1. General Discussion
1.1 Background
1.1.1 History
Air samples were received at SLTC
collected on Chromosorb 106 tubes requesting analysis for
2,2,4-trimethyl-1,3-pentanediol diisobutyrate. Analysis by gas
chromatography with a flame ionization detector was chosen, because
this compound is a liquid at room temperature. Carbon disulfide was
selected for the extraction solvent and was found to give an
extraction efficiency of 100.1%. The analyte was found to be well
retained on the Chromosorb 106 tubes, with a retention efficiency
recovery of 100.4% and the storage stability recovery of 99.5% on Day
14 of ambient storage. Along with these studies, charcoal tubes were
also explored. The extraction efficiency on charcoal tubes using
carbon disulfide as a solvent showed non-linear extraction, with an
extraction efficiency of 98.1% for a loading of 23.34 mg to 88.6% for
a loading of 1.167mg. The extraction efficiency with 99:1 carbon
disulfide:dimethyl formamide averaged 100.8% over the range of 1.167
to 23.34 mg. The retention efficiency averaged 99.8%. The storage at
ambient temperature was 98.2% on Day 14, indicating that charcoal
tubes are a good alternative to the Chromosorb 106 tubes.
1.1.2
Toxic effects (This section is for information only and should not be
taken as the basis of OSHA policy.)1
2,2,4-Trimethyl-1,3-pentandiol
diisobutyrate is a contact irritant affecting the skin and mucous
membrane.
1.1.3 Workplace exposure2,3
2,2,4-Trimethyl-1,3-pentanediol
diisobutyrate is used as an intermediate in the manufacture of
plasticizers, surfactants, pesticides, and resins. It is used as a
viscosity control agent in plastisol, rotomolding, and rotocasting
operations. It is used in the production of vinyl flooring as a
hardening agent. Production exceeds one million pounds
annually.
1.1.4 Physical properties and other descriptive
information4
| CAS number: |
6846-50-0 |
|
|
| RTECS number: |
SA1420000 |
molecular weight: |
286.41 |
| melting point: |
-70 °C |
boiling point: |
280 °C |
| appearance: |
clear liquid |
molecular formula: |
C16H30O4 |
| odor: |
musty |
flash point: |
109 °C (230 °F)(cc) |
| auto ignition |
|
density: |
0.941 |
| temperature: |
423 °C |
|
|
| synonyms: |
Isobutyric
acid, 1-isopropyl-2,2-dimethyltrimethyl ester; Kodaflex TXIB;
2,2,4-trimethylpentanediol-1,3-diisobutyrate; TXIB |
| solubility: |
acetone, alcohol, benzene,
and carbon tetrachloride |
| IMIS:5 |
T350 |
|
|
| structural formula: |
 |
This method was evaluated according to the OSHA SLTC
“Evaluation Guidelines for Air Sampling Methods Utilizing Chromatographic
Analysis”6.
The Guidelines define analytical parameters, specify required laboratory
tests, statistical calculations and acceptance criteria. The analyte air
concentrations throughout this method are based on the recommended
sampling and analytical parameters.
1.2 Detection limit of the overall
procedure (DLOP) and reliable quantitation limit (RQL)
The DLOP
is measured as mass per sample and expressed as equivalent air
concentrations, based on the recommended sampling parameters. Ten
samplers were spiked with equal descending increments of analyte, such
that the highest sampler loading was 10.35 µg of 2,2,4-
trimethyl-1,3-pentanediol diisobutyrate. This is the amount spiked on a
sampler that would produce a peak approximately 10 times the response
for a sample blank. These spiked samplers were analyzed with the
recommended analytical parameters, and the data obtained used to
calculate the required parameters (standard error of estimate and slope)
for the calculation of the DLOP. The slope was 770.3 and the SEE was
101.8. The RQL is considered the lower limit for precise quantitative
measurements. It is determined from the regression line parameters
obtained for the calculation of the DLOP, providing 75% to 125% of the
analyte is recovered. The DLOP and RQL were 0.397µg and 1.32 µg
respectively.
Table 1.2
Detection Limit of the Overall Procedure for
2,2,4-Trimethyl-1,3-pentanediol diisobutyrate
|
mass per
sample
(µg) |
area
counts
(µV-s) |
|
0.00
1.04
2.07
3.11
4.14
5.18
6.21
7.25
8.28
9.32
10.35
|
0
638
1368
2265
3170
3966
4640
5620
6409
7029
7767
| |
Figure 1.2.1. Plot of data to determine
the DLOP/RQL for 2,2,4-trimethyl-1,2-pentandiol diisobutyrate. (Y
= 770X - 90.8) |
Below are chromatograms of the RQL level.
 |
 |
| Figure 1.2.2. Chromatogram of the RQL of
2,2,4-trimethyl-1,3-pentanediol diisobutyrate. (1 = carbon
disulfide; 2 = benzene (contaminant in the carbon disulfide); 3 =
p-cymene; and 4 = 2,2,4-trimethyl-1,3-pentanediol diisobutyrate)
|
Figure 1.2.3. Chromatogram of the
2,2,4-trimethyl-1,3-pentanediol diisobutyrate peak in the standard
near the RQL. | 2. Sampling Procedure
All safety practices that apply
to the work area being sampled should be followed. The sampling equipment
should be attached to the worker in such a manner that it will not
interfere with work performance or safety.
2.1 Apparatus
2.1.1 Samples are collected using a
personal sampling pump calibrated, with the sampling device attached,
to within ±5% of the recommended flow rate.
2.1.2 Samples are
collected with 7-cm × 4-mm i.d. × 7-mm o.d. glass sampling tubes
packed with two sections (100/50 mg) of Chromosorb 106. The sections
are held in place and separated with a glass wool plug and two
urethane foam plugs. For this evaluation, commercially prepared
sampling tubes were purchased from SKC, Inc. (catalog no. 226- 110).
2.2 Reagents
None required. 2.3 Technique
2.3.1 Immediately before sampling,
break off the ends of the flame-sealed tube to provide an opening
approximately half the internal diameter of the tube. Wear eye
protection when breaking ends. Use tube holders to minimize the hazard
of broken glass. All tubes should be from the same lot.
2.3.2
The smaller section of the adsorbent tube is used as a back-up and is
positioned nearest the sampling pump. Attach the tube holder to the
sampling pump so that the adsorbent tube is in an approximately
vertical position with the inlet facing down during sampling. Position
the sampling pump, tube holder and tubing so they do not impede work
performance or safety.
2.3.3 Draw the air to be sampled
directly into the inlet of the tube holder. The air being sampled is
not to be passed through any hose or tubing before entering the
sampling tube.
2.3.4 After sampling for the appropriate time,
remove the adsorbent tube and seal it with plastic end caps. Seal each
sample end-to-end with an OSHA-21 form as soon as possible.
2.3.5 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.
2.3.6 Record sample air
volumes (liters), sampling time (minutes) and sampling rate (mL/min)
for each sample, along with any potential interferences on the
OSHA-91A form.
2.3.7 Submit the samples to the laboratory for
analysis as soon as possible after sampling. If delay is unavoidable,
store the samples at refrigerator temperature. Ship any bulk samples
separate from the air samples. 2.4 Extraction efficiency
The extraction efficiency
was determined by liquid-spiking Chromosorb 106 with 2,2,4-trimethyl-
1,3-pentandiol diisobutyrate at 0.1 to 2 times the target concentration.
These samples were stored overnight at ambient temperature and then
extracted for 30 minutes with occasional shaking, and analyzed. The mean
extraction efficiency over the studied range was 100.1%. The wet
extraction efficiency was determined at 1 times the target concentration
by liquid spiking the analyte onto Chromsorb 106 tubes which had 10-L
humid air (absolute humidity of 15.9 mg/L of water, about 80% relative
humidity at 22.2°C) drawn through them immediately before spiking. The
mean recovery for the wet samples was 99.8%.
Table
2.4
Extraction Efficiency (%) of 2,2,4-Trimethyl-1,3-pentandiol
diisobutyrate |
|
| level |
sample number |
×target
concn |
mg per
sample |
1 |
2 |
3 |
4 |
5 |
6 |
mean |
|
0.1
0.25
0.5
1.0
1.5
2.0
1.0 (wet)
|
1.17
2.92
5.83
11.7
17.5
23.3
11.7
|
97.4
99.9
99.3
100.9
100.1
99.2
99.8
|
100.0
100.4
99.2
101.2
100.4
100.3
100.1
|
101.6
100.8
99.7
102.0
99.5
98.7
99.1
|
99.6
99.7
100.5
101.8
99.3
100.2
100.4
|
100.6
100.4
100.0
98.9
99.9
100.1
99.5
|
99.6
100.3
101.4
99.1
100.1
99.9
99.9
|
99.8
100.3
100.0
100.7
99.9
99.7
99.8
|
2.5 Retention
efficiency
Six Chromosorb 106 tubes were spiked with 23.34 mg
(199.2 ppm) of 2,2,4-trimethyl-1,3- pentanediol diisobutyrate and
allowed to equilibrate for 6 h. The tubes had 10 L humid air (absolute
humidity of 15.9 mg/L of water, about 80% relative humidity at 22.2°C)
pulled through them at 0.1 L/min. The samples were extracted and
analyzed. The mean recovery was 100.4%. There was no analyte found on
the backup section of any of the tubes.
Table
2.5
Retention Efficiency (%) of 2,2,4-Trimethyl-1,3-pentandiol
diisobutyrate |
|
| sample number
|
| section |
1 |
2 |
3 |
4 |
5 |
6 |
mean |
|
front
rear
total
|
100.8
0.0
100.8 |
100.4
0.0
100.4 |
99.1
0.0
99.1 |
102.1
0.0
102.1 |
100.5
0.0
100.5 |
99.5
0.0
99.5 |
100.4
0.0
100.4
|
2.6 Sample
storage
Nine Chromosorb 106 tubes were each spiked with 11.67 mg
(99.62 ppm) of 2,2,4-trimethyl-1,3- pentanediol diisobutyrate. They were
allowed to equilibrate for 6 h, then 10 L of air, with an absolute
humidity of 15.7 milligrams of water per liter of air (about 80%
relative humidity at 22.2°C), was drawn through them. Three samples were
analyzed immediately, and the rest were sealed and stored at room
temperature. Three more were analyzed after 7 days of storage and the
remaining three after 14 days of storage. The amounts recovered, which
are corrected for extraction efficiency, indicate good storage stability
for the time period studied.
Table
2.6
Storage Test for 2,2,4-Trimethyl-1,3-pentandiol
diisobutyrate (% Recovery) |
|
| sample number |
| time (days) |
1 |
2 |
3 |
mean |
|
0
7
14 |
100.9
98.0
99.6 |
101.2
99.1
99.6 |
101.2
99.1
99.6 |
100.3
98.6
99.5
|
2.7 Recommended air
volume and sampling rate.
Based on the data collected in this
evaluation, 10-L air samples should be collected at a sampling rate of
0.1 L/min for 100 minutes.
2.8 Interferences (sampling)
2.8.1 There are no known compounds which will severely
interfere with the collection of 2,2,4- trimethyl-1,3-pentanediol
diisobutyrate.
2.8.2 Suspected interferences should be
reported to the laboratory with submitted samples.
3. Analytical
Procedure
Adhere to the rules set down in your Chemical Hygiene
Plan. Avoid skin contact and inhalation of all chemicals and review all
appropriate MSDSs.
3.1 Apparatus
3.1.1 A gas chromatograph equipped with an FID. For this
evaluation, a Hewlett-Packard 5890A Series II Gas Chromatograph
equipped with a 7673A Automatic Sampler was used.
3.1.2 A GC
column capable of separating 2,2,4-trimethyl-1,3-pentanediol
diisobutyrate from the desorption solvent, internal standard and any
potential interferences. A 60-m × 0.32-mm i.d. capillary DB-WAX with a
0.5-µm df (J&W Scientific, Folsom, CA) was used in the evaluation.
3.1.3 An electronic integrator or some other suitable means of
measuring peak areas. A Waters Millennium32 Data System was used in
this evaluation.
3.1.4 Glass vials with
poly(tetrafluoroethylene)-lined caps. For this evaluation 2-mL vials
were used.
3.1.5 A dispenser capable of delivering 1.0 mL of
desorbing solvent to prepare standards and samples. If a dispenser is
not available, a 1.0-mL volumetric pipet may be used.
3.1.7
Volumetric flasks - 10-mL and other convenient sizes for preparing
standards.
3.1.8 Calibrated 10-µL syringe for preparing
standards. 3.2 Reagents
3.2.1 2,2,4-Trimethyl-1,3-pentandiol diisobutyrate,
Reagent grade. Aldrich 99% (lot 08515DS) was used in this evaluation.
3.2.2 Carbon disulfide, Reagent grade. Omni-Solv 99.99% (lot
34279) was used for this evaluation.
3.2.3 p-Cymene, Reagent
grade. Aldrich 99% (lot 11703TR) was used in this evaluation.
3.2.4 The extraction solvent was 0.25 µL/mL p-cymene in carbon
disulfide.
3.2.5 GC grade nitrogen, air, and
hydrogen. 3.3 Standard preparation
3.3.1 Prepare working analytical standards by injecting
microliter amounts of 2,2,4-trimethyl-1,3- pentanediol diisobutyrate
into volumetric flasks containing the extraction solvent. An
analytical standard at a concentration of 11.67 mg/mL (12.4 µL/mL) is
equivalent to 99.61 ppm based on a 10-liter air volume.
3.3.2
Bracket sample concentrations with working standard concentrations. If
sample concentrations are higher than the concentration range of
prepared standards, either analyze higher standards, or dilute the
sample. The higher standards should be at least as high in
concentration as the highest sample. Diluted samples should be
prepared with extracting solvent to obtain a concentration within the
existing standard range. The range of standards used in this study was
from 0.001 to 28.23 mg/mL. 3.4 Sample preparation
3.4.1 Remove the plastic end caps from the sample tubes
and carefully transfer the adsorbent sections to separate 2-mL vials.
Discard the glass tube, urethane foam plug and glass wool plug.
3.4.2 Add 1.0 mL of extraction solvent to each vial using the
same dispenser as used for preparation of standards.
3.4.3
Immediately seal the vials with poly(tetrafluoroethylene)-lined caps.
3.4.4 Shake the vials vigorously by hand several times during
the next 30 minutes. 3.5 Analysis
3.5.1 Gas chromatograph conditions.
| GC
conditions: |
|
| zone
temperatures: |
100°C (column),
hold 2 min, ramp at 10°C/min to 180°C, hold 10 min 250°C
(injector) 250°C (detector) |
| run time: |
20 min |
| column gas flow: |
2.9 mL/min
(hydrogen) |
| septum purge |
1.9 mL/min
(hydrogen) |
| injection size: |
1.0 µL (19:1
split) |
| column: |
60-m × 0.32-mm
i.d. capillary DB-WAX (0.5-µm df) |
| retention
times: |
3.98 min (carbon
disulfide); 4.61 min (benzene contaminate in the carbon
disulfide); 7.41 min (p-cymene); 18.01 min
(2,2,4-trimethyl-1,3-pentanediol diisobutyrate) |
| FID
conditions: |
|
| hydrogen flow: |
38 mL/min |
| air flow: |
450 mL/min |
| makeup flow: |
30 mL/min
(nitrogen) |
|
|
Figure 3.5.1. A
chromatogram of 941 µg/mL 2,2,4-trimethyl-1,3-pentanediol
diisobutyrate in carbon disulfide with 0.25 µL/mL internal
standard. Key: (1) carbon disulfide; (2) benzene contaminant in
the carbon disulfide; (3) p-cymene; (4)
2,2,4-trimethyl-1,3-pentanediol diisobutyrate. |
|
3.5.2 Peak areas are measured by an integrator or other
suitable means.
3.5.3 An internal standard (ISTD) calibration
method is used. A calibration curve can be constructed by plotting
ISTD- corrected response of standard injections versus milligrams of
analyte per sample. Bracket the samples with freshly prepared
analytical standards over a range of concentrations.
Figure
3.5.3. Calibration curve of
2,2,4-trimethyl-1,3-pentanediol
diisobutyrate
(Y = 3.34E5× +
5808). | 3.6
Interferences (analytical)
3.6.1 Any compound that produces a GC response and has a
similar retention time as the analyte is a potential interference. If
any potential interferences were reported, they should be considered
before samples are extracted. Generally, chromatographic conditions
can be altered to separate an interference from the analyte.
3.6.2 When necessary, the identity or purity of an analyte
peak may be confirmed by mass spectrometry or by another analytical
procedure. The mass spectrum in Figure was from the NIST spectral
library.
Figure 3.6.2. The
mass spectrum of
2,2,4-trimethyl-1,3-pentanediol
diisobutyrate. | 3.7 Calculations
The amount of analyte per sampler
is obtained from the appropriate calibration curve in terms of
micrograms per sample, uncorrected for extraction efficiency. This total
amount is then corrected by subtracting the total amount (if any) found
on the blank. The air concentration is calculated using the following
formulas.
 |
where |
CM is concentration by weight (mg/m³)
M is micrograms per sample
V is liters of air sampled
EE is extraction efficiency, in decimal
form
|
 |
where |
CV is concentration by volume (ppm)
VM is molar volume at 25 °C and 1 atm = 24.46
CM is concentration by weight
Mr is
molecular weight = 286.41 | 4. Recommendations for Further Study
Collection,
reproducibility, and other detection limit studies need to be performed to
make this a validated method.
1 Lewis, R, Sax's Dangerous Properties of Industrial Materials, Van
Nostrand Reinhold: New York, 1992, p. 3415.
2
Howe-Grant, M., Kroschwitz, J., Ed, Encyclopedia of
Chemical Technology, John Wiley & Sons: New York, 1992, vol 4
p. 741.
3 Environmental Defense Fund. http:
www.scorecard.org/chemical-profiles/summary.tcl?edf_substance_id=6846-50-0
(accessed 11/16/99).
4 Material Safety Data Sheet:
2,2,4-trimethyl-1,3-pentandiol diisobutyrate, Aldrich Chemical Co.,
Milwaukee, WI, Oct. 1999.
5 OSHA Chemical Sampling
Information. http://www.osha.gov/ChemSamp_data/CH_273990.html (accessed
11/17/99).
6 Burright, D.; Chan, Y.; Eide, M.;
Elskamp, C.; Hendricks, W.; Rose, M. C. EVALUATION
GUIDELINES FOR AIR SAMPLING METHODS UTILIZING CHROMATOGRAPHIC
ANALYSIS; OSHA Salt Lake Technical Center, U.S. Department of
Labor: Salt Lake City, UT, 1999. |
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