LITERATURE CITED (1) K. Govindaraju, G. Mevelle. and C. Chouard, Chem. Geol., 8, 131 (1971). (2) K. Govindaraju, G. Mevelle, and C. Chouard, Bull. SOC.Fr. Ceram., 96, 47 (1972). (3) K. Govindaraju, R. Hermann, G. Mevelle, and C. Chouard, At. Absorpt. Newsl., 12, 73 (1973). (4) K. Govindaraju, G. Mevelle, and C. Chouard, Anal. Chem., 46, 1672 (1974). (5) 'M. A. Coudert and J. M. Vergnaud, C.R. Acad. Scb, 268, 1225 (1969); Anal. Chem., 42, 1303 (1970). (6) S.A. Shipltsyn, V. V. Kiryuskin. and A. A. Ermolaev, Zavod. Lab., 31, 253 (1965). (7) S. A. Shipitsyn, V. V. Kiryuskin, and N. Y. Kuklina, Zh. Anal. Khim., 21, 779 (1966). (8) N. A. Panichev and Y. I. Turkin, Zh. Prikl. Spektrosk., 12, 213 (1970). (9) P. T. Gilbert, Jr., Anal. Chem., 34, 1025 (1962). (10) J. L. Mason, Anal. Chem., 35, 874(1963). (11) V. I. Lebedev, Zh. Anal. Khim., 24, 337 (1969). (12) M. Kashiki and S. Oshima, Anal. Chim. Acta, 51, 387 (1970). (13) W. W. Harrison and P. 0. Juiiano, Anal. Chem., 43, 248 (1971). (14) J. A. Burrows, J. C. Heerdt, and J. B. Willis, Anal. Chem., 37, 579 (1965). (15) A. Lacour, C. Teinturier, and D. B. Isabelle, Methodes Phys. Anal. (GAMS), 7, 49 (1971). (16) T. T. Bartels and M. P. Slater, At. Absorpf. Newsl., 9, 75 (1970). (17) R . H. Kriss and T. T. Bartels, At. Absorpt. Newsl., 9, 78 (1970). (18) J. H. Taylor, T. T. Barteis, and N. L. Crump, Anal. Chem., 43, 1780 (1971). (19) D. F. Kelsall and J. C. H. McAdam, Trans. inst. Chem. fng., 41, 84
(1963). (20) IUPAC Information Bulletin "Appendices on Tentative Nomenclature on Symbols, Units, and Standards-No. 27. Nomenclature, Symbols, Units and their Usage in Spectrochemical Analysis-Ill. Analytical Flame Spectroscopy and Associated Procedures", November 1972. (21) J. B. Willis. Spectrochim Acta, Part A, 23, 811 (1967). (22) P. L. Larkins and J. B. Willis, Spectrochim. Acta, PartB, 29, 319 (1974). (23) N. C. Ciampitt and G. M. Hieftje. Anal. Chem., 44, 1211 (1972). (24) P. D. Johnston, Combust. Flame, 18, 373 (1972). (25) i. W. Smith, "Heat Transfer Processes within Hot Fluid-Fine Particle Suspensions," MSc. Thesis, University of New South Wales, Sydney, Australia, 1970. (26) C. S.Ram, J. Sci. lnstrum., 44, 227 (1967), and personal communication. (27) G. M. Hieftje and H. V. Malrnstadt, Anal. Chem., 40,1660 (1968). (28) G. J. Bastiaans and G. M. Hieftje, Anal. Chem., 46, 901 (1974). (29) D. J. Halls and A. Townshend, Anal. Chim. Acta, 36, 278 (1966). (30) C. Th. J. Alkernade, in "Flame Emission and Atomic Absorption Spectrometry", J. A . Dean and T. C. Rains, Ed., VoI. 1. Dekker, New York, 1969. (31) D. H. Cotton and D. R. Jenkins, Trans. faraday SOC.,64, 2988 (1968). (32) E. M. Bulewicz and P. J. Padley, Proc. Roy. SOC., Ser. A., 323, 377 (1971). (33) L. de Galan and G. F. Samaey, Spectrochim. Acta, Pari B, 25, 245 (1970). (34) J. B. Willis, Spectrochim. Acta, Part B, 25, 487 (1970). (35) J. B. Willis, Spectrochim. Acta, Part B, 26, 177 (1971). (36) I. RubeSka, Spectrochim. Acta, Part B, 29, 269 (1974).
RECEIVED for review March 17, 1975. Accepted May 9, 1975.
Atomic Absorption Spectrometric Study of the Extractability of Selected Molybdoheteropoly Acids Stephen J. Simon and D. F. Boltz Department of Chemistry, Wayne State University, Detroit, Mich. 48202
Atomic absorption spectrometry has been used to follow the partitioning of molybdophosphorlc, molybdosilicic, molybdoarsenic, and molybdogermanic acids between aqueous and nonaqueous phases. After the extract is subjected to acidic washings to remove excess molybdate, it is then contacted with a basic buffer solution to decompose the molybdoheteropoly acid and transfer the equlvalent molybdate to the aqueous phase. The molybdate is then determlned by measurement of the absorbance of the 313.3-nm resonance line of molybdenum. The distrlbution ratios for each molybdoheteropoly acid as a function of acidity and selectivity of extractant were determined. The optimum acidities for the extraction of each molybdoheteropoly acid have been delineated for the following extractants: diethyl ether, diethyl ether-1-pentanol (5:1), butyl acetate, methyl isobutyl ketone, and chloroform-n-butanol (4:l).
Molybdoheteropoly acids have become increasingly important in the indirect atomic absorption determination of certain elements which exhibit poor sensitivity by conventional AAS. Indirect atomic absorption spectrometric methods have been published for phosphate (1-5), silicate (1, 2, 6, 7), arsenate (6,8-10), and germanate ( 1 1 ) based on the use of binary molybdoheteropoly acids. In addition, indirect atomic absorption methods for the elements thallium (12), niobium ( 1 3 ) ,thorium (14), titanium (15), vanadium (16, 1 7 ) , and cerium (18) have been published utilizing ternary complexes of molybdophosphoric acid. All indirect AAS methods involving molybdoheteropoly acids require the separation of the molybdoheteropoly acid from the excess molybdate reagent before measuring the equivalent molybdenum associated with the central element. 1758
These indirect methods are also characterized by mutual interferences unless a selective separation of the desired molybdoheteropoly acid is accomplished. A liquid-liquid extraction of the molybdoheteropoly acid has been used in most cases for the separation step, followed by a wash step of the organic extract to remove any of the coextracted molybdate reagent before determining the molybdenum associated with the central element by AAS. Little quantitative distribution data have been gathered concerning the solvent extraction equilibria involved with molybdoheteropoly acids. This paper reports the results of a study of the extractability of the binary molybdoheteropoly acids of phosphate, silicate, arsenate, and germanate using atomic absorption spectrometry to follow the partitioning. Distribution ratios were determined for each molybdoheteropoly acid as a function of solution acidity in five representative organic solvents. The distribution ratio is defined as the total concentration of the molybdoheteropoly complex in the organic phase divided by the total concentration of the complex remaining in the aqueous phase. Thus, a knowledge of the distribution behavior of each molybdoheteropoly acid in each solvent allows the analyst to choose the proper solvent and conditions for the quantitative extraction of each molybdoheteropoly acid, and for avoiding or minimizing the extraction of any interfering molybdoheteropoly acid. The method used in this study involves the formation of a known amount of the molybdoheteropoly complex, extraction of the heteropoly acid with an immiscible organic solvent, washing of the organic extract to remove any excess molybdate, decomposition of the molybdoheteropoly acid with a basic solution in order to transfer the molybdate to the basic aqueous phase, and measurement of the molybdenum by AAS. The amount of molybdenum associ-
ANALYTICAL CHEMISTRY, VOL. 47, NO. 11, SEPTEMBER 1975
ous layer into a 100-ml volumetric flask. Add another 15 ml of the buffer solution and shake the funnels for another 15 to 30 seconds. Drain the aqueous phase into the same 100-ml volumetric flask and dilute to the mark with distilled water. This solution contains the molybdate from the decomposition of the extracted molybdophosphoric acid. Use atomic absorption spectrometry to determine the molybdenum concentration in the aqueous buffer solutions. Adjust the current to 15 mA for the hollow cathode lamp. Use a spectral band width of 0.40 nm and adjust the monochromator wavelength to obtain maximum transmittance at 313 nm. Use a reducing air-acetyApparatus. The atomic absorption spectrometric measurelene flame with a support gas pressure of 21 psi and an acetylene ments were made using a Beckman Model 1301 Atomic Absorption pressure of 7 psi; adjust the fuel flow rate while aspirating a 20Accessory, a Beckman DB-G grating spectrophotometer equipped ppm molybdenum solution until maximum absorbance is obwith a Beckman potentiometric recorder and a Beckman laminar tained. Also, adjust the burner height for maximum absorbance flow burner. The hollow cathode molybdenum source was neonwhile aspirating a 20-ppm molybdenum solution. Aspirate the filled and supplied by Beckman. A Thomas mechanical shaker was known and unknown solutions and record the per cent transmitused for the extractions. tance. Aspirate water between all samples to clean the premix Reagents. Standard Phosphate Solution, 10 fig of phosphorus chamber and check the base line. Determine the concentration of per ml. Dissolve 2.200 g of potassium dihydrogen phosphate, the molybdenum unknowns from a calibration graph prepared KHzP04, in distilled water and dilute to 1 liter. Dilute a 20.00-ml using standard molybdate solutions having the identical buffer aliquot of this solution to 1 liter with distilled water. matrix. Standard Silicate Solution, 10 fig of silicon per ml. Dissolve 5.40 This procedure gives the molybdenum(V1) concentrations in the g of sodium silicate, NazSiOr9Hz0, in distilled water and dilute to extracted phase, initially present as molybdophosphoric acid. On 1 liter. Standardize this solution gravimetrically, and then use a the basis of knowing the total concentration of the molybdenum in microburet to transfer sufficient silicate solution to a 500-ml voluthe back-extracted organic phase (as determined by AAS), the volmetric flask so that on dilution to the mark, the final silicate soluumes of both phases, and the amount of molybdenum originally tion contains 10 fig of silicon per ml. present as the molybdoheteropoly acid in the aqueous phase, the Standard Arsenate Solution, 25 fig of arsenic per ml. Dissolve total concentration of the molybdenum associated with the hetero0.1320 g of arsenious oxide, As&, in 10 ml of 0.1 N sodium hypoly acid remaining in the aqueous phase was calculated. The disdroxide, add 5 ml of concentrated hydrochloric acid, and dilute to tribution ratio, D = (CM,)O/(CM,)H~O, the ratio at equilibrium for 1 liter with distilled water. Dilute a 25.00-ml aliquot of this soluthe total molybdophosphoric acid concentration in the organic tion to volume in a 100-ml volumetric flask. phase to that in the aqueous phase, was calculated for each extracStandard Germanate Solution, 25 fig of germanium per ml. tion acidity. For acidities where the extraction is 199% complete Transfer 0.1803 g of reagent grade germanium dioxide, GeOz, to a with equal phase volumes, decrease the volume of the organic solplatinum crucible. Mix thoroughly with 1 gram of sodium carbonvent (V,) to obtain an approximate upper value for the distribuate and fuse the mixture for 10 minutes or until a clear melt is obtion ratio. tained. After cooling, dissolve in 10 ml of distilled water. Adjust to Procedure I1 (for the determination of distribution ratios for pH 2 to 3 with 1:l sulfuric acid and dilute to 500 ml with distilled molybdosilicic acid). Add to a series of 125-ml separatory funnels, water. Dilute a 50.00-ml aliquot of this solution to volume in a 10.00-ml aliquots of the standard silicate solution and continue 500-ml volumetric flask. The pH should be approximately 3 to 4. with Procedure I. Ammonium Molybdate Solution, 10% w/v. Dissolve 25.0 g of reagent grade ammonium molybdate, ( N H ~ ) ~ M o ~ O ~ Cin~disH ~ O , Procedure 111 (for the determination of distribution ratios for molybdoarsenic acid). Add to a series of 125-ml separatory funnels, tilled water and dilute to volume in a 250-ml volumetric flask. 10.00-ml aliquots of the standard arsenate solution. Dilute the soBuffer Solution. Dissolve 53.5 g of reagent grade ammonium lutions with distilled water so that on addition of subsequent rechloride in 500 ml of distilled water. Add 70 ml of concentrated agents the final aqueous volume is 50.0 ml. Add 4.0 ml of the 10% ammonium hydroxide and dilute to 1 liter with distilled water. ammonium molybdate reagent and 1.0 ml of bromine water to oxiThe final pH is about 9.3. dize any arsenic(II1) to arsenic(V). Arsenic(II1) does not form a Bromine Water. Add 2 ml of liquid bromine to 100 ml of disheteropoly molybdate. The solution should be slightly yellow. Add tilled water. 1.0 ml of the 4N hydrochloric acid, swirl the separatory funnels to Soluents. Diethyl ether, n-butyl acetate, methyl isobutyl ketone mix, and allow to stand for 10 minutes. The pH of these solutions (MIBK), a 1:5 mixture of 1-pentanol and diethyl ether, and a 1:4 should be approximately 1.3. Continue with Procedure I. mixture of n-butanol and chloroform. Procedure IV (for the determination of distribution ratios for All chemicals were reagent grade and stored in polyethylene botmolybdogermanic acid). Add to a series of 125-ml separatory funtles. Solvent mixtures were prepared fresh daily. nels, 4.0 ml of the 10% ammonium molybdate reagent. Add a Procedure I (for the determination of distribution ratios for 10.00-ml aliquot of the standard germanate solution and 0.5 ml of molybdophosphoric acid). To a series of 125-ml separatory fun4N hydrochloric acid. Dilute the solution with distilled water so nels, add a 10.00-ml aliquot of the standard phosphate solution, that on the addition of subsequent reagents, the final aqueous vol1.0 ml of 4.ON hydrochloric acid, and dilute the solutions with disume is 50.0 ml. Swirl the separatory funnels to mix and allow to tilled water so that the final volume after addition of all subsestand for 30 minutes. The pH of these solutions should be approxiquent aqueous reagents is 50.0 ml. Add 4.0 ml of the 10% ammomately 1.5. Continue with Procedure I. nium molybdate reagent, mix thoroughly by swirling, and allow the solutions to stand for 10 minutes. The pH of these solutions should be approximately 1.3. Add concentrated hydrochloric acid RESULTS AND DISCUSSION to each funnel to bring the extraction acidity to the desired value. Extraction of Molybdoheteropoly Acids with DiSwirl the solutions to mix and allow to stand an additional 5 minethyl Ether. Figure 1 shows the distribution ratios plotted utes. Adjust, if necessary, the final aqueous volume to 50.0 ml. Add a 50.0-ml aliquot of the selected solvent or solvent mixture to the vs. log acidity for each heteropoly acid. When VIVOI1.7, separatory funnel and shake on a mechanical shaking apparatus molybdophosphoric acid is quantitatively extracted with for 3 minutes. (This shaking time is sufficient time to obtain equidiethyl ether over the acidity range of 0.9 to 1.3N hydrolibrium.) Allow adequate time for the layers to separate and dischloric acid while molybdosilicic acid remains unextracted card the aqueous layer containing the excess molybdate and any over the entire acidity range of 0.08 to 4.ON hydrochloric unextracted molybdophosphoric acid. Rinse the separatory funnel acid. Thus, it is possible to extract quantitatively molybdotip with a stream of distilled water. Wash the organic extract twice with 25-ml portions of 1 : l O hydrochloric acid. For each wash, phosphoric acid in the presence of molybdosilicic acid with shake the organic phase with the wash solution for 30 seconds, an extraction acidity of 0.90 to 1.3N hydrochloric acid. allow the two phases to separate, and withdraw the aqueous phase. Separations of traces of phosphate from solutions containFollowing the second wash step, rinse the funnel tip with distilled ing both phosphate and silicate have been accomplished water to remove any remaining traces of excess molybdate. Add 30 using diethyl ether as the extractant for the corresponding ml of the ammonium hydroxide-ammonium chloride buffer solumolybdophosphoric acid (I). tion to the funnels and shake for 15 to 30 seconds. Drain the aque-
ated with the heteropoly acid in the remaining aqueous phase can then be calculated by difference. From the total molybdenum content of each phase, and the known volumes of both phases, the distribution ratio is then calculated for each extraction acidity. Log D vs. log acidity plots for each molybdoheteropoly acid in each solvent are then constructed. EXPERIMENTAL
ANALYTICAL CHEMISTRY, VOL. 47, NO. 11, SEPTEMBER 1975
1759
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Figure 1. Distribution diagram for the extraction of molybdohetero-
Flgure 3. Distribution diagram for the extraction of molybdohetero-
poly acids with diethyl ether
poly acids with n-butyl acetate
-201
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,
,
,
,
,
,
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,
,
00
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Figure 2. Distribution diagram for the extraction of molybdoheteropoly acids with 5: 1 diethyl ether-1-pentanol
Molybdoarsenic acid is partly extracted over the entire acidity range and has a minimum D value of 0.15 falling within the acidity range for complete extraction of molybdophosphoric acid. Thus, arsenate would interfere with the extraction of molybdophosphoric acid unless it was removed, masked, or was a t a very low concentration level. Molybdogermanic acid is not extracted by diethyl ether over the acidity range of 0.08 to 0.50N hydrochloric acid. At acidities greater than 0.50N hydrochloric acid, the molybdogermanic acid is very slightly extracted. However, a t acidities of 0.9 to 1.3N hydrochloric acid, the distribution ratios are low enough to permit virtually complete separation of molybdophosphoric acid from molybdogermanic acid using diethyl ether as extractant. Extraction of Molybdoheteropoly Acids with 5:l Diethyl Ether:l-Pentanol. The experimental data obtained using the 5:l diethyl ether-1-pentanol mixture are plotted as a distribution diagram in Figure 2. As indicated by Figure 2, all four molybdoheteropoly acids can be quantita1760
e
tively extracted with the solvent mixture over part of the acidity range under study. The extraction of molybdophosphoric acid is virtually 100% efficient over an acidity range of 0.08 to 1.5N hydrochloric acid when VIVOI4.2 but decreases rapidly at [H+] I 1.5N hydrochloric acid. The extraction of molybdoarsenic acid is also quantitative when V/Vo I4.2 over the acidity range 0.08 to 1.5N hydrochloric acid. Thus, molybdophosphoric and molybdoarsenic acids show practically the same extraction behavior in this solvent mixture and would not be able to he separated. Molybdogermanic and molybdosilicic acids show similar extraction behavior and cannot be completely separated with this solvent mixture over the acidity range investigated. However, molybdosilicic acid is extracted at a much higher acidity than either molybdophosphoric or molybdoarsenic acid, and it would be possible to separate molybosilicic acid from solutions also containing molybdophosphoric acid and molybdoarsenic acid by utilizing an extraction acidity corresponding to about 2.5N hydrochloric acid. Molybdogermanic acid is quantitatively extracted over the narrow acidity range of 1.0 to 1.3N hydrochloric acid. As indicated by Figure 2, little selectively is possible for this heteropoly acid using 5:l diethyl ether-1-pentanol. Extraction of Molybdoheteropoly Acids with nButyl Acetate. Figure 3 summarizes the extraction data and is the corresponding distribution diagram for the extraction of molybdoheteropoly acids with n-butyl acetate. n-Butyl acetate is a highly selective extractant for molybdophosphoric acid with a distribution ratio of approximately 620 for the acidity range of 0.08 to 1.ON hydrochloric acid. Molybdosilicic acid is not extracted except at acidities greater than 1.5N hydrochloric acid, and molybdogermanic acid is not extracted until the acidity is greater than O.5ON hydrochloric acid. Both molybdosilicic and molybdogermanic acids were extracted at 1.5N and 2.ON hydrochloric acid acidities. However, on the wash steps to remove any excess molybdate that is coextracted with the heteropoly acid, the characteristic yellow color of these molybdoheteropoly acids disappeared indicating decomposition of these complexes. Thus, extractions of molybdophosphoric acid in the presence of molybdosilicic and molybdogermanic acid at an acidity greater than 0.50N hydrochloric acid should be avoided. However, no other solvent investigated demonstrated both the specificity and efficiency for the extraction of molybdophosphoric acid as does n-
ANALYTICAL CHEMISTRY, VOL. 47, NO. 11, SEPTEMBER 1975
t30
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Flgure 4. Distribution diagram for the extraction of molybdoheteropoly acids with methyl isobutyl ketone
Figure 5. Distribution diagram for the extraction of molybdoheteropoly acids with 4: 1 chloroform-n-butanol
butyl acetate. Thus, quantitative extraction of molybdophosphoric acid can be accomplished over a recommended acidity range of 0.08 to 0.50N hydrochloric acid without any appreciable interference from molybdosilicic, molybdogermanic, or molybdoarsenic acid. Extraction of Molybdoheteropoly Acids with Methyl Isobutyl Ketone. MIBK has been used extensively as an extractant for molybdoarsenic acid (8, 10). I t was decided to further investigate the extractability of molybdoheteropoly acids to determine if any selectivity can be accomplished with MIBK and also obtain quantitative distribution data for molybdoheteropoly acid extractions. The results of this study are presented in the corresponding distribution diagram (Figure 4). The four molybdoheteropoly acids studied show similar distribution behavior in MIBK. Only molybdosilicic can be selectively extracted in the presence of molybdophosphoric and molybdoarsenic acid a t an extraction acidity 1 2.5N hydrochloric acid. Molybdophosphoric acid and molybdoarsenic acid can be quantitatively extracted with MIBK from acidic solutions ranging from 0.08 to 1.5N hydrochloric acid when VIVOI 6.3. Molybdosilicic acid has a maximum distribution ratio of approximately 710 from 0.08 to 4.ON hydrochloric acid and, thus, can be quantitatively extracted over this entire acidity range. Molybdogermanic acid can be quantitatively extracted from 0.08 to 2.ON hydrochloric acid when VIVOI 6.3. Solution acidities greater than 2.ON hydrochloric acid were not investigated for molybdogermanic acid; thus, extraction of this heteropoly acid with MIBK is recommended to be within the 0.08 to 2.ON hydrochloric acid range. It should be noted that extractions performed below an acidity of 0.50N hydrochloric acid gave abnormally high results unless the organic extract was washed a t least three time with 25-ml portions of the acidic wash solution. The high results seem to be due to an abnormally high amount of excess molybdate being transferred to the organic phase. Extraction of Molybdoheteropoly Acids with 4:l Chloroform-n-Butanol. A 4:l mixture of chloroform-nbutanol was originally shown by Alekseev (19) and Filippova and Kuznetsova (20) to selectively extract molybdophosphoric acid in the presence of arsenate and silicate. Other investigations have demonstrated its use in the extraction and determination of molybdophosphoric acid (21, 22) and in separations of the molybdophosphoric acid
formed simultaneously with various mixed heteropoly complexes (15,17,18). This solvent mixture has a higher density than water and is more convenient to use in separating molybdophosphoric acid from other heteropoly acids. The distribution diagram for this solvent mixture is shown in Figure 5. This solvent is specific for molybdophosphoric acid over the acidity range under investigation. However, it is not as efficient a solvent as n-butyl acetate for the extraction of molybdophosphoric acid. Its maximum distribution ratio is 1.2 over the acidity range of 0.5 to 1.5N hydrochloric acid. Nature of the Distribution Diagrams for Molybdoheteropoly Acids. The distribution diagrams for molybdoheteropoly acids shown in Figures 1 to 5 exhibit some similarity to several other “onium-salt” systems such as the iron(II1) extraction from hydrochloric acid solutions (23, 24). However, the problem of reducing the extraction behavior of molybdoheteropoly acids to analytical expressions that can quantitatively describe the relation between the extent of reaction and experimental data is difficult. One problem is that the high electrolyte concentrations employed in this and other heteropoly acid studies lie in the range in which great disparities exist between concentrations and activities. Thus, relatively small changes in concentrations may result in significant activity changes and thus reduce the ability of the mass action expressions used to describe the experimental extraction data. More important, however, is the large number of equilibria involved in the formation of the extractable 12-molybdoheteropoly acid species which leads to extremely complex relationships for the extraction parameters. At present, knowledge of isopolymolybdate formation is still minimal and no formation constants are available for the isopolymolybdates or the molybdoheteropoly acids. Aveston et al. (25) have investigated the acid dependence of isopolymolybdate formation. Other possible reactions in the organic phase and further polymerizations are still unknown with respect to molybdoheteropoly extraction equilibria. However, several similarities do exist between the molybdoheteropoly acid extraction system and oxonium and/ or ion-association extraction systems. The first major similarity is the nature of the solvent on the extraction efficiency. The large water content of molybdoheteropoly acids and the subsequent hydrogen-bonding in the outer molyb-
ANALYTICAL CHEMISTRY, VOL. 47, NO. 11, SEPTEMBER 1975
1781
Table I. Summary: Extraction of Molybdoheteropoly Acids by Various Extractants Molybdoheteropcly acid
Extractant
v=
Outimum acidity for extraction, Distribution N o f HC1 ratio
v0
MOlybdoDiethyl ether' phosphoric acid Diethyl ether1-pentanol (5:l)b n-Butyl acetate' MIBK' Chloroformn-butanol (4:l) Molybdosilicic Diethyl ether acid Diethyl ether1-pentanol (5 :1) n-Butyl acetate MIBK~
Molybdoarsenic acid
Molybdogermanic acid
Chloroformn-butanol (4:l) Diethyl ether Diethyl ether1-pentanol ( 5 : l ) b n-Butyl acetate MIBKC Chloroformn-butanol (4:l) Diethyl ether Diethyl ether1-pentanol (5:l) n-Butyl acetate MIBK' Chloroformn-butanol (4:l)
1.0-1.3 0.1-1.5
165 410
0.1-1.0 0.1-1.5 0.5-1.5
620 620 1.2
0.1-4.0
