Gas Chromatographic Separation of Hydrogen Sulfide, Carbonyl Sulfide, and Higher Sulfur Compounds with a Single Pass System Larry Kremer and Leonard D. Spicer University of Utah, Salt Lake City, Utah 84 112
Gas chromatographic analysis of reaction product mixtures containing a wide variety of sulfur compounds is a difficult problem, primarily because such systems often contain small amounts of hydrogen sulfide and carbonyl sulfide in addition to the more easily separated higher boiling components. Various mixtures of these sulfur compounds occur in laboratory studies of sulfur atom chemistry (1-3) as well as in industrial processes such as coal and oil gasification (4, 5), refinery operation, and kraft paper pulp processing (6-8). The difficulty in separating H2S and COS by gas chromatography is well known ( 1 , 9) and several accounts have recently addressed themselves to this problem (9-12). In these reports, little consideration has been given the additional problem of higher boiling components which are often present in practical mixtures. The best separation of the low boiling components has been achieved using Deactigel (9). Although after a n acid wash treatment this material is reported to give good separations regardless of batch purchased, it suffers from significant batch variations as do the various silica gels. To avoid this difficulty and also produce a single analysis separation of both low and high boiling mercaptans, tritolyl phosphate liquid phase has been used on Chromosorb P support. In our work with sulfur atom chemistry, we often encounter COS and H2S as well as mercaptans, sulfur dioxide, and sulfenyl chloride compounds. It is desirable to have available a single analysis scheme which allows separation of the individual components of such a mixture. We have developed such a procedure using two chromatographic columns and a gas flow reversal technique which gives a variable effective column length for the individual sulfur compounds.
EXPERIMENTAL The chromatography columns used in this study were made from Y 4 - h aluminum tubing packed with 30% tritolyl phosphate on Chromosorb P support. Tritolyl phosphate was obtained from Eastman and used without further purification. This liquid phase selection was made on the basis that a short (6-ft) column of tri(1) P. Fowles, M. deSorgo. A. J. Yarwood, 0. P. Strausz, and H . E. Gunning, J. Amer. Chem. SOC.,89, 1352 (1967). (2) L. Church and F. S.Rowland, Radiochim. Acta, 16, 55 (1971). (3) M . L. Hyder and S. S. Markowitz, J. Inorg. Nucl. Chem., 26, 257 (1964). (4) W . Strauss, "Air Pollution Control," Wiley-lnterscience, New York, N.Y., 1970, p 110. (5) H. A. Gollmar, "Removal of Sulfur Compounds From Coal Gas," in "Chemistry of Coal Utilization," Vol. 2, John Wiley and Sons, New York, N . Y . , 1945. (6) W. Summer, "Odour Pollution of Air," Leonard Hill, London, 1971. (7) T. Applebury and M . J. Schaer, J. Air Pollut. Contr. Ass., 20, 83 (1970). (8) D. F. Adams. R. K. Koppe, a n d W. N . Tuttle, J. Air Pollut. Contr. Ass., 15, 31 (1965). (9) W. L. Thornsberry, Anal. Chem., 43, 452 (1971). (10) H . Brinkmann. Chem. Tech. (Leipig), 17, 168 (1965). (11) E. L. Obermiller and G . 0. Charlier, J. Gas. Chromatogr., 6, 446 ( 1 968). (12) E. L. Obermiller and G . 0. Charlier, J. Chromatogr. Sci., 7, 580 (1969).
SWITCH 1 / n S W l T C H
SWITCH 2
u/
3
THERM ISTER DETECTOR
SWITCH 4
Figure 1. Schematic drawing of the switching system employing two gas chromatography columns tolyl phosphate was reported to provide an adequate separation of higher boiling organic sulfur compounds (13). Both 10-foot and 20-foot columns were used in the study reported here. The gas
chromatograph used is a homebuilt unit completely fabricated from stainless steel and glass. Research grade chemicals were used in all cases for standards. The two-column switching system for flow reversal is schematically illustrated in Figure 1. Four Whitey 316 Stainless Steel toggle valves are incorporated in the system. Column A is 20 feet long and column B is 10 feet long. The detector used is a GowMac thermister cell although much more sensitive detectors exist (7, 14-16) for use with sulfur compounds. Helium carrier gas was used typically at a flow rate of 60 ml/min with the column at a temperature of 22 "C. The sample mixture was injected into the system with valves 1 and 4 open and valves 2 and 3 closed. After a preselected time long enough to allow H2S and COS to pass through column A, the valves are reversed: 2 and 3 opened, 1 and 4 closed. The flow is thus reversed in column A while being maintained in the same direction in column B. This procedure results in two different effective column lengths for different fractions of the sample. The low boiling fraction (HzS, COS) must pass through the entire 30 feet of column whereas the higher boiling fraction is effectively separated by only 10 feet of column.
RESULTS AND DISCUSSION Using this method we have adequately separated the following sulfur compounds: COS, HzS, SC12, CHsSH, SOz, CzHsSH, CS2, CH2SCH2, Cl&SCl, and thiophene. Switching the valves at 10.0 min after the appearance of air (15 min after injection), the retention volumes listed in Table I are obtained. A typical strip chart record of the chromatogram obtained from a mixture of six components is shown in Figure 2. One of the significant results of this work is the separation of H2S and COS. Since these compounds are often found in the presence of a large excess of air, an effort was made to determine whether an analysis without significant loss of H2S and COS could be made by first pumping out the air from a closed transfer vessel containing the (13) A. P. Ronald and W. A. B. Thornson, J. Fish. Res. Ed, Can.. 21, 1481 (1964). (14) R . M. Daynall, S. J. Pratt. T. S. West, a n d D. R. Deans, Talanta, 16, 797 (1969). (15) R . K. Stevens, J. D. Mulik, A. E. O'Keeffe. and K. J. Krost. Anal. Chem., 43,827 (1971). (16) F. Bruner, A. Liberti, M . Possanzini, and I . Allegrini, Anal. Chem., 44, 2070 (1972).
ANALYTICAL C H E M I S T R Y , VOL. 45, N O . 1 1 , SEPTEMBER 1973
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Table I. Retention Volumes for Selected Sulfur Compounds Compound
Retention volume, m W b
cos
385
HzS
507 1761
sc12 CH3SH
2253
so2
2477 3429 3780 7425 9347
CH3CHzSH
cs2
CHzSCHz CC13SCI Thiophene
19560
Carrier (He): 60 ml/min, column temperature 22 “C. Retention volumes reported are relative to air which appears at 300 ml after injection. The precision of thesevalues is & l o % .
mixture a t liquid nitrogen temperature. Recovery of the sulfur-containing components was excellent. With the detection system employed, however, it was not possible to study the recovery of these gases a t levels below 100 ppm in the air. Recent reports showing a method for analysis in the range below 1 ppm have appeared and indicate that a nonmetallic system is important at these low concentrations (15, 16). Presumably a system of this type can be constructed utilizing the switching technique described here. TIME ( m i n t
Figure 2. Chromatogram of sulfur compound mixture analyzed on switching system with helium carrier flow, 60 ml/min; temperature, 22 “C. Switching occurred after 15 min (arrow) (1) Air, (2) carbonyl sulfide, (3) hydrogen sulfide, (4) methyl mercaptan,
(5)sulfur dioxide, (6) ethyl mercaptan, (7) ethylene sulfide
Received for review February 7, 1973. Accepted April 23, 1973. The authors acknowledge support of this research by NATO under Research Grant No. 592 and by the United States AEC under Contract No. AT (11-1)-2190. LK would also like to acknowledge the Phillips Petroleum Company for graduate fellowship support. LDS is a Camille and Henry Dreyfus Teacher-Scholar (1971-76).
Determination of Dicyclomine in Plasma by Gas Chromatography Peter J. Meffin, George Moore, and Jack Thomas Department of Pharmacy, University of Sydney, Sydney, N. S. W. 2006, Australia A method was required to determine plasma concentrations of dicyclomine (P-diethylaminoethyl-l-cyclohexylcyclohexanecarboxylate hydrochloride) following its administration at normal therapeutic dose levels to human subjects in order to carry out bioavailability studies on different dose forms of dicyclomine. The oral dosage contemplated was either 20 mg in a “normal” tablet formulation or 40 mg in a sustained release tablet formulation. A previous report ( I ) indicated that maximum plasma concentrations of dicyclomine following oral administration of 30 mg to adult volunteers was in the order of 30 X g/ml. This value was obtained using 14C-labeled dicyclomine and was an estimate based on counts/min/ml of plasma. A method of analysis of dicyclomine was required, therefore, which was sensitive and quantitative to 1-2 x 10-9 g/ml of plasma. Since it was important to be able to discriminate between dicyclomine and its metabolites, a technique based on total radioactive counting ( 1 ) I . E. Danhof, E. C. Schreiber, D. S. Wiggans, and H . M. Leyland, Toxicoi. Appi. Pharrnacoi., 13, 16 (1968).
1964
methods was not satisfactory. It was also considered to be undesirable to administer radioactive drug to subjects for a routine analytical procedure. Further, multiple blood sampling would be required during the course of bioavailability experiments; hence, the volume of blood required for each determination had to be kept to a minimum, preferably 10 ml or less. A method is described which satisfies the above criteria. A gas chromatographic procedure is described which uses a nitrogen sensitive flame detector and a novel method of concentrating the extracted sample of dicyclomine prior to injection into the gas chromatograph. EXPERIMENTAL Equipment. A Hewlett-Packard 5750 series gas chromatograph fitted with a nitrogen sensitive flame detector (Hewlett-Packard, model 15161A)was used. Gas Chromatograph Conditions. The column was glass Ys-in. 0.d. and 5 feet long, packed with 3% O.V. 225 on Gas Chrom Q (100-120mesh). Column efficiency was 600 plates per foot. It was important to ensure that the column was well conditioned since
ANALYTICAL CHEMISTRY, VOL. 45, NO. 11, SEPTEMBER 1973
