Anal. Chem. 1982, 5 4 , 1913-1914
ACKNOWLEDGMENT We appreciate both the advice and assistance offered by Gerda Shultz-Sibbel and John Richard. LITER.ATURECITED (1) Ember, L. R. Chem. Eng. News 1981,59 (37),20. (2) LaBastille, A. Natl. Geogr. 1981, 160 (5),652. (3) Ember, L. R. Chem. Eng. News 1981, 59(38),14. (4) Galeano, S. F.; Tucker, T. w.; Duncan, L. J. Alr POMO~.control ASSOC.
1972,22 (lo), 790. (5) Shultz-Sibbeh G. M. W.; GJerde, D. T.; Chrisweli, C. D.; Fritz, J. S. Talanfa , In
press.
(6) Flanigen, E. M.; Bennet, J. M.; Grose, R. W.; Cohen, J. P.; Patton, R.
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L.; Kirchner, R. M.; Smith, J. V. Nature (London) 1978,271 (9), 512. (7) Kleln, S.M. Master of Science Thesls, Iowa State Unlversity, Ames, IA, 1982.
RECEIVED for review March 22, 1982. Accepted June 8, 1982. The Ames Laboratory is operated by Iowa State University for the U.S. Department of Energy under Contract No. W7405-eng-82. This work Was supported in Part by the Assistant Secretary for the Environment, Office of Health and Environmental~ ~contract ~W P A S ~- H A - O ~~-and ~ ~ in , part ~ by the Solar Energy Research Institute.
Comparison of Cointinuous Extractors for the Extraction and Concentration of Trace Organics from Waiter T. L. Peters Analytical Laboratories, The Dow Chemlcal Company, Midland, Michigan 48640
Current and proposed environmental regulations require analysis of a wide variety of organic compounds by gas chromatography/mass spectrometry. Since the required detection limits are a t the parts-per-billion level, an extraction/concentration step in sample preparation is a necessity. While liquid-liquid extraction employing separatory funnel and manual shaking is widely used, large sample volumes and emulsion problems make this a time-consuming procedure at best. Although continuous liquid-liquid extractors (CLLE) are available as an alternative,the time required for an extraction (18-24 h) is usually quobed as a reason for not using them. However, since any number may be run simultaneously, this does not present an insurmountable problem. In addition, the continuous extractors are suited for unattended (i.e., overnight) operation. A great variety of extraction devices have been described in the literature and many are commercially available but little has been done to compaire the relative merits of these extractors. The purpose of this study was to make a comparison and provide direction as to what extractor will best handle a specific problem.
EXPERIMENTAL SECTION Apparatus. The following extractors and solvents were used in this work: (1)Liquid-Liquid Extractor (LLE) (Kontes K-583250 or Ace Glass 6841-10). A commercial extractor in which a heavierthan-water solvent (methylene chloride) is dripped through the water sample. (2) Steam Codistillatiori Extractor (SCDE) (Ace Glass no. 6826-40 or J&W Scientific). This unit allows simultaneous condensation of a steam distillate and an immiscible extraction solvent. In this work, methylene chloride was used. (3) Steam Distillation Extractor (SDE) (Ace Glass no. 6555). This extractor passes sample steam distillate through an immiscible lighter-than-water solvent. Although hexane was used in this study, other lighter-than-watersolvents me also applicable. (4) Flow Under Extractor (FUE) (Custom ScientificGlass, Inc.). In this extractor, the heavier-than-water solvent (methylene chloride) and sample do not inix but only contact at the interface. (5) Flow Over Extractor (FOE).A logical extension of the FUE, this extractor was construlcted by the Dow Glass Fabrication Laboratory (Figure 1). Again, a lighter-than-water solvent, hexane, was used with this extractor. Reagents. All solvenltti used were Burdick & Jackson (Muskegon, MI) spectrograde with no further purification. Procedure. A total of fiive 18-h extractions were made with each extractor. The sampllc was acidified (pH 2) blank water fortified with 50 ppb each of the following chemicals: chloro-
benzene, phenol, 2-chlorophenol, 2-nitrophenol, naphthalene, 4-chlorophenol, 1,2,3,4-tetrachlorobenzene, dimethyl phthalate, 4-nitrophenol, and pentachlorophenol. In each case, a 1-L sample was used. The solvents (either methylene chloride or hexane) were concentrated to 5 mL via Kuderna-Danish evaporative distillation techniques. Before analysis, anthracene-d,, was added as an internal standard. Extracts were analyzed in duplicate by capillary gas chromatography with a flame ionization detector.
RESULTS AND DISCUSSION Table I summarizes the recovery data obtained by using the extractors. Since samples had to be concentrated prior to analysis, values are given for the recovery of the entire procedure, recovery corrected for concentration losses, and the standard deviation. Within experimental error, the LLE and the FUE are equivalent. These extractors can be thought of as general purpose, extracting the widest variety of compounds. The FUE has a slight edge over the LLE in that emulsions with actual samples are nearly impossible to generate using this extractor. The FOE should be considered as complementary to the FUE. The same principle is employed, but more selectivity can be realized using a nonpolar hydrocarbon solvent. Lower recoveries observed in some cases are due to the solvent. In the case of 4-nitrophenol, 4-chlorophenol, 2-chlorophenol, and phenol, and low recoveries are due to a solubility problem. Chlorobenzene losses most likely occurred during the Kuderna-Danish concentration. The higher boiling point of hexane vs. methylene chloride would explain the recovery difference. Use of pentane solvent rather than hexane could partially alleviate this loss. Nonrecovery of 4-nitrophenol indicates that neither hydrocarbon solvents nor distillation techniques can be used to extract this component. Although the SDE and SCDE both rely on steam distillation as a preliminary separation step, the similarity ends there. The SDE recycles the steam condensate through a small (5-10 cm3) volume of lighter-than-water solvent. In the SCDE, the steam condensate mixes with solvent condensate on the condenser walls. The phases are separated and each returned to their respective distillation pots (steam condensate to sample chamber and solvent to solvent chamber). Fresh solvent continually contacts the steam condensate, so marginally soluble species are concentrated in the solvent chamber. The SCDE also has an advantage in that either heavier- or lighter-than-water solvents can be used. In this study, however, only methylene chloride was used.
0003-2700/82/0354-1913$01.25/0 0 1982 American Chemlcal Society
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Anal. Chem. 1982, 5 4 , 1914-1917
Table I. Extractor Efficiency Column 1 % recovery of entire procedure Column 2 standard deviation Column 3 % recovery corrected for concentration losses LLE FUE FOE compound 1 2 3 1 2 3 1 2 3 chlorobenzene 72 8.9 96 78 10.5 104 43 4.3 107 phenol 72 5.4 90 81 6.8 101 no recovery 2-chlorophenol 73 5.9 91 85 8.0 106 50 4.9 79 2-nitrophenol 83 7.5 99 91 6.1 108 82 3.9 102 naphthalene 82 5.9 91 91 4.1 101 82 4.1 91 4-chlorophenol 69 2.9 83 76 4.7 91 32 3.3 42 1,2,3,4-tetrachlorobenzene 82 5.3 89 90 3.7 98 87 3.3 96 dimethyl phthalate 96 5.5 98 91 1.1 93 101 1.8 105 4-nitrophenol 98 7.6 102 92 2.7 97 norecovery pentachlorophenol 86 3.8 93 88 5.3 96 71 6.4 78
SDE 1 2 59 1.8 no recovery 77 2.5 97 1.5 95 4.3 no recovery 80 6.5 45 7.2 no recovery 85 2.9
SCDE 2 7.9 9.8 3.4 1.9 2.6
1 82 79 80 83 87 1.7 66 87 4.7 62 4.5 no recovery 86 3.9
3 90 82 86 88 92 72 93 64 90
graphic column. A prediction of whether or not a particular compound will steam strip from water can be made on the basis of its “relative volatility to water” ( I ) . The small volumes of solvent normally used in steam distillation techniques (20 cm3 in SCDE vs. 700 cm3 in FUE) facilitates solvent concentration and minimizes interfences due to solvent impurities and/or preservatives. Temperature stability of each solute to be steam distilled must be demonstrated in the matrix. Extreme care must be exercised to be certain the species is neither formed nor destroyed during the extraction. Any samples that form emulsions during conventional liquid-liquid extractions may foam when used in a steam distillation apparatus. The extent of foaming can range from inconsequential to severe-filling the entire apparatus with foam. Experimentation is the only way to determine whether or not the sample will foam. Flgure 1. Flow over extractor: 1, solvent distillation pot; 2, 6 in. diameter X 4 In. helght; 3, 45/50 joint for sample addition and stirrer; 4, 24/40 joint to condenser.
Since no concentration of the SDE extract was made, losses of chlorobenzene can probably be attributed to volatilization through the condenser. Phenol and 4-chlorophenol, although they do distill, are insufficiently soluble in the hexane under these conditions to be concentrated. The low relative volatility of dimethyl phthalate with respect to water results in low recoveries with both distillation techniques. Normally, species that can be steam distilled can also be gas chromatographed. This results in a “cleaner” extract and reduces the buildup of residue at the front of the chromato-
CONCLUSION In general, the SCDE and FUE/FOE appear to be the most useful. For general purpose work where the aim is to extract everything possible with the solvent being used, the FUE/FOE would be optimum. When more specificity and a cleaner extract are desired, the SCDE can be used provided adequate precautions are taken (i.e., thermal stability, foaming problems, etc.). LITERATURE CITED (1) Robbins, L. A. U.S. Patent No. 4236973, Dec 2, 1980.
RECEIVED for review January 18,1982. Accepted May 27,1982.
Determination of Water by an Automated Stopped-Flow Analyzer with Pyridine-Free Two-Component Karl Fischer Reagent Michael A. Koupparis’ and Howard V. Malmstadt”2 Department of Chemistty, University of Illinois, 1209 W. California St., Urbana, Illinols 6 180 1
Water or moisture content in a wide variety of materials is a matter of universal importance, and the determination of water has become one of the commonest routine procedures in chemical laboratories. Among the many methods used (I, Present address: Laboratory of Analytical Chemistry, University of Athens, 104 Solonos St., Athens (144), Greece.
‘-Present address: 75-5786 Niau Place, Kailua, Kona, HI 96740. 0003-2700/82/0354-1914$01.25/0
2 ) , e.g., gravimetric, spectroscopic (NMR, UV, IR), refractometric, titrimetric (Karl Fischer), etc., the last one, introduced in 1935, is the most generally used. The Karl Fischer reagent that consists of iodine and s u l f u r dioxide in pyridinemethanol solution is used as titrant and the end point is nearly always obtained electrometrically by biamperometric or bipotentiometric technique. Various types of apparatus have been designed to automate the titration. 0 1982 American Chemical Society
