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Spectrophotometric determination of molybdenum by extraction of a green molybdenum(v) species
Tahnro,
Vol. 20, pp. 1207-1210. Pergamon
Press, 1973. Printed in Great Britain
SHORT
COMMUNICATIONS
SPECTROPHOTOMETRIC DETERMINATION OF MOLYBDENUM BY EXTRACTION OF A GREEN MOLYBDENUM(V) SPECIES (Received
18 April
1973. Accepted 10 May 1973)
Methods for the determination of milligram amounts of molybdenum in natural and industrial samples by gravimetry or titrimetry require its prior separation from several elements.’ The gravimetric methods area ften tedious. The calorimetric methods are generally suitable for microgram amounts of molybdenum.’ The calorimetric thiocyanate method is used for the rapid determination of l-6 % of molybdenum but there are difficulties and inaccuracies’ and separation from several interfering elements is neceu%ry.3 Molybdenum forms a brown MO(V)species in sulphuric acid and also a green one at higher concentrations of hydrochloric acid.” The former species has been used for the determination of milligram amounts of molybdenum.4-’ The method presented below makes use of the green species, which is extractable by organic solvents. EXPERIMENTAL
Reagents and test solutions Solutions ofthe elements. Molybdenum solution was prepared by dissolving sodium molybdate dihydrate in water to give 10 mg of MO per ml, and standardized by the oxinate method.’ Solutions of other ions were prepared by dissolving their easily available salts to give 10 or 20 mg of ion per ml, and standardi by conventional methods8 Zsoamyl acetate. The fraction distilling at up to 130” was used. Hydrazine sulphate. Samples. Synthetic
samples were prepared by mixing hydrochloric or sulphuric acid solutions of the ions to give the required composition (Table 3). Ferromolybdenum. Finely powdered sample (0.1 g) was dissolved in 3 ml of concentrated hydrochloric acid and 1 ml of concentrated nitric acid by gentle warming. Nitrate was destroyed by careful addition of solid hydrazine sulphate. The solution was then subjected to the procedure. Procedure
To a hot lo-ml aliquot of sample solution containing not more than 135 mg of molybdenum and other ions (in 55M hydrochloric acid) add solid hydraxine sulphate (1 mg for mg of each reducible ion) and boil the solution for 2 min in a 50-ml covered beaker, with occasional stirring. Cool the solution under tap water, transfer it to a lOO-ml separatory funnel, adjust it to be 7M in hydrochloric acid in a final 20-ml volume (adding the acid last) and mix well. Then extract with one lo-ml and three 5-ml portions of isoamyl acetate, shaking each time for 1 min. Two extractions, each with 10 ml of solvent, are sticient for up to 10 mg of molybdenum. Combine the extracts and dilute to 25 ml in a volumetric flask. Pass the solution through a Whatman No. 41 filter paper, rejecting the first few drops, and measure the absorbance at 720 nm against a similarly treated reagent blank, within 45 min. Samples containing iron. To the hot solution, after reduction of molybdenum by hydraxine sulphate, add concentrated stannous chloride solution dropwise in calculated slight excess to reduce all the iron(II1) (approximately known). Before repeating the extraction with the solvent, add a drop or two of the stannous chloride solution to reduce any iron oxidized during the previous equilibration. Samples containing tungsten. Add enough tartaric acid to the neutral or just alkaline sample solution to mask all the tungsten and then apply the procedure. Samples containing copper. After reduction of molybdenum, add enough thiourea to mask the copper. RESULTS
Eflect of varying experimental
AND
DISCUSSION
conditions
Reductants other than hydrazine are not suitable-metallic 1207
mercury forms insoluble mercurous chloride,
making phase separation diiBcuIt, stannous chloride does not produce a single oxidation state,’ and ascorbic acid in excess suppresses the extraction. The effect of conditions of reduction and extraction on the green MO(V) absorbance is shown in Table 1. Solvent extraction of molybdenum solutions obtained by reduction Tabk 1. Dependence of the absorbance of green Ma(V) on acidity of the aqueous phase (MO = 1976 mg/ml of sokent phase) [Ha] for reduction, M Absorbance*
O-860
O-5
1.0 O-430
[HCll for extractiont, M AbsorbattCe
S-5 @348
60 0.360
1.5 0.416
2.0 0409
:I:67
7.0 O-374
35 0.390
Z81
07:;70
8.0 O-359
z74
* After extraction from 7&f HCl. t After reduction in 55&f HCI. in <5iU hydrochloric acid and below the boiling point, gives a slightly dlfkrent green colour in the solvent phase; a b&wash from the solvent shows a blue colour indicating that some “molybdenum blue” is still present after r&ction under these ronbitions. If the reduction is carried out in > SM hydrochlork acid and at boiIing point, a ba&extraction from the green solvent phase gives a brown to orange colour. Moly~~ blues once formed, is su&ierttly stable even in 7M hydrochlork acid, hence its fetid should be prevented by carrying out the reduction in > J&4hydrochloric acid. The presence even small amounts of molybdenum blue e&ances the absorbance at 720 nm as it has very much higher molar absorptivity than the green MO(V). This can be se@nfrom Table 1, Reduction with hydraxine is complete in 2 min and gives a single oxidation state, Mo(V).t” At hydrochloric acid concentrations > 5&&the brown species decreases and the green species increases abruptly.4 When the aqueous phase is made 7&f in hydrochloric acid, the acid should be added last, otherwise the absorbance is slightly lowered. Extraction from 7M hydrochloric acid gives maximum absorbance, These conditions are incorporated in the procedure and give satisfactory rmults ~pr~~ibk to f0.2 mg. The oxygenated solvents, isoamyl acetate , isoamyl alcohol, methyl isobutyl ketone, n-butyl acetate and trl-n-butyl phosphate, extract the &p-eenMO(V)but the absorbance is the highest in isoamyl acetate at 720 nm. Isoamyl acetate also extracts less of the other elements. The absorption maxima at 305 nm and 440 nm are not so useful, Extraction of MO(V) is complete after the four separate equilibrations. Beer’s kw is obeyed at 720 nm from O+O8to 5.4 mg of molybdenum per ml. The absorbance is constant for 45 min. The spectrum mat&tea that known to correspond to H*MoUCld .
of
Table 2. Extraction of other elements Element* CO CU
E#
Pdt U Ni, Ru, Pt. Cr. V, Mn, Se, Te, Cu,li Fe.7 Ce Nb_ Ti, Zr, BG$ Th, Be, Mg, Q% Ba, Sr, Zn, Al, Pb, Cd, Bi, La, W, Sb, Sn, As
Colour of extract
0.298
Blue c$!eglt
Absorbance
Yellow
Faintly coloured Orange yellow Faintly yellow
O-047 O*Of8
O-002 oXlO OJXJO
Colourfess
O-00
Colourkss
0030
* 5 m&ml, in its normal oxidation state, unkss otherwise stated. # 3.75 m&ml; 7 l-5 mgjmi; $0-005 mgiml. 8 On adding 2 g of thiourea. .y On adding stannous chloride.
1209
SHORT COMMUNICATIONS
Effect of diverse ions Sulphate has no effect, and acetate, oxalate, tartrate, citrate, phosphate and EDTA even in saturation amounts, decrease the extraction only slightly. Excess of ascorbic acid gives a dark brown aqueous solution and lowers the extraction of the green species. Fluoride (> 25 mg/ml) decreases the extraction considerably. Except for cobalt and very large amounts of palladium and osmium, other elements do not interfere (Table 2) in the method. Particularly remarkable is the absence of interference from Ti, V, Nb, Cr, W, Fe, Ni, Cu, U and Sb, which have to be separated for most methods of moybdenum determination. Applications The wide applicability and of ferromolybdenum
of the method is shown by the satisfactory analysis of different synthetic samples (Table 3). Samples weighing 0.2-5 g (not containing cobalt and large amounts of Table 3. Analysis of samples by the proposed method
Sample composition*
V(100) Ti(40) Mn(30) V(20) Ni(40) V(10) Ni(20) Cr(50) Ru(9) Pt(l0) Nb(15) U(100) W(20)
MO added, mg
MO found, mg
Sample composition*
19.3 57.9 28.9 67.6 25.0 38.6
19.1, 19.2 57.9, 58.0 29.1 67.7 25.0 38.7
W(50) Ti(100) Fe(40) Fe(20) Ni(6O)t Fe(1000) Ferromolybdenum$
MO added, mg 2i.o” 48.3 19.3 45.6 -
MO found, mg 9.7 20.0 48.4 19.3 45.7 58.6 %
* Amounts (mg) are given in brackets. t Analogous to Hastelloy A. $ 58.8 % by oxinate method.’ platinum metals) can be directly analysed for l-60 % of molybdenum in 15 min or less with sufficient accuracy for all routine purposes. The method requires only simple reagents and is also useful for rapid series analyses. Acknowledgements-The authors wish to thank Prof. S. M. Mukherji, Head of the Chemistry Department, for laboratory facilities and the authorities, Kurukshetra University, for the award of a research scholarship to J. R. Chemistry Department v. YATIRUAM University of Kurukshetra JASWANT RAM Kurukshetra, India REFERENCES
1. K. Kodama, Methods of Quantitative Inorganic Analysis, pp. 215-l 8. Interscience, New York, 1963. 2. D. H. Killeffer and A. Linz, Molybdenum Compounds, p. 154. Interscience, New York, 1952. 3. E. B. Sandell, Calorimetric Determination of Traces of Metals, 3rd Ed., p. 648. Interscience, New York, 1959. 4. C. F. Hiskey and V. W. Meloche, J. Am. Chem. Sot., 1940,62, 1819. 5. T. Yuasa, Bunseki Kagaku, 1962, 11,449. 6. M. A. Ashy and J. B. Headridge, Anal. Chim. Acta, 1972, 59,217. 7. V. M. Tarayan and A. N. Pogosyan, Arm. Khim. Zh., 1966,19,586. 8. K. Kodama, Methods of Quantitative Inorganic Analysis. Interscience, New York, 1963. 9. C. E. Crouthamel and C. E. Johnson, Anal. Chem., 1954,26, 1284. 10. A. I. Busev, Analytical Chemistry of Molybdenum, pp. 70-71. Israel Program for Scientific Translations, Jerusalem, 1964. Summary-A simple method is described for the rapid spectrophotometric determination of molybdenum in samples containing l-60% MO, with satisfactory accuracy. Molybdenum is reduced with excess of hydrazine sulphate in boiling 5.5M hydrochloric acid and extracted with isoamyl acetate from 7M hydrochloric acid. The green colour is measured at 720 nm against a reagent blank. Beer’s law is obeyed over the range 0.08-5.4 mg of molybdenum per ml. Interference from iron and copper is removed by adding stannous chloride and thiourea respectively in slight excess. Titanium, vanadium, niobium, chromium, tungsten, nickel, uranium, and antimony do not interfere even in large amounts. Only cobalt interferes seriously.
1210
SHORT
COMMUNICATIONS
Z-E& cinfache Methode wird bcschrieben, urn Molybd&n in Proben, die l-60% MO enthaltcn, rasch und hinreichcnd genau spektrophotometrisch zu bcstimmen. Molyti wird mit elncm UbcrschuB von Hydraxlnsulfat in siedcnder 5,5M Sal&lure und mit Isoamylacetat aus 7M Salx&tre extrahicrt. Die grilne Farbe wird bci 720 nm gcgen eine Reagentien~Blindprobe gemcssen:Das Becrsche Gcsetz wird im Bereich 0,0&5,4 mg Molybdlln pro ml bkfolgt. Die St&ung durch Eisen bxw. Kupfer wird b&t& indcm man Zinn(II)-chlorld bxw. ThlohamstotTin schwa&cm Uberschug xugibt. Titan, Vanadium, Niob, Chrom, Wolfram, Nickel, Ursa und Antimon storms such in grogen Mcngen nicht. Nur Kobalt start in crhcblichcm AusmaD. R&utt&Gn dhit me mbhode simple pour le dosage spectrophotomttrique rapide du molyb&tte dam dss 6chantillons contenant 1-6p% de MO, avec une prdcision satisfaisante. Lc molybd&na est r&tit par un ends de sulfate d’hydraxine en acide chlorhydrlque 5, 5 M bouillant et extrait par &&ate d’lsoamyle a partir d’acide chlorhydrique 7M. On mesum la coloration verte B 720 nm par rapport a un t6moin dcs r6actifs. La loi de Beer cst suivie dans le domaine 0$X-5,4 mg de molybd&ne par ml. On &mine l’interf6rcnce du fer et du cuivrc par addition en l&r cx& de chlorure stanneux et de thiourte rcspectivement. Lcs titane, vanadium, niobium, chrome, tungstlne, nickel, uranium et antimoine n’interf&rent pas, m6me en fottcs quantit6s. Scul le cobalt interf&e s&icuscment.
T&ma,
Vol. 20, pp. 12104213.
Peqsmoa
THIOTROPOLONE SIMULTANEOUS
Preu, 1973. Printed in Great Britain
AS A CHROMOGENIC REAGENT FOR THE DETERMINATION OF COBALT(I1) AND NICKEL(II)
(Received 20 March 1973. Accepted 12 May 1973)
Thiotropolone (TT) is a chelatmg agent, the complexes of which with certain metal ions have been iso1ated.t However, no solution studies have been reported. The present paper &als with investigation of the use of thiotropolone as a chromogenic reagent for the simultaneous determination of cobalt and nickel, in metals and alloys. Cobalt and nickel form reddish-brown and violet insoluble complexes respectively, extractable into chloroform and other non-polar solvents. EXPERIMENTAL
Rcogents
Thiotropolone was synthesized by the method of Nozoc er af.‘s3 and a stock solution (O.OlM) in chloroform prepared. Cobalt(I1) and nickel(H) solutions were prepared by dissolving the corresponding sulphates in doubly distilled water and standard&d gravimetrically. Acetate buffers, hydrochloric acid and sodium hydroxide were used for pH adjustments. All other chemicals used were of reagent grade. Procedure
To a suitable aliquot containing 6.0-25.0 ,ug of cobalt or 7.545~7 pg of nickel, add an excess of chloroform solution of thiotropolone, keeping the pH at 7.0. Make the volumes of both phases 10 ml and shake the mixture for 5 min. Separate the organic layer and measure its absorbance (at 500 nm for cobalt and 580 nm for nickel) against the corresponding reagent blank. Read the cobalt or nickel concentration from a previously prepared calibration curve. RESULTS
AND
DISCUSSIONS
Absorption spectra, and effect of pH and reagent concentration
The cobalt and nickel complexes exhibit maximum absorbance at 500 and 580 nm rsepectively (Fig. 1). Absorbance due to the reagent is negligible at 580 nm. Therefore subsequent studies on the nickel complex were done with a chloroform blank, but reagent blanks were used for cobalt.
Vol. 20, pp. 1207-1210. Pergamon
Press, 1973. Printed in Great Britain
SHORT
COMMUNICATIONS
SPECTROPHOTOMETRIC DETERMINATION OF MOLYBDENUM BY EXTRACTION OF A GREEN MOLYBDENUM(V) SPECIES (Received
18 April
1973. Accepted 10 May 1973)
Methods for the determination of milligram amounts of molybdenum in natural and industrial samples by gravimetry or titrimetry require its prior separation from several elements.’ The gravimetric methods area ften tedious. The calorimetric methods are generally suitable for microgram amounts of molybdenum.’ The calorimetric thiocyanate method is used for the rapid determination of l-6 % of molybdenum but there are difficulties and inaccuracies’ and separation from several interfering elements is neceu%ry.3 Molybdenum forms a brown MO(V)species in sulphuric acid and also a green one at higher concentrations of hydrochloric acid.” The former species has been used for the determination of milligram amounts of molybdenum.4-’ The method presented below makes use of the green species, which is extractable by organic solvents. EXPERIMENTAL
Reagents and test solutions Solutions ofthe elements. Molybdenum solution was prepared by dissolving sodium molybdate dihydrate in water to give 10 mg of MO per ml, and standardized by the oxinate method.’ Solutions of other ions were prepared by dissolving their easily available salts to give 10 or 20 mg of ion per ml, and standardi by conventional methods8 Zsoamyl acetate. The fraction distilling at up to 130” was used. Hydrazine sulphate. Samples. Synthetic
samples were prepared by mixing hydrochloric or sulphuric acid solutions of the ions to give the required composition (Table 3). Ferromolybdenum. Finely powdered sample (0.1 g) was dissolved in 3 ml of concentrated hydrochloric acid and 1 ml of concentrated nitric acid by gentle warming. Nitrate was destroyed by careful addition of solid hydrazine sulphate. The solution was then subjected to the procedure. Procedure
To a hot lo-ml aliquot of sample solution containing not more than 135 mg of molybdenum and other ions (in 55M hydrochloric acid) add solid hydraxine sulphate (1 mg for mg of each reducible ion) and boil the solution for 2 min in a 50-ml covered beaker, with occasional stirring. Cool the solution under tap water, transfer it to a lOO-ml separatory funnel, adjust it to be 7M in hydrochloric acid in a final 20-ml volume (adding the acid last) and mix well. Then extract with one lo-ml and three 5-ml portions of isoamyl acetate, shaking each time for 1 min. Two extractions, each with 10 ml of solvent, are sticient for up to 10 mg of molybdenum. Combine the extracts and dilute to 25 ml in a volumetric flask. Pass the solution through a Whatman No. 41 filter paper, rejecting the first few drops, and measure the absorbance at 720 nm against a similarly treated reagent blank, within 45 min. Samples containing iron. To the hot solution, after reduction of molybdenum by hydraxine sulphate, add concentrated stannous chloride solution dropwise in calculated slight excess to reduce all the iron(II1) (approximately known). Before repeating the extraction with the solvent, add a drop or two of the stannous chloride solution to reduce any iron oxidized during the previous equilibration. Samples containing tungsten. Add enough tartaric acid to the neutral or just alkaline sample solution to mask all the tungsten and then apply the procedure. Samples containing copper. After reduction of molybdenum, add enough thiourea to mask the copper. RESULTS
Eflect of varying experimental
AND
DISCUSSION
conditions
Reductants other than hydrazine are not suitable-metallic 1207
mercury forms insoluble mercurous chloride,
making phase separation diiBcuIt, stannous chloride does not produce a single oxidation state,’ and ascorbic acid in excess suppresses the extraction. The effect of conditions of reduction and extraction on the green MO(V) absorbance is shown in Table 1. Solvent extraction of molybdenum solutions obtained by reduction Tabk 1. Dependence of the absorbance of green Ma(V) on acidity of the aqueous phase (MO = 1976 mg/ml of sokent phase) [Ha] for reduction, M Absorbance*
O-860
O-5
1.0 O-430
[HCll for extractiont, M AbsorbattCe
S-5 @348
60 0.360
1.5 0.416
2.0 0409
:I:67
7.0 O-374
35 0.390
Z81
07:;70
8.0 O-359
z74
* After extraction from 7&f HCl. t After reduction in 55&f HCI. in <5iU hydrochloric acid and below the boiling point, gives a slightly dlfkrent green colour in the solvent phase; a b&wash from the solvent shows a blue colour indicating that some “molybdenum blue” is still present after r&ction under these ronbitions. If the reduction is carried out in > SM hydrochlork acid and at boiIing point, a ba&extraction from the green solvent phase gives a brown to orange colour. Moly~~ blues once formed, is su&ierttly stable even in 7M hydrochlork acid, hence its fetid should be prevented by carrying out the reduction in > J&4hydrochloric acid. The presence even small amounts of molybdenum blue e&ances the absorbance at 720 nm as it has very much higher molar absorptivity than the green MO(V). This can be se@nfrom Table 1, Reduction with hydraxine is complete in 2 min and gives a single oxidation state, Mo(V).t” At hydrochloric acid concentrations > 5&&the brown species decreases and the green species increases abruptly.4 When the aqueous phase is made 7&f in hydrochloric acid, the acid should be added last, otherwise the absorbance is slightly lowered. Extraction from 7M hydrochloric acid gives maximum absorbance, These conditions are incorporated in the procedure and give satisfactory rmults ~pr~~ibk to f0.2 mg. The oxygenated solvents, isoamyl acetate , isoamyl alcohol, methyl isobutyl ketone, n-butyl acetate and trl-n-butyl phosphate, extract the &p-eenMO(V)but the absorbance is the highest in isoamyl acetate at 720 nm. Isoamyl acetate also extracts less of the other elements. The absorption maxima at 305 nm and 440 nm are not so useful, Extraction of MO(V) is complete after the four separate equilibrations. Beer’s kw is obeyed at 720 nm from O+O8to 5.4 mg of molybdenum per ml. The absorbance is constant for 45 min. The spectrum mat&tea that known to correspond to H*MoUCld .
of
Table 2. Extraction of other elements Element* CO CU
E#
Pdt U Ni, Ru, Pt. Cr. V, Mn, Se, Te, Cu,li Fe.7 Ce Nb_ Ti, Zr, BG$ Th, Be, Mg, Q% Ba, Sr, Zn, Al, Pb, Cd, Bi, La, W, Sb, Sn, As
Colour of extract
0.298
Blue c$!eglt
Absorbance
Yellow
Faintly coloured Orange yellow Faintly yellow
O-047 O*Of8
O-002 oXlO OJXJO
Colourfess
O-00
Colourkss
0030
* 5 m&ml, in its normal oxidation state, unkss otherwise stated. # 3.75 m&ml; 7 l-5 mgjmi; $0-005 mgiml. 8 On adding 2 g of thiourea. .y On adding stannous chloride.
1209
SHORT COMMUNICATIONS
Effect of diverse ions Sulphate has no effect, and acetate, oxalate, tartrate, citrate, phosphate and EDTA even in saturation amounts, decrease the extraction only slightly. Excess of ascorbic acid gives a dark brown aqueous solution and lowers the extraction of the green species. Fluoride (> 25 mg/ml) decreases the extraction considerably. Except for cobalt and very large amounts of palladium and osmium, other elements do not interfere (Table 2) in the method. Particularly remarkable is the absence of interference from Ti, V, Nb, Cr, W, Fe, Ni, Cu, U and Sb, which have to be separated for most methods of moybdenum determination. Applications The wide applicability and of ferromolybdenum
of the method is shown by the satisfactory analysis of different synthetic samples (Table 3). Samples weighing 0.2-5 g (not containing cobalt and large amounts of Table 3. Analysis of samples by the proposed method
Sample composition*
V(100) Ti(40) Mn(30) V(20) Ni(40) V(10) Ni(20) Cr(50) Ru(9) Pt(l0) Nb(15) U(100) W(20)
MO added, mg
MO found, mg
Sample composition*
19.3 57.9 28.9 67.6 25.0 38.6
19.1, 19.2 57.9, 58.0 29.1 67.7 25.0 38.7
W(50) Ti(100) Fe(40) Fe(20) Ni(6O)t Fe(1000) Ferromolybdenum$
MO added, mg 2i.o” 48.3 19.3 45.6 -
MO found, mg 9.7 20.0 48.4 19.3 45.7 58.6 %
* Amounts (mg) are given in brackets. t Analogous to Hastelloy A. $ 58.8 % by oxinate method.’ platinum metals) can be directly analysed for l-60 % of molybdenum in 15 min or less with sufficient accuracy for all routine purposes. The method requires only simple reagents and is also useful for rapid series analyses. Acknowledgements-The authors wish to thank Prof. S. M. Mukherji, Head of the Chemistry Department, for laboratory facilities and the authorities, Kurukshetra University, for the award of a research scholarship to J. R. Chemistry Department v. YATIRUAM University of Kurukshetra JASWANT RAM Kurukshetra, India REFERENCES
1. K. Kodama, Methods of Quantitative Inorganic Analysis, pp. 215-l 8. Interscience, New York, 1963. 2. D. H. Killeffer and A. Linz, Molybdenum Compounds, p. 154. Interscience, New York, 1952. 3. E. B. Sandell, Calorimetric Determination of Traces of Metals, 3rd Ed., p. 648. Interscience, New York, 1959. 4. C. F. Hiskey and V. W. Meloche, J. Am. Chem. Sot., 1940,62, 1819. 5. T. Yuasa, Bunseki Kagaku, 1962, 11,449. 6. M. A. Ashy and J. B. Headridge, Anal. Chim. Acta, 1972, 59,217. 7. V. M. Tarayan and A. N. Pogosyan, Arm. Khim. Zh., 1966,19,586. 8. K. Kodama, Methods of Quantitative Inorganic Analysis. Interscience, New York, 1963. 9. C. E. Crouthamel and C. E. Johnson, Anal. Chem., 1954,26, 1284. 10. A. I. Busev, Analytical Chemistry of Molybdenum, pp. 70-71. Israel Program for Scientific Translations, Jerusalem, 1964. Summary-A simple method is described for the rapid spectrophotometric determination of molybdenum in samples containing l-60% MO, with satisfactory accuracy. Molybdenum is reduced with excess of hydrazine sulphate in boiling 5.5M hydrochloric acid and extracted with isoamyl acetate from 7M hydrochloric acid. The green colour is measured at 720 nm against a reagent blank. Beer’s law is obeyed over the range 0.08-5.4 mg of molybdenum per ml. Interference from iron and copper is removed by adding stannous chloride and thiourea respectively in slight excess. Titanium, vanadium, niobium, chromium, tungsten, nickel, uranium, and antimony do not interfere even in large amounts. Only cobalt interferes seriously.
1210
SHORT
COMMUNICATIONS
Z-E& cinfache Methode wird bcschrieben, urn Molybd&n in Proben, die l-60% MO enthaltcn, rasch und hinreichcnd genau spektrophotometrisch zu bcstimmen. Molyti wird mit elncm UbcrschuB von Hydraxlnsulfat in siedcnder 5,5M Sal&lure und mit Isoamylacetat aus 7M Salx&tre extrahicrt. Die grilne Farbe wird bci 720 nm gcgen eine Reagentien~Blindprobe gemcssen:Das Becrsche Gcsetz wird im Bereich 0,0&5,4 mg Molybdlln pro ml bkfolgt. Die St&ung durch Eisen bxw. Kupfer wird b&t& indcm man Zinn(II)-chlorld bxw. ThlohamstotTin schwa&cm Uberschug xugibt. Titan, Vanadium, Niob, Chrom, Wolfram, Nickel, Ursa und Antimon storms such in grogen Mcngen nicht. Nur Kobalt start in crhcblichcm AusmaD. R&utt&Gn dhit me mbhode simple pour le dosage spectrophotomttrique rapide du molyb&tte dam dss 6chantillons contenant 1-6p% de MO, avec une prdcision satisfaisante. Lc molybd&na est r&tit par un ends de sulfate d’hydraxine en acide chlorhydrlque 5, 5 M bouillant et extrait par &&ate d’lsoamyle a partir d’acide chlorhydrique 7M. On mesum la coloration verte B 720 nm par rapport a un t6moin dcs r6actifs. La loi de Beer cst suivie dans le domaine 0$X-5,4 mg de molybd&ne par ml. On &mine l’interf6rcnce du fer et du cuivrc par addition en l&r cx& de chlorure stanneux et de thiourte rcspectivement. Lcs titane, vanadium, niobium, chrome, tungstlne, nickel, uranium et antimoine n’interf&rent pas, m6me en fottcs quantit6s. Scul le cobalt interf&e s&icuscment.
T&ma,
Vol. 20, pp. 12104213.
Peqsmoa
THIOTROPOLONE SIMULTANEOUS
Preu, 1973. Printed in Great Britain
AS A CHROMOGENIC REAGENT FOR THE DETERMINATION OF COBALT(I1) AND NICKEL(II)
(Received 20 March 1973. Accepted 12 May 1973)
Thiotropolone (TT) is a chelatmg agent, the complexes of which with certain metal ions have been iso1ated.t However, no solution studies have been reported. The present paper &als with investigation of the use of thiotropolone as a chromogenic reagent for the simultaneous determination of cobalt and nickel, in metals and alloys. Cobalt and nickel form reddish-brown and violet insoluble complexes respectively, extractable into chloroform and other non-polar solvents. EXPERIMENTAL
Rcogents
Thiotropolone was synthesized by the method of Nozoc er af.‘s3 and a stock solution (O.OlM) in chloroform prepared. Cobalt(I1) and nickel(H) solutions were prepared by dissolving the corresponding sulphates in doubly distilled water and standard&d gravimetrically. Acetate buffers, hydrochloric acid and sodium hydroxide were used for pH adjustments. All other chemicals used were of reagent grade. Procedure
To a suitable aliquot containing 6.0-25.0 ,ug of cobalt or 7.545~7 pg of nickel, add an excess of chloroform solution of thiotropolone, keeping the pH at 7.0. Make the volumes of both phases 10 ml and shake the mixture for 5 min. Separate the organic layer and measure its absorbance (at 500 nm for cobalt and 580 nm for nickel) against the corresponding reagent blank. Read the cobalt or nickel concentration from a previously prepared calibration curve. RESULTS
AND
DISCUSSIONS
Absorption spectra, and effect of pH and reagent concentration
The cobalt and nickel complexes exhibit maximum absorbance at 500 and 580 nm rsepectively (Fig. 1). Absorbance due to the reagent is negligible at 580 nm. Therefore subsequent studies on the nickel complex were done with a chloroform blank, but reagent blanks were used for cobalt.