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Gas chromatographic identification of sulfur gases in soil atmospheres
GAS CHROMATOGRAPHIC IDENTIFICATION SULFUR GASES IN SOIL ATMOSPHERES W. L. Department
BANWART
of Agronomy.
OF
and J. M. BREMNER
Iowa State University,
Ames. Iowa
Summary PSimplc gas chromatographic methods for idcntihcation of sulfur gases in soil atmospheres are described. They involve the use of a flame photometric detector fitted with a sulfur filter and of Teflon columns packed with Chromosorb T and Deactigel. The methods permit identification of 13 volatile sulfur compounds (sulfur dioxide. hydrogen sulfide. carbon disuhide. carbonyl sulfide, sulfur hexafluoride, methyl mercaptan. ethyl mercaptan. rr-butyl mcrcaptan. dimethyl sulfide. ethyl methyl sulfide, diethyl sulfide. dimcthyl disulfidc. and diethyl disullidc) in an containing trace (nanogram) amounts of these compounds, and they are not subject to interference by vartous gases known to be evolved from soils under aerobic or anaerobic conditions. The Deactigel column is not required if the gas mixture analyzed does not contain hydrogen sulfide or carbonyl sulfide.
INTRODUCTION
on the sulfur cycle has been hindered by the lack of sensitive and specific methods of studying evolution and sorption of sulfur gases by soils. The need for such methods has been emphasized by recent work showing that soils have the capacity to sorb substantial amounts of sulfur gases identified as atmospheric pollutants (Smith. Bremner and Tabatabai. 1973) and can evolve volatile sulfur compounds, particularly if they contain residues of cruciferous plants (Lewis and Papavizas. 1970; Lovelock, Maggs and Rasmussen, 1972). The purpose of this paper is to describe gas chromatographic methods that have proved satisfactory in our laboratory for research on evolution and sorption of sulfur gases by soils. These methods allow separation and identification of trace (nanogram) amounts of all the volatile sulfur compounds recognized as air pollutants (see Leithe, 1970) or known to be evolved from soils or produced by microorganisms (see Freney, 1967; Lewis and Papavizas. 1970; Kadota and ishida, 1972; Lovelock et cd.. 1972). Sulfur hexafluoride (SF,) was included because it has been proposed as a tracer gas for air pollution research (Saltzman. Coleman and Clemens. 1966). Research
MATERIALS AND METHODS
Ethyl mercaptan (CH,CH,SH), ,r-butyl mercaptan (CH,CH,CH,CH,SH). carbon disulfide (CS,). ethyl methyl sulfide (CH,CHZSCH,). dimethyl sulfide (CH,SCH,), diethyl sulfide (CH,CH,SCH,CH& dimethyl disulfide (CH,SSCH,). and diethyl disulfide (CH, CH, SSCH,CH, ) were obtained from Fisher Scientific Co., Chicago, Illinois. Methyl mercaptan (CH,SH), hydrogen sulfide (HZS). sulfur dioxide (SO,),
carbonyl sulfide (COS), sulfur hexafluoride (SF,). nitric oxide. nitrous oxide, nitrogen dioxide, hydrogen, acetylene, carbon methane, ethylene, ammonia, monoxide. and carbon dioxide were obtained (as purified compressed products) from Matheson Company, Joliet. Illinois. The gas mixtures used to develop and evaluate the gas-chromatographic methods described were prepared by injecting small amounts of the test compounds into air contained in glass bottles sealed with the Mininert valves supplied by Precision Sampling Corporation, Baton Rouge, Louisiana (these valves are Teflon. gas-tight. bottle-closure devices that permit injection or removal of gas samples by gas syringes). The syringes used were the leak-proof, Pressure-Lok gas syringes supplied by Precision Sampling Corporation. The gas chromatograph used was a Beckman GC-4 instrument equipped with a Melpar flame photometric detector (Tracer Inc.. Austin, Texas) connected to a Beckman Model 1005 1-mV lo-in. recorder. The detector was fitted with a sulfur tilter (394 nm) and was operated at I I O-‘C with a H, flow rate of 75 ml min ‘, an 0, flow rate of 20 ml mini’, and an air flow rate of60mlmin~’ The columns used were: (I) 1020 cm of 2.16 mm (i.d.) Teflon (FEP) tubing packed with 40-60 mesh Chromosorb T coated with polyphenyl ether (IY’,,) and H, PO, (0.5%); (2) 30 cm of 2.16 mm (i.d.) Teflon (FEP) tubing packed with 12@140 mesh Deactigel. The Chromosorb T column was obtained from Supelco Inc., Bellefonte. Pennsylvania. The materials used to prepare the Deactigel column were obtained from Applied Science Laboratories, State College, Pennsylvania. Both columns were operated isothermally (Chromosorb T column, 1OO’C; Deactigel column. 50°C) with nitrogen as the carrier gas (N, flow rate. 80 ml min _ ’ ), 113
114
W. L. RESL’LTS
AND
and J. M. BREM~~K
BANWAKT
DISCUSSION
The methods described are based on work by Stevens. Mulik. O’KeetTc and Krost (1971). who showed that trace amounts of H,S. SO,, CH,SH, and CH,SCH, in air could be separated and identified by gas chromatography using a flame photometric detector and a Teflon column packed with Haloport-F coated with a mixture of polyphcnyl ether and H,PO, (see also Stevens and O’Keeffe. 1970). The Chromosorb T column described here is essentially the same as that used by Stevens er ~1. (1971) (Haloport-F and Chromosorb T are trade names for Teflon products), but the column temperature is higher (100 instead of 50 C). A column temperature of 100-C was adopted in our work because we found that this was the optimum temperature for separation and identification of the 13 sulfur compounds studied [Stevens et ul. (1971) studied onlv four of these compounds]. The separations achieved with the Chromosorb T column at 100°C are illustrated by Fig. 1. which shows that this column permits identification of nanogram amounts of II of the 13 compounds studied and gives a composite peak with HIS and COS that is separated from the peaks obtained with other sulfur compounds. Figure 2 shows that the presence of COS can readily be established by gas chromatography using a flame photometric detector and the Deactigel column described because Deactigel sorbs H,S, mercaptans, and alkyl sulfides, but allows separation and identification of trace amounts of COS, CS,. and SF,. Analyses of 500-~1 samples of air treated with different amounts of COS and other sulfur compounds showed that the Deactigel procedure described permits identification of I ng of COS in the presence of 2000 ng of H,S, mercaptans, and
alkyl sulfides. Trace amounts of COS have been detected in the headspace above manure incubated anaerobically in sealed containers (Elliot and Travis, 1972), but we have been unable to detect evolution of COS from soils incubated under aerobic or anaerobic conditions. We have, however. detected evolution of carbon disulfidc from soils trcatcd with cysteine or cystine and evolution of methyl mercaptan. dimethyl sulfide, and dimethyl disulfide from soils treated with methionine. Interference tests showed that identification of sulfur gases in air samples by the methods described is not affected by the presence of substantial amounts of various nonsulfur gases known or suspected to be evolved from soils under aerobic or anaerobic conditions. For example. tests showed that these methods were satisfactory when applied to 100-/*l samples of air containing cu. 3 ng of each of the 13 sulfur compounds listed in Fig. 1 and approximately 2 per cent (v/v) of each of the following gases: carbon dioxide, carbon monoxide, methane, ethylene. ammonia. hydrogen. nitric oxide, and nitrous oxide. The flame photometric detector used in the methods described was developed by Brody and Chancy (1966) for gas chromatographic analysis of sulfur and phosphorus compounds. and we have confirmed previous evidence that, when fitted with a 394-nm optical filter, this detector exhibits high selectivity and sensitivity for sulfur (Brody and Chaney. 1966; Grice. Yates and David. 1970: Stevens e’t a/.. 1971). For example, we found that, whcrcas this detector showed a marked response with as little as I ng of each of the 13 sulfur compounds listed in Fig. 1. it showed very little, if any, response with as much as 1500 ng of nonsulfur gases
2
4 5 6
Fig. 1. Gas chromatogram
of 100 1’1 of air containing trace amounts (Chromosorb T column).
(t.5 ng) of 13 sulfur compounds
Gas chromatographic
identification
of sulfur gases
r
. . I
I
I
I
I
0
2
4
6
8
TIME
Fig. 2. Gas chromatogram
Ll
!
’
A~lirloa’/cdU~,,lfrl1~JournaI Paper No. J-7630 of the Iowa Agriculture and Home Economics Experiment Station. Ames. Iowa. Project 1835.
REFERENCES BRODY S. S. and CHANCY J. E. (1966) The application of a specific detector for phosphorus and for sulfur compounds-sensitive to subnanogram quantities J. Gas Chron~. 4, 42 46. EI.I.IOTTL. F. and TRAVIS T. A. (1972) Detection of carbonyl
I 30
I 32
I
(MIN)
of 100 btl of air containing trace amounts listed in Fig. I (Deactigel column).
such as nitric oxide, nitrous oxide, nitrogen dioxide, hydrogen, ammonia, methane, ethylene. acetylene. carbon dioxide, and carbon monoxide. The minimum concentration of sulfur gas detectable by the methods described depends upon the volume of the air sample taken for analysis. When 2-ml samples of air treated with small amounts of the 13 sulfur compounds listed in Fig. 1 were analyzed, the minimum concentration of sulfur compound detectable was less than 0.5 pg/l. When 5-ml samples were analyzed, the minimum concentration of sulfur compound detectable was less than 0.2 pg/l [i.e. ~0.13 parts of sulfur gas/lo6 parts of air (v/v basis)]. Use of the Melpar flame photometric detector for quantitative gas chromatographic analysis of sulfur gases has been discussed by Mizany (1970), Stevens and O’Keeffe (1970), Stevens et al. (1971) and Greer and Bydalek (1973). Our studies support their conclusion that to use this detector satisfactorily for quantitative analysis of sulfur gases, it is necessary to calibrate the detector for each sulfur gas analyzed.
‘28
(~5 ng) of the 13 sulfur compounds
sulfide and other gases above anaerobically incubated manure. Aymr~. Ah.str., p. 95. FUNI y J. R. (1967) Sulfur-containing organics. In Soil Biochrvlisrry (A. D. McLarcn and G. H. Pctcrson, Eds) pp. 229 259. Marcel Dekker. New York. GRl:I K D. G. and B\ I).&LI:I
LI.I~~I~ W. (1970) The Awly.\i.s o/ .Arr Pollutmts. Ann Arbor Science Publishers, Ann Arbor. Michigan. LI WIS J. A. and PAPAVILASG. C. (1970) Evolution of colatile sulfur-containing compounds from decomposition of crucifers in soil. S0il Biol. Hiochc,J,1. 2, 239 246. LOV~LOCK J. E., MA~;~;s R. J. and RASMUSSI:N R. A. (1972) Atmospheric dimethyl sulphide and the natural sulphur cycle. Nuture. Lonti. 237, 452. MIZANY A. 1. (1970) Some characteristics of the Melpar flame photometric GC detector in the sulfur mode. J. Chron1. sci. 8, I5 1 154. SALTL~~ANB. E.. COLI.MAN A. 1. and CILWONS C‘. A. (1966) Halogenated compounds as gaseous meteorological tracers. And. ChcJm. 38, 753-758. SMITH K. A.. BRFMN~R J. M. and TABATAHAI M. A. (1973) Sorption of gaseous atmospheric pollutants by soils. Soil Sci. (In press). ST~VLNSR. K. and O’Ktt+r+ A. E. (1970) Modern aspects of air pollution monitoring. Anal. Chon. 42, 143A- 148A. SWVINS R. K.. MULIK J. D.. O’Kr:~btt A. E. and KKOCT K. J. (1971) Gas chromatography of reactive sulfur gases in air at the parts-per-billion level. Awl. Chum. 43, 827- 83 I
BANWART
of Agronomy.
OF
and J. M. BREMNER
Iowa State University,
Ames. Iowa
Summary PSimplc gas chromatographic methods for idcntihcation of sulfur gases in soil atmospheres are described. They involve the use of a flame photometric detector fitted with a sulfur filter and of Teflon columns packed with Chromosorb T and Deactigel. The methods permit identification of 13 volatile sulfur compounds (sulfur dioxide. hydrogen sulfide. carbon disuhide. carbonyl sulfide, sulfur hexafluoride, methyl mercaptan. ethyl mercaptan. rr-butyl mcrcaptan. dimethyl sulfide. ethyl methyl sulfide, diethyl sulfide. dimcthyl disulfidc. and diethyl disullidc) in an containing trace (nanogram) amounts of these compounds, and they are not subject to interference by vartous gases known to be evolved from soils under aerobic or anaerobic conditions. The Deactigel column is not required if the gas mixture analyzed does not contain hydrogen sulfide or carbonyl sulfide.
INTRODUCTION
on the sulfur cycle has been hindered by the lack of sensitive and specific methods of studying evolution and sorption of sulfur gases by soils. The need for such methods has been emphasized by recent work showing that soils have the capacity to sorb substantial amounts of sulfur gases identified as atmospheric pollutants (Smith. Bremner and Tabatabai. 1973) and can evolve volatile sulfur compounds, particularly if they contain residues of cruciferous plants (Lewis and Papavizas. 1970; Lovelock, Maggs and Rasmussen, 1972). The purpose of this paper is to describe gas chromatographic methods that have proved satisfactory in our laboratory for research on evolution and sorption of sulfur gases by soils. These methods allow separation and identification of trace (nanogram) amounts of all the volatile sulfur compounds recognized as air pollutants (see Leithe, 1970) or known to be evolved from soils or produced by microorganisms (see Freney, 1967; Lewis and Papavizas. 1970; Kadota and ishida, 1972; Lovelock et cd.. 1972). Sulfur hexafluoride (SF,) was included because it has been proposed as a tracer gas for air pollution research (Saltzman. Coleman and Clemens. 1966). Research
MATERIALS AND METHODS
Ethyl mercaptan (CH,CH,SH), ,r-butyl mercaptan (CH,CH,CH,CH,SH). carbon disulfide (CS,). ethyl methyl sulfide (CH,CHZSCH,). dimethyl sulfide (CH,SCH,), diethyl sulfide (CH,CH,SCH,CH& dimethyl disulfide (CH,SSCH,). and diethyl disulfide (CH, CH, SSCH,CH, ) were obtained from Fisher Scientific Co., Chicago, Illinois. Methyl mercaptan (CH,SH), hydrogen sulfide (HZS). sulfur dioxide (SO,),
carbonyl sulfide (COS), sulfur hexafluoride (SF,). nitric oxide. nitrous oxide, nitrogen dioxide, hydrogen, acetylene, carbon methane, ethylene, ammonia, monoxide. and carbon dioxide were obtained (as purified compressed products) from Matheson Company, Joliet. Illinois. The gas mixtures used to develop and evaluate the gas-chromatographic methods described were prepared by injecting small amounts of the test compounds into air contained in glass bottles sealed with the Mininert valves supplied by Precision Sampling Corporation, Baton Rouge, Louisiana (these valves are Teflon. gas-tight. bottle-closure devices that permit injection or removal of gas samples by gas syringes). The syringes used were the leak-proof, Pressure-Lok gas syringes supplied by Precision Sampling Corporation. The gas chromatograph used was a Beckman GC-4 instrument equipped with a Melpar flame photometric detector (Tracer Inc.. Austin, Texas) connected to a Beckman Model 1005 1-mV lo-in. recorder. The detector was fitted with a sulfur tilter (394 nm) and was operated at I I O-‘C with a H, flow rate of 75 ml min ‘, an 0, flow rate of 20 ml mini’, and an air flow rate of60mlmin~’ The columns used were: (I) 1020 cm of 2.16 mm (i.d.) Teflon (FEP) tubing packed with 40-60 mesh Chromosorb T coated with polyphenyl ether (IY’,,) and H, PO, (0.5%); (2) 30 cm of 2.16 mm (i.d.) Teflon (FEP) tubing packed with 12@140 mesh Deactigel. The Chromosorb T column was obtained from Supelco Inc., Bellefonte. Pennsylvania. The materials used to prepare the Deactigel column were obtained from Applied Science Laboratories, State College, Pennsylvania. Both columns were operated isothermally (Chromosorb T column, 1OO’C; Deactigel column. 50°C) with nitrogen as the carrier gas (N, flow rate. 80 ml min _ ’ ), 113
114
W. L. RESL’LTS
AND
and J. M. BREM~~K
BANWAKT
DISCUSSION
The methods described are based on work by Stevens. Mulik. O’KeetTc and Krost (1971). who showed that trace amounts of H,S. SO,, CH,SH, and CH,SCH, in air could be separated and identified by gas chromatography using a flame photometric detector and a Teflon column packed with Haloport-F coated with a mixture of polyphcnyl ether and H,PO, (see also Stevens and O’Keeffe. 1970). The Chromosorb T column described here is essentially the same as that used by Stevens er ~1. (1971) (Haloport-F and Chromosorb T are trade names for Teflon products), but the column temperature is higher (100 instead of 50 C). A column temperature of 100-C was adopted in our work because we found that this was the optimum temperature for separation and identification of the 13 sulfur compounds studied [Stevens et ul. (1971) studied onlv four of these compounds]. The separations achieved with the Chromosorb T column at 100°C are illustrated by Fig. 1. which shows that this column permits identification of nanogram amounts of II of the 13 compounds studied and gives a composite peak with HIS and COS that is separated from the peaks obtained with other sulfur compounds. Figure 2 shows that the presence of COS can readily be established by gas chromatography using a flame photometric detector and the Deactigel column described because Deactigel sorbs H,S, mercaptans, and alkyl sulfides, but allows separation and identification of trace amounts of COS, CS,. and SF,. Analyses of 500-~1 samples of air treated with different amounts of COS and other sulfur compounds showed that the Deactigel procedure described permits identification of I ng of COS in the presence of 2000 ng of H,S, mercaptans, and
alkyl sulfides. Trace amounts of COS have been detected in the headspace above manure incubated anaerobically in sealed containers (Elliot and Travis, 1972), but we have been unable to detect evolution of COS from soils incubated under aerobic or anaerobic conditions. We have, however. detected evolution of carbon disulfidc from soils trcatcd with cysteine or cystine and evolution of methyl mercaptan. dimethyl sulfide, and dimethyl disulfide from soils treated with methionine. Interference tests showed that identification of sulfur gases in air samples by the methods described is not affected by the presence of substantial amounts of various nonsulfur gases known or suspected to be evolved from soils under aerobic or anaerobic conditions. For example. tests showed that these methods were satisfactory when applied to 100-/*l samples of air containing cu. 3 ng of each of the 13 sulfur compounds listed in Fig. 1 and approximately 2 per cent (v/v) of each of the following gases: carbon dioxide, carbon monoxide, methane, ethylene. ammonia. hydrogen. nitric oxide, and nitrous oxide. The flame photometric detector used in the methods described was developed by Brody and Chancy (1966) for gas chromatographic analysis of sulfur and phosphorus compounds. and we have confirmed previous evidence that, when fitted with a 394-nm optical filter, this detector exhibits high selectivity and sensitivity for sulfur (Brody and Chaney. 1966; Grice. Yates and David. 1970: Stevens e’t a/.. 1971). For example, we found that, whcrcas this detector showed a marked response with as little as I ng of each of the 13 sulfur compounds listed in Fig. 1. it showed very little, if any, response with as much as 1500 ng of nonsulfur gases
2
4 5 6
Fig. 1. Gas chromatogram
of 100 1’1 of air containing trace amounts (Chromosorb T column).
(t.5 ng) of 13 sulfur compounds
Gas chromatographic
identification
of sulfur gases
r
. . I
I
I
I
I
0
2
4
6
8
TIME
Fig. 2. Gas chromatogram
Ll
!
’
A~lirloa’/cdU~,,lfrl1~JournaI Paper No. J-7630 of the Iowa Agriculture and Home Economics Experiment Station. Ames. Iowa. Project 1835.
REFERENCES BRODY S. S. and CHANCY J. E. (1966) The application of a specific detector for phosphorus and for sulfur compounds-sensitive to subnanogram quantities J. Gas Chron~. 4, 42 46. EI.I.IOTTL. F. and TRAVIS T. A. (1972) Detection of carbonyl
I 30
I 32
I
(MIN)
of 100 btl of air containing trace amounts listed in Fig. I (Deactigel column).
such as nitric oxide, nitrous oxide, nitrogen dioxide, hydrogen, ammonia, methane, ethylene. acetylene. carbon dioxide, and carbon monoxide. The minimum concentration of sulfur gas detectable by the methods described depends upon the volume of the air sample taken for analysis. When 2-ml samples of air treated with small amounts of the 13 sulfur compounds listed in Fig. 1 were analyzed, the minimum concentration of sulfur compound detectable was less than 0.5 pg/l. When 5-ml samples were analyzed, the minimum concentration of sulfur compound detectable was less than 0.2 pg/l [i.e. ~0.13 parts of sulfur gas/lo6 parts of air (v/v basis)]. Use of the Melpar flame photometric detector for quantitative gas chromatographic analysis of sulfur gases has been discussed by Mizany (1970), Stevens and O’Keeffe (1970), Stevens et al. (1971) and Greer and Bydalek (1973). Our studies support their conclusion that to use this detector satisfactorily for quantitative analysis of sulfur gases, it is necessary to calibrate the detector for each sulfur gas analyzed.
‘28
(~5 ng) of the 13 sulfur compounds
sulfide and other gases above anaerobically incubated manure. Aymr~. Ah.str., p. 95. FUNI y J. R. (1967) Sulfur-containing organics. In Soil Biochrvlisrry (A. D. McLarcn and G. H. Pctcrson, Eds) pp. 229 259. Marcel Dekker. New York. GRl:I K D. G. and B\ I).&LI:I
LI.I~~I~ W. (1970) The Awly.\i.s o/ .Arr Pollutmts. Ann Arbor Science Publishers, Ann Arbor. Michigan. LI WIS J. A. and PAPAVILASG. C. (1970) Evolution of colatile sulfur-containing compounds from decomposition of crucifers in soil. S0il Biol. Hiochc,J,1. 2, 239 246. LOV~LOCK J. E., MA~;~;s R. J. and RASMUSSI:N R. A. (1972) Atmospheric dimethyl sulphide and the natural sulphur cycle. Nuture. Lonti. 237, 452. MIZANY A. 1. (1970) Some characteristics of the Melpar flame photometric GC detector in the sulfur mode. J. Chron1. sci. 8, I5 1 154. SALTL~~ANB. E.. COLI.MAN A. 1. and CILWONS C‘. A. (1966) Halogenated compounds as gaseous meteorological tracers. And. ChcJm. 38, 753-758. SMITH K. A.. BRFMN~R J. M. and TABATAHAI M. A. (1973) Sorption of gaseous atmospheric pollutants by soils. Soil Sci. (In press). ST~VLNSR. K. and O’Ktt+r+ A. E. (1970) Modern aspects of air pollution monitoring. Anal. Chon. 42, 143A- 148A. SWVINS R. K.. MULIK J. D.. O’Kr:~btt A. E. and KKOCT K. J. (1971) Gas chromatography of reactive sulfur gases in air at the parts-per-billion level. Awl. Chum. 43, 827- 83 I