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Calmagite as a spectrophotometric reagent for aluminium
Talanta, 1968, Vol. 15, pp 321 to 325. Pcrgamon Press Prlntcd in Northern Ireland
CALMAGITE AS A SPECTROPHOTOMETRIC REAGENT FOR ALUMINIUM COLIN WOODWARD*and HCNRY FREISER@ Department
of Chemistry,
University of Arizona, Tucson, Arizona 85721, U.S.A.
(Received 11 August 1967. Accepted 30 October 1967) Summary-Calmaglte is proposed as a sensltlve spectrophotometrlc reagent for alummmm, es70mp = 42000. After aqueous phase rcactlon at pH 8 6, the metal-reagent complex is extracted mto chloroform by formation of an Ion-association complex with a quatemary ammomum salt. The method is free from interference by common anions, and catiomc interferences may be eliminated by the use of cyanide and EDTA as masking agents.
NUMEROUSspectrophotometric methods for the determination of aluminium have been published. I The most frequently used reagent is probably aluminon, but, more recently, more sensitive reagents e.g., stilbazo (E = 34600), Eriochrome Cyanine R (E = 57000) and Chrome Azurol S (E - 50000) have been widely applied. Almost all methods are carried out in the pH range 3-7 and are subject to many interferences. In the present study, the metallochromic properties of a number of o,o’-dihydroxyazo dyes were investigated both in aqueous solution and after extraction into chloroform as ion-association complexes. Several potentially applicable reactions were noted. This communication describes the work which has been carried out to characterize the aluminium-Calmagite system. Calmagite, 1-(1-hydroxy4methyl-2-phenylazo)-2-naphthol4sulphonic acid, was first introduced by Lindstrom and DiehP as a stable replacement for Eriochrome Black T in the EDTA titration of calcium and magnesium. Its behaviour is summarized in Diehl’s mon0graph.s After aqueous phase reaction between the metal and Cahnagite at pH 8.6, the negatively-charged complex is extracted into chloroform by association with a chloride is used as the quaternary ammonium saIt. Methyltricaprylylammonium extracting agent but several other tertiary ammonium salts are equally suitable. Many interferences may be eliminated by the use of cyanide and EDTA as masking agents. EXPERIMENTAL Apparatus Samples were prepared in 45ml cyhndncal tubes, fitted with polyethylene stoppers and plastic screw-caps. These were shaken m an Eberbach Reciprocatmg Shaker at the high-speed setting. Water at 250 f 0 2’ from a Wilkens-Anderson Co. Lo-Temp. bath was circulated through the jacketed shaker tray. Absorption spectra and quantitative spectrophotometric measurements were obtained with a A Beckman Model G pH meter with a glass-calomel electrode pair Beckman DB spectrophotometer. l
Present address: 70803, U.S.A.
Department
of Chemistry, Louisiana State University, Baton Rouge, Louisiana 321
322
C. WIXIDWARDand H. FRUSER
was calibrated with Beckman buffer solutions at pH 7.00 and 10 00, and used for all pH measurements. Reagents EufferpH 8.6. Volumes of 450 ml of O-l&f boric acid (ARgrade. Mallinckrodt) and 250 ml of O*lM were mrxed and dduted to 2 1. with distrlled water. Anhydrous sodium perchlorate (39*4g, G. F. Smith Chemical Co.) was added to make the ionic strength of the stock buffer solutton 0.3. CalmagUe. A 0.15-g amount of Calmagite (Crty Chemical Corp.) was drssolved in 1 litre of distdled water. The slight turbidity which persrsted even after prolonged sturmg was removed by filtration. Thus solution was used for all the work on the development of the analytical procedure. The purity of this reagent was checked by measuring the molar absorpttvtty of solutions at pH 10.0 and 610 mc”.5 These expertments indtcated a purity of 47 ‘A if it was assumed that none of the tmpurmes present absorbed at thrs wavelength. The stock reagent solution used was therefore approxtmately 1 94 x lo-*M. The purtty of another sample of Cahnagite (K and K Labs.) was found to be approx. 60% and soluttons prepared from “corrected” weights of this sample were used for the experiments to determine the nature of the complex. It was noted that both batches of Calmagrte had a strong phenohc odour, probably mdtcatmg the presence of p-cresol, one of the starting materials m the syntheses of Calmagrte. Methyltrrcaprylylammonium chloride. Thus reagent was obtained as Aliquat 336 (General Mdls, Chemrcal Dtvaton, Kankakee, Ilhnois). No attempt was made at purrficatton An approximately 0 IM solutton was prepared by dtssolvmg 40 g in 1 litre of chloroform (AR grade, Mallmckrodt). Alumuuum and other metal ion soluttons were prepared from their perchlorates (G. F. Smith Chemical Co.). Aniomc mterferences were investigated by using the sodium salts (generally analytical grade).
sodium tetraborate (AR grade, Mallmckrodt)
Spectrai characteristics Ftgure 1 shows the absorption spectra of Calmagrte and its aluminium complex after extraction with a chloroform solution of Aliquat 336 from aqueous solution at pH 8 7. Under these condmons the ahumnmm complex is purple and the reagent blank is orange. The optimum wavelength for measurement of the alumuuum complex IS 570 m,u. Establishment of optimum conditions for aluminium determmation The factors affectmg the system and Its potential as a spcctrophotometrtc procedure were investtgated m a standard manner.’ During the preiimmary qualitattve mvestrgattons, the extractable purple aluminium-Calmagrte complex was observed to form above ca. pH 8. The absorbance of thts complex was maximal over the range pH 8.2-8 8. The optimum pH regron for the analytical determinatron 1s 8.6-8.7. Since the pK for the dissociation of Calmagtte, HID- P HD*- + H+, IS 8 14,* at pH 8 6 approx. 75 % of the dye IS present in the form HD+. It was shown that a five-fold molar excess of reagent over alummuun was sufficient to develop fully the colour of the complex and that a further increase in the reagent concentration had no effect on the absorbance due to a given amount of aluminium. A ten-fold molar excess of Calmagtte was used m the analytrcal work. It was also shown that a nommal3000-fold molar excess of Ahquat 336 over alumrnium was necessary to ensure total extractton of the metal complex and this concentration was used. The aluminium_Calmagrte complex IS not formed instantaneously at pH 8.6 and 30 mm should be allowed after mlxmg of the alumuuum, reagent and buffer soluttons for the aqueous phase comAfter addition of the chloroform solutron of Ahquat 336, a plexatton to proceed to completton. shaking time of 2 min IS adequate to ensure total extractton of the ion-assoctattlon complex. The absorbance of the extract is then constant for several hr and is convement!y measured after 30-60 mm. Procedure To 5 ml of nH 8.6 buffer m a shakine-tube, add 4 ml of4 x IO-‘MCalmagite, appropriate vohunes up to 5 ml of soluttoncontaining l*l-5.2 pgofaluminium, and dtsttlled wate;as r&es&y to make the volumes eoual. Mix well and allow to stand for 30 min. Now add 10 ml of 0.025M solution of Aliquat 336 in chloroform, stopper the tubes and agttate them for two minutes. Allow the solutions to settle for a further 30 min. then measure the absorbance of the organic phase at 570 mp, using the alummium-free solution as reference. The phase should be filtered through glass wool into the spectrophotometer cells to remove traces of water.
Calmagitc as a spectrophotometric reagent
323
The calibration curve prepared under these conditions is hnear over this concentration range, i.e., 0.1 l-0-54 ppm Al. The molar absorptlvlty at 570 rnp is 42000 which corresponds to a sensitivky index (SandeIF) of 0 00064 r&cm* for an absorbance of 0 001. The sensmvlty of the reactaon may, however, be Improved by extracting the complex from a Iarge aqueous volume mto a smaller volume of organic solvent. The extent of extraction of Calmaglte itself IS dependent on the volume ratio, but, If the reagent blank solution IS prepared under simdar condltlons, tius problem IS ehmmated.
WAVE LENGTH
(my)
FIG. L-Absorbance of Cahnagite and its ahnninium complex after extraction with 0*05&fsolution of Ahquot 336 m chloroform, pH &7. Measured in l-cm cells with 0 OSM Aliquot 336 in chloroform as reference, A-8 x lo-‘M Calma@e B-8 x 1O-6M Caimagrte -+ 16 X lO+M upturn. RESULTS
AND
DISCUSSION
Efect of foreign ions
Several cations, notably transition metal ions, also react with Calmagite under the proposed conditions of the aluminium determination and thus cause interference with the method. It has previously been demonstrated, however,6 that cyanide and EDTA may be used as general masking agents in the spectrophotometric determination of aluminium by extraction from aIkalme medium with 8-hydroxyquinoline. Although no extensive ex~na~on of the effects of foreign ions on the present method has been undertaken, some preliminary experiments were carried out to demonstrate that these masking agents were also effective in this system. In the presence of 10-BM cyanide and 5 x IO444 EDTA (added as the calcium-EDTA complex with excess of calcium ions present to prevent the possibility of EDTA complexing the a~u~nium), the effects of H&fold molar excesses of such ions as Cu, Ni, Zn, Cd and Pb on the determination of 0.22 ppm of Al were < f 10 %. Undoubtedly, any interference by such ions could be totally eliminated by the addition of appropriate amounts of these
324
C. WOODWARD and H. FREISER
masking agents. It may be preferable for the purpose of ehmination of interferences to carry out the determination of alumimum at a pH higher than 8.6 even though this will result in some decrease in sensitivrty. Taking pk;, for hydrocyanlc acid as 9.3,’ it is obvious that only approximately 17 “/ of the cyamde added wrll be present as CN- at pH 8.6, CJ 50% at pH 9.3 and 83 % at pH 10.0. Thus the effecttveness of a given amount of sodium cyamde as a masking agent will mcrease consrderably with a relatively small increase in pH. Also, at pH 9.3 (8.6) the logarithms of the conditional stability constants* of varrous metal-EDTA complexes are approximately: Al 3*8(5-O), Ca 9*6(9*0), Zn 14*6(14*5), Cd 14*6(14+5),Cu 16+4(16=3),Fe(M) 13.8(13*8), Co(I1) 14*8(14*6), so the effectiveness of EDTA as a masking agent would also be increased by an increase in pH. The effects of a number of common anions on the absorbance due to aluminium were also examined. At the 80-fold molar excess level none of the anions examined, viz., fluoride, chloride, bromide, iodide, perchlorate, borate, nitrate, nitrite, sulphate, sulphite, thiosulphate, bisulphate, carbonate, bicarbonate, cyanide, thiocyanate, phosphate, acetate. formate and citrate, caused a significant change. Fluoride and phosphate were then examined at the 800-fold moiar excess level but no interference was found. Probably fluoride complexing of aiuminmm is prevented by the maskmg action of the borate buffer used. For practical purposes, it would be preferable to replace the stoppered vials which were used for this expIoratory work by separatory funnels. It may aiso be convenient and time-saving to prepare a composite solution containing appropriate amounts of buffer, Calmagite and masking agents. Nature of complex
The composition of the anionic aluminium~almagite complex has been investigated by the standard spectrophotometric methods, viz., mole-ratio,v slope-ratro”O and continuous variations procedures. LL~*eAs discussed above, it was known that the Calmagite sample used was only 60% pure and solution concentration were, therefore, corrected m a suttable manner. Also, to avoid the further comphcatron that at pH 86 significant amounts of both H,D- and HD2- are present in solution, these experrments were carried out at pH 9.5, under whrch conditions virtually all Caimagite is present as HD2-. The slope-ratio studies indicated a 3: 1 Calmagite. Al complex and the mole-ratio studies a complex of greater than 2.1 molar proportions. The m~imum of the continuous variations curves appeared in the region of 2: 1 molar proportions, but the shape of these curves was such that the position of the maximum was difficult to determine. On the basis of these experiments and by comparison with previous observations with a very similar reagent, I3 it seems reasonable to suggest that the complex formed between aluminium and Calmagite at pH 8~6 is of 1: 3 molar proportions. CONCLUSION
The sensitivity of this reaction, coupled with its simplhty, suggests that it may find application to the determination of aluminlum in numerous ~lrcumstan~es. The solvent extraction step permits concentration so that the sensrtrvrty may be increased beyond that of reactions carried out totally in the aqueous phase. Furthermore, the
Cahnagite as a spectrophotometric reagent
325
ease of elimination of interferences indicates that it should also have advantages in selectivity over existing methods. Acknowk&e~eni--The authors gratefully acknowledge the financial support of the US. Atomic Energy Commrssion. Zusannnenf~almagit wird als empfindliches spektrophotometrisches Reagens fitr Alummium rmt Q~,,,,,,,= 42000 vorgeschlagen. Nach Reaktlon m w&Bnger Phase bei pH 8,6 wlrd der IComplex aus Metal1 und Reagens durch Bddung emcs Ionenassoziats rmt eincm quart&en Ammoniumsalz m Chloroform extrahlert. Die Methode wird durch die haufig vorkommenden Amonen mcht gestort; katlonische Sttirungen konnen nut Cyamd und EDTA als Masloerungsmlttel beseitlgt werden. R&ma&-On propose la c&nag&e comme r&a&f s~trophotom~triq~ sensible pour I’alummmm, .5s70ma= 42000. Apr&sr&ction en phase aqueuse a pH 8,6, le complexe m&al-rtactlf est extract en chloroformc par formation d’un complexe d’association ionique avec un se1 d’ammonium quaternatre. La m&hode est exempte d’mterftrence par l&s anions communs, et I’on peut iliiiner les mterf&rences cationiques par l’emplol de cyanure et d’EDTA comtne agents de stimulation. REFERENCES 1. V. N. Tikhonov, Z/I. Am&r. K&n., 1966,21,829. 2 F. Lindstrom and H. Diehl, Anat. Chem., 1960,32, 1123. 3. H. Diehl, Ctzlcein, Cdmqgite and o,o -D~~~x~o~~e~e: Ti~r~~~r~~,Calorimetric and Fbrwtetric Reqgentsfir G&urn and M~tt&um, G. F. Smith Chemical Co., Columbus, 1964. 4. G. F. Kirkbright, TuLzntu,1966,13, 1. 5. E. B. Sandell, Cobrimetric Determination of Traces of Metals, 3rd Ed., p. 83. Interscience, New Yorlt, 1959. 6. A. CfasJen,L. Bastin and J. Vissler, And. Chim. Acta, 1954, 10,373. 7. L. 0. Sill& and A. E. Ear tell, &a&i&y Consta&s of Metai-ion Complexes. Chem Sot., London,
1964. 8. A. Ringbom in I. M. Kolthoff and P. J. Elving, Treatise on Adyt~cd Chemistry, Part 1, Vol. 1, p. 575. Iatcrscic~~, New York, 1959. 9. J. H. Yoe and A. L. Jones, Irut. Eng. Chcm. (Anal., Ed.) 1944,16,111. 10. A. R Harvey and D. L. Manning, J, Am. Chem. Sot., 1950,72,448, 11. P. Job, Ann. Chim., 1928,9,113. 12. W. C. Vosburgh and G. R. Cooper, J. Am. C&em.Sot., 1941,63,437. 13. M. Perkins and 6. F. Reynolds, Anal. Chim. Acta, 1958.19, 54.
CALMAGITE AS A SPECTROPHOTOMETRIC REAGENT FOR ALUMINIUM COLIN WOODWARD*and HCNRY FREISER@ Department
of Chemistry,
University of Arizona, Tucson, Arizona 85721, U.S.A.
(Received 11 August 1967. Accepted 30 October 1967) Summary-Calmaglte is proposed as a sensltlve spectrophotometrlc reagent for alummmm, es70mp = 42000. After aqueous phase rcactlon at pH 8 6, the metal-reagent complex is extracted mto chloroform by formation of an Ion-association complex with a quatemary ammomum salt. The method is free from interference by common anions, and catiomc interferences may be eliminated by the use of cyanide and EDTA as masking agents.
NUMEROUSspectrophotometric methods for the determination of aluminium have been published. I The most frequently used reagent is probably aluminon, but, more recently, more sensitive reagents e.g., stilbazo (E = 34600), Eriochrome Cyanine R (E = 57000) and Chrome Azurol S (E - 50000) have been widely applied. Almost all methods are carried out in the pH range 3-7 and are subject to many interferences. In the present study, the metallochromic properties of a number of o,o’-dihydroxyazo dyes were investigated both in aqueous solution and after extraction into chloroform as ion-association complexes. Several potentially applicable reactions were noted. This communication describes the work which has been carried out to characterize the aluminium-Calmagite system. Calmagite, 1-(1-hydroxy4methyl-2-phenylazo)-2-naphthol4sulphonic acid, was first introduced by Lindstrom and DiehP as a stable replacement for Eriochrome Black T in the EDTA titration of calcium and magnesium. Its behaviour is summarized in Diehl’s mon0graph.s After aqueous phase reaction between the metal and Cahnagite at pH 8.6, the negatively-charged complex is extracted into chloroform by association with a chloride is used as the quaternary ammonium saIt. Methyltricaprylylammonium extracting agent but several other tertiary ammonium salts are equally suitable. Many interferences may be eliminated by the use of cyanide and EDTA as masking agents. EXPERIMENTAL Apparatus Samples were prepared in 45ml cyhndncal tubes, fitted with polyethylene stoppers and plastic screw-caps. These were shaken m an Eberbach Reciprocatmg Shaker at the high-speed setting. Water at 250 f 0 2’ from a Wilkens-Anderson Co. Lo-Temp. bath was circulated through the jacketed shaker tray. Absorption spectra and quantitative spectrophotometric measurements were obtained with a A Beckman Model G pH meter with a glass-calomel electrode pair Beckman DB spectrophotometer. l
Present address: 70803, U.S.A.
Department
of Chemistry, Louisiana State University, Baton Rouge, Louisiana 321
322
C. WIXIDWARDand H. FRUSER
was calibrated with Beckman buffer solutions at pH 7.00 and 10 00, and used for all pH measurements. Reagents EufferpH 8.6. Volumes of 450 ml of O-l&f boric acid (ARgrade. Mallinckrodt) and 250 ml of O*lM were mrxed and dduted to 2 1. with distrlled water. Anhydrous sodium perchlorate (39*4g, G. F. Smith Chemical Co.) was added to make the ionic strength of the stock buffer solutton 0.3. CalmagUe. A 0.15-g amount of Calmagite (Crty Chemical Corp.) was drssolved in 1 litre of distdled water. The slight turbidity which persrsted even after prolonged sturmg was removed by filtration. Thus solution was used for all the work on the development of the analytical procedure. The purity of this reagent was checked by measuring the molar absorpttvtty of solutions at pH 10.0 and 610 mc”.5 These expertments indtcated a purity of 47 ‘A if it was assumed that none of the tmpurmes present absorbed at thrs wavelength. The stock reagent solution used was therefore approxtmately 1 94 x lo-*M. The purtty of another sample of Cahnagite (K and K Labs.) was found to be approx. 60% and soluttons prepared from “corrected” weights of this sample were used for the experiments to determine the nature of the complex. It was noted that both batches of Calmagrte had a strong phenohc odour, probably mdtcatmg the presence of p-cresol, one of the starting materials m the syntheses of Calmagrte. Methyltrrcaprylylammonium chloride. Thus reagent was obtained as Aliquat 336 (General Mdls, Chemrcal Dtvaton, Kankakee, Ilhnois). No attempt was made at purrficatton An approximately 0 IM solutton was prepared by dtssolvmg 40 g in 1 litre of chloroform (AR grade, Mallmckrodt). Alumuuum and other metal ion soluttons were prepared from their perchlorates (G. F. Smith Chemical Co.). Aniomc mterferences were investigated by using the sodium salts (generally analytical grade).
sodium tetraborate (AR grade, Mallmckrodt)
Spectrai characteristics Ftgure 1 shows the absorption spectra of Calmagrte and its aluminium complex after extraction with a chloroform solution of Aliquat 336 from aqueous solution at pH 8 7. Under these condmons the ahumnmm complex is purple and the reagent blank is orange. The optimum wavelength for measurement of the alumuuum complex IS 570 m,u. Establishment of optimum conditions for aluminium determmation The factors affectmg the system and Its potential as a spcctrophotometrtc procedure were investtgated m a standard manner.’ During the preiimmary qualitattve mvestrgattons, the extractable purple aluminium-Calmagrte complex was observed to form above ca. pH 8. The absorbance of thts complex was maximal over the range pH 8.2-8 8. The optimum pH regron for the analytical determinatron 1s 8.6-8.7. Since the pK for the dissociation of Calmagtte, HID- P HD*- + H+, IS 8 14,* at pH 8 6 approx. 75 % of the dye IS present in the form HD+. It was shown that a five-fold molar excess of reagent over alummuun was sufficient to develop fully the colour of the complex and that a further increase in the reagent concentration had no effect on the absorbance due to a given amount of aluminium. A ten-fold molar excess of Calmagtte was used m the analytrcal work. It was also shown that a nommal3000-fold molar excess of Ahquat 336 over alumrnium was necessary to ensure total extractton of the metal complex and this concentration was used. The aluminium_Calmagrte complex IS not formed instantaneously at pH 8.6 and 30 mm should be allowed after mlxmg of the alumuuum, reagent and buffer soluttons for the aqueous phase comAfter addition of the chloroform solutron of Ahquat 336, a plexatton to proceed to completton. shaking time of 2 min IS adequate to ensure total extractton of the ion-assoctattlon complex. The absorbance of the extract is then constant for several hr and is convement!y measured after 30-60 mm. Procedure To 5 ml of nH 8.6 buffer m a shakine-tube, add 4 ml of4 x IO-‘MCalmagite, appropriate vohunes up to 5 ml of soluttoncontaining l*l-5.2 pgofaluminium, and dtsttlled wate;as r&es&y to make the volumes eoual. Mix well and allow to stand for 30 min. Now add 10 ml of 0.025M solution of Aliquat 336 in chloroform, stopper the tubes and agttate them for two minutes. Allow the solutions to settle for a further 30 min. then measure the absorbance of the organic phase at 570 mp, using the alummium-free solution as reference. The phase should be filtered through glass wool into the spectrophotometer cells to remove traces of water.
Calmagitc as a spectrophotometric reagent
323
The calibration curve prepared under these conditions is hnear over this concentration range, i.e., 0.1 l-0-54 ppm Al. The molar absorptlvlty at 570 rnp is 42000 which corresponds to a sensitivky index (SandeIF) of 0 00064 r&cm* for an absorbance of 0 001. The sensmvlty of the reactaon may, however, be Improved by extracting the complex from a Iarge aqueous volume mto a smaller volume of organic solvent. The extent of extraction of Calmaglte itself IS dependent on the volume ratio, but, If the reagent blank solution IS prepared under simdar condltlons, tius problem IS ehmmated.
WAVE LENGTH
(my)
FIG. L-Absorbance of Cahnagite and its ahnninium complex after extraction with 0*05&fsolution of Ahquot 336 m chloroform, pH &7. Measured in l-cm cells with 0 OSM Aliquot 336 in chloroform as reference, A-8 x lo-‘M Calma@e B-8 x 1O-6M Caimagrte -+ 16 X lO+M upturn. RESULTS
AND
DISCUSSION
Efect of foreign ions
Several cations, notably transition metal ions, also react with Calmagite under the proposed conditions of the aluminium determination and thus cause interference with the method. It has previously been demonstrated, however,6 that cyanide and EDTA may be used as general masking agents in the spectrophotometric determination of aluminium by extraction from aIkalme medium with 8-hydroxyquinoline. Although no extensive ex~na~on of the effects of foreign ions on the present method has been undertaken, some preliminary experiments were carried out to demonstrate that these masking agents were also effective in this system. In the presence of 10-BM cyanide and 5 x IO444 EDTA (added as the calcium-EDTA complex with excess of calcium ions present to prevent the possibility of EDTA complexing the a~u~nium), the effects of H&fold molar excesses of such ions as Cu, Ni, Zn, Cd and Pb on the determination of 0.22 ppm of Al were < f 10 %. Undoubtedly, any interference by such ions could be totally eliminated by the addition of appropriate amounts of these
324
C. WOODWARD and H. FREISER
masking agents. It may be preferable for the purpose of ehmination of interferences to carry out the determination of alumimum at a pH higher than 8.6 even though this will result in some decrease in sensitivrty. Taking pk;, for hydrocyanlc acid as 9.3,’ it is obvious that only approximately 17 “/ of the cyamde added wrll be present as CN- at pH 8.6, CJ 50% at pH 9.3 and 83 % at pH 10.0. Thus the effecttveness of a given amount of sodium cyamde as a masking agent will mcrease consrderably with a relatively small increase in pH. Also, at pH 9.3 (8.6) the logarithms of the conditional stability constants* of varrous metal-EDTA complexes are approximately: Al 3*8(5-O), Ca 9*6(9*0), Zn 14*6(14*5), Cd 14*6(14+5),Cu 16+4(16=3),Fe(M) 13.8(13*8), Co(I1) 14*8(14*6), so the effectiveness of EDTA as a masking agent would also be increased by an increase in pH. The effects of a number of common anions on the absorbance due to aluminium were also examined. At the 80-fold molar excess level none of the anions examined, viz., fluoride, chloride, bromide, iodide, perchlorate, borate, nitrate, nitrite, sulphate, sulphite, thiosulphate, bisulphate, carbonate, bicarbonate, cyanide, thiocyanate, phosphate, acetate. formate and citrate, caused a significant change. Fluoride and phosphate were then examined at the 800-fold moiar excess level but no interference was found. Probably fluoride complexing of aiuminmm is prevented by the maskmg action of the borate buffer used. For practical purposes, it would be preferable to replace the stoppered vials which were used for this expIoratory work by separatory funnels. It may aiso be convenient and time-saving to prepare a composite solution containing appropriate amounts of buffer, Calmagite and masking agents. Nature of complex
The composition of the anionic aluminium~almagite complex has been investigated by the standard spectrophotometric methods, viz., mole-ratio,v slope-ratro”O and continuous variations procedures. LL~*eAs discussed above, it was known that the Calmagite sample used was only 60% pure and solution concentration were, therefore, corrected m a suttable manner. Also, to avoid the further comphcatron that at pH 86 significant amounts of both H,D- and HD2- are present in solution, these experrments were carried out at pH 9.5, under whrch conditions virtually all Caimagite is present as HD2-. The slope-ratio studies indicated a 3: 1 Calmagite. Al complex and the mole-ratio studies a complex of greater than 2.1 molar proportions. The m~imum of the continuous variations curves appeared in the region of 2: 1 molar proportions, but the shape of these curves was such that the position of the maximum was difficult to determine. On the basis of these experiments and by comparison with previous observations with a very similar reagent, I3 it seems reasonable to suggest that the complex formed between aluminium and Calmagite at pH 8~6 is of 1: 3 molar proportions. CONCLUSION
The sensitivity of this reaction, coupled with its simplhty, suggests that it may find application to the determination of aluminlum in numerous ~lrcumstan~es. The solvent extraction step permits concentration so that the sensrtrvrty may be increased beyond that of reactions carried out totally in the aqueous phase. Furthermore, the
Cahnagite as a spectrophotometric reagent
325
ease of elimination of interferences indicates that it should also have advantages in selectivity over existing methods. Acknowk&e~eni--The authors gratefully acknowledge the financial support of the US. Atomic Energy Commrssion. Zusannnenf~almagit wird als empfindliches spektrophotometrisches Reagens fitr Alummium rmt Q~,,,,,,,= 42000 vorgeschlagen. Nach Reaktlon m w&Bnger Phase bei pH 8,6 wlrd der IComplex aus Metal1 und Reagens durch Bddung emcs Ionenassoziats rmt eincm quart&en Ammoniumsalz m Chloroform extrahlert. Die Methode wird durch die haufig vorkommenden Amonen mcht gestort; katlonische Sttirungen konnen nut Cyamd und EDTA als Masloerungsmlttel beseitlgt werden. R&ma&-On propose la c&nag&e comme r&a&f s~trophotom~triq~ sensible pour I’alummmm, .5s70ma= 42000. Apr&sr&ction en phase aqueuse a pH 8,6, le complexe m&al-rtactlf est extract en chloroformc par formation d’un complexe d’association ionique avec un se1 d’ammonium quaternatre. La m&hode est exempte d’mterftrence par l&s anions communs, et I’on peut iliiiner les mterf&rences cationiques par l’emplol de cyanure et d’EDTA comtne agents de stimulation. REFERENCES 1. V. N. Tikhonov, Z/I. Am&r. K&n., 1966,21,829. 2 F. Lindstrom and H. Diehl, Anat. Chem., 1960,32, 1123. 3. H. Diehl, Ctzlcein, Cdmqgite and o,o -D~~~x~o~~e~e: Ti~r~~~r~~,Calorimetric and Fbrwtetric Reqgentsfir G&urn and M~tt&um, G. F. Smith Chemical Co., Columbus, 1964. 4. G. F. Kirkbright, TuLzntu,1966,13, 1. 5. E. B. Sandell, Cobrimetric Determination of Traces of Metals, 3rd Ed., p. 83. Interscience, New Yorlt, 1959. 6. A. CfasJen,L. Bastin and J. Vissler, And. Chim. Acta, 1954, 10,373. 7. L. 0. Sill& and A. E. Ear tell, &a&i&y Consta&s of Metai-ion Complexes. Chem Sot., London,
1964. 8. A. Ringbom in I. M. Kolthoff and P. J. Elving, Treatise on Adyt~cd Chemistry, Part 1, Vol. 1, p. 575. Iatcrscic~~, New York, 1959. 9. J. H. Yoe and A. L. Jones, Irut. Eng. Chcm. (Anal., Ed.) 1944,16,111. 10. A. R Harvey and D. L. Manning, J, Am. Chem. Sot., 1950,72,448, 11. P. Job, Ann. Chim., 1928,9,113. 12. W. C. Vosburgh and G. R. Cooper, J. Am. C&em.Sot., 1941,63,437. 13. M. Perkins and 6. F. Reynolds, Anal. Chim. Acta, 1958.19, 54.