REVIEW OF FUNDAMENTAL DEVELOPMENTS IN ANALYSIS
I
Extraction GEORGE H. MORRISON, Research Laborafories, Sylvania Necfric Producfs Inc., Bayside, N. Y. HENRY FREISER, Deparfmenf o f Chemistr,,, Universify o f Piftsburgh, Pittsburgh 7 3, Pa.
T
HIS REVIEW, the first by the present authors, is a continuation of the series on extraction formerly written by L. C. Craig (36). A change in emphasis will be noted, with particular stress given to theapplication of this technique to the separation of inorganic materials rather than to organic and biochemical substances. I n keeping with the theme of the fundamentalreview series, this paper is an attempt to evaluate critically the progress of the past two years in the field of analytical extractions. For more detailed coverage of the subject, both during and prior to the period covered by this review, the book by the reviewers (143) is suggested.
REVIEWS AND BOOKS
Although solvent extraction as a method of separation has long been familiar to the chemist, only in recent years has it begun to achieve recognition among analysts as a powerful separation technique. I n view of this recent recognition, there has been only a limited number of reviews and books on the subject. For completeness’ sake they are surveyed here. The field of solvent extraction may be conveniently divided into two major groups-inorganic and organic. In the former class the early reviews of Morrison ( I @ ) , Irving (91), and IZuznetsov (112) provide the oiily comprehensive surveys of the large number of extractions involving inorganic materials for use in analysis. More recently West (211, 212) has surveyed the applications of liquidliquid extraction to inorganic analysis with particular reference to metallurgical analysis. A recent book (149) offers the first comprehensive treatment of extraction as applied to inorganic analysis and covers both the principles and practical aspects of the field in addition to presenting procedures for the extraction of the elements. The reviews of Craig (86) in ANALYTICAL CHEMISTRY present an excellent survey of the developments in organic and biochemical materials, with particular emphasis on the technique of countercurrent distribution. Hecker (80, 82), Metzsch (133, 134, Verzele
632
ANALYTICAL CHEMISTRY
(No),and iCIunicio (149) similarly supply valuable information on the extraction behavior of org,anic solutes. The books by Hecker ( S I ) and Vigneron (202) and the chapters by Craig and Craig (87’) and Weisiger (209) treat the subject of organic extraction and countercurrent clistribution in considerable detail and offer much to the organic chemist concerned with isolation and purification of materials. The extensive survey by Collander (85) on the distribution behalrior of organic compounds is invaluable. Finally, several reviews (192), books (4, 198), and chaptcrs (180) have been written on the eng neering aspects of solvent extraction; their value to analytical application, however, is very limited. EXTRACTIOhI SYSTEMS
From the point 0 ‘ view that an uncharged species is pr jbably required for extraction into an oiganic solvent, it is useful t o base the clsmificatioii of metal extraction systems on the manner in which the extractable species is formed (143). Two broad [nodes of complex formation may be readily recognizedcoordination and ioii association. Because most extractable species which involve solely coordin,]tion are chelates, the term chelate cvtractioii systems is employed here in preference to the broader term. The few others, inorganic coordination complexes such as the halides of mercuxy and germanium, are more conveniently classed with ion association extraction systems. Chelate extractior systems include only those involving neutral chelates, as charged chelates-for example, bisphenanthroline-copper(1) cation or the cobalt-(nitroso R salt) anion-may pair with an oppositely charged ion to form an extractable specicbs by ion association. Differentiation of ion association sy-stems is logically based on the sign of the charge of the member of the ion pair containing the metal. !I7ith systems involving metal-containing anions, a further differentiation is h s e d on the nature of the cation partne. of the ion pair. Thus, oxonium extrac ;ions involve those systems in which a protonated oxygen-
containing solvent is part of the extractable ion pair-eg., (C2H&0-H+,FeCla-). The other “onium” systems are analogous. Table I lists the various extraction systems according t o the classification just described. The names given the systems reflect the reagents used t o achieve complexation or association. An increasing number of extraction studies have been published within the past two years, and representative samples of the various systems investigated are presented here. The distribution studies describe the extraction behavior of various elements under different experimental conditions so that, although they are not presented as established analytical procedures, the information should be of considerable help in the further development of analytical separation procedures. Chelate Extraction Systems. CUPFERRON AND ANALOGOUS REAGENTS. Cupferron extractions of a number of metals into a mixed solvent of 1 to 1 benzene and isoamyl alcohol have been studied (66). Thorium, zirconium, and iron extracted a t a low pH, although a series of divalent metals, including magnesium, mas remored a t higher pH values. The extraction of cupferronates of niobium, tantalum, and titanium into isoamyl alcohol was also studied (5). AT-Phenylbenzohydroxamic acid was investigated as an extractant for lanthanum, thorium, and uranium using chloroform as solvent (52). Both thorium and uranium can be separated from lanthanum, but not from each other. D~THIZONE. I n addition to a review of dithizone extractions (95),a study of dithizone extraction of zinc, cobalt, copper, and nickel from tartrate solutions was reported (59). The extraction of polonium from hydrochloric acid with dithizone has been studied (13). ~-QUIXOLINOLS. The distribution of scandium between water and a benzene solution of 8-quinolinol (197), and the distribution of lant2ianumJ thorium, and uranium between water and chloroform solutions of various 5,7-dihalo-5-quinolinols (66) have been studied. Metal complexes of the dihalo derivatives may be extracted a t somewhat lower pH values than with 8-quinolinol itself. TOLUENE-3,4-DITHIOL. Whereas 601-
uene-3,4-dithiol is not very stable, its diacetyl or dibenzoyl derivatives are (35). These may generate the free dithiol as needed. 0-DIKETONES.The extraction behavior of uranium(VI), lead, copper, and bismuth with acetylacetone has been studied (111). The extraction of all of these metals except uranium(V1) was strongly affected by EDTA. The distribution of protactinium(1V) (25) and of plutonium(1V) (39) using thenoyltrifluoroacetone has been described. NITROSONAPHTHOLS. The extraction behavior of thorium, uranium, lanthanum, plutonium, and a number of transition metals with both l-nitroso-2naphthol and 2-nitroso-1-naphthol in chloroform has been studied (65). Thorium and uranium can be separated from each other and from lanthanum by using either reagent. OTHERCHELATING AGENTS. The use of a number of chelating agents for the extraction of lanthanide and actinide elements has been reviewed ( 5 4 , as well as chelating agents suitable for plutonium (25, 116). A group of polydentate chelating agents designated as di(salicyla1)-alkylenediimines have been used to separate uranium(V1) from trivalent lanthanides by solvent extraction (6-0. Ion Association Systems. ALKYLPHOSPHORIC ACIDS. One of the most recent extraction systems investigated involves the use of dialkylphosphoric acids as complexing agents; indications are t h a t important analytical separations are possible (214). The use of di-(2-ethylhexyl)-phosphoric acid for the fractionation of the lanthanides using a carrier solvent such as toluene has been reported (161) and berkelium(1V) has been separated from the remainder of the actinide elements (162). The use of this reagent for the extraction of uranium and vanadium has been demonstrated (19). Dioctyl acid pyrophosphate in butanol was investigated as an extractant for iron(III), cobalt, and nickel from sulfuric acid solutions (181). CARBOXYLICACIDS. The use of carboxylic acids as complexing agents for extraction has only recently been fully appreciated, and recent mork by HokBernstrom (84-86) further emphasizes the importance of reagents such as salicylic, cinnamic, 3,5-dinitrobenzoic, and methoxybenzoic acids for the extraction of uranium(VI), plutoniuni(IV), thorium(IV), and lanthanum(II1); the most promising solvent is methyl isobutyl ketone. Separations include thorium from lanthanum and from uranium. NITRATES. M c I h y and associates (5,16, 78, 79, 85,178) have made an intensive study of tributyl phosphate as an extracting solvent for actinide and fission product nitrates. Among the elements that n-ere found to extract
appreciably were zirconium, cerium, plutonium(1V) and (VI), and thorium. The system can also be used to extract and separate yttrium and the lower lanthanides (La-Gd). Separation factors as high as 2 have been attained for successive lanthanides. I n all the studies the effects of nitric acid concentration and salting-out agents were evaluated. In an extension of earlier mork (168) Peppard and associates (167) have further investigated the fractionation of the trivalent lanthanides as a function of solvent concentration, nitric acid concentration, and atomic number and have observed a nonmonotonic ordering of the lanthanides. A study by Wendlandt and Bryant (210)of the solubilities of a large number of metal nitrate salts in pure tributyl
phosphate reveals many inore possibilities for the separation of the elements. Nitrate extractions involving other organic solvents have revealed the great importance of tkis system t o the separation of actinides and fission product elements. Rydbwg and Bernstrom (175) determined the distribution ratios of uranium(V1), p Iu t onium (IV) and (VI), thorium(IV), :rirconium(IV), lanthanum(III), calcium, and sodium between methyl isobutll ketone and aqueous solutions of varying nitric acid and calcium nitrate cclncentrations. As a result of this study possible methods are presented for the separation of uranium and plutoniunt from certain fission products. The conditions for the extraction of tracts of polonium from nitric acid solutions using ethyl ether and other
Table 1. Metal Extraction System; I. Chelate Systems A. &membered ring systems Reactive Grouping 1. Dialkyldithiocarbamates
-x-.-c-s-
I
\
- ),
I -\
2 . Xanthates
B. 5-membered ring systems
3. a-Dioximes
4. Dithizone 5. 8-Quinolinols 6. Toluene-3,4-dithiol
7. Catechol C. 6-membered ring systems 1. P-Diketones and hydroxycarbonyls
Acetylacetone b. Thenoyltrifluoroacetone(TTA) c. Morin d. Quinalizarin a.
2 . Nitrosonaphthols
3. Salicylaldoxime D. Polydentate systems
1. Pyridylazonaphthol (PAN) I
11. Ion Association Systems A. Metal contained in cationic member of ion pair 1. Alkylphosphoric acids 2 . Carboxylic acids 3. Cationic chelates a. Phenanthrolines b. Polypyridyls 4. Nitrate 5. Trialkylphosphine oxides B. Metal contained in anionic member of ion paira 1. Halides (GaC14-) 2 . Thiocyanates [Co(CNS)4--] 3. Oxyanions ( MnOa-) 4. Anionic chelates [Co(nitroso R salt)t---] a The cation member associated with these metal-containine anions is usuallv of an "onium" type: Oxonium-e.g., ROH, +,RlOH f, RzCOH + Ammonium-e.g., RNH, +,. . .R4K + Arsonium, RaAs" Phosphonium, RJ'+ Stibonium, R4Sb++ Sulfonium, R3S I
VOL. 30, NO. 4, APRIL 1958
633
solvents have also been determined (41, 43). HALIDES.A comprehensive study has been made of the distribution of many elements between aqueous 1 to 20N hydrofluoric acid solutions and ethyl ether (20). Of all the elements, which included fluorides of all groups of the periodic system, only rhenium(VII), niobium(V), and tantalum(V) were extracted more than 50%; the applicability of this system is therefore limited to the development of analytical methods for only these elements. Extraction of elements from hydrochloric acid solutions has always been of popular and practical interest; among the more recent studies is that of Irvine and associates (24) on the behavior of arsenic(II1) and germanium(IV). The distribution ratios mere generally found to increase in a regular manner as the acid concentration was varied from 2 to 12N using carbon tetrachloride, chloroform, P,p’-dichloroethyl ether, or benzene as solvent. The differences in extractive power between the various solvents were relatively small. Arcend (11) similarly studied the behavior of arsenic(II1) using P,P‘-dichloroethyl ether as solvent. Other studies of chloride extractions include the behavior of protactinium using diiiopropyl ketone (70, 71), astatine using ethyl ether (16$), polonium using diisopropyl ketone (28), and iron and molybdenum using butyl acetate (218). The distribution of mercuric chloride to various alcohols and ketones and mixtures of these with heptane have been investigated by Kuznetsov and Mitrofanova (1IS). Distribution ratios mere duplicated by mixed solvents when consideration was given to the number of carbon atoms in the solvents. The behavior of mercuric iodide in benzene has also been examined (144. Chloride extractions have been made using tributyl phosphate and very promising separations have been noted. Thus Peppard and associates have separated thorium, protactinuni, and uranium in one case (169), and scandium, thorium, and zirconium in another study (160), using hydrochloric acid solutions. Another detailed study on the distribution of zirconium has been reported (116). Extraction of indium from hydrobromic acid solutions has been studied using a variety of solvents (92, 107); it is possible to separate indium from zinc in 0.5 to 6M hydrobromic acid using isopropyl ether. A most interesting observation has been made by Bock and Hoppe (21) on the extractability of the alkali metals, The polyiodides of these elements result in high distribution ratios, using nitromethane. Although not completely successful, attempts were made to sep-
634 * ANALYTICAL CHEMISTRY
arate the respwtive alkali metals from each other usir g mixed solvents. THIOCYANAT i;. A few new studies on the extraction of thiocyanate complexes of metals which in the past has been of great use in colc imetric procedures have been published. Thus, the extraction of scandium wii,h ethyl ether has been reinvestigated 2nd provides the basis for the removal of this element from ores (20201). Similarly, the behavior of tungsten under a v,iriety of conditions has been re-examincbd using a variety of solvents (194). The use of tributylamine in the extracticn of iron(II1) thiocyanate by amyl acstate has been described (228, 239) and definitely involves the ammoniuni rather than oxonium cation. Tributylamine knctions in the same way for thiocyanate extraction of cobalt ($93, 225). OXY ANIOXS. The tetraphenylphosphonium and te1,raphenylarsonium salts of phosphate, apsenate, vanadate, and polyvanadate hs,ve been prepared and their extraction into chloroform has been studied (224. ANIONICCHELATES. An interesting recent development concerns the utilization of anionic chelate-formers such as nitroso-R salt, 7-iodo-8-quinolinol-5sulfonic acid (fert on), and sulfosalicylic acid. These forrri negatively charged metal chelates rrhich can pair with cations such as tributylammonium, tetraphenylarson um, and tetraphenylphosphonium to give rise to extractable species (223, 225 -2%’). Magnesium is reported to forri an anionic complex with three molecules of 8-quinolinol, which pairs with lmtylammonium ion to give a chloroform-extractable species (195). Similarly, an anionic 8-quinolinol complex 01’ uranium has been described as eo nbining with tetraalkylammonium ions (34). Nonaqueous 13xtraction Systems. A relatively n t w development in liquid-liquid extrriction is the use of molten salt-molten metal or twometal systems. This work, initiated by decontaminat on problems arising out of the liquid metals fuel reactor program, is of bwderline interest in analytical chemisixy now but may well be of more direct use to analysts before t o o long. Rare earths have been extracted from molten bismuthuranium by cowtact with molten lithium and potassium chloride (14, 16, 51, 124) and the distribution of plutonium between aluminum and bismuth (126) and betmeex uranium and silver (203,208) has been ntudied. THIi 0RY
A helpful organjxational pattern for the extraction process, based on three essential aspects coinmon to every metal extraction process, has been proposed (143). These steps include formation
of an uncharged complex, distribution of this uncharged, extractable complex, and chemical interactions of the complex in the organic phase. Although specific details of the nature of the interactions obviously must differ from one metal extraction system to another, the treatment helps to unify the large variety of extraction systems in the literature. Of continuing theoretical interest are equilibrium extraction studies designed to yield equations for D, the distribution ratio, in terms of all the pertinent experimental parameters. Such equations are not only useful in making accurate predictions of extraction characteristics which are of practical aid to the analyst but serve as bases for the detailed description of the nature of the extractable species. The development of such equations is used to advantage in studying a great variety of metal complexes (other than the extractable complex) in the aqueous phase. Irving, Rossotti, and Williams (93) have developed a generalized equation for D which may be applied equally well to chelate and ion association extractions and is useful in evaluating such aspects of the extractable complex as the extent of polymerization (of particular interest in ion association systems) and the average charge of the metal species in each of the two phases. n70rk of this nature applied t o halide extractions has been described for nickel and cobalt (IS@, molybdenum(V1) (46, 47), a variety of trivalent metals (116, 176), thallium (88), and gold(III), gallium(111), and indium(II1) (167, 168). Nitrate systems involving tributyl phosphate (TBP) have come in for considerable attention (3, 16, 62, 78, 79, 83, 98, 177, 178). Perchlorates of nickel and cobalt have also been studied (139). Other recent applications of solvent extraction systems to the study of metal complexes include work on chelate complexes of uranium ( l 7 4 ) , thorium (63,66),polonium ( I S ) , and lanthanum (62) and on the chloro complexes of astatine (162) and mercury (127). Icatzin (60,103,104)has discussed the factors affecting the extractability of inorganic salts into oxonium solvents. The base strength of the solvent will affect the number of anions in the coordination sphere of the metal ion and, hence, will determine whether or not a neutral, extractable species is formed. Katzin concludes from a study of ternary phase diagrams that under certain conditions a metal can exhibit more than one eoordination number. Burger ($7) found the extraction ability of phosphorus compounds for uranium and plutonium to increase in the order phosphate04 Bivalent elements, ele- Acetylacetone, Trilon 13 ments in bronze A1 pH 8, 2-methj4-8-quin~linol NaCN, Na diethylditkiocarbamate 3Ietallurgical products Na diethyldithiocarbainate Bi2lZ(Th-C)from pH 2.6 to 3.0, acetate buffer PbZ1z(Th-B) FAICI,, HC1 Si pH 2-3, &SO4 Si HF, NH4F. HF, HzOz Si Methylene blue, HF U HCl, NH4 citrate, NaOH Fission products I N His04 Fission products 9111 HNOa Xany elements pH > 4, EDTA HC1 Many elenient,s 1-8M HCI Fe Fe, Ti Ni Sn, Pb Ge Ge, P, Si
Fe, Bi, V, U, Mo, W, H&O,, KSCK, NaF, ti,ibutylamine Mn Fe, ill e-Furilmonosinie in p j Tidine, HC1 Steel NH,SCN, ( KHI)~SOI, NazSiOa, IZI, NazHP04 pH 8, pyridine, ICCNO Many elements PH 6
Copper
pH 7, bathocuproine Ti pH 4-6, neocuproine in ethyl alcohol Pb, Ag, Au, Pt, Pd, Os, pH 8.5, NHd citrate Sb, Te, T1, Bi sol-(C6Hs)lSb + salt Dilute HC1 Erio OS 7M HC1
Fluorine Gallium
Germanium Indium
Other elements Ga Zn Cd Cu, Zn, Ni Many elements Ti, A1 Al, M g Al, R'lg, Zn, Pb Many elements
Iron
Lead
Ni, Co, Zn, Al, hlg Cu, Sn, Bi Bi, T1
Lithium hIagnesium
Alkali metals Ca hlany elements
Mercury Molybdenum
hlany elements Silicate rocks
636
ANALYTICAL CHEMISTRY
Slightly acid, cupferron HC1
Organic phase Benzene Chloroform Benzene Isopropyl ether Amyl acetate Carbon tetrachloride Carbon tetrachloride Isobutyl alcohol 1-Butanol in chloroform Carbon tetrachloride Chloroform Chloroform 1-Pentanol or 1-butanol O . O l ~ odithizone in chloroform Ethyl ether hlethanol-isopropyl ether 0 . O l M (CP,H&ASCI in chloroform Dichloroethane Dithizone in carbon tetrachloride 0.5M TTA in xy!ene Methyl isobutyl ketone Acetylacetone Butyl acetate, or methyl isobutyl ketone 0.2M tri-n-octylphosphine oxide in benzene Amyl alcohol Chloroform Cyclohexanone Chloroform 8-hydroxy quinaldine in 1:l chloroformbenzene Hexanol Chloroform Diethyldithiocarbamate in chloroform Chloroform, carbon tetrachloride 5,7-Dibromo-8-quinolinol in chloroform
Chloroform
0.lilI tri-n-octylphosphine oxide in cyclo-
hexane Methyl isobutyl ketone Carbon tetrachloride
0.25iM ICI, 0.lN HZSO, Cyclohexanone 0.5-6N HBr Isopropyl ether 8-Quinolinol in benzene or chloroform pH 5.1-8.2 5.5-7N HC1 4-Methyl-2-pentanone NH4SCN,tributylamine Amyl acetate pH 5.3,8-hydroxyquina. dine Chloroform 1-Nitroso-2-naphthol in acetone Chloroform KSCN, HC1, antipyrint! Ethyl acetate 7-Iodo-8-quinolinold-SL ifonic acid, tri- Isoamyl alcohol butylamine pH 1.0 Soy0 acetylacetone in chloroform pH 9-10, ICCN Dithizone in chloroform or benzene Diethylammonium diethyldithiocarba1 . 5 s HCl mate in chloroform LON KOH 0.lN dipivaloylmethane in ethyl ether pH 10.0-10.2, butyl Ce dosolve 3% 8-quinolinol in chloroform pH 10.5-13.6, n-butylamine 0.1% Bquinolinol in chloroform HCl, ICI, antipyrine Chloroform I N acid Dithizone in chloroform GAf HCl, 0.4il.I HF Methyl isobutyl ketone HCI, Na diethyldithiocrirbamate Chloroform 0-1.8N HCl, a-benzoinosime Chloroforni
Table II.
Element Extracted
Neptunium Nickel
Niobium Osmium Palladium
Phosphorus
Extraction Procedures (Continued) Semrated Solvent System (before Mixing) from Aqueous phase Organic phase Reference 6 N HzS04 Acetylacetone in chloi,oform (112) Citric acid, phosphoric acid, toluene- Light petroleum (97) 3,4-dithiol Steel including W and HCl, NaF, EDTA, KSCN Amyl alcohol-carbon ietrachloride (199) Ti Most, metals NaF or EDTA, 0.1-0.5N HC1 Morin in 1-butanol (8) pH 1.11-1.56, K ethyl xanthate Toluene, chlorobenzene, or chloroform (119) TTA in xylene (137) Fission products, U, 1M HC1 Pu, Am, Cm All but Co Wide pH range a-benzildioxime Chloroform cu pH 6.5-8.9, dimethylglyoxime Chloroform a-Furildioxime, K2Cr2O7, Na citrate, Chloroform NH, Nb, T a CateEiiol 1-Butanol Ammoniacal, nioxime cu Benzene Fission products Tribu tyl phosphate H*SOa, H F (1411 Fission products AI(NOa)3, "03 Tributyl phosphate (109) Ru Concd. HCl, (C6H&AsC1 Chloroform Pt, Rh, Ir, and most 1% isopropylacetylene in methanol, Chloroform or amyl acetate transition e1ement.s weakly acid HCI, KI, antipyrine Chloroform Salicylaldehyde, hydroxylamine Benzene l,a-Naphthaquinone, hydroxylamine Chloroform Si, As, Cu, various HC1, HiYO, or HzS04, (NH4)2Rfo04 1-Butanol or butanol in ethyl ether or (68, 166, radionuclides chloroform lYf?, 185, 221)
Rhenium
hIo, TV
AI0 Rhodium Scandium Selenium Si1icon Silver Tantalum Tellurium Thallium Thorium Tin Titanium Tungsten
6N HCl, 2,4-diphenylthiosemicarbazide Chloroform ( CGH&As+ salt Chloroform 6N HCl, 4-hydroxy-3-mercaptotoluene Chloroform-2-isobutanc,l
Weakly acid, 1-nitroso-2-naphthol pH 9.7-10.5, 8-quinolinol Cu &lo, Fe, Ti, Cr, Ni, 3,3'-Diarninobenzidine-HCl, pH 6-7 60,Te, As Ni Cu, Bi, Pb, Au Nb, Ti pH 3, catechol, NHa oxalate 6 M H2S04, 0.4M HF u, Pu Ti 231 H?SOd Many elements IN HCl, 0.6N NaI PH 1 hIany elements Sulfosalicylic acid, HCl, methyl violet Pb, Zn, Cd HBr pH 0.3-0.8, cupferron Divalent metals pH 2.0 Triethyltin from di- Borate buffer, EDTA ethyhin Fe, A1 pH 5.3,8-hydroxyquinaldine Nb, Ta pH 5, cupferron, NHI tartrate Nb, Ta pH 3, catechol, NHI oxalate Silicate rocks 0-1.8N HC1, a-benzoinoxime Ta, Ti, Zr "21, SnC12, toluene-3,4-dithiol
Uranium Th, Bi, and ores Many elements Fission products
Vanadium
Yttrium Zinc Zirconium
7M HC1 pH 0-3, Al(N03)3 Cupferron pH 6, Na diethyldithiocarbamate V, Fe 1-Nitroso-2-naphthol Most metals pH 4.6, EDTA u, Mo pH 3-3.5, salicylhydroxamic acid Rfn Cupferron Ti pH 4.5-5.0, Na diethyldithicarbamate Ferrous materials pH 2.0 pH 8.5 Ga, In, Ti, U, Pb, Sn, NH*SCN, pyridine Bi, Sb Ni pH 5, KCN, dithizone 2M HNOa Divalent metals pH 0.3-1.0, cupferron
Benzene Benzene Toluene
(.fW
Amyl alcohol Dithizone in carbon tetrachloride 1-Butanol Methyl isobutyl ketone Cyclohexane n-Amyl alcohol-ethvl et ier 1.8 x 10-3M dithizone in carbon tetrachloride Benzene Isopropyl ether Benzene-isoamyl alcohol 0.5M TTA in carbon teirachloride Chloroform
(71)
(76) (121) (108) (166) (66)
(131)
Chloroform Isoamyl alcohol 1-Butanol Chloroform Amyl acetate 0.131 tridecyl or triorrtyl phosphine oxides in Varsol Tributyl phosphate Methyl isobutyl ketone Ethyl ether Chloroform Isoamyl alcohol Acetylacetone Ethyl acetate Chloroform Chloroform Acetylacetone-chloroform
8-Quinolinol in chloroform Chloroform Carbon tetrachloride or c'iloroform 0.5Aj TTA in xylene Benzene-isoamyl alcohol
(94) (89)
(64, 106)
VOL. 30, NO. 4, APRIL 1958
(136) (66)
637
final method of estimation obviously enters into the choice of extraction. In view of the large number of procedures, no attempt has been made to evaluate their worth critically; however, the survey should be a useful starting point for those interested in using the technique of extraction for specific analytical problems. Most of these procedures are modifications of previously published studies.
1738 (1956).
Chernikov, Y . it.,Tramni, R. S., Pevzner, I
