where X = As or P, and R refers to the divalent ion of 4(2-pyridy1azo)resorcinolabbreviated as H2R. The increase of the distribution ratio with the increase of niobium concentration may indicate polymerization of the extracted complex in the organic phase.
CONCLUSION The strongly colored complex of niobium with 4-(2-pyridylazo)resorcinol, which is formed in the oxalato solutions at pH 5.5 can be extracted from the aqueous solutions in chloroform by means of tetraphenylphosphonium and tetraphenylarsonium chlorides as extractants. The system is complex and too complicated for a quantitative description of extraction equilibria. However, distribution ratio dependence upon the reactants concentration, as well as comparison of the absorbance of aqueous solutions and absorbance of chloroform extracts could be explained by the following assumption. In aqueous oxalate solutions, there are several complex niobium species which display a different reactivity towards 4-(2-pyridylazo)resorcinol.Upon extraction, the equilibrium between the colored species that contains PAR and the colorless oxalato complexes is shifted towards the formation of larger equilibrium concentration of the colored niobium complex ion, since the later is the only one being extracted into the chloroform phase. The colored complex species is present in aqueous solution in the anionic form and can be extracted by hydrophobic organic cations as an ion-association complex. The latter has a tendency to polymerization in the organic phase. The highly colored chloroform extract is suitable for the spectrophotometric determination. Quantitative determi-
nation in the organic phase has certain advantages over the determination of niobium in aqueous solutions. The sensitivity and selectivity of the determination is increased, and Beer's law is obeyed in a significantly wider concentration range.
ACKNOWLEDGMENT The authors are grateful to Mrs. G. Lalovie and D. Krhatlic for the technical assistance.
LITERATURE CITED ( 1 ) H. E. Affsprung and J. L. Robinson, Anal. Chim. Acta, 37, 81 (1967). (2) H. E. Affsprung, N. A. Barnes, and H. A. Potratz, Anal. Chem., 23, 1680 (1951). (3) R. J. Magee and M. A. Khattak, Microchem. J., 8, 285 (1964). (4) J. W. Murphy and H. E. Affsprung, Anal. Chim. Acta, 30, 501 (1964). (5) M. Shinogawa, H. Matsuo, and R. Kohara, Jpn. Anal., 5, 29 (1956). (6) M. pchlabsky and L. Sommer, Talanta, 15, 887 (1968). (7) M. Siroki and C. Djordjevic, Anal. Chim. Acta, 57, 301 (1971). (8) M. Siroki, Lj. Maric, 2 . Stefanac, and M. J. Herak, Anal. Chim. Acta, 75, 101 (1975). (9) Lj. Maric, M. Siroki. and M. J. Herak, J. lnorg. Nucl. Chem., in press. (10) M.Siroki and C. Djordjevic, Anal. Chem., 43, 1375 (1971). (11) R. W. Moshier, "Analytical Chemistry of Niobium and Tantalum", Pergamon Press, London, 1964. (12) T. Belcher, T. V. Ramakrishna, and T. S. West, Talanta, I O , 1013 (1963). (13) i.P. Aiirnarin and Han Si-i, Zh.Anal. Khim., 18, 182 (1963). (14) S.V. Elinson and L. I. Pobedina, Zh. Anal. Khim., 18, 189 (1963). (15) D. F. Woodand J. T. Jones, Analyst(London), 93, 131 (1968). (16) P. Pakains, Anal. Chim. Acta, 41, 283 (1968). (17) C. L. Luke, Anal. Chim. Acta, 34, 165(1966). (18) S. V. Elinson, L. I. Pobedina, and A. T. Rezova, Zh.Anal. Khim.. 20, 676 (1965). (19) H. J. Bhattacharya. J. Indian Chem. Soc., 29, 871 (1952). (20) A. K. Babko, Zh.Neorg. Khim., 13, 718 (1968). (21) B. I. Nabivanec, Zh. Neorg. Khim., 11, 2732 (1966). (22) N. Kheddar and B. Spinner, Bull. Soc. Chim. Fr., 2, 502 (1972).
RECEIVEDfor review June 18, 1975. Accepted August 25, 1975.
Extraction of Colored Complexes with Amberlite XAD-2 Raymond B. Willis" and Darrel Sangster Department of Chemistry, Kentucky State University, Frankfort, Ky. 4060 7
iron was analyzed by forming the 1,lO-phenanthroline complex and extractlng the complex from aqueous solution using the adsorbent Amberlite XAD-2. This has several advantages. The iron complex can be extracted using the adsorbent under conditions that would not work for an organic solvent, the iron can be concentrated by a factor greater than 200; and the interference of any ion is no greater when the adsorbent is used and, in the case of chromium(lii), the interference Is totally eliminated.
The usefulness of a colorimetric analytical procedure can be enhanced by extracting the colored species into a nonaqueous solvent. In so doing, it is possible to concentrate the colored species by factors approaching 10 or 20. Also, it is often possible to eliminate interferences that would otherwise make the method useless. Unfortunately, there are times when a nonaqueous solvent cannot be found into which the colored species can be extracted. There are also times when it is necessary to concentrate the species being
measured by factors greater than 10 or 20. In cases like this, a simple solution is to use a solid adsorbent that has a high affinity for organic species and a very low affinity for ionic species. Using a solid adsorbent, it is possible to extract colored complexes that cannot be extracted using a nonaqueous solvent. The complex can be concentrated by much greater factors than can be achieved with a nonaqueous solvent, and some interferences can be eliminated in the process. Alternatively, it is possible to achieve large factors of concentration by using any one of a number of methods of preconcentration and then taking the desired species, form a colored complex and measure the absorbance. An example of this is a method for phenol by Vinson and co-workers ( I ) . In this case, it is necessary that the sample undergo treatment both before and after being concentrated on a column. In the example used in this study, nothing needs to be done to the sample after being concentrated on the column, other than to measure the absorbance of the eluted solution. ANALYTICAL CHEMISTRY, VOL. 48, NO. 1, JANUARY 1976
59
EXPERIMENTAL
Table I. Effect of Other Ions Ion
Added as
500 500 500 5 00
Al(II1)
As( 111) Ba( 11) Ca(I1) Cd( 11) Co( 11) Cr(II1) Cu( 11) Hg(II) K(I) Mg(I1) Mn( 11) Mn( VII) Mo( VI) N4I) NH,+ Ni(I1) Pb(I1) Sn(1V) Zn(I1) Borate BrCitrate c10,-
Concentra tion, pprn
KCI Mg(NO 3 1 2 MnC1, KMnO, (NH4)6M07024 NaCl NH,C1
c10 4
CNC0,'Crzi3,z-
50 20 1750 20 5 1000 500 500 200 50 1000 500 5 500 50 10 500 500 500 500 500 50 500 500 500
Footnotes
a
b C
b, d d, e
f d, g
a
h d
Na2C03 Na,Cr, 0, FNH4F 500 KI I500 NaNO, NO,d, i 500 Oxalate "4( )2 c2 0 , Na HP 0 50 PO,,- a~ P,O, 500 SCNKSCN 10 s,032Na2S203 d 500 Na2S0, SO,'500 so,=K2S0, 500 Tartrate (NH4)2C4H406 Concentration of iron in all cases, 2.0 p p m . a Used Fe(NO,), in dil. HNO, as standard. b 5 m l water passed through column just before eluting iron-1,lO-phenanthroline complex. C Used 9 m l 1,lO-phenanthroline solution. d Eluted with methanol-hydroxylammonium chloride eluent. e pH adjusted to 3.5. f Used 5 m l hydroxylammonium chloride solution rather than 0.5 ml. g p H adjusted to 7 . 7 . h pH adjusted to 2.5. i p H adjusted t o 8.0.
,
An adsorbent meeting the criteria listed above is Amberlite XAD-2. This adsorbent has been shown to adsorb from aqueous solutions m a n y organic compounds such as morphine (2),morphine metabolites (3, 4 ) , steroids (3, 4 ) , f a t s (5), etc. The uses of XAD-2 have been exhaustively reviewed through 1972 b y Grieser (6) who has also worked out a mathematical relationship showing that the distribution coefficient of a n y compound for XAD-2 depends on the fraction of that compound existing as the neutral species (6, 7). The colorimetric procedure chosen to illustrate the extraction of colored complexes using a solid adsorbent was the determination of iron using 1,lO-phenanthroline based on a method described b y F o r t u n e and Mellon (8). T h e ferrous 1,lO-phenanthroline complex can be extracted into an organic solvent only if the right anionic species is present and if the right organic solvent is used (9-11). It can b e extracted from aqueous solution using the adsorbent XAD-2 and can be concentrated b y factors exceeding 200. Using XAD-2, iron can be determined i n the presence of a n y other ion which does n o t interfere when XAD-2 is not used and can be determined i n the presence of ions that d o interfere when XAD-2 is not used. 60
ANALYTICAL CHEMISTRY, VOL. 48, NO. 1, JANUARY 1976
General Procedure. A volume of aqueous solution containing from 0 to 50 gg of iron was taken and to this was added 5 ml of purified 10% hydroxylammonium chloride, 3 ml ji4% 1,lO-phenanthroline, and 5 ml 10% sodium acetate. This solution was allowed to pass through the column by gravity. For volumes greater than 100 ml, this was done by placing the solution in a volumetric flask to which was fitted a 1-hole rubber stopper with the hole slightly enlarged. Through the hole in the stopper was inserted a 9-mm 0.d. glass tube with each end cut a t an angle. The flask containing the solution was turned upside down over the column so that the end of the glass tube protruded several cm down into the column but not touching the resin bed. In this way, the solution will flow through the column without needing to be monitored and a t an approximately constant head. A slightly modified version of the technique has been described (12). When the solution has passed through the column, the column was washed with 2 to 4 ml water and eluted with the methanol-hydroxylammonium chloride eluent. The red complex was collected in a 10-ml volumetric flask beginning just before the red color reached the bottom of the column. The absorbance of the solution was measured a t 510 nm and compared to a standard. The volume of iron containing solution used in this procedure was 2.013 1. or less. Standards were prepared by using 0 to 10 ml of 4-ppm iron stock solution plus the reagents as described above. Procedure for Interference Studies. Solutions to be analyzed for the effect of interferents were made up of 10 ml of the 10-ppm iron stock solution, varying quantities of interferent, 0.5 ml 10% hydroxylammonium chloride (unpurified), 3 ml l/*% 1,lO-phenanthroline, and 5 ml 10% sodium acetate. This was diluted to 50 ml with water and the precaution taken to always add the reagents in the same order. Ten-ml aliquots were taken and passed through the column. From here on, the procedure used was the same as that described in the general procedure. In most cases, the pH of the solution that was passed through the column was the pH that was obtained when adding sodium acetate buffer which was about 5.0. The cases where a different pH was used were cases where pH 5 was not within the recommended range as described by Fortune and Mellon and so a pH within the recommended range was chosen. This value was obtained by adding varying amounts of 1M HC1 or 1 M NaOH in place of the sodium acetate. The exact value used is shown in Table I. If the added ion was either lead or barium, the iron compound used was ferric nitrate dissolved in dilute nitric acid rather than ferrous ammonium sulfate dissolved in dilute sulfuric acid. Adsorbent. The adsorbent used was Amberlite XAD-2 which was obtained from Rohm & Haas as the 100-400 mesh cut. The resin was stirred with methanol in a 250-ml beaker and allowed to settle for 15 to 30 sec and the fines decanted. This was repeated many times and that which remained was used. It is believed that the resulting mesh distribution approximately equaled 100-150 mesh. Column Preparation. Glass columns were used that were 11-mm i.d. and 30 cm long. The column was packed by adding a slurry of the resin in methanol until the height of the resin bed was 5 to 6 cm. Reagents. Iron Stock Solutions. Ten-ppm stock solutions were made up by dissolving 0.14 g ferrous ammonium sulfate in 5 ml concentrated sulfuric acid and diluting to 2 1. with water. The 4-ppm iron stock solution was prepared by dissolving 1.4 g of ferrous ammonium sulfate in 5 ml concentrated sulfuric acid and diluting to 2 1. with water. Next 80 ml of this and 5 ml of concentrated sulfuric acid were taken and diluted to 2 1. 1,IO-phenanthroline. Fisher Certified reagent was used and dissolved in water. 10% H y d r o x y l a m m o n i u m Chloride. Prepared from reagent grade dissolved in water. The solution was purified by mixing 5 ml of y4% 1,lO-phenanthroline with each 100 ml of solution. This was passed through the column of XAD-2. In so doing, any ferrous 1,lO-phenanthroline that was formed and the excess 1,lO-phenanthroline were adsorbed to the top of the column. The hydroxylammonium chloride passes through with little or no retention. The iron complex can be removed from the top of the column by eluting with the methanol-hydroxylammonium chloride eluent. Methanol-Hydroxylammonium Chloride Eluent. Prepared by mixing 95 volumes of methanol with 5 volumes of 10% hydroxylammonium chloride. Interferent Solutions. The salt of the desired ion as designated in Table I was dissolved in water or dilute acid.
The KAl(S04)2 was purified by taking 250 ml of solution containing 10.989 g KAl(S04)z and 1.5 g hydroxylammonium chloride dissolved in water and adding 5 ml of 1,lO-phenanthroline solution to it. This was passed through a column of XAD-2 which adsorbed the 1,lO-phenanthroline and any ferrous 1,lO-phenanthroline that was formed. The potassium aluminum sulfate and hydroxylammonium chloride pass right through the column. The concentration of aluminum was checked after passing through the column by titrating with EDTA and found to be equal to the concentration before passing through the column. When the sample solution was made up to test for the interference of KAl(S04)z on iron, no hydroxylammonium chloride was added since there was already enough present with the KAl(S04)z.
RESULTS When a solution containing the red ferrous 1,lO-phenanthroline complex is passed through a column of XAD-2, the complex is retained in a tight band a t the top of the column, even when large quantities of aqueous solution are passed through the column. Any inorganic ions that are present will pass right through. When solutions containing a high percentage of methanol are passed through the column, the red complex is quickly eluted with the minimum percentage of methanol needed to elute the complex being about 50%. Calibration Curve. Two calibration curves were prepared, one using 500 ml as the volume of iron solution taken and the other using 2 1. with the treatment being that described in the general procedure. Double distilled water was used. The absolute amounts of iron were the same in both cases varying from 0 to 28 pg so, if expressed as concentration, the concentration varied from 0 to 56 ppb for the 500-ml solution and from 0 to 14 ppb for the 2-1. solution. When the calibration curves are plotted as the absorbance vs. wg of iron, the two graphs exactly superimpose and are linear; this indicates that the volume of water in which the iron is dissolved does not affect the results. Thus, to analyze for very dilute solutions of iron, it is only necessary to use larger volumes of solution. No attempt was made to use volumes greater than 2 1. but there was no evidence to indicate that much larger volumes could not be used. For large volumes of iron solution, it was necessary to increase the amount of hydroxylammonium chloride to be added. When the volume of iron solution was 50 ml, 1hml of hydroxylammonium chloride was sufficient. For 500 ml of iron solution, the results were low. Increasing the amount of hydroxylammonium chloride solution added to 5 ml gave the correct results for both the 500-ml and 2-1. iron solutions. Effect of Flow Rate. The effect of flow rate was studied by preparing a solution as described in the procedure for interference studies using 5 mi of the 4-ppm iron stock solution. One 10-ml aliquot of the aqueous solution containing the red iron complex was passed through the column by gravity resulting in a flow rate of 1.1 ml/min. A second 10-ml aliquot was passed through the column using a rubber bulb resulting in a flow rate of 15 ml/min. In both cases, the iron complex was eluted from the column with the methanol-hydroxylammonium chloride eluent a t the same flow rate of 15 ml/min. The second case gave a result that was 1.2% lower indicating that the flow rate of the aqueous solution through the column does not affect the results. Effect of O t h e r Ions.'Studies on the possible interference of ions were made using an iron concentration of 2 ppm and a concentration of added ion of 500 ppm. A relative error of less than 3% was considered to be no interference. If the relative error was greater than that, the concentration of added ion was reduced until the relative error was less than 3%. Table I shows the maximum concentration of other ions that may be present.
For every one of the ions studied, the maximum concentration of interferent ion that could be present was as high or higher than it was if no column was used (8). Colored ions whose reaction with iron or 1,lO-phenanthroline is much slower or have smaller formation constants, do not interfere because they pass right through the column with the aqueous solution. T o illustrate this, chromium(II1) did not interfere when present a t a concentration of 1750 ppm. Even if the concentration of iron is reduced from 2 to 1 ppm while retaining the same chromium(II1) concentration, there is no interference. The procedure described in this paper will also work in determining iron a t very low concentrations in the presence of an interferent a t relatively high Concentration. T o show this, 500 ml of an aqueous solution containing iron and potassium aluminum sulfate was made up. The concentration of each was: iron, 40 ppb; aluminum, 500 ppm; potassium, 724 ppm; sulfate, 1780 ppm. The analysis was carried out as described in the general procedure and the potassium aluminum sulfate was purified as described in the reagent section. The result was 40 ppb iron found as compared to 40 ppb actually present. When the interferent ion was thiosulfate at a concentration of 500 ppm, there were times when it caused a considerable interference and times when it caused no interference a t all while using the same procedure. If a column was not used and the procedure of Fortune and Mellon was used, the same erratic behavior was observed in contradiction to their results. To be sure thiosulfate caused no interference, it was necessary to reduce its concentration to 10 PPm. Choice of Eluent. In many cases, quantitative results are obtained if pure methanol is used to elute the iron complex from the column. However, there are times when quantitative recovery is not obtained. For example, if oxalate is present at a concentration of 500 ppm along with the iron a t 2 ppm and the pH is adjusted to 8.0 which is within the recommended range ( 8 ) , the red color is fully formed. If this solution is passed through the column and pure methanol is used to elute it, the red color at the top disappears but the effluent is clear. If the pure methanol is followed by methanol mixed with a small amount of 10% hydroxylammonium chloride, the red color is then eluted. So, if oxalate is present, it is necessary to use the methanol-hydroxylammonium chloride eluent to elute the iron complex. For a mixture containing copper at 20 ppm and iron at 2 ppm, attempting to elute the iron complex with pure methanol results in a yellow solution with a A,, of 440 nm being eluted. If the methanol-hydroxylammonium chloride eluent is used, the eluted solution is red as it should be, and the results are quantitative. For a mixture of iron and molybdenum, when attempting to elute the iron complex from the top of the resin bed with methanol, part of it is eluted and part is not. In this case, there is no color change. If the methanol-hydroxylammonium chloride eluent is used to elute the iron complex, the results are quantitative. As a result of these cases, it was decided that a mixture of methanol and hydroxylammonium chloride should be considered the eluent of choice. Choice of Adsorbent. One other adsorbent that has been shown to adsorb polar organic compounds is Amberlite XAD-7 (13, 14). When an aqueous solution containing the iron complex was passed through a column containing XAD-7, the iron complex went right through. If some of the iron complex was placed on top of the column and the attempt made to elute it with methanol, the iron complex remained a t the top of the column. Based on these results, XAD-7 is unacceptable for extracting the iron complex ANALYTICAL CHEMISTRY, VOL. 48, NO. 1, JANUARY 1976
61
from aqueous solution. There is one potential use for the XAD-7, however. In case there is a colored organic compound present, the chances are good that it would be adsorbed by XAD-7. If this is the case, the aqueous solution containing the iron complex and interfering organic compound could be passed through a column of XAD-7 before being passed through the column of XAD-2. This should eliminate the interference of the colored organic compound.
CONCLUSION Two advantages exist for fotming the colored complex before concentrating it on the column rather than preconcentrating the ion and then forming the colored complex. Less preparation of the sample has to be carried out and the colored complex can be concentrated on the column of a liquid chromatograph. If the liquid chromatograph is equipped with an optical detector having a variable wavelength capability, the colored complex can be detected as it is eluted and the peak plotted with a strip-chart recorder. Instead of measuring the absorbance of a 10-ml solution, the height or area of the peak can be measured. This should be much more sensitive. Whereas this has not yet been tried, the next item of research proposed by one author of this paper is to try and see if it is indeed more sensitive.
ACKNOWLEDGMENT The authors thank Cecil Webb at the Kentucky Department of Human Resources for the contribution of certain chemicals and supplies and L. R. McConnell of Rohm and Haas Company for supplying the XAD-2.
LITERATURE CITED (1) J. A. Vinson, G. A. Burke, B. L. Hager, D. R. Casper, W. A. Nylander. and R. J. Middlemiss. Environ. Left., 5, 199 (1973). (2) J. M. Fujimoto and V. 8. Haarstad, J. Pharmacol. Exp. Ther., 165, 45, (1969). (3) C. H. L. Shackleton. J. Sjovall. and 0. Wisen, Clin. Chim. Acta, 27, 354 (1970). (4) H. L. Bradlow, Steroids, 11, 265 (1968). (5)W. Scheider and J. K. Fuller, Biochem. Eiophys. Acta, 221, 376 (1970). (6) M. D. Grieser, Ph.D. Thesis, Univeisity of Iowa. Iowa City, Iowa, 1972. (7) M. D. Grieser and D. J. Pietrzyk, Anal. Chem., 45, 1348 (1973). (8) W. B. Fortune and M. G. Mellon, hd. Eng. Chem., Anal. Ed., 10, 60 (1938). (9) R. Powell and C. G. Taylor, Chern. h d . London, 1954,726. (10) D. W. Margerum and C. V. Banks, Anal. Chem., 26, 200 (1954). (11) B. G. Stevens and H. A . Suddeth. Anal. Chem.. 39, 1478 (1967). (12) P. G. McCormick, J. Chem. Educ., 51, 15 (1974). (13) A. K. Burnham, G. V. Calder, J. S. Fritz, G. A. Junk, H. J. Svec, and R. B. Willis, Anal. Chem., 44, 139 (1972). (14) J. S.Fritz and R. B. Willis, J. Chromatogr.,79, 107 (1973).
RECEIVEDfor review June 6, 1975. Accepted September 24, 1975.
Separation of Gallium(lll), Indium(lll), and Thallium(lll) by Solvent Extraction with 4-Methyl-2-pentanol S. B. Gawali and V. M. Shinde' Department of Chemistry, Shivaji University, Kolhapur-4 16 004, India
The solvent extraction and mutual separation of Ga( ill), In(lil), and Ti( 111) from hydrochloric acid media using methyl isobutyl carbinol as an extractant are described. The percentage extractions of 99.6 to 100 are computed by stripping the metal ions from the organic phase and subsequent complexometric titration in the aqueous phase.
4-Methyl-2-pentanol (methyl isobutyl carbinol) has been used in this laboratory for the solvent extraction of molybdenum ( I ) , tungsten ( 2 ) , rhenium ( 3 ) ,gold ( 4 ) , and iron ( 5 ) .This paper describes studies on the solvent extraction and separation of tervalent gallium, indium, and thallium from hydrochloric acid media using methyl isobutyl carbinol as an extractant. The proposed method provides for the separation of these metals from a large number of other ions present at microgram level. Various methods for the solvent extraction of gallium, indium, and thallium have been summarized by different authors in their monographs (6-IO), but only a few methods such as T B P ( I I ) , N-benzylaniline (12) and mesityl oxide (13-15) are available for the mutual separation of these metals by solvent extraction. These methods, however, suffer from drawbacks such as pre-equilibration of phases, multiple scrubbing, multiple extractions, and coextractions of a large number of elements. The proposed method is free from these limitations. 62
ANALYTICAL CHEMISTRY, VOL. 48, NO. 1, JANUARY 1976
EXPERIMENTAL Gallium. Place an aliquot of chloride solution containing up to 5.4 mg of gallium in a separatory funnel; add enough hydrochloric acid to make its concentration 5.5M in a total volume of 10 ml. Shake the aqueous phase with 10 ml of 40% methyl isobutyl carbinol in benzene for 15 sec. Separate the layers and discard the aqueous phase. Strip gallium from the organic phase with two 10-ml portions of water and determine gallium complexometrically (16). Indium. Place an aliquot of chloride solution containing up to 5.1 mg of indium in a separatory funnel; add enough hydrobromic acid to make its concentration 6.5M in a total volume of 10 ml; and extract for 15 sec with 10 ml of undiluted methyl isobutyl carbinol. Separate the phases and strip indium from the organic phase with two 10-ml portions of water and then estimate complexometrically (16).
Thallium. Place an aliquot of nitrate solution containing up to 5 mg of thallium in a beaker; add a few drops of bromine water to oxidize thallium; warm to remove excess bromine; cool and transfer to a separatory funnel. Add enough hydrochloric acid to make its concentration 0.25M in a total volume of 10 ml and extract for 30 sec with 15 ml of undiluted methyl isobutyl carbinol. Allow the phases to separate, strip thallium from the organic phase with 30 X 2 ml of acetate buffer solution (prepared by dissolving 27.2 g of sodium acetate trihydrate in 200 ml of water, adding 1'7ml of glacial acetic acid, and diluting to 1 liter; pH 4-5), collect the extracts, add excess of EDTA solution, a few drops of 0.1% alizarin red indicator, and back titrate with 0.01M thorium nitrate (16).
RESULTS AND DISCUSSION Effect of Variable Conditions. The extraction of trivalent gallium (5.4 mg), indium (5.1 mg), and thallium ( 5 mg) into carbinol as a function of hydrochloric and hydrobro-
