Document RpDXdXR1K8RnRnY1X3VbjLNXn

VCl Personnel Monitor - Activated Carbon Trap Analytical Procedure SUMMARY A flame ionization gas chromatographic procedure is used to assay the amount of vinyl chloride adsorbed on activated charcoal. The vinyl chloride adsorbed on approximately 8. 3 g of activated carbon is removed with carbon disulfide washing. The carbon disulfide solution is chromatographed over a DC-200 column and vinyl chloride is detected and measured with a flame ionization detector. Quantification is made with reference to a calibration curve of detector response versus vinyl chloride concentration. We report a detection limit of 0. 01 mg of vinyl chloride from 8. 3 g of activated carbon. Furthermore, we have measurement with good precision at the 0. 1 mg level for vinyl chloride from 8. 3 g of activated carbon. In practice the stated limits refer to the detection of a specified amount of vinyl chloride in 50 ml of carbon disulfide. (50 ml of carbon disulfide is the recommended amount of washing solvent for our carbon trap personnel monitors.) The analytical method translates into a monitoring sensitivity of 0. 2 parts per million. This sensitivity is obtained by (a) using 8. 3 g of activated carbon in a trapping tube; (b) sampling for 4 hours at a flow rate of 1 liter per minute;and (c) washing the activated carbon with 50 ml of carbon disulfide and injecting up to 25ul of the solution into a flame ionization gas chromatogrz.ph. We are not certain at this time of the efficiency for removing vinyl chloride from activated carbon with carbon disulfide. In our best judgement, the efficiency is 80%. That is, it appears that we can remove 80% of the vinyl chloride adsorbed on the activated carbon. INTRODUCTION Activated carbon is reported to be an efficient and useful trapping mater for collecting analytical samples of vinyl chloride from the air*' .For this reason, we have adopted the use of activated carbon as the trapping media in our personnel monitors. The reported analyses of the activated carbon traps for vinyl chloride use carbon disulfide as a "washing-off" solvent and a flame ionization gas chromatography as the method of detection^. We have demonstrated that this method is successful in measuring vinyl chloride. It is a convenient method and it is a rapid method. 8 a BFG63616 2- - THE ANALYSIS The following description of the method is intended to provide a procedure for trapping the vinyl chloride in air with an activated carbon trap and measur ing the vinyl chloride adsorbed on activated carbon. Equipment and Reagents 1. Gas chromatograph with flame ionization detector (Hewlett Packard Model 5711A) 2. Wrist action shaker 3. Glass screw cap bottles, 8 oz. 4. Carbon disulfide, reagent grade 5. Wire rack (that will hold the 8 oz. bottles) 6. Rubber Serum stoppers (to fit the 8 oz. bottles) 7. Charcoal adsorbing cylinder, 150 mm polypropylene straight-drying tubes 8. Activated carbon, NUCHAR WV-H, 8x30 mesh; Westvaco Corp. , Covington, Va. 24426 9. Personnel monitoring pump; Bendix, Environmental Science Division, micronair, 8 hour, battery operated; available from: Twyman & Templeton & Co. , 1832 Akron-Peninsula Road, Akron, Ohio 44313, Telephone 216-929-3388 10. Syringes; glass, Pressure-Lok (Precision Sampling Corp.) 10 and 25 micro liter; and 100 jll gas sampling Pressure-Lok 11. Column, 10' x 1/8" stainless steel packed with 5% DC-200 on Chromosorb G GC Operating Conditions a. oven temperature - 65C b. injector temperature - 180C c. detector temperature - 250C BFG6361'! -3- d. carrier flow - 70 ml/min e. hydrogen flow ~20 ml/min f. air flow ~220 ml/min g- sample size: 10 micro liter; if peak is detected at range 10 or 1 repea t with 25 ul sample 12. Calibration curve: a calibration curve is prepared with the method of serial dilution reported by Ed DeCapita^ 13. 25 ml graduated cylinder 14. 250 ml soap bubble gas flow device; available from P. M. Zakriski 15. Tygon tubing 16. Personnel Equipment Harness: Part #26025-01; available from Safety First Supply Co. , 4900 Campbell Road, Willoughby, Ohio 44094, 216-946-1880 Preparation of Adsorption Tube The activated carbon (approximately 8. 3 g) is measured as carbon in a 25 ml graduated cylinder to the 20 ml mark. This carbon is used to fill a polypropylene drying tube plugged with glass wool at one end. On top of the "20 ml" of carbon, place a second glass wool plug. The tapered ends of the drying tubes are cut so as to fit 10 mm tygon tubing (which connects the tube to the pump). The carbon trap tubes may be prepared in advance and stored sealed with rubber bulbs. (The bulbs normally used on medicine droppers. ) Exposure of the Activated Carbon Tubes Each labeled tube is connected (with tygon tubing) to a pump and the combination of pump and adsorption tube is checked for flow rate. The w o\ recommended rate is 1 liter per minute. (When using the 250 cc soap bubble F* flow meter, a 15 second travel period will correspond to 1 liter per min. ) O0 After calibration, the tube/pump combination is stationed in the field (either u> on a man or on a fixture) and run for four hours. At the end of the four hour & period the flow of the tube/pump combination is measured and recorded befor e&> the pump is shut off. The tube is then removed, capped and sent to the laboratory for analysis. BFG63618 -4- Desorption of Vinyl Chloride The activated carbon is poured from the polypropylene tube into 50 ml of carbon disulfide which has been chilled in dry ice for 30 minutes. Immediately,, a serum stopper is used to seal the bottle. The carbon disulfide/carbon mb: bottles are supported in a wire rack in the dry ice bath. These bottles are kept in the dry ice 5 minutes after adding the activated carbon to the carbon disulfide. The bottles are then removed and placed on a wrist action shaker for 25 minutes (no more cooling necessary). The bottles are then removed and a gas chromato graphic analysis of the solution is performed. Gas Chromatography Normal operating conditions are to inject 10 microliters of the carbon disulfide into the injection port of the gas chromatograph. In the event that the peak is less than 25% of full scale when using the range 10 control, switch to a 25 microliter sample for the analysis. All samples are analyzed in triplicate and the average value of the VCl peak height is taken as the most reliable measure ment. The vinyl chloride elutes in approximately 2 minutes, followed at about 5 min. by the weak carbon disulfide peak. When vinylidene chloride is absent an internal standard of dichloromethane or 2-chloropropane can be used. Both elute immediately after vinyl chloride and before the carbon disulfide. We have noted that methanol (and we suspect ethanol) elutes simultaneously with vinyl chloride. Therefore, care must be taken to determine that methar.ol is not present. Methanol can be detected by following the procedure of DeCapita mentioned earlier. DISCUSSION To check the vinyl chloride desorption efficiency of carbon disulfide we carried out 2 separate experiments. We field loaded several carbon adsorption tubes adjacent to the Bendix analyzer in Building 451 at the Avon Lake General Chemical Plant. Then, we analyzed these tubes and calculated the building vinyl chloride concentration. This work showed the carbon tube values to be 70% of the Bendix, time weighted average, values. L>0 0 BFG63619 -5- The second experiment was to load carbon adsorption tubes with vinyl chloride using the apparatus of O'Mara and Lees^. The carbon adsorption tubes were then analyzed by our chromatographic procedure. The values from gas chromatography are +10% of the loadings reported by O'Mara and Lees. This agreement was for carbon samples holding 14 mg, 8 mg and 6 mg vinyl chloride. I interpret the results as an indication that at least 80% of the vinyl chloride is desorbed from the activated carbon. The difference between the two efficiency tests may be due to poor flow control during the field loading of tubes or the fundamental difference between the Bendix value and the carbon value. We have observed that the pumps do not hold a constant flow. A gradually reducing flow during our tests would account for the lower values. Regarding the second point, we note that the carbon tube is a collection, continuously, over four hours, and therefore is a true integration. The Bendix value is based upon a collection of short measurement (Z minutes each) generated every 12 minutes. Therefore, the carbon tube represents a true integration of vinyl chloride over a period of time while the Bendix value is an extrapolation to the vinyl chloride present over a 4 hour period. We have used external calibration but find it to be less reliable than an internal standard procedure. Instrument operating conditions (flame temp.and efficiency) change regularly and are not accounted for with a procedure in which a calibration curve is generated weekly or monthly. Furthermore, in preparing standards containing vinyl chloride, dilution errors are always possible. During a serial dilution procedure the first standard should contain no more than 0. 1 vinyl chloride. If it contains more than 0. 1 g, there will be significant partiohing of vinyl chloride between the solution and head space. Consequently, the aliquot used for dilution will be low in vinyl chloride. The internal standard technique has not been used yet. We have not completed its development. This change is expected soon and it will be incorporated into the procedure. Finally, we have investigated the use of Water, methanol, dichlorometha, ne and bromobenzene as desorbing solvents for vinyl chloride from activated carton. None of these is as efficient as carbon disulfide. I wish to acknowledge the help and cooperation of the following people: Joe DiSalvo Pete Dmyterko Roy Whitacre Lynn Wallis Bob Zimmer Bernie Booth Lin Crider John Me Cool BFG63620 6- - FOOTNOTES A. A. Allemang and R. A. Gondeau, Dow Chemical Co., Midland, Michigan, "Monitoring Personnel Exposure to Chlorinated Hydrocarbons in an Industrial Work Environment. " 2. R. C. Borne, S. P. Smock (Dow Chemical Co., Glycerine Products Dept., January 15, 1974, "Analysis of Environmental Air Samples. " 3. E. G. DeCapita, BFG Chemical Co., Avon Lake Technical Center, Procedure #978, May 16, 1973. 4. M. M. O'Mara and G. A. Lees, "An Analytical System for Measuring the Adsorption of VCM on Charcoal, " B. F. Goodrich Chemical Co. , Avon Lake Technical Center, February 28, 1974. 5. J. B. Pausch, "Evaluation of Some Activated Carbons for Use in the Vinyl Chloride Monomer Personnel Monitor, Research Report, B. F.Goodrich, March 13, 1974. By: P. M. Zakriski B. F. Goodrich R&D Center BFG63621 25133096 DISTRIBUTION Cleveland W. F. Bixby W. E. Brodine H. R. Calsing R. J. Coffey B. A. DiLiddo C. R. Flynn K. Greene E. W. Harrington R. P. Kenney T. R. Linak J. F. Malone J. L. Nelson E. B. Osborne H. R. Rex M. E. Roha G. D. 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