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 com- pounds occur in laboratory studies of sulfur atom chemis- try (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 consider- ation has been given the additional problem of higher boiling components which are often present in practical mixtures. The best separation of the low boiling compo- nents has been achieved using Deactigel (9). Although after an 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 sin- gle analysis separation of both low and high boiling mer- captans, tritolyl phosphate liquid phase has been used on Chromosorb P support.

In our work with sulfur atom chemistry, we often en- counter COS and H2S as well as mercaptans, sulfur diox- ide, and sulfenyl chloride compounds. It is desirable to have available a single analysis scheme which allows sepa- ration of the individual components of such a mixture. We have developed such a procedure using two chromato- graphic 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

(1 964). (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, and 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

(1 969).

S W I T C H 1 / n S W l T C H 3

THERM ISTER DETECTOR

S W I T C H 2 u/ S W I T C H 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 schemati- cally illustrated in Figure 1. Four Whitey 316 Stainless Steel tog- gle valves are incorporated in the system. Column A is 20 feet long and column B is 10 feet long. The detector used is a Gow- Mac 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 re- versed: 2 and 3 opened, 1 and 4 closed. The flow is thus reversed in column A while being maintained in the same direction in col- umn B. This procedure results in two different effective column lengths for different fractions of the sample. The low boiling frac- tion (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 separa- tion 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 signifi- cant 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, and D. R. Deans, Talanta,

16, 797 (1969). (15) R . K. Stevens, J. D. Mul ik , 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 (1 972).

ANALYTICAL CHEMISTRY, VOL. 45, NO. 11 , SEPTEMBER 1973 1963

Table I. Retention Volumes for Selected Sulfur Compounds Compound Retention volume, m W b

HzS 507 sc12 1761 CH3SH 2253 so2 2477 CH3CHzSH 3429

CHzSCHz 7425

Thiophene 19560 Retention

volumes reported are relative to air which appears at 300 ml after injec- tion. The precision of thesevalues is &lo%.

cos 385

cs2 3780

CC13SCI 9347

Carrier (He): 60 ml/min, column temperature 22 “C.

mixture a t liquid nitrogen temperature. Recovery of the sulfur-containing components was excellent. With the de- tection 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 concentra- tions (15, 16). Presumably a system of this type can be constructed utilizing the switching technique described here.

T I M E ( m i n t

Figure 2. Chromatogram of su l fur compound mixture analyzed on switching system with helium carrier flow, 60 ml/min; tem- perature, 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 Cam- ille 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 concentra- tions of dicyclomine (P-diethylaminoethyl-l-cyclohexylcy- clohexanecarboxylate hydrochloride) following its admin- istration at normal therapeutic dose levels to human subjects in order to carry out bioavailability studies on different dose forms of dicyclomine. The oral dosage con- templated was either 20 mg in a “normal” tablet formula- tion or 40 mg in a sustained release tablet formulation. A previous report ( I ) indicated that maximum plasma con- centrations 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 dicy- clomine and was an estimate based on counts/min/ml of plasma. A method of analysis of dicyclomine was re- quired, 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 metabo- lites, 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 (1 968).

methods was not satisfactory. I t 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 bioavail- ability 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 (100-120 mesh). Column efficiency was 600 plates per foot. It was important to ensure that the column was well conditioned since

1964 ANALYTICAL CHEMISTRY, VOL. 45, NO. 11, SEPTEMBER 1973