laboratory,
they should be kept in a freezer. The samples should be placed in a
freezer upon receipt at the laboratory.
2.4. Breakthrough (Breakthrough was defined as the relative amount
of analyte found on the backup section of the tube in relation to the
total amount of analyte collected on the sampling tube.)
Five-percent breakthrough occurred after sampling a test atmosphere
containing 2.0 ppm 1,3-butadiene for 90 min at 0.05
L/min. At the end of this time 4.5 L of air had been sampled and 20.1
µg of the analyte was collected. The relative humidity of the sampled
air was 80% at 23°C. (Section 4.4.)
Breakthrough studies have shown that the recommended sampling
procedure can be used at air concentrations higher than the target
concentration. The sampling time, however, should be reduced to 45 min
if both the expected 1,3-butadiene level and if the
relative humidity of the sampled air are high. (Section 4.4.)
2.5. Desorption efficiency
The average desorption efficiency for 1,3-butadiene
from TBC coated charcoal over the range of from 0.6 to 2 times the
target concentration was 96.4%. The desorption efficiency was
essentially constant over the range studied. (Section 4.5.)
2.6. Recommended air volume and sampling rate
2.6.1. The recommended air volume is 3 L.
2.6.2. The recommended sampling rate is 0.05 L/min for 1 h.
2.7. Interferences (sampling)
There are no known interferences to the sampling method.
2.8. Safety precautions (sampling)
2.8.1. Attach the sampling equipment to the worker in such a
manner that it will not interfere with work performance or safety.
2.8.2. Follow all safety practices that apply to the work area
being sampled.
3. Analytical Procedure
3.1. Apparatus
3.1.1. A gas chromatograph (GC), equipped with a flame
ionization detector (FID). A Hewlett-Packard Model 5840A GC was used
for this evaluation. Injections were performed using a
Hewlett-Packard Model 7671A automatic sampler.
3.1.2. A GC column capable of resolving the analytes from
potential interferences. A 20-ft × 1/8-in. o.d.
stainless steel GC column containing 20% FFAP on 80/100 mesh
Chromosorb W-AW-DMCS was used for this evaluation.
3.1.3. Two milliliter glass vials with Teflon-lined caps.
3.1.4. Disposable Pasteur-type pipets, volumetric flasks, pipets
and syringes for preparing samples and standards, making dilutions
and performing injections.
3.2. Reagents
3.2.1. Carbon disulfide. Fisher Scientific Company A.C.S.
Reagent Grade solvent was used in this evaluation. The benzene
contaminant that was present in the carbon disulfide was used as an
internal standard (ISTD) in this evaluation.
3.2.2. Nitrogen, hydrogen, and air, GC grade.
3.2.3. 1,3-Butadiene of known high purity. Matheson Gas Products,
CP Grade 1,3-butadiene was used in this study.
3.3. Standard preparation
3.3.1. Prepare standards by diluting known volumes of
1,3-buta-diene gas with carbon disulfide. This can be accomplished
by injecting the appropriate volume of 1,3-butadiene
into the headspace above the 1 mL of carbon disulfide contained in
sealed 2-mL vial. Shake the vial after the needle is removed from
the septum. A standard containing 7.71 µg/mL (at ambient temperature
and pressure) was prepared by diluting 4 µL of the gas with 1 mL of
carbon disulfide.
3.3.2. The mass of 1,3-butadiene gas which was used
to prepare standards can be determined by use of the following
equations:
MV = (22.41)(760/BP)(273+T)/(273)
where |
22.41 MV BP T |
= = = =
|
molar volume at STP ambient molar
volume ambient barometric pressure ambient
temperature |
µg/µL = 54.09/MV
µg per standard = (µg/µL)(µL)(p)
where |
µg/µL µL p |
= = =
|
ambient density of
1,3-butadiene gas µL of
1,3-butadiene used to prepare standard purity
of 1,3-butadiene, (decimal
form) |
3.4. Sample preparation
3.4.1. Transfer the c section of the sampling tube to a 2-mL
vial. Place the 50-mg section in a separate vial. If the glass wool
plugs contain a significant amount of charcoal, place them with the
appropriate sampling tube section.
3.4.2. Add 1 mL of carbon disulfide to each vial.
3.4.3. Seal the vials with Teflon-lined caps and then allow them
to desorb for 1 h. Shake the vials by hand with vigorous force
several times during the desorption time.
3.4.4. If it is not possible to analyze the samples within 4 h of
desorption, separate the carbon disulfide from the charcoal, using a
disposable Pasteur-type pipet, following the 1-h desorption time.
This separation will improve the stability of desorbed samples.
(Tables 4.5.1.2. and 4.5.1.3.)
3.4.5. Save the used sampling tubes to be cleaned and repacked
with fresh adsorbent.
3.5. Analysis
3.5.1. GC Conditions
column temperature: |
95°C |
injector temperature: |
180°C |
detector temperature: |
275°C |
carrier gas flow rate: |
30 mL/min |
injection volume: |
0.80 µL |
GC column: |
20-ft × 1/8-in. o.d. stainless steel GC column
containing 20%FFAP on 80/100 Chromosorb W-AW
DMCS |
3.5.2. Chromatogram See Section 4.9.
3.5.3. Use a suitable method, such as electronic integration or
peak heights, to measure detector response.
3.5.4. Prepare a calibration curve using several standard
solutions of different concentrations. Prepare the calibration curve
daily. Program the integrator to report the results in µg/mL.
3.5.5. Bracket sample concentrations with standards.
3.6. Interferences (analytical)
3.6.1. Any compound with the same general retention time as the
analyte and which also gives a detector response is a potential
interference. Possible interferences should be reported to the
laboratory with submitted samples by the industrial hygienist.
3.6.2. GC parameters (temperature, column, etc.) may be changed
to circumvent interferences.
3.6.3. A useful means of structure designation is GC/MS. It is
recommended that this procedure be used to confirm samples whenever
possible.
3.7. Calculations
3.7.1. Results are obtained by use of calibration curves.
Calibration curves are prepared by plotting detector response
against concentration for each standard. The best line through the
data points is determined by curve fitting.
3.7.2. The concentration, in µg/mL, for a particular sample is
determined by comparing its detector response to the calibration
curve. If any analyte is found on the backup section, this amount is
added to the amount found on the front section. Blank corrections
should be performed before adding the results together.
3.7.3. The 1,3-butadiene air concentration can be
expressed using the following equation:
mg/m3 = (A)(B)/(C)(D)
where |
A = µg/mL from Section 3.7.2. B = desorption
volume C = liters of air sampled D = desorption
efficiency |
3.7.4. The following equation can be used to convert results in
mg/m3 to ppm:
ppm = (mg/m3)(24.46)/54.09
where |
mg/m3 |
= |
result from Section 3.7.3. |
|
24.46 |
= |
molar volume of an ideal gas at 760 mm Hg and
25°C |
3.8. Safety precautions (analytical)
3.8.1. Avoid skin contact and inhalation of all chemicals.
3.8.2. Restrict the use of all chemicals to a fume hood whenever
possible.
3.8.3. Wear safety glasses and a lab coat in all lab areas.
4. Backup Data
4.1. Detection limit data
4.1.1. Detection limit of the analytical procedure
The injection size recommended in the analytical procedure (0.80
µL) was used in the determination of the detection limit for the
analytical procedure. The detection limit of the analytical
procedure was 304 pg per injection. This was the amount of
1,3-butadiene which gave a measurable response relative
to interferences present in a standard. This detection limit was
determined by the analysis of a standard containing 380 ng/mL of
1,3-butadiene in carbon disulfide. Figure 4.1.1. is a
chromatogram of the detection limit of the analytical procedure.
4.1.2. Detection limit of the overall procedure
The injection size recommended in the analytical procedure (0.80
µL) was used in the determination of the detection limit of the
overall procedure. 1,3-Butadiene was diluted for use in this study
by adding the pure analyte to a sealed, silanized vial containing
air and a few crystals of TBC. Samples were prepared by injecting
100-mg portions of TBC coated charcoal with appropriate
amounts of the diluted 1,3-butadiene. The samples were
stored in a freezer overnight before analysis to allow complete
adsorption of the analyte. Each result is the average of at least 2
samples. The results of this study are presented in Table 4.1.2. and
in Figure 4.1.2.
Table 4.1.2. Detection Limit Data
|
sample number |
µg spiked |
µg recovered |
percent recovered |
|
1 2 3 4 5 6 7 |
0.38 0.58 0.76 0.96 1.2 1.4 1.9 |
0.26 0.34 0.48 0.67 1.0 1.3 1.9 |
68.4 58.6 63.2 69.8 83.3 92.8 100.0 |
|
The detection limit of the overall procedure was determined
graphically (Figure 4.1.2.) from the data in Table 4.1.2. This
amount was 0.60 µg per sample.
4.2. Reliable quantitation limit data
The recommended injection size of 0.80 µL was used in the
determination of the reliable quantitation limit (RQL). The amount of
1,3-butadiene which provided a recovery of 75% from the
sampling media was determined graphically (Figure 4.2.1.) from the
data in Table 4.1.2. This amount was 1.03 µg. A chromatogram of the
RQL is presented in Figure 4.2.2. Six samples were used to determine
the precision at the RQL. The samples were prepared in a similar
manner as those in Section 4.1.2. The results of this study are
presented below and in Figure 4.2.1.
Table 4.2. Reliable Quantitation Limit Data
|
sample number |
µg spiked |
µg recovered |
percent recovered |
|
1 2 3 4 5 6
|
1.03 1.03 1.03 1.03 1.03 1.03 |
0.854 0.754 0.829 0.779 0.836 0.836 |
82.9 73.2 80.5 75.6 81.2 81.2 |
|
![mean](../mean.gif) |
1.03 |
0.815 |
79.1 |
|
|
|
4.3. Sensitivity and precision (analytical method only)
The sensitivity and precision of the analytical procedure were
evaluated by performing multiple injections of analytical standards at
0.6, 1, and 2 times the target concentration. The standards were
prepared by injecting appropriate amounts of 1,3-buta-diene gas
diluted with carbon disulfide. The data are presented in Table 4.3.
and also in Figure 4.3. The ISTD data are the results of an internal
standard calibration using the benzene contaminant present in carbon
disulfide as the internal standard.
Table 4.3. 1,3-Butadiene Sensitivity and Precision
Data
|
|
0.6× |
1× |
2× |
|
3.86 µg/sample |
6.75 µg/sample |
13.5 µg/sample |
|
ISTD |
area |
ISTD |
area |
ISTD |
area |
|
![mean](../mean.gif) CV
= |
3.85 3.89 3.85 3.81 3.81 3.95
3.86 0.0138
0.011 |
1332 1509 1507 1345 1416 1354 |
6.66 6.73 6.78 6.78 6.86 6.75
6.76 0.00977 |
2371 2386 2369 2393 2529 2327 |
13.4 13.5 13.7 13.5 13.6 13.3
13.5 0.0105 |
5190 5167 5076 5097 5045 5087 |
|
The sensitivity for 1,3-butadiene was 387 area counts
per µg/mL.
4.4. Breakthrough data
Breakthrough was defined as the relative amount of
1,3-butadiene found on the 50-mg sampling tube section in
relation to the total amount collected on the sampling tube.
Three breakthrough studies were performed at twice the target level
with the recommended air sampler. The test atmospheres were generated
by diluting the effluent of a gas cylinder containing 100 ppm of
1,3-butadiene with humid air. The concentrations of the
test atmospheres were determined by direct injection of the atmosphere
into a gas chromatograph. The gas chromatograph was calibrated using
1,3-butadiene from another source that had been diluted
with dry air in a Teflon gas bag. The average concentration of the
test atmospheres was 2.0 ppm. The average relative humidity of these
test atmospheres was 80% at 23°C. The sampling rates were about 0.05
L/min. The results of these studies are presented in Table 4.4.1.
Table 4.4.1. 1,3-Butadiene Breakthrough at Twice the Target
Concentration
|
sampling time, min |
amt. on
100-mg section, µg |
amt. on 50-mg section,
µg |
breakthrough, % |
|
91 124 155 60 91 121 50 76 92 105 125 |
23.4 27.8 30.4 14.6 21.6 25.5 8.6 13.0 14.4 15.7 17.0 |
0.0 3.1 6.1 0.0 1.2 3.5 0.0 0.0 0.6 2.2 2.4 |
0.0 10.0 16.7 0.0 5.3 12.1 0.0 0.0 4.0 12.3 12.4 |
|
When the results of the three studies were combined, 5%
breakthrough occurred after sampling for 90 min. The air volume
sampled after this time was 4.5 L and the amount of
1,3-butadiene collected was 20.1 µg.
Additional breakthrough studies were performed at concentrations
higher than twice the target level in order to determine if the
recommended sampling procedure would be reliable at those
concentrations. The test atmospheres used in these studies were
generated and their concentrations were determined using the
techniques previously described. Percent recovery values were
calculated using sample results and the actual concentration of the
test atmospheres. The sampling rates were about 0.05 L/min. The
results of these studies are presented in Tables 4.4.2. through 4.4.4.
Table 4.4.2. 1,3-Butadiene Breakthrough Study at 7.3
ppm (Relative Humidity = 77% at 22°C)
|
sampling time, min |
air volume sampled,
L |
percent breakthrough |
percent recovery |
|
15 30 45 60 75 90 |
0.73 1.6 2.2 3.1 3.5 4.5 |
0.0 0.0 0.0 0.0 0.6 8.4 |
80.2 94.2 96.8 99.4 96.7 95.8 |
|
Five-percent breakthrough occurred after sampling for 84 min. At
the end of this time, 4.2 L of air had been sampled and 68 µg of
1,3-butadiene had been collected.
Table 4.4.3. 1,3-Butadiene Breakthrough Study at 32
ppm (Relative Humidity = 47% at 24°C)
|
sampling time, min |
air volume sampled,
L |
percent breakthrough |
percent recovery |
|
15 46 60 90 105 120 155 |
0.71 2.3 3.2 4.3 5.2 6.3 8.2 |
0.0 0.0 0.0 0.0 0.0 0.0 0.0 |
87.3 87.2 91.2 94.8 95.0 97.5 93.0 |
|
No breakthrough was observed, even after sampling for 155 min. This
data shows that, at low relative humidity, the recommended sampling
media has considerable capacity for 1,3-butadiene.
Table 4.4.4. 1,3-Butadiene Breakthrough Study at 36
ppm (Relative Humidity = 90% at 21°C)
|
sampling time, min |
air volume sampled,
L |
percent breakthrough |
percent recovery |
|
36 47 60 75 90 105 121 |
1.9 2.2 3.0 3.9 4.3 5.8 6.3 |
0.0 0.0 21.6 30.0 30.6 32.1 31.1 |
105.8 98.8 90.2 96.0 76.4 57.6 56.7 |
|
It is apparent from the data in Tables 4.4.2. through 4.4.4. that
the recommended sampling and analytical method can be used at
1,3-butadiene levels higher than the target
concentration. The relative humidity of the sampled air has a
significant effect on the ability of the sampling device to retain the
analyte.
4.5. Desorption efficiency and stability of desorbed samples
4.5.1. Pretreated charcoal coated with TBC
The desorption efficiency of 1,3-butadiene was
determined by injecting the gas onto 100-mg portions of
the recommended collection medium. The samples were spiked and then
stored in a freezer overnight prior to analysis. The average
desorption efficiency over the range of 0.6 to 2 times the target
concentration was 96.4%. The individual results are presented in
Table 4.5.1.1.
The stability of desorbed samples was investigated by reanalyzing
the target concentration desorption samples at various times after
carbon disulfide addition. Freshly prepared standards were used for
each analysis. The sample vials were resealed immediately after each
analysis. The results of this study are presented in Table 4.5.1.2.
The percent recovery is based on the theoretical amount of
1,3-butadiene added to the original samples.
Table 4.5.1.1. The Desorption Efficiency of
1,3-Butadiene from Charcoal Coated with TBC
|
× target conc. µg/sample |
0.6× 3.86 |
1× 6.75 |
2× 13.5 |
|
desorption efficiency, %
![mean](../mean.gif) |
94.3 95.4 96.4 96.9 94.8 96.9 95.8
95.8 |
100.0 97.0 102.0 96.0 94.3 98.8 98.0
98.0 |
97.5 97.5 95.8 95.2 93.4 92.5 95.3
95.3 |
|
Table 4.5.1.2. The Stability (% Recovery) of
1,3-Butadiene After Desorption from Charcoal Coated with
TBC
|
time |
sample number |
h |
1 |
2 |
3 |
4 |
5 |
6 |
![mean](../mean.gif) |
|
1 4 9 16 24 58 |
100.0 98.7 90.2 84.2 82.4 66.8 |
97.0 95.1 89.4 92.2 76.8 50.4 |
102.0 97.7 92.2 84.1 79.7 52.3 |
96.0 89.0 88.7 81.3 76.6 61.5 |
94.3 88.6 88.0 80.3 72.3 60.6 |
98.8 87.4 89.4 86.6 79.0 64.2 |
98.0 92.8 89.6 83.1 77.8 59.3 |
|
To determine if the stability of desorbed samples could be
improved, the following experiment was performed: twelve samples
were prepared by injecting 1,3-butadiene gas, at the
target concentration, onto 100-mg portions of the
recommended sampling media. The samples were spiked and then stored
in a freezer overnight prior to analysis. Following desorption and
analysis, the carbon disulfide was separated from the charcoal for
six of the samples. The other six samples were not separated. All of
the samples were reanalyzed using freshly prepared standards and the
results of this study are shown below.
Table 4.5.1.3. Effect of Charcoal on the Stability of
Butadiene in CS2
|
storage time h |
CS2/charcoal separated |
|
CS2/charcoal not
separated |
|
1 |
2 |
3 |
![mean](../mean.gif) |
|
1 |
2 |
3 |
![mean](../mean.gif) |
|
6 28 |
93.1 88.9 |
91.8 90.1 |
93.5 92.4 |
92.8 90.5 |
|
93.6 76.8 |
91.3 74.0 |
93.1 76.2 |
92.7 75.7 |
|
It appears that the stability of desorbed samples can be improved
by separating the carbon disulfide from the charcoal.
4.5.2. Untreated charcoal
The desorption efficiency of 1,3-butadiene was also
determined for untreated SKC, Inc. Lot 120 coconut shell charcoal in
the same manner as used for the recommended medium. The average
desorption efficiency over the range of 0.6 to 2 times the target
concentration was 60.4%. The individual results are presented in
Table 4.5.2.1.
The stability of 1,3-butadiene desorbed from
untreated SKC, Inc. Lot 120 charcoal was investigated in the same
manner as was the recommended medium. The results of this study are
presented in Table 4.5.2.2.
Table 4.5.2.1. The Desorption Efficiency of
1,3-Butadiene from SKC, Inc. Lot 120 Charcoal
|
× target conc. µg/sample |
0.6× 3.86 |
1× 6.75 |
2× 13.5 |
|
desorption efficiency, %
![mean](../mean.gif) |
61.6 66.7 61.5 54.4 52.3 51.7
58.0 |
67.3 64.1 61.7 62.0 57.9 53.3
61.0 |
67.1 65.0 62.8 61.4 58.7 58.8
62.3 |
|
Table 4.5.2.2. The Stability of 1,3-Butadiene After
Desorption From SKC, Inc. Lot 120 Charcoal (percent
recovery)
|
storage time |
sample number |
h |
1 |
2 |
3 |
4 |
5 |
6 |
![mean](../mean.gif) |
|
5 |
43.8 |
44.0 |
40.1 |
40.6 |
38.8 |
38.4 |
41.0 |
|
These data show that SKC, Inc. Lot 120 charcoal is inadequate for
this application because of sample instability.
4.6. Storage data
4.6.1. Pretreated charcoal coated with TBC
The test atmosphere was generated by diluting the effluent of a
gas cylinder, containing 100 ppm 1,3-butadiene, with
humid air. The resultant atmosphere contained 1 ppm
1,3-butadiene, the relative humidity of the air was 75%
and its temperature was 25°C. The 1,3-butadiene content
of the test atmosphere was determined by direct injection of 100 µL
of the atmosphere into a gas chromatograph. The gas chromatograph
was calibrated using 1,3-butadiene from another source
which had been diluted with dry air in a Teflon gas bag. Samples
were collected, using the recommended method, and they were stored
either at -25°C or at ambient temperature. The results of the
storage test are presented in Table 4.6.1. and also in Figures
4.6.1.1. and 4.6.1.2.
Table 4.6.1. 1,3-Butadiene Storage Test Using TBC Coated
Charcoal
|
storage time (days) |
%
recovery (ambient) |
|
storage time (days) |
%
recovery (refrigerated) |
|
0 3 6 10 13 17 |
102.2 97.8 100.9 93.8 82.1 81.2 |
102.2 93.3 98.7 87.5 88.8 76.3 |
99.1 93.3 100.9 83.9 80.8 76.8 |
|
0 4 7 11 14 18 |
97.0 99.5 93.2 98.6 104.1 84.3 |
101.8 96.9 104.9 94.6 96.9 94.6 |
97.8 98.7 102.2 92.4 98.2 96.4 |
|
4.6.2. Untreated charcoal
An additional ambient temperature storage test was performed
using untreated SKC, Inc. Lot 120 charcoal as sampling media. The
test atmosphere was generated and its concentration determined in
the same manner as was used for the recommended method. The
concentration of the test atmosphere was 1 ppm. The relative
humidity of this atmosphere was 70% at 23°C. Sampling was performed
at 0.05 L/min for 1 h. The results of this study are presented in
Table 4.6.2. and also in Figure 4.6.2.
Table 4.6.2. 1,3-Butadiene Ambient Temperature Storage
Test Using SKC, Inc. Lot 120 Charcoal
|
storage time days |
% recovery |
|
0 3 6 10 13 17 |
33.5 31.3 17.9 29.0 25.2 18.2 |
36.3 30.1 12.8 22.5 23.8 19.8 |
33.5 29.0 14.9 22.6 19.9 17.4 |
|
4.7. Reproducibility data
Samples were collected from a test atmosphere which was generated
by diluting the effluent of a gas cylinder, containing 100 ppm
1,3-butadiene, with humid air. The resultant atmosphere
contained 1 ppm 1,3-butadiene and the relative humidity
of the air was 84% at 23°C. The 1,3-butadiene content of
the test atmosphere was determined by the direct injection of 100 pL
of the atmosphere into a GC. The GC was calibrated using
1,3-butadiene, from another source, which had been
diluted with dry air in a Teflon gas bag. The samples and a draft copy
of this evaluation were given to a chemist unassociated with this
work. The samples were analyzed after 3 days storage at reduced
temperature. The results are presented in Table 4.7.
Table 4.7. Reproducibility
|
% recovery |
statistics |
|
100.0 102.9 100.5 98.0 96.6 85.4 |
= 97.2 SD = 6.2 |
|
4.8. A procedure to prepare specially cleaned charcoal coated with
TBC
4.8.1. Apparatus
4.8.1.1. Magnetic stirrer and stir bar.
4.8.1.2. Tube furnace capable of maintaining a temperature of
700°C and equipped with a quartz tube that can hold 30 g of
charcoal. A Lindberg Type 55035 tube furnace was used in this
evaluation.
4.8.1.3. A means to purge nitrogen gas through the charcoal
inside the quartz tube.
4.8.1.4. Water bath capable of maintaining a temperature of
60°C.
4.8.1.5. Miscellaneous laboratory equipment: One-liter vacuum
flask, 1-L Erlenmeyer flask, 350-mL Buchner funnel with a coarse
fritted disc, 4-oz brown bottle, rubber stopper, Teflon tape, etc.
4.8.2. Reagents
4.8.2.1. Phosphoric acid, 10%, by weight, in water. "Baker
Analyzed" Reagent grade was diluted with deionized water for use
in this evaluation.
4.8.2.2. 4-tert-Butylcatechol (TBC). The Aldrich Chemical
Company 99% grade was used in this evaluation. CAUTION- The bottle
was labeled: Sensitizer! Severe irritant! Toxic! Refrigerate!
4.8.2.3. Specially cleaned coconut shell charcoal, 20/40 mesh.
Specially cleaned charcoal (Lot number 482338) was obtained from
Supelco, Inc. for use in this evaluation. The cleaning process
used by Supelco is proprietary.
4.8.2.4. Nitrogen gas, GC grade.
4.8.3. Procedure
Weigh 30 g of charcoal into a 500-mL Erlenmeyer flask. Add about
250 mL of 10% phosphoric acid to the flask and then swirl the
mixture. Stir the mixture for 1 h using a magnetic stirrer. Filter
the mixture using a fritted Buchner funnel. Wash the charcoal
several times with 250-mL portions of deionized water to remove all
traces of the acid. Transfer the washed charcoal to the tube furnace
quartz tube. Place the quartz tube in the furnace and then connect
the nitrogen gas purge to the tube. Fire the charcoal to 700°C.
Maintain that temperature for at least 1 h. After the charcoal has
cooled to room temperature, transfer it to a tared beaker. Determine
the weight of the charcoal and then add an amount of TBC which is
10% of the charcoal, by weight. CAUTION- TBC is toxic and should
only be handled in a fume hood while wearing gloves. Carefully mix
the contents of the beaker and then transfer the mixture to a 4-oz
bottle. Stopper the bottle with a clean rubber stopper which has
been wrapped with Teflon tape. Clamp the bottle in a water bath so
that the water level is above the charcoal level. Gently heat the
bath to 60°C and then maintain that temperature for 1 h. Cool the
charcoal to room temperature and then transfer the coated charcoal
to a suitable container.
The coated charcoal is now ready to be packed into sampling
tubes. The sampling tubes should be stored in a sealed container to
prevent contamination. Sampling tubes should be stored in the dark
at room temperature. The sampling tubes should be segregated by
coated adsorbent lot number.
4.9. Chromatograms
The chromatograms were obtained using the recommended analytical
method. The chart speed was set at 1 cm/min for the first three min
and then at 0.2 cm/min for the time remaining in the analysis.
Figures 4.2.2. and 4.9.2 are chromatograms of
1,3-butadiene desorbed from the recommended sampling
media. The peak which eluted just before 1,3-butadiene is
a reaction product between an impurity on the charcoal and TBC. This
peak is always present, but it is easily resolved from the analyte.
The peak which eluted immediately before benzene is an oxidation
product of TBC.
Figure 4.1.1. Chromatogram of detection limit of the analytical
procedure. Peak identification was as follows: 1,
1,3-butadiene; 2, carbon disulfide; 3,
benzene.
Figure 4.2.2. Chromatogram of the reliable quantitation
limit. Peak identification was as follows: 1,
1,3-butadiene; 2, carbon disulfide; 3,
benzene.
Figure 4.1.2. Determination of the detection limit of the
overall procedure.
Figure 4.2.1. Determination of the reliable quantitation
limit.
Figure 4.3. 1,3-Butadiene calibration
curve.
Figure 4.6.1.1. Ambient temperature storage test for
1,3-butadiene collected on TBC coated
charcoal.
Figure 4.6.1.2. Reduced temperature storage test for
1,3-butadiene collected on TBC coated
charcoal.
Figure 4.6.2. Ambient temperature storage test for
1,3-butadiene collected on untreated
charcoal.
Figure 4.9.1. Chromatogram of a standard. Peak identification
was as follows: 1, 1,3-butadiene; 2, carbon disulfide;
3, benzene.
Figure 4.9.2. Chromatogram of a sample. Peak identification
was as follows: 1, 1,3-butadiene; 2, carbon disulfide;
3, benzene.
5. References
5.1. "Current Intelligence Bulletin 41, 1,3-Butadiene", U.S. Dept.
of Health and Human Services, Public Health Service, Center for
Disease Control, NIOSH.
5.2. "NIOSH Manual of Analytical Methods", 2nd ed.; U.S. Dept. of
Health Education and Welfare, National Institute for Occupational
Safety and Health: Cincinnati, OH. 1977, Vol. 2, Method No. 591 DHEW
(NIOSH) Publ. (US), No. 77-157-B.
5.3. Hawley, G. G., Ed. "The Condensed Chemical Dictionary", 8th
ed.; Van Nostrand Rienhold Company: New York, 1971; 139.
5.4. Chem. Eng. News (June 10, 1985), (63), 22-66.
|