Elimination of Interference of Acetaldehyde in Gas Chromatographic Quantitation of Low Levels of Vinylchloride Anoop Krishen' and Ralph 0. Tucker The Goodyear Tire & Rubber Company, Research Division, Akron, Ohio 443 16
Stringent regulations for the use and handling of vinylchloride have been promulgated by the Occupational Safety and Health Administration. This has necessitated sampling and analytical techniques capable of detecting VCM (vinylchloride monomer) a t less than one part per million levels in various atmospheres, polymeric powders, films, and other fabricated materials. Quantitation of VCM has been achieved by three different approaches: 1) Adsorption of gaseous samples on charcoal followed by desorption with a solvent and determination by gas chromatography ( I , 2 ) . 2) Dissolution of solid sample in a solvent followed by gas chromatographic determination. 3) Gas chromatographic analysis of head space gas over a solution or powder a t an elevated temperature
3 8 1
(3).
In every case, extraneous components derived from the atmosphere, solvents, and processing conditions had to be resolved from VCM by use of appropriate columns in gas chromatography. One of the extraneous compounds expected to be present under widely varying conditions is acetaldehyde. I t has been reported to be produced on oxidation of propane ( 4 ) , aliphatic esters ( 5 , 6 ) , polypropylene (7), ethanol ( 8 ) , and ethane under appropriate thermal conditions. Its formation has also been observed among the gaseous products evolved during processing of poly(vinylch1oride) films and leathers (9). Thus, it is important to eliminate any interference due to acetaldehyde when analyzing for low levels of VCM.
DEAD VOLUME
'ill
IU SAMPLE TLBE
Figure 1. Calculation of the dead volume of the sampling system
EXPERIMENTAL Apparatus. The gas chromatographic unit was a Varian-Aerograph 1200 flame ionization chromatograph equipped with a 1-mV Brown Electronik recorder (Minneapolis-Honeywell Company, Brown Instrument Division, Phi!adelphia, Pa.). The peaks were recorded a t an electrometer range of 1 and a chart speed of 1h inch per minute. The column was a stainless steel tube 6-ft X I/s-in. 0.d. packed with 80-100 mesh Porapak Q (Waters Associates, Inc., Framingham, Mass.) The column was operated at 100 "C with helium flow of 40 ml per minute. A precolumn was prepared by packing a 6-in. X lh-in. 0.d. stainless steel tubing with a mixture of sodium bisulfite and glass wool. This column was installed ahead of the Porapak Q column. Known gas volumes were delivered by sampling tubes of different volumes on a Model 260 Loenco Pyrolyzer (Loenco Division, Infotronics Corp., Altadena, Calif.) Reagents. Calibrated mixtures of vinylchloride in air were obtained from Precision Gas Products, Inc., 681 Mill Street, Rahway, N.J. 07065. Sodium bisulfite, catalog No 3556 was obtained from J.T. Baker Chemical Company, Phillipsburg, N.J.
RESULTS AND DISCUSSION Retention Data. Retention times for a number of materials were obtained by direct injection of individual components. The data obtained are given in Table 1. Sensitivity. Dead volume of the sampling system was obtained by chromatographing the same VCM mixture using sample tubes of different volumes ( 1 0 ) and plotting the response vs. volume of the sampling tube as shown in Figure 1. The chromatogram obtained with 20.5 ng of VCM is shown in Figure 2. The lower limit of detectability for VCM was found to be 1 ng by injecting successively more dilute samples.
WYUTES
Figure 2. Gas chromatogram of 20.5 ng of VCM
2
L P
IO
Figure 3. Gas chromatogram of a mixture of acetaldehyde and VCM on a Porapak Q column (1) Acetaldehyde, (2) VCM
ANALYTICAL CHEMISTRY, VOL. 48, NO. 2 , FEBRUARY 1976
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was chromatographed again with the precolumn. T h e chromatogram obtained is shown in Figure 4. Acetaldehyde was completely eliminated and no diminution in the response for VCM was observed. Even at the 1-ng level, the VCM peak could be quantitated accurately.
LITERATURE CITED
0
2
4
6
6
'
0
$1 I h bTE 5
Figure 4. Gas chromatogram of a mixture of acetaldehyde and VCM on
a Porapak Q column with a sodium bisulfite precolumn
Table I. Retention Data on a 6-ft x I/Jn. Porapak Q Column at 100 "C with Helium Flow of 40 ml per Minute Component
Oxygen Methane Ethene Ethane Propene Pro pan e Propadiene
Retention time. sec
19
28 62 76 205 234 246
Component
Methylacetylene Methylchloride Cyclopropane Formaldehyde Acetaldehyde Vinylchloride Dichloromethane
Retention time. sec
2 48
252 264 277 422 446 1440
(1) S. A. Myers, J. H. Quinn, and W. C. Zook, Am. ind. Hygiene Assoc. J., 36, 332 (1975). (2) C. L. Fraust, Am. lnd. Hygiene Assoc. J., 36, 278 (1975). (3) A. R. Berens, 168th National Meeting, American Chemical Society, Atlantic City, N.J., 1974. (4) K. E. Kruglyakova and N. M. Emanuel, Izwest. Akad. Nauk SSSR, Otdel. Khim. Nauk, 1959, 1211; Chem. Abstr., 54, 7315b (1960). (5) E. W. Malmberg and B. Weinstein, Ohio J. Sci.. 59, 303 (1959); Chem. Abstr., 54, 2156h (1960). (6) A. Fish and A. Waris. J. Chem. SOC., 1962, 4513; Chem. Abstr., 58, 4349 (1963). (7) V. B. Miller, M. B. Nelman, V. S.Pudov, and L. I. Lafer, Vysokomol. Soedin., 1, 1969 (1959): Chem. Abstr., 54, 191231(1960). (8) E. A. Blyumberg, G. E. Zaikov, K. M. Maims, and N. M. Emanuei, Kinet. Katal., 1, 510 (1960); Chem. Abstr., 55, 205826 (1961). (9) G. A. D'Yakova and M. V . Aldyreva, Vopr. Gig. Tr. Profzaboi., Mater. Nauch. Konf. 1977, 132 (1972); Chem. Abstr., 81, 136909h (1974). (10) J. E. Cuddeback, S. R . Birch, and W. R. Burg, Anal. Chem., 47, 355 (1975). (11) J. A. Kerr and A. F. Trotman-Dickenson, Nature, 182, 466 (1958). (12) D. A. Leathard and B. C. Shurlock, "identification Techniques in Gas Chromatography." Wiley-lnterscience, New York, N.Y.. 1970, p 76.
RECEIVEDfor review August 18, 1975. Accepted October 8, 1975. Presented a t the 170th National Meeting, American Chemical Society, Chicago, Ill., August 28, 1975. Permission of T h e Goodyear Tire & Rubber Company to publish is gratefully acknowledged.
Acetaldehyde Interference. A mixture of acetaldehyde and VCM in air was injected and it produced the chromatogram shown in Figure 3. Under the concentration ratios of the two components present, satisfactory quantitation could be obtained for VCM. However, when the level of VCM was decreased. the gas chromatographic peak for it was reduced t o an imperfectly resolved shoulder. The normal peak broadening inherent when air volumes of 1 ml or more were injected, also seriously compromised the detection limit. Elimination of Interference. Analyses on different gas chromatographic columns failed to provide the required separation between acetaldehyde and VCM. When separation of these components was acceptable, interference from some of the other materials present in samples was encountered. T o completely eliminate this problem, the abstraction technique used by Kerr and Trotman-Dickenson (11, 12) was tried. The glycol-sodium bisulfite mixture used by them was replaced with dry sodium bisulfite mixed with glass wool. The use of glass wool avoided any problems in gas flow due to compaction of the dry powder. A 6-inch column of sodium bisulfite was installed ahead of the column. The mixture of acetaldehyde and VCM shown in Figure 3
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ANALYTICAL CHEMISTRY, VOL. 48, NO. 2, FEBRUARY 1976
CORRECTIONS Electrochemistry of Cobalt Tetraphenylporphyrinin Aprotic Media
In this article by L. A. Truxillo and D. G. Davis, Anal. Chem., 47, 2260 (1975), the p values for PrCN in both sections of Table VI11 are incorrect. The third line of the first section should read: 2
1
PrCN
4.6 X lo1'
Pyridine
T h e second line in the second section should read: 1
0
PrCN
4.0 X IO2
Pyridine
Electrochemical Characterization of Iron Porphyrin Complexes in Aprotic Solvents
In this article by L. A. Constant and D. G. Davis, Anal. Chem., 47,2253 (19751, Figures 1 and 2 have been reversed. However, the captions are correct.
