1. General Discussion
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
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
1.1.4 Physical properties and other descriptive information4
||109 °C (230 °F)(cc)
||Isobutyric acid, 1-isopropyl-2,2-dimethyltrimethyl ester; Kodaflex
||acetone, alcohol, benzene, and carbon tetrachloride
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)
2. Sampling Procedure
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
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.
Detection Limit of the Overall Procedure for 2,2,4-Trimethyl-1,3-pentanediol diisobutyrate
|mass per sample
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
Figure 1.2.3. Chromatogram of the 2,2,4-trimethyl-1,3-pentanediol diisobutyrate peak in the standard near the
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.
3. Analytical Procedure
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-
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.
2.4 Extraction efficiency
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
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.
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%.
Extraction Efficiency (%) of 2,2,4-Trimethyl-1,3-pentandiol diisobutyrate
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.
Retention Efficiency (%) of 2,2,4-Trimethyl-1,3-pentandiol diisobutyrate
| sample number
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.
Storage Test for 2,2,4-Trimethyl-1,3-pentandiol diisobutyrate (% Recovery)
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-
2.8.2 Suspected interferences should be reported to the laboratory with submitted samples.
Adhere to the rules set down in your Chemical Hygiene Plan. Avoid skin contact and inhalation
of all chemicals and review all appropriate MSDSs.
4. Recommendations for Further Study
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
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
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
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.
3.2.1 2,2,4-Trimethyl-1,3-pentandiol diisobutyrate, Reagent grade. Aldrich 99% (lot 08515DS)
was used in this evaluation.
3.3 Standard preparation
3.2.2 Carbon disulfide, Reagent grade. Omni-Solv 99.99% (lot 34279) was used for this
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.
3.3.1 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.
3.4 Sample preparation
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.
3.4.1 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
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.
3.5.1 Gas chromatograph conditions.
3.6 Interferences (analytical)
||100°C (column), hold 2 min, ramp at 10°C/min to 180°C, hold 10 min
250°C (injector) 250°C (detector)
|column gas flow:
||2.9 mL/min (hydrogen)
||1.9 mL/min (hydrogen)
||1.0 µL (19:1 split)
||60-m × 0.32-mm i.d. capillary DB-WAX (0.5-µm
||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)
||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
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
(Y = 3.34E5× + 5808).
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
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.
||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
||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
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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