suction stream was confined to very small slugs which sporadically blanked off the field of vision of the 3/8-in. diameter sight window in the photography cell. The results of the field sampling, while limited, indicated that the influent droplet size distribution used in the laboratory for the evaluation of oil scavenging devices was representative and slightly more severe than one would expect in practice-i.e., a greater fraction of the oil concentration is attributed to smaller size droplets in the laboratory system. It also appears that the oil concentrations (1000-2000 ppm) used in the lab were typical of practice. The laboratory system represented a conservative yet realistic basis of evaluation for candidate ballast water clarifiers. The field results also emphasized that a ballast water clarifier should possess the capability to handle oil fines, if it is to be located on-deck which, of course, will place it a t the discharge side of a pump. The separation process would be measurably facilitated if suction-side clarification could be accommodated. However, such an approach is not practical with existing vessels, the design and oper-
ation of which are generally not amenable to the introduction of additional equipment in the pump wells.
Literature Cited ASTM Procedure ~1178.“Determination of Chloroform Extractables,” 1970 Lester, T. E., BP North America Inc.. Drivate communication, 1970. Norris, R. O., Bassett, R. S., “Combustion of Crude Oil in Ships Boilers,” Annual Tanker Conf., Division of Transportation, Am. Petroleum Inst., Absecon, N.J., May 15-17, 1967. Permutit Co., “Research and Development for a Shipboard Oil and Water Separation System,” Report to the U.S. Department of Commerce, Maritime Administration, under Contract Number MA-2722, December 1966. Seelinger, J., U.S. Office of Research and Development, Maritime Administration, Department of Commerce, private communication, 1969. Shacklet‘on, L. R., Douglas, E., Walsh, T., “Pollution of the Sea by Oil,” Inst. Marine Engrgs Trans.. 72, 409-15 (1960). Received for recieu Februan. 2, 1973. Accepted Jul? 19. 197;1. Work supported by the Maritime Administration, I’.S. Department of Commerce, under Contract N o . (2-0-35467.
NOTES
Solvent Extraction of Sulfur from Marine Sediment and Its Determination by Gas Chromatography Kenneth Y . Chen,’ Mohsen Moussavi, and Amancio Sycip Environmental Engineering Programs, University of Southern California, Los Angeles, Calif. 90007
Among a group of organic solvents studied, toluene and benzene exhibited a good recovery of elemental sulfur from marine sediment. A t a column temperature of 19o”C, the major peaks were produced by Sq,Sg, and SS; with the optimum carrier gas flow rate, the s8 peak predominated. The plot of peak area vs. sulfur injected was linear up to 3 ng in two gas chromatographs equipped with electron capture detectors. The detection limit was a t the picogram level, unmatched by other known methods. Neither the coefficient of variation nor mean values for sulfur were significantly different in comparisons between the gc method and a standard colorimetric method. The level of elemental sulfur in marine sediment is of great interest because sulfur is a reservoir: for the generation of hydrogen sulfide under anaerobic conditions. While the toxicity of hydrogen sulfide is generally known, the presence of elemental sulfur has also been mentioned as the probable intoxicant in fish kills (Vamos, 1964). In addition, sulfur may participate in various biogeochemical interactions important to the transport of pollutants in sediment.
To whom correspondence should be addressed 948
Environmental
Science & Technology
Despite the importance of sulfur to the chemistry of marine sediments, little research has been devoted to its quantification. The purpose of this paper is to examine the feasibility of elemental sulfur extraction and analytical determination by gas chromatography (gc). There are few known methods for the quantitative determination of elemental sulfur in sediment. In the past, determination of the amount of sulfur in soil or sediment was mainly carried out either through reduction of sulfur to sulfide with subsequent applications of spectrophotometric or volumetric titration methods for sulfide determination or oxidation of sulfur to sulfate, then titration with Ba+2 or S r + 2 potentiometrically or polarographically. A number of procedures are available for the measurement of elemental sulfur in a variety of materials (Furman, 1962, Karchmer, 1970) and in soil (Hart, 1961; The Sulfur Institute, 1968). These processes involve extraction and analysis, usually by means of titrimetry, turbidimetry, or colorimetry. The conversion of sulfur to sulfide using metallic copper is also widely used (ASTM, 1971). The copper sulfide is then treated with acid to produce hydrogen sulfide for determination using iodine titration. Kaplan et al. (1963) analyzed the sulfur content in the sediment of Southern California Coastal Waters using a mixture of benzene, methanol, and acetone as extraction solvent, with extensive subsequent treatment and purifi-
cation. The entire procedure requires more than five days of preparation before the final gravimetric measurement. Juvet and Fisher (1966) converted sulfur to volatile sulfur hexafluoride in a special injector system. Struble (1972) reported the microquantitative determination of soluble elemental sulfur with the use of electron capture (EC) and flame photometric detectors (FPD). Pearson et al. (1967) found that sulfur interfered with the detection of organochlorine pesticides and that it behaved like aldrin when chromatographed.
Experirnen t a 1 Choice of Solvents. The detrimental effects of watermiscible solvents and chloroform on gas chromotographic columns and electron capture detectors have been shown by many studies (Hewlett-Packard, 1972; McNair and Bonelli, 1969); solvents such as acetone, alcohols, and pyridine were therefore not considered. Other solvents, such as aniline, 1,2-dichloroethane, carbon disulfide, and carbon tetrachloride, were eliminated because they exhibited excessive tailing in the preliminary investigation. The number of solvents finally used in the investigation was narrowed down to five- hexane, benzene, toluene, petroleum ether, and a mixture of aniline and benzene. Standards. In the preparation of standard solutions, recrystallized, rhombic sulfur crystals (99.999% pure) were dissolved in petroleum ether (6O-llO0C). (The crystals were supplied by Research Organic/Inorganic Chemical Corp. of Sun Valley, Calif.) Calibration curves were prepared from standard solutions diluted to desired concentrations. Standard runs were necessary prior to every analytical run because shifts in operating parameters may occur even under identical resettings. Equipment. For all gas-liquid chromatography, a Varian Aerograph model 600D equipped with tritium electron capture detector, as well as a Hewlett-Packard Research Model 5750 equipped with 63Ni Electron Capture detector, was used. The columns were 1/8 in. and in. o.d., 6-ft long borosilicate glass tubes packed with 5% DC-200 and 7.5% QF 1 stationary phase on Chromosorb W high-performance SO/lOO mesh material supplied by Varian Aerograph, of Walnut Creek, Calif. The carrier gas was controlled with 50 psi pressure at the column inlet. For the Varian gc, the gas was purified nitrogen, for the H-P gc, it was composed of 5% methane and 95% argon. A SargentWelch Recorder Model SRG (chart paper speed of 30 in./ hr) recorded all outputs. Handling of Sediments and Extraction Procedure. The sediment samples were obtained from the nearshore coastal waters of southern California. A homogeneous representative mass was obtained by thoroughly mixing each batch of sediment before weighing. To avoid effects from biological activities, all samples were kept frozen. The extraction method chosen was the refluxing of sediment with mixtures of solvent and water at their boiling points. A sample sediment was stirred, weighed, then dispersed in deaerated water and allowed to stand several hours with occasional flushing of purified nitrogen through the mixture to remove trace amqunts of oxygen. One of the test solvents was then added, and the mixture was refluxed for a specific length of time in an Erlenmeyer flask connected to a water condenser by ground glass joints. A magnetic stirrer-heater was used for stirring and heating in each instance. Preliminary extractions were performed using different solvent mixtures containing 50 ml of solvent, 20 ml of distilled water, and 10 ml of saturated NaCl solution. Extractions of sediment samples, weighing 0.5 f 0.1 gram, consisted of 90-min digestions.
The solvent portion was separated by centrifugation for 15 min a t a speed of 2550 rpm in an International Centrifuge, Model CM. The volume of solvent recovered was readily determined through the use of graduated centrifuge tubes. The solvent layer was slowly decanted through a filter column packed with 4% in. of Florisil and 1% in. of anhydrous sodium sulfate to remove the last traces of organic impurities and moisture. The extracts were then diluted to concentrations suitable for gc injections. Gc Procedure. A Hamilton 10-pl. syringe was used to inject the samples into the gc. An 'injection size of approximately 1.0 pl. was maintained and delivered as uniformly as possible, as a slug, to achieve maximum repetitive response. Areas under the peaks, determined from the ball and disc integration on the recorder, were used to quantify the sulfur by comparison to standard calibration curves. Controls. To estimate the level of elemental sulfur in sediment and to establish a basis for correlating the fmdings by gc methods, the colorimetric methods described by Bartlett and Skoog (1954) were also followed, and the results were compared. To check on the precision of the size of sample injections, additional internal calibrations were carried out by the addition of a standardized DDE solution.
Results and Discussion Sulfur Identification. Upon injecting the sulfur standards in petroleum ether into the gc, a total of 10 peaks were detected. Figure 1 shows a magnified sulfur chromatogram. Identification of the sulfur homologs can be made by plotting the log of the retention time vs. the number of sulfur atoms in the molecule (McNair and Bonelli, 1969). This is shown in Figure 2. The major peaks depicted in Figure 1 represent the S4, SS, and SS species, but the predominant species changed with different experimental conditions. A tenfold change in carrier gas flow interchanged the highest and lowest of the major
IOOL
90
-
Bo-
70
c
-
60-
I L?
-
5
Y50Y
9n.
40
-
30
-
20
-
IO
-
0 I
5
P
I
I
' 0
i
2
I
4
RECORDING
i
6
SPEE
I
8
Figure 1. Magnified sulfur c h r o m a t o g r a m Column temperature. 190°C V o l u m e 7 , N u m b e r 10, October 1973
949
Table I . Recovery Values of Different Solvents (Mg S recovered/g dry sediment)
-4 -
Solvent
Colorimetric
Benzene Hexane Toluene Petroleum ether Aniline and benzene
I
Y
F
H+z
GC
3.85 2.75 3.68 1.59 6.00
4.16 3.16 3.72 1.99 3.12
W
I-W
Table II. Extraction of Sulfur from Marine Sediment (Average of duplicate determinations, mg S/g sed.)
W
3
s:
Solvent
Colorimetric
Gc12/6/72
Benzene Toluene Std dev O/O standard error
0.364 0.349 0.0350 4.9%
0.348 0.353 0.0304 4.3%
a m
SULFUR SPECIES
Figure 2. Identification of sulfur homologs from chromatogram
0.375 0.331 0.0377 5.3%
0.0235 0.0374
0.004 20%
Difference between colorimetric and gc methods Significance level (T test) Difference between benzene and toluene Significance level (T test)
i
Std dev
0.018 70%
30
R H ~ ~ ~ BSULFUR IC IN BENZENE IoNlZAflON FVTENTIAL 70ev
75
Gc-
12/10/72
J
RHOMBIC SULFUR IN BENZENE l 2 e v
W
a
lool
SEDIMENT SAMPLE EXTRACTED IN PETROLEUM ETHER a ETHYL ETHER 70ev
75
50t I
?
P
1"
25tlh4-A: 0
0
50
100
150
200
250
300
M A S S NUMBER
Figure 3. Mass spectral analysis of sulfur species
0
100
50
8 8.
150
2(
SULFUR ADDED
Figure 4. Recovery of Elemental Sulfur from a Marine Sediment
Temperature, 220°C
peaks in another experiment. Interestingly enough, there were even indications of minute quantities of Sz, Sg, S7, Sll, S14, and s16. Speciation of these sulfur homologs clearly takes place through interactions of sulfur in the chromatographic column and possibly with the solvents in the extraction process; thus the results have little significance in identifying the actual forms existing in the aquatic environment. In this study, rhombic sulfur standards and sediment from a nearshore coastal water were extracted with benzene and petroleum ether, and the mass spectral analysis was carried out by the EPA laboratory in Alameda, Calif. The results, shown in Figure 3, indicate a lower sulfur number per molecule than that of the gc study; this is probably the result of bond rupture by electron bombardment. Similar results of mass spectral analysis were shown by Berkowitz (1965). The results of the mass spectral analysis furnish further confirmation that speciation results from the experimental conditions rather than the actual forms of sulfur in the sediment. 950
Environmental Science & Technology
Optimal Gc Conditions for Sulfur Analysis. To get maximum response from the gc, various experiments were performed using different parameter settings. The operating conditions at which optimum responses for sulfur were obtained occurred at the following settings: Injection port temperature Oven column temperature EC detector temperature Gas flow
220°C 190°C 265°C 84-90 ml/min
At the above-mentioned settings, after injection of standards or extracts, the predominant sulfur species eluted were S4, s6, and Sa.The Sa species exhibits the largest area and peak height. The other two are relatively minor in comparison. The remaining species eluted in trivial amounts. The striking response of the peak height of the three major peaks to changes in carrier gas flow suggests that the eluate is strongly dependent upon kinetics in the column.
Extraction Efficiency of Solvents. The recovery of sulfur from sediment was carried out initially with a sediment sample of unknown sulfur content. The purpose was to evaluate the efficiency of different solvents in recovering sulfur and to evaluate their suitability for subsequent determinations by both colorimetry and chromatography. The mixture of aniline and benzene performed poorly in both tests. In the colorimetric determination, turbidity occurred and resulted in an unusually high absorbance reading. In the gc method, base line drifts of abnormal proportions made quantitative estimation very difficult. Low recovery values were obtained from both hexane and petroleum ether, probably owing to the relatively low solubility of sulfur in both solvents. Only benzene and toluene exhibited high recovery efficiencies and showed consistent results in both methods. Recovery values of these solvents are listed in Table 1. Additional experiments on extractions were performed, modifying different variables in each test. The maximum recovery values were obtained with 90 min or more of digestion time. Sulfur powder was stirred into an anaerobic sediment suspended in 30 ml of distilled water and allowed to stand overnight. These mixtures were then extracted with 100 ml of solvent using 90-min digestions. The recoveries of sulfur by gc analysis of the benzene layers are shown in Figure 4. Table 11 compares the colorimetric method with the gc method using both benzene and toluene as solvents. Standard deviations for single measurements are shown for each column and row. The difference between the means for the two methods was not significant-even at the 50% level using Student’s T test with lumped variances. The same test on the difference between the benzene and tolu-
ene shows no significance at the 70% confidence level. A study of the calibration curves shows that better responses and linearity were obtained when injections of lower concentrations of standard sulfur solutions were used. The ideal injection contained 1-3 ng; larger amounts caused a loss of linearity owing to the saturation of the EC detector.
Literature Cited ASTM, 1971Annual Standards, Part 17, D 130-68,p 78,1971. Bartlett, J. K., Skoog, D. A., Anal. Chem., 26, 1008’(1954). Berkowitz, J., “Elemental Sulfur,” Beat Meyer, Ed., Interscience, New York, N.Y., 1965. Furman, N. H., Ed., “Standard Methods of Chemical Analysis,” Van Nostrand, New York, N.Y., Vol. 1, p 1003, 1962. Hart, M. G. R., Analyst (London) 86,472 (1961). Hewlett-Packard Cat. No. 5950-8287, “The Electron Capture Detector, Applications and Troubleshooting Manual,” 1972. Juvet, R. S., Jr., Fisher, R. L., Anal. Chem., 38,1860 (1966). Kaplan, I. R., Emery, K. O., Rittenberg, S. C., Geochim. Cosmochim. Acta, 27,297 (1963). Karchmer, J. H., Ed., “The Analytical Chemistry of Sulfur and Its Compounds,” Part I, Wiley-Interscience, New York, N.Y., 1970. McNair, H. M., Bonelli, E. J., “Basic Gas Chromatography,” Varian Aerograph, Walnut Creek, Calif. 1969. Pearson, J. R., Aldrich F. D., Stone, A. W., J. Agr. Food Chem., 15,938 (1967). Struble, D. L., J . Chromatogr. Sei., 10,57 (1972). The Sulphur Institute, “Determination of Sulphur in Soils & Plant Materials,” Washington, D.C., Tech. Bull. No. 14, 1968. Vamos, R., J . Soil Sei., 15, 103(1964). Receiued for reuiew February 28, 1973, Accepted July 2, 1973. This work uas supported in part by the Petroleum Research Fund, a d ministered by the American Chemical Society, and in part by Grant ~04-3-158-45to the C’nicersit?,of Southern California from the National Sea Grant Program, L’.S. Department of Commerce.
Competitive Binding of Mercuric Chloride in Dilute Solutions by Wool and Polyethylene or Glass Containers Merle Sid Masri’ and Mendel Friedman Western Regional Research Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Berkeley, Calif. 94710
Comparison of binding efficiencies of native, reduced, and S+-( 2-pyridylethyl) wool for mercuric chloride over a wide concentration range shows that the modified wools are more effective than native wool in the parts-per-million range but that the three wools are nearly equivalent in the parts-per-billion range. The modified wools thus have a greater total capacity for mercury salts at the higher (parts-per-million) mercury levels. Competitive sorption of mercuric chloride by polyethylene and glass surfaces of containers may take place at low mercury salt levels. The results show that mercuric chloride is distributed between the liquid phase, wool, and the container and that wool competes effectively with the container for mercuric chloride. Chloride ions and hydrochloric acid desorb mercuric chloride from the container. In a previous communication (Friedman and Waiss, 1972), we have shown that wool is a promising filter material to remove and recover mercuric and methylmercuric chloride from contaminated sources. As the concentration of mercuric salt decreased, sorption by wool became very efficient since the partition coefficient-i.e., the relative distribution of mercuric salt between the aqueous phase
and the solid (wool) phase-reaches very high values at equilibrium. Because of the potential utility of wool for adsorbing mercury salts from contaminated waters and beverages and because of the potential value of wool as an analytical tool to concentrate mercury salts in the partsper-billion range, we wished to determine whether competitive sorption of HgC12 by polyethylene or glass containers may take place at low mercury levels. Wool is highly efficient in binding mercuric chloride from dilute solutions and effectively competes with polyethylene or glass container surfaces for mercuric ions. This information is fundamentally interesting and practically useful for testing whether wool or any other adsorbent may be used to concentrate mercury salts a t low levels. Binding studies of HgClz to native wool ( N ) ,to wool in which the disulfide bonds have been reduced to sulfhydryl groups ( R ) , to wool in which the SH group of reduced wool have been alkylated with 2-vinyl-pyridine ( P ) were carried out as previously described (Friedman and Waiss, 1972; Masri and Friedman, 1972). Additional details are given in the table legends. To whom correspondence should be addressed. Volume 7 , Number 10, October 1973
951
