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DIMETHYL SUCCINATE
Method number: |
PV2021 |
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Target concentration: |
1.5 ppm (10 mg/m3) |
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Procedure: |
Samples are collected by drawing a known volume of air
through a charcoal tube. Samples are desorbed with 1 mL of 1:99 dimethyl
formamide:carbon disulfide (DMF:CS2 ) for 30 minutes with
shaking and analyzed by gas chromatography using a flame ionization
detector (GC-FID). |
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Recommended air volume and sampling rate: |
20 L at 0.2 L/min |
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Reliable quantitation limit: |
0.013 ppm (0.081 mg/m3) |
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Special requirements: |
Samples should be refrigerated after sampling as soon
as possible, and analyzed within one week. |
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Status of method: |
Partially Evaluated Method. This method has been
subjected to established evaluation procedures, and is presented for
information and trial use. |
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Date: October, 1995 |
Chemist: Mary E. Eide |
Organic Service Branch I
OSHA Salt Lake Technical Center
Salt Lake City, UT 84165-0200
1. General Discussion
1.1 Background
1.1.1 History
The OSHA SLTC received samples collected on charcoal tubes requesting
analysis for dimethyl succinate (DMSU). A desorption study using carbon
disulfide showed poor recovery, 72%, when a concentration of 448 µg DMSU
was spiked on the tubes. Desorption studies using 1:99 DMF:CS2
averaged 93.8% recovery over the concentration range of 22.4 to 448 µg
DMSU. The retention study showed no loss of DMSU. The storage studies
had a loss of DMSU with samples collected with 20 liters humid air (80%
RH at 22°C), especially those stored at room temperature, but samples
stored under refrigeration had better recoveries. Storage recoveries,
corrected for desorption, on day 7 were: dry refrigerated 101%, dry
ambient 100%, humid refrigerated 92.8%, and humid ambient 82.2%. Storage
recoveries, corrected for desorption, on day 14 were: dry refrigerated
100%, dry ambient 98.8%, humid refrigerated 86.3%, and humid ambient
76.3%. Samples should be refrigerated as soon as possible after sampling,
and should be analyzed within one week of receiving them.
1.1.2 Toxic effects (This section is for information only and should not
be taken as the basis of OSHA policy.) (Ref. 5.2)
DMSU is a skin, eye, and mucous membrane irritant. The Canadian
recommended exposure limit for DMSU is 10 mg/m3. At the
time this study was written, there was no PEL or TLV for DMSU.
1.1.3 Workplace exposure (Ref. 5.2 and 5.3)
DMSU is used as a solvent in paints, lacquers, varnishes, nitrocellulose,
paint strippers, dyes, fats, photography, and waxes. DMSU is used in
perfumes and flavorings for candy, ice cream, and gum. DMSU is used in
the manufacture of other succinates.
1.1.4 Physical properties and other descriptive information (Ref. 5.2, 5.3, and 5.4)
Synonyms: |
Butanedioic acid, dimethyl ester; Dimethyl butanedioate;
Succinic acid, dimethyl ester |
CAS number: |
106-65-0 |
DOT: |
NA 1993 (flammable liquid) |
IMIS: |
D917 |
RTECS: |
WM7675000 |
Molecular weight: |
146.1 |
Flash point: |
85°C (185 °F)(cc) |
Boiling point: |
200°C |
Melting point: |
18°C |
Odor: |
sweet winey or fruity odor |
Color: |
clear liquid |
Density: |
1.1198 |
Molecular formula: |
C6H10O4 |
Structural formula: |
 |
The analyte air concentrations throughout this method are based on the
recommended sampling and analytical parameters. Air concentrations
listed in ppm are referenced to 25°C and 101.3 kPa (760 mmHg).
1.2 Limit defining parameters
1.2.1 Detection limit of the overall procedure (DLOP)
The detection limit of the overall procedure is 0.484 µg per sample
(0.00405 ppm or 0.0242 mg/m3). This is the amount of analyte
spiked on the sampler that will give a response that is significantly
different from the background response of a sampler blank.
The DLOP is defined as the concentration of analyte that gives a response
(YDLOP) that is significantly different (three standard
deviations (SDBR)) from the background response
(YBR).
YDLOP - YBR = 3(SDBR)
The direct measurement of YBR and SDBR in
chromatographic methods is typically inconvenient, and difficult because
YBR is usually extremely low. inconvenient, and difficult
because YBR is usually extremely low. Estimates of these
parameters can be made with data obtained from the analysis of a series
of samples whose responses are in the vicinity of the background
response. The regression curve obtained for a plot of instrument
response versus concentration of analyte will usually be linear.
Assuming SDBR and the precision of data about the curve
are similar, the standard error of estimate (SEE) for the regression
curve can be substituted for SDBR in the above equation.
The following calculations derive a formula for the DLOP:
Yobs |
= |
observed response |
Yest |
= |
estimated response from regression curve |
n |
= |
total no. of data points |
k |
= |
2 for a linear regression curve |
At point YDLOP on the regression curve
YDLOP = A(DLOP) +YBR |
A = analytical sensitivity (slope) |
therefore
Substituting 3(SEE) + YBR for YDLOP gives
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 lowest sampler loading was 1.12 µg/sample. This is the amount,
when spiked on a sampler, that would produce a peak approximately 10
times the background response for the sample blank. These spiked
samplers, and the sample blank were analyzed with the recommended
analytical parameters, and the data obtained used to calculate the
required parameters (A and SEE) for the calculation of the DLOP. Values
of 93.7 and 15.11 were obtained for A and SEE respectively. DLOP was
calculated to be 0.484 µg/sample (0.00405 ppm or 0.0242 mg/m3).
Table 1.2.1 Detection Limit of the Overall Procedure
|
mass per sample |
area counts |
(µg) |
(µV-s) |
|
0 |
0 |
1.12 |
125 |
2.24 |
241 |
3.36 |
354 |
4.48 |
419 |
5.60 |
544 |
6.72 |
670 |
7.84 |
770 |
8.96 |
855 |
10.1 |
955 |
11.2 |
1085 |
|
Figure 1.2.1. Plot of data to determine the DLOP/RQL.
1.2.2 Reliable quantitation limit (RQL)
The reliable quantitation limit is 1.61 µg per sample (0.013 ppm). This
is the amount of analyte spiked on a sampler that will give a signal that
is considered the lower limit for precise quantitative measurements.
The RQL is considered the lower limit for precise quantitative
measurements. It is determined from the regression line data obtained
for the calculation of the DLOP (Section 1.2.1), providing at least 75%
of the analyte is recovered. The RQL is defined as the concentration
of analyte that gives a response (YRQL) such that
YRQL - YBR 10(SDBR)
therefore
RQL = 1.61µg per sample (0.013 ppm)
Figure 1.2.2. Plot of data to determine the RQL.
Table 1.2.2 Reliable Quantitation Limit
|
mass per sample |
mass recovered |
recovery |
(µg) |
(µg) |
(%) |
|
1.12 |
0.981 |
87.6 |
2.24 |
2.09 |
93.3 |
3.36 |
3.20 |
95.2 |
4.48 |
4.31 |
96.2 |
5.60 |
5.23 |
93.4 |
6.72 |
6.40 |
95.2 |
7.84 |
7.59 |
96.8 |
8.96 |
8.43 |
94.1 |
10.1 |
9.47 |
93.8 |
11.2 |
10.5 |
93.8 |
|
Figure 1.2.3. Chromatogram of the RQL.
2. Sampling Procedure
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 tubes 7 cm × 4 mm i.d. × 6 mm o.d.
glass sampling tubes packed with two sections of charcoal, lot 120. The
front section contains 100 mg and the back section contains 50 mg of
charcoal, lot 120. The sections are held in place with glass wool plugs
and are separated by a urethane foam plug. For this evaluation,
commercially prepared sampling tubes were purchased from SKC Inc.,
(Eighty Four PA) catalog No. 226-01, Lot 120.
2.2 Technique
2.2.1 Immediately before sampling, break off the ends of the sampling
tube. All tubes should be from the same lot.
2.2.2 Attach the sampling tube to the 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 passes through the front section
of the tube first.
2.2.3 Air being sampled should not pass through any hose or tubing before
entering the sampling tube.
2.2.4 Attach the sampling tube vertically with the front section pointing
downward, in the worker's breathing zone, and positioned so it does not
impede work performance or safety.
2.2.5 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.
2.2.6 Submit at least one blank sample with each set of samples. Handle
the blank sample in the same manner as the other samples except draw no
air through it.
2.2.7 Record sample volumes (in liters of air) for each sample, along with
any potential interferences.
2.2.8 Ship any bulk samples separate from the air samples.
2.2.9 Submit the samples to the laboratory for analysis as soon as possible
after sampling. If delay is unavoidable, store the samples in a
refrigerator.
2.3 Desorption efficiency
The desorption efficiencies of DMSU were determined by liquid-spiking the
charcoal tubes with the analytes at 0.1 to 2 times the target
concentration. The loadings on the tubes were 22.4, 112, 224, and 448 µg
of DMSU. These samples were stored overnight at ambient temperature and
then desorbed with 1 mL of 1:99 DMF:CS2 with 0.25 µL/mL
p-cymene internal standard, and analyzed by GC-FID. The average
desorption efficiency over the studied range was 93.8%.
Table 2.3. Desorption Efficiency of DMSU
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% Recovery |
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|
0.1 X |
0.5 X |
1.0 X |
2.0 X |
Tube # |
22.4µg |
112µg |
224µg |
448µg |
|
1 |
93.6 |
95.4 |
94.4 |
92.4 |
2 |
92.7 |
92.1 |
92.0 |
93.1 |
3 |
92.4 |
92.8 |
95.4 |
96.1 |
4 |
91.5 |
93.6 |
96.0 |
94.3 |
5 |
91.6 |
93.8 |
94.6 |
95.2 |
6 |
92.1 |
95.0 |
95.4 |
95.7 |
average |
92.3 |
93.8 |
94.6 |
94.5 |
overall average |
93.8 |
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standard |
±1.50 |
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deviation |
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2.4 Retention efficiency
The glass wool in front of the front section of the charcoal tube was
pulled towards the end, so that none of it was in contact with the
charcoal. The glass wool was spiked with 448 µg DMSU, and the charcoal
tube had 24 L humid air (80% RH at 21°C) pulled through it at 0.2 L/min.
The glass wool was spiked to determine if DMSU would volatize off the
glass wool and collect onto the charcoal. They were opened, desorbed,
and analyzed by GC-FID. The retention efficiency averaged 98.7%. The
values in Table 2.4 were corrected for desorption efficiency. There was
no DMSU found on the glass wool indicating that all of it vaporized off.
There was no DMSU on the back sections of the tubes, indicating that no
breakthrough occurred.
Table 2.4 Retention Efficiency of DMSU
|
Tube # |
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% Recovered |
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Glass wool |
Front section |
Back section |
Total |
|
1 |
0.0 |
99.3 |
0.0 |
99.3 |
2 |
0.0 |
99.3 |
0.0 |
99.3 |
3 |
0.0 |
100 |
0.0 |
100 |
4 |
0.0 |
100 |
0.0 |
100 |
5 |
0.0 |
97.8 |
0.0 |
97.8 |
6 |
0.0 |
95.9 |
0.0 |
95.9 |
|
average |
98.7 |
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2.5 Sample storage
The front sections of twelve sampling tubes were each spiked with 448 µg
(3.75 ppm) of DMSU, then six tubes were stored in the refrigerator (-10°C),
and six were stored at room temperature 23°C. Twelve more tubes were
spiked with 448 µg DMSU, and had 20 liters of humid air (80% RH at 21°C)
drawn through them, before six tubes were stored in the refrigerator
(-10°C), and six were stored at room temperature 23°C. Three of each type
of samples were analyzed after 7 days and the remaining three samples of
each type after 14 days. The amounts recovered indicate that humidity
and temperature affect the ability of charcoal to retain intact the DMSU.
The recoveries decreased with time and/or added humidity, with the worst
recovery on day 14 day storage with humidity. Results are corrected for
desorption efficiency.
Table 2.5 Storage Test for DMSU
|
Time (days) |
%Recovery Humid Ambient |
%Recovery Humid Refrigerated |
%Recovery Dry Ambient |
%Recovery Dry Refrigerated |
|
7 |
79.6 |
93.5 |
101 |
101 |
7 |
79.7 |
92.3 |
101 |
101 |
7 |
87.3 |
92.6 |
98.8 |
100 |
average |
82.2 |
92.8 |
100 |
101 |
14 |
74.5 |
87.0 |
96.7 |
101 |
14 |
76.1 |
86.1 |
98.6 |
100 |
14 |
78.5 |
85.7 |
101 |
100 |
average |
76.3 |
86.3 |
98.8 |
100 |
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2.6 Recommended air volume and sampling rate.
Based on the data collected in this evaluation, 20 L air samples should
be collected at a sampling rate of 0.2 L/min.
2.7 Interferences (sampling)
2.7.1 It is not known if any compounds will severely interfere with the
collection of DMSU on the sampling tubes. In general, the presence of
other contaminant vapors in the air will reduce the capacity of the
charcoal tube to collect DMSU.
2.7.2 Suspected interferences should be reported to the laboratory with
submitted samples.
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.
2.8.3 Wear eye protection when breaking the ends of the glass sampling
tubes.
3. Analytical Procedure
3.1 Apparatus
3.1.1 The instrument used in this study was a gas chromatograph equipped
with a flame ionization detector, specifically a Hewlett Packard model
5890.
3.1.2 A GC column capable of separating the analyte from any interferences.
The column used in this study was a 60 meter capillary column with a
0.5 µm coating of DB-WAX, with an I.D. of 0.32 mm.
3.1.3 An electronic integrator or some suitable method of measuring peak
areas.
3.1.4 Two milliliter vials with TeflonTM-lined caps.
3.1.5 A 10µL syringe or other convenient size for sample injection.
3.1.6 Pipets for dispensing the desorbing solution. A Repipet®
dispenser was used in this study.
3.1.7 Volumetric flasks - 5 or 10 mL and other convenient sizes for
preparing standards.
3.2 Reagents
3.2.1 GC grade nitrogen, hydrogen, and air.
3.2.2 Dimethyl succinate (DMSU), Reagent grade
3.2.3 Carbon disulfide (CS2), Reagent grade
3.2.4 Dimethyl formamide (DMF), Reagent grade
3.2.5 p-Cymene (internal standard), Reagent grade
3.2.6 Desorbing solution was 1:99 DMF:carbon disulfide with 0.25 µL/mL
p-cymene internal standard.
3.3 Standard preparation
3.3.1 At least two separate stock standards are prepared by diluting a
known quantity of DMSU with the desorbing solution of 1:99 DMF:carbon
disulfide with 0.25 µL/mL p-cymene internal standard. The
concentration of these stock standards was 0.2 µL/mL or 224 µg/mL.
3.3.2 A third standard at a higher concentration was prepared to check
the linearity of the calibration. For this study, two analytical
standards were prepared at a concentration of 0.2 µL/mL (224 µg/mL), and
one at 1.0 µL/mL (1120 µg/mL) DMSU in the desorbing solution.
3.4 Sample preparation
3.4.1 Sample tubes are opened and the front and back section of each tube
are placed in separate 2 mL vials.
3.4.2 Each section is desorbed with 1 mL of the desorbing solution of
1:99 DMF:carbon disulfide with 0.25 µL/mL p-cymene internal
standard.
3.4.3 The vials are sealed immediately and allowed to desorb for 30
minutes with constant shaking.
3.5 Analysis
3.5.1 Gas chromatograph conditions.
Injection size: |
1 µL |
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Flow rates (mL/min) |
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Nitrogen (make-up): |
30 |
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Hydrogen(carrier): |
2 |
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Hydrogen(detector): |
40 |
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Air: |
420 |
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Temperatures (°C) |
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Injector: |
200 |
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Detector: |
220 |
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Column: |
50° for 2 min then 10°/min to 170° for 15 min |
Figure 3.5.1 Chromatogram of an analytical standard at the target concentration. Peak
identification: (1) carbon disulfide, (2) p-cymene, (3) DMF, and (4) DMSU.
3.5.2 Peak areas are measured by an integrator or other suitable means.
3.6 Interferences (analytical)
3.6.1 Any compound that produces a 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 desorbed. Generally, chromatographic conditions can be altered to
separate an interference from the analyte.
Figure 3.6.1 A mass spectra of dimethyl succinate (DMSU).
3.6.2 When necessary, the identity or purity of an analyte peak may be
confirmed by GC-mass spectrometer or by another analytical procedure.
3.7 Calculations
3.7.1 The instrument was calibrated with a standard of 224 µg/mL DMSU in
the desorbing solution. The linearity of the calibration was checked
with a standard of 1120 µg/mL.
3.7.2 If the calibration is non-linear, two or more standard at different
concentrations must be analyzed, bracketing the samples, so a calibration
curve can be plotted and sample values obtained.
3.7.3 To calculate the concentration of analyte in the air sample the following formulas are used:
(µg/m) (desorption volume) (desorption efficiency) |
= mass of analyte in sample |
(mass of analyte in sample) molecular weight |
= number of moles of analyte |
(number of moles of analyte) |
(molar volume at 25°C & 760mm) |
= |
volume the analyte will occupy at 25°C & 760mm |
(volume analyte occupies) (106)* (air volume) |
= ppm |
* All units must cancel.
3.7.4 The above equations can be consolidated to the following formula.
(µg/mL)(DV)(24.46)(106)(g)(mg) (20 L)(DE)(MW)(1000mg)(1000µg) |
= ppm |
µg/mL | = | concentration of analyte in sample or standard |
24.46 | = | Molar volume (liters/mole) at 25° and 760 mm Hg. |
MW | = | Molecular weight (g/mole) |
DV | = | Desorption volume |
20 L | = | 20 liter air sample |
DE | = | Desorption efficiency |
3.7.5 This calculation is done for each section of the sampling tube and the results added together.
3.8 Safety precautions (analytical)
3.8.1 Avoid skin contact and inhalation of all chemicals.
3.8.2 Wear safety glasses, gloves and a lab coat at all times while in the laboratory areas.
4. Recommendations for Further Study
Collection studies need to be performed from a dynamically generated test
atmosphere. Other sampling medias should be explored to find one that
will provide better storage stability.
5. References
5.1 Trade names Database on CCINFO CD-ROM Disc 95-2, Canadian Centre for
Occupational Health and Safety, Hamilton, Ontario.
5.2 Lide, D.R., "Handbook of Chemistry and Physics", 73rd Edition, CRC
Press Inc., Boca Raton FL, 1992, p. 3-470.
5.3 Windholz, M., "The Merck Index", Eleventh Edition, Merck & Co.,
Rahway N.J., 1989, p. 1399.
Page last updated: 03/30/2010
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