![]() DIMETHYL SUCCINATE
Organic Service Branch I 1. General Discussion
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)
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).
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
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:
At point YDLOP on the regression curve
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).
Detection Limit of the Overall Procedure
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)
Reliable Quantitation Limit
2. Sampling Procedure
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. 2.2 Technique
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 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
Desorption Efficiency of DMSU
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
Retention Efficiency of DMSU
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.
Storage Test for DMSU
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)
2.7.2 Suspected interferences should be reported to the laboratory with submitted samples. 2.8 Safety precautions (sampling)
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
3.1.2 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 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 RepipetŪ 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
3.2.2 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
3.3.2 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
3.4.2 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
Figure 3.5.1 Chromatogram of an analytical standard at the target concentration. Peak
identification: (1) carbon disulfide, 3.5.2 Peak areas are measured by an integrator or other suitable means. 3.6 Interferences (analytical)
3.6.2 When necessary, the identity or purity of an analyte peak may be
confirmed by 3.7 Calculations
3.7.2 If the calibration is 3.7.3 To calculate the concentration of analyte in the air sample the following formulas are used:
* All units must cancel. 3.7.4 The above equations can be consolidated to the following formula.
3.7.5 This calculation is done for each section of the sampling tube and the results added together. 3.8 Safety precautions (analytical)
3.8.2 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
5.2 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. |