962
Anal. Cham. 1986, 58, 962-965
Extraction of Organic Compounds from Solid Samples G. A.
Junk* and J. J. Richard
USDOE, Ames Laboratory, Ames, Iowa 50011
EXPERIMENTAL SECTION
Pyridine, benzene, cyclohexane, methylene chloride, dimethyl sulfoxide, dlmethylformamlde, and n -methylpyrrolidone have been compared for the extraction of polycyclic organic materials (ROMs) from urban air, diesel, and stack particulate samples. Both sonic and Soxhlet techniques have been examined for both natural environmental particulates and particulates spiked with selected ROMs. The extraction results vary for different polycyclic compounds adsorbed on different solid matrices, so no single solvent or extraction technique could be unambiguously recommended. However, comparative average results for 14 compounds spiked onto fly ash at 0.1, 0.25, and 1.0 jitg/g showed pyridine to have 1.5 times more extraction efficiency than benzene. These and other reported results suggest that pyridine deserves more attention as an extractant for particulate samples. In separate tests, recoveries of ROMs from fly ash were not Improved by deactivation with aqueous solutions of ammonium hydroxide, thiocyanate and carbonate, and sodium nitrite prior to the
Reagents and Chemicals. The solvents were all purchased “distilled in glass" grade from Burdick and Jackson Laboratories (Muskegon, MI) and were used as received except dimethyl sulfoxide, Me2SO, which was recrystallized from acetone at -80 as
°C.
The PAHs were obtained from Aldrich (Milwaukee, WI) and without further purification. The fly ash samples were collected from the hopper of an electrostatic precipitator (ESP) at a coal-fired power plant. The stack ash samples were taken from the stack after the ESP using an EPA source assessment sampling train. Standard solutions containing 0.05, 0.125, and 0.5 µ of each PAH/mL of benzene were prepared. The air particulate standard reference material, SRM 1649, and diesel particulate sample were obtained from the National Bureau of Standards (Washington, DC). Spiking. The fly ash sample used in the spiking study was analyzed initially for PAHs and none were found. Spiked fly ash samples were prepared by adding 10 mL of the standard solutions of PAHs in benzene to 5-g samples of this fly ash in 100-mL beakers. The beakers were shaken gently to mix the solutions with the ash, and the benzene was allowed to evaporate at room temperature. The concentrations of the spiked fly ash samples, prepared by this evaporation procedure, were 0.1, 0.25, and 1.0 µ of each PAH/g of ash. Extraction. Ultrasonic extraction was accomplished with an Artex-sonic dismembrator (Farmingdale, NY) equipped with a 1.9-cm probe and operated at 250 W. Normally, 5-g samples of spiked fly ash were sonic extracted for 8 min using 25 mL of solvent. This solvent was filtered and the sonic extraction repeated 2 more times. The three combined filtrates were concentrated by using a rotary evaporator. Soxhlet extraction was accomplished for 5-g samples of spiked fly ash using a 25-mm-o.d. glass thimble with a coarse frit containing a 1-cm layer of 80-100 mesh sodium sulfate pretreated at 400 °C for 4 h. The fly ash was extracted for 24 h after which the solvent extract was concentrated by using a rotary evaporator. A micro Soxhlet extractor was employed for the extraction of 1-g samples of SRM 1649 and diesel particulates. The concentrated extracts of these samples were classified according to the procedure of Later et al. (27) to isolate the PAH fraction. When the high-boiling solvents, dimethyl sulfoxide (Me2SO), dimethylformamide (DMF), and N-methylpyrrolidone (NMP) were used as extracting solvents, the spiked fly ash in 25 mL of solvent was heated to 150 °C with stirring for 10 min. The solution was filtered while hot, and the PAHs in the filtrate were partitioned into benzene after the addition of water. Deactivation of the fly ash to enhance recoveries was studied by adding 5 mL of a 10% aqueous solution of the deactivating reagent to 5 g of ash prior to the extraction with benzene. The deactivating agents were ammonium hydroxide, sodium nitrite, ammonium thiocyanate, and ammonium carbonate. The gas chromatographic analyses were performed on a Garbo Erba fratovap (Peabody, MA) equipped with an FID. A 30-m DB-5 fused silica capillary column from J and W (Rancho Cordova, CA) and hydrogen carrier gas were used for separating the PAHs. Splitless injection was employed with a 2-min temperature hold followed by temperature programming at 5 °C/min from were used
extraction.
Many extraction procedures have been used to recover organic compounds from different solid samples. Soxhlet (1-6) and ultrasonic (7-12) extractions are most frequently used; high-intensity mechanical treatment (13, 14) and vacuum sublimation (15) have also been employed. The Soxhlet extraction of polycyclic aromatic hydrocarbons (PAHs) from air particulate samples has received the most study. Greater than 95% recoveries have been reported using benzene as the solvent (2, 6). In comparison studies, ultrasonic extraction of air particulate samples (9,16,17) for 15-30 min gave recoveries of PAHs equal to or better than Soxhlet extraction for 6-8 h with the same solvent. Benz[o]pyrene (B[a]P) spiked onto air particulate samples was also recovered with high efficiency using sonic extraction (17-19). Recovery studies of 14C labeled B[o]P spiked onto diesel particulate samples showed toluene to be the best solvent for Soxhlet extraction (20). For recovery of PAHs and other organic compounds, toluene plus an alcohol were found to be the most efficient (20). These toluene results agree with other studies (21,22) where higher boiling solvents were more efficient in removing polycyclic organic material (POM) from carbon black. Soxhlet extraction with naphthalene recovered more PAHs than extraction with benzene, especially six- and seven-ring compounds (21); Soxhlet extraction with chlorobenzene recovered greater amounts of nitropyrene than extraction with toluene (22). Studies of the recoveries of PAHs from fly ash are limited, even though these compounds are emitted during the generation of electricity by the combustion of coal (23). Low recoveries have been reported for fly ash spiked with 14C labeled B[a]P and other PAHs (11, 24-26). Our experience with the extraction of organic compounds has been similar to that described above; low and inconsistent recoveries have been obtained for some compounds in some solid matrices when a variety of solvents and extraction techniques were used. Some of the more interesting results of our search for better solvents and extraction techniques are presented in this report. 0003-2700/86/0358-0962$01.50/0
70 to 325 °C.
RESULTS AND DISCUSSION
Spiked Samples. Soxhlet and sonic extraction of fly ash a mixture of PAHs were initially attempted using
spiked with ©
1986 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 58, NO. 4, APRIL 1986
Table I. Pyridine (PYR) and Benzene (BZ) for the Recovery of Different Concentrations of PAHs
963
·
Fly Ash
on
% recovered0
Soxhlet
sonic
1.0 ppm
0.25 ppm
0.1 ppm
Soxhlet
sonic
Soxhlet
sonic
BZ
PYR
BZ
PYR
BZ
PYR
BZ
PYR
BZ
PYR
BZ
PYR
phenanthrene fluoranthene pyrene benz [o]anthracene chrysene benz [ 6 ] fluoranthene benz [fej fluoranthene
56 62 65 40 46 14
68
benz [e] pyrene benz [o] pyrene
20
76 84 76 76 82 66 60 66 58 68 10 24 26
96 90 87 89 84 75 73 76 80 68 52 76 49 35
75 91 85 68 69 30 28 29 13 10
98 86 85 92 89 79 73 66 62 41 33 45
88 97 98 95 102 91 100 91 85 77 71 78 66 45
57 68 68 61 61 36 34 36 18 8 8
25 18
74 70 72 65 67 68 68 66 66 61 38 51 40 17
67 81 85 92 89 86 78 70 55 32 34 49 25 19
75 82 84 86 85 82 83 83 82 75 58 67 64 39
88 93 93 97 94 92 88 86 83 80 67 71 65 47
75
40
63
59
85
34
62
75
82
PAH
perylene
indeno[l,2,3-d]pyrene dibenz [o ,h] anthracene benz [g/ii] perylene coronene av %
recovery
13 7 7 -
-
-
73 78 78 73 61 58 47 39 39 24 22 -
-
-
24
47
55
The average standard deviations for these recoveries
were
5 7 7 -
±4 to 7% based
on
9 10 -
3-5 determinations, and dash denotes less than 1%
recovery.
those solvents commonly employed for recovering organic compounds from air particulate samples. These solvents were benzene, toluene, benzene/methanol, methylene chloride, acetone, and cyclohexane. Although benzene, toluene, and benzene/methanol gave the best recoveries, these solvents still gave low recoveries for the higher molecular weight PAHs. Pyridine has been reported (28,29) to give higher recoveries of PAHs in comparisons of solvents for the extraction of air particulate samples. Our results using pyridine to extract fly ash at three different PAH concentrations of 0.1, 0.25, and I. 0 /ug/g and using both sonic and Soxhlet extraction are listed in Table I. Recoveries using benzene are also listed for comparative purposes. In addition to the results given in Table I, the recoveries were also checked using pyridine for fly ash spiked with only B[o]P at 0.1 ppm. These results showed sonic and Soxhlet extraction recoveries of B[o]P to be 40 ± 4% and 71 ± 4%, respectively. Comparative extraction efficiencies for air particulate samples using Me2SO and other solvents have also been reported (29). In addition, Me2SO has been used to extract fly ash samples so that the mutagenicity of the extracts could be tested directly without solvent transfer (30,31). Me2SO has also been used to extract air particulates (16) and particulates (32) from the exhaust of gasoline and diesel engines. The results from these studies indicate that Me2SO is comparable to other extracting solvents. Me2SO, along with two other aprotic solvents, DMF and NMP, was evaluated for its ability to extract PAHs from spiked fly ash. Two extraction procedures were used to evaluate the solvents, sonic extraction and heating to ~150 °C with stirring. The recovery results for the heating and stirring investigations are given in Table II. None of these PAHs spiked onto fly ash at 0.25 ppm were recovered using sonic extraction. The pretreatment of fly ash was also investigated as a means of improving the recoveries. Water has been used extensively to deactivate alumina and silica in chromatographic separations, to improve the extractability of herbicides and insecticides from air-dried soils and sediments (33), and to increase the extractability of organochlorine compounds from fly ash (34). In the present study, inorganic complexing agents were added to the water to compete with the active adsorption sites for PAHs and hopefully increase their extractability. The results in Table III indicate that the addition of water containing complexing agents to the fly ash had little effect on
Table II. Aprotic Solvents for the Extraction of 0.25 ppm PAHs from Fly Ash Using Heating and Stirring % recovery0
PAH
Me2SO
DMF
NMP
phenanthrene fluoranthene pyrene benz [a ] anthracene chrysene benz [ b] fluoranthene benz [k ] fluoranthene benz[e]pyrene benz[o]pyrene perylene indeno[l,2,3-d]pyrene dibenz[o,Zi]anthracene benz [ghi] perylene
54 36 28 18 20
44 22
33
8
-
8
11
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
6
coronene
11 11
17
-
-
'Dash denotes less than 1% recovery.
Table III. Sonication with Benzene for the Recovery of 0.25 ppm PAHs from Deactivated Fly Ash % recovery 0
PAH phenanthrene fluoranthene pyrene benz[o]anthracene chrysene
benz[b]fluoranthene benz[fe]fluoranthene benz[e]pyrene benz[o]pyrene perylene indeno[l,2,3-d]-
none
after deactivation with:
NH4OH NaN02
75 91 85
65
68
nh4cns nh4c2o4
36
65 59 58 41
53 63 62 46
69 58 50 36
69 30
41 21
45 20
49 24
40 18
28
18
21
24
17
29 13 10 5
18 10 8
22 12
23 9
15 8
73 60
8
5
-
‘ -
-
-
-
-
-
-
-
-
-
-
-
pyrene
dibenz[a,h]anthracene benz [ghi] perylene coronene 0
7 7 -
Dash denotes less than
1
% recovery.
964
ANALYTICAL CHEMISTRY, VOL. 58, NO. 4, APRIL 1986
·
Table IV. Different Solvents and Extraction Techniques Used in the Determination of PAHs Present on Urban Air Particulates (SRM 1649)
Table V. Pyridine and Methylene Chloride Used in the Determination of POMs Present on Diesel Particulates concn, Mg/g, using:
concn, Mg/g, using:
PAH phenanthrene fluoranthene pyrene benz [a] fluoranthene chrysene benz [ b] fluoranthene benz [k ] fluoranthene benz[e]pyrene benz[o]pyrene perylene indeno [ ] anthracene benz[ght]perylene
methylene chloride0 pyridine6 4.5 7.1 7.2 2.6 3.5 6.2 2.0 3.3 3.0 0.8 0.4 4.5
4.7 6.2 5.9 2.2 4.2 6.1 2.4 2.9 3.0 0.5 0.9 2.6
Me2SOc 3.9 6.0 5.0 2.7 4.3 5.8 3.4 3.3 6.4 1.2 1.4 5.0
cyclohexaned 3.3 7.6 5.8 2.9 4.3
NMe
NM 2.7 3.3
NM 0.4 5.0
°NBS certified values using Soxhlet extraction. 6 Soxhlet extraction. c Extraction using heat and stirring. d Sonic extraction, from ref 12. eNM, not measured. recoveries. The failure of complexing agents in improving the recoveries is an indication that either the right deactivating agent has not been found or that there are no complexes formed between the PAHs and the fly ash. This speculation is consistent with the reported absence of charge-transfer complexes (35,36) when aromatics were adsorbed on alumina and silica, known constituents of fly ash, and by the results of Griest and Tomkins (37) showing strong interactions between the PAHs and the carbonaceous content of fly ash particles. The agents in Table III would have little effect on
any
-
complexes.
Field Samples. Pyridine
was further evaluated as an extracting solvent using several different types of particulate samples known to contain PAHs. The samples investigated were an air particulate sample, SRM 1649, a diesel particulate sample, and a size-fractionated particulate sample taken from the stack of a coal-fired power plant. Table IV gives the PAH recovery values obtained for the air particulate sample using Soxhlet extraction with pyridine. The recovery values obtained with Me2SO and cyclohexane as extractants are also included. The PAHs appear to be removed readily from air particulate samples, probably because most of the organic material is coated on the surface of the particles and the amounts are high relative to stack and fly ash samples. The results in Table IV indicate that solvent selection and the extraction technique are not nearly so critical for air particulate samples. Table V gives the PAH recovery values obtained for the diesel particulate sample using Soxhlet extraction with pyridine. Also included are the recovery values obtained using the more popular extracting solvent, methylene chloride. The higher recoveries reported for pyridine in Table V may be due to the greater solubility of the diesel particulates in this solvent compared to methylene chloride. Pyridine dissolves approximately 50% of the sample compared to only 20% for methylene chloride. As more material is dissolved more surface area is exposed leading to higher recoveries of entrapped PAHs. A value of 0.13 jtg/g was obtained when pyridine was used to extract B[o]P from the stack ash sample. This compares favorably with a value of 0.16 Mg/g reported previously for this sample using a high-temperature extraction with diphenylmethane and Shpolskii’ spectrometry (38) for analysis of the extract. Pyridine has not found extensive use in the extraction of solid samples. In the two studies (28, 29) where it has been used, it compared favorably to other solvents. Elutropic series
POM
methylene chloride
pyridine
9-fluorenone phenanthrene fluoranthene pyrene benz[a]anthracene
44 35 38 45
chrysene
20 22
62 73 58 94 10 35 35
l-nitropyrene
7
for polar adsorbents (39) list pyridine as a strong solvent indicating that it will compete favorably for a site on the adsorbent surface. This plus the expected higher solubility of polar oxygenated compounds in pyridine could explain why better recoveries for PAHs were observed in some instances when this solvent was used as an extractant. Our results from the study of fly ash, stack ash, and urban air and diesel particulate samples suggest that subtle differences in the composition of the particles can have a profound influence on the extractability of different organic constituents.
CONCLUSIONS There is neither a single extraction technique nor a solvent that is effective for the efficient extraction of all organic compounds from all types of solid matrices. This conclusion is based on (1) our own past experience with the extraction of a variety of solid samples; (2) the experiences of others, as reviewed briefly in the introduction to this paper, who have obtained low and variable recoveries for some components present in different solid samples when techniques such as Soxhlet, sonic batch, sonic probe, and batch reflux have been employed with a variety of solvents; and (3) the results presented in this current report. In the absence of a universal extraction procedure, efficient recovery of a specific compound from a particular solid matrix is achieved by tailoring both the extraction technique and the solvent. The results presented in this paper suggest that pyridine, a solvent seldom used in extraction studies, should be included in these tailoring experiments. It is superior to other solvents in extracting some polycyclic compounds from air and diesel particulate samples. Whether this superiority applies to other organic compounds, present in different solid samples, must await the results of future investigations using different extraction techniques and solid samples.
ACKNOWLEDGMENT We grateful for the administrative assistance and encouragement of V. A. Fassel and the technical support of Mike Avery. are
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(16) Soderburg, R. H. In “Measurement and Monitoring of Non-Criteria (Toxic) Contaminants In Air”; Frederick, E. R., Ed.; Publishers Choice Book Mfg. Co.: Mars, PA, 1983; pp 489-499. (17) Golden, C.; Sawicki, E. Int. J. Environ. Chem. 1975, 4, 9-23. (18) Sawicki, E.; Belsky, T.; Frledel, R. A.; Hyde, D. L; Monkman, J. L; Rasmussen, R. A.; Rlpperton, L. A.; White, L. D. Health Lab. Sci. 1975, 12, 407-414. (19) Seifert, B.; Stelnbach, I. Z. Anal. Chem. 1977, 287, 264-270. (20) Lee, F. S-C.; Schuetzle, D. In "Handbook of Polycyclic Aromatic Hydrocarbons”; Bjorseth, A., Ed.; Marcel Dekker: New York, 1983;
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Received forreview September 20,1985. Accepted December 16,1985. This work was performed in the laboratories of the U.S. Department of Energy under Contract W-7405-Eng-82. The work was supported by the Office of Health and Environmental Research, Office of Energy Research.
Determination of Thioglycolic Acid and Dithiodiglycolic Acid in Mineral Flotation Systems Megan Mclean, Stan Van Wagenen, Donna Wiedemann, and Quintus Fernando*
Department of Chemistry, University of Arizona, Tucson, Arizona 85721
Srini Raghavan Department of Materials Science and Engineering, University of Arizona, Tucson, Arizona 85721
the aid of aqueous solutions of sodium sulfide or ammonium sulfide or mixtures of these two compounds. Another example is the use of aqueous sulfite solutions to depress sphalerite during the flotation separation of copper sulfide from zinc sulfide. The mineral processing industry has been in search of suitable reagents to replace aqueous sulfide solutions, because the massive dosage requirements of inorganic depressants (e.g., 10-40 lbs of sodium hydrosulfide/ton of copper molybdenum concentrate) have resulted in severe odor and disposal problems. Short-chain organic compounds such as mercaptocarboxylic acids and mercapto alcohols have been considered as possible replacements for aqueous sulfide solutions. Promising results were obtained in some initial work that was carried out with short-chain mercapto compounds such as d-mercaptoethanol (HS-CH2-CH2OH), and mercaptoacetic acid (thioglycolic acid, HS-CH2-COOH), (1,2). The maximum potential of these compounds, however, has not been realized mainly because there is a lack of fundamental information on the mode of interaction of these mercapto compounds, either with minerals or with collector-coated minerals. The interaction of thioglycolic acid, the first member of the aliphatic mercaptocarboxylic acids, with chalcocite has been investigated in the pH range 3-10 (2). The analytical technique that was employed in these studies was the classical iodimetric titration with a standard iodine solution and a starch indicator (3). Serious difficulties were experienced with
When aqueous solutions of thioglycolic acid are equilibrated with sphalerite, a zinc sulfide mineral, a large fraction of the thioglycolic add is either adsorbed on the sphalerite surface or oxidized to dithiodiglycolic acid. The total concentration of thioglycolic and dlthloglycolic acid In solution has been determined by molecular emission cavity analysis (MECA). The fraction of the thioglycolic acid that Is not adsorbed on the mineral surface and remains In solution has been determined by a coulometric titration In which Iodine is electrogenerated In situ and the end point located by an amperometrlc method. Attempts to determine the thioglycolic acid that was adsorbed on the mineral surface directly by MECA gave unreliable results. This has been attributed to the wide variation In the surface area as well as the surface chemical composition of small samples (1-2 mg) of the mineral that must be used In the sample cup In MECA. Thioglycolic acid also leaches traces of metal Ions from the mineral surface. The concentration of zlnc(II) In solution reflects the extent of leaching that has occurred.
The use of aqueous solutions of sulfur compounds to achieve selectivity in sulfide mineral flotation has been in vogue for more than five decades. For example, the selective flotation of molybdenite from concentrates containing molybdenum and copper sulfides is currently carried out industrially with 0003-2700/86/0358-0965$01.50/0
©
1986 American Chemical Society
