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Spectrophotometric determination of vanadium as V(III) oxinate
596 Talanta,
SHORT COMMUNICATIONS Vol 23,pp 596598 PergamonPress. 1976Prmtedm GreatBr~tam
SP~CTROPHOTO~ETRIC
V. Department
of Chemistry,
D~TER~I~ATIO~ V(II1) OXINATE YATIRAJAM
Kurukshetra
OF VANADIUM
and S. P. ARYA
University,
Kurukshetra
132119, Haryana,
(Receiaed 22 October 1975. Accepted 13 January
Almost all the numerous photometric methods for vanadium determmatmn are based on vanadium(V) complexes. Only a few are based on vanadmm(IV) complexes. There are even fewer methodslm4 based on vanadium(II1). Although some of them are highly sensitive, it would be advantageous to have methods with higher tolerance limits to anafyttcally important elements to avoid prehminary separations. The limitation in usmg vanadium(III) appears to be its production and the stability of tts complexes amalgam6 or stannous chloride4 reduction Electrolytic,’ IS frequently used for producmg vanadium(II1). A greater choice of reagents and condittons should be posstble if introduction of metal tons can be avoided in the reduction. Accordmgly, we present below a method of producing vanadium(II1) by sodium dithionite reduction and its extraction by oxine for its spectrophotometric determination.
EXPERIMENTAL
Reagents and solutzons Vanadium solution. A stock solution (10 mg of V/ml) was prepared from sodium metavanadate and standardized by suitable dilution gave lOO- and the oxine method;7 lo-flgcglml solutions. 8-Hydroxyqutnoline. A 2% solution in carbon tetrachloride. Solutions of’ other elements. Prepared by dissolvmg suitable salts in water or dilute sulphunc acid to give 10 or 1 mg of element per ml. Samples. Synthetic samples were prepared by mixing solutions of the ions to give the required compositions (see Table 4). Rutile and Yemenite Finely powdered sample (1.0 g) was fused’ with 5 g of fusion mixture in a platinum crucible for nearly 30 mm. The melt was cooled and taken up m hot water. The msoluble restdue was filtered off on Whatman No. 41 paper and washed 4 times with 5 ml of hot water each time. The filtrate was just acidified to htmus wtth dilute sulphurtc acid and boiled to expel carbon dioxide. Any precipitate was filtered off, and washed twice with 5-ml portions of hot water. The filtrate and washings were cooled and made up to 5 ml. Aliquots of this solution were then used for the determinatton of vanadium by the procedure. Determination procedure To 20 ml of solution containing < 175 pg of vanadium at pH 3-10, in a 150-ml separatory funnel, solid sodium dithiomte (05-2.Og) was added. After wattmg for 2 mm the funnel was stoppered and shaken gently for 2 min with lOm1 of the oxine solution in carbon tetrachloride, can bemg taken to release the pressure occasionally. After tht. layers had separated, the solvent phase was removed and passed through Whatman No. 41 paper (moistened with carbon tetrachlortde) into a 25-ml volumetric flask. The extraction was repeated wtth another 1Oml of the oxine
AS
India
1976)
solution. Any complex sticking to the filter paper was washed mto the flask, with oxine solution added dropwise. The solutton was made up to the mark with carbon tetrachloride and mixed. The absorbance of the yellow complex was measured in l-cm cells at 420 nm with a Beckman DU sp~trophotometer~ against a stmdarly treated reagent blank. The latter gave an absorbance of 0.006 against oxme in carbon tetrachloride. Samples containing other elements. Masking agents were added after the reduction to vanadium(III), as shown m Table 3. In the case of tungsten, the tartrate was added to the solution at pH 8.5-10, before reduction. RESULTS AND DISCUSSION
When sodmm dtthionite is added to mg amounts of vanadium(V) in slightly alkaline or acid solution, the pH decreases gradually, depending upon the amount of the reductant. The green solution obtained shows an absorption spectrum similar to the one obtamed for vanadium(II1) prepared by electrolyttc reduction’ or mercury reductor.’ When the solutton is shaken with oxine m carbon tetrachloride a yellow complex is extracted quantitatively, showing an absorption peak at 420nm. An initial pH of 3-10 before addition of dtthionite gives a constant absorbance; the absorbance is lower if the inittal pH is outside this range. Carbon tetrachloride is found to be the best solvent (Table l), giving the highest absorbance. A single extraction with 10ml of solvent was made from 20ml of aqueous phase. The colour 1s not stable m other solvents except benzene, and in it has lower absorbance at the same L,X. The effect of vartous parameters on the V(III)-oxmate absorbance in carbon tetrachloride is shown in Table 2. the other conditions in each study being kept at the lower end of the optimum range. The optimum condittons for maximum absorbance are, inmal pH of the aqueous phase 3-10, reduction with 0.552.0 g of sodium dithtonite, 2 mm waiting after mtxing and 2-3 min equtlibration with l-4”,; oxine solution in carbon tetrachloride. A single extractton with oxme m carbon tetrachloride removes more than 99’%; of the vanadmm but a second extraction with 10 ml of the solvent ts recommended for 100% recovery On the basis of Job’s curves. the extracted specres has a 3: I hgand:metal composition.” The species has an Table 1. Absorbance different solvents
of vanadium(III)-oxmate complex (V 5 pg/ml m the aqueous phase)
Solvent Carbon tetrachlorlde Benzene Chloroform Methyl isobutyl ketone Amy1 acetate Amy1 alcohol
Absorbance 103 0.995 0.858 0.940 0.920 0.662
in
SHORT
Table 2. Dependence
Oxine/CCl,, Absorbance
of the V(III)-oxinate
%
Sodium dlthionite, Absorbance Time of contact, Absorbance
g
min
extraction on different phase)
0.02 0.70
0.05 0.96
0.1 0.98
0.1 0.7
0.2 0.98
0.5-2.0 1.03
0.25 0.93
0.5 1.00
1.0 1.01
absorption maximum at 42@425 nm, with sensitivity for vanadium of 0.004 pg/cm2 (Fig. 1). At wavelengths shorter than 370nm, the blank absorbs highly. There 1s no other peak at wavelengths up to 850 nm even at 0.8 mg/ml vanadium concentration. Beer’s law is obeyed up 7 pg of V per ml of solvent phase. The absorbance remains constant for 45 min Eflect of diverse
ions
Sodium chloride (5 g), sulphate (5 g), tartrate (2 g), acetate (3 g), thiourea (1 g) and ascorbic acid (1 g) have no effect on the extraction of vanadium. Only limited amounts of sulphosalicylic acid (0.4 g), thioglycollic acid (0.6 ml) and potassium cyamde (0.2g) can be tolerated. Nitrate can be tolerated up to 5 mg/ml. Phosphate (2 g of the sodium salt) decreases the extractlon. Fluoride and oxalate in > 50 mg/ml and EDTA m > 5 mg/ml concentrations mask the vanadium extraction completely. Table
3. Extraction
Tolerance hmit mg/20 ml*
Element Al(II1) Zn( II) Cu(II)f WI) Fe(III) Co(I1)
100 100 20 10 2 15
WVI)
80
Th(IV)
30
Ti(IV)
1
Sn(I1) Sb(II1) Ni(I1)
100 30 15
Cr(V1)
50
Cr(VI), Ca(II), Bi(V)f As(V) PbUI) Hg(II), Mg(II), Ba( II)
Ce(IV) Cd(I1)
Mn(II), SrUI),
597
COMMUNICATIONS
5 20 20 40 50 100
parameters
(V 5 pg/ml in the aqueous
0.2 0.99
0.5 1.005
2.0-3.0 1.03
5.0 1.01
1.0 1.016
2.0-4.0 1.03
020
s 46 $ 2
010
0 400
350
450
500
550
x, “rn Fig. 1. Absorption spectrum of V(III)-oxinate; (b) 0.4 pg/ml of solvent phase. of diverse elements Colour of extract Yellowish green Yellow Yellow Yellow Blackish brown Yellow
Faintly
yellow
Faintly
yellow
Yellow Yellow Greenish Yellow
yellow
Masking
agent9
SSAt(0.4 g) SSAt(0.4 g) SSAt(0.4 g) SSAt(0.4 g) SSAt(0.4 g) SSAt(0.4 g) or cyanide (0.2 g) Tartrate (0.5 g) Citrate (0.05 g) Tartrate (2.0 g) TGAI(0.6 ml) TGAI(0.6 ml) Cyanide (0.2 g) Ascorbic acid (l.Og)
Colourless Colourless Colourless Colourless Colourless Colourless
* For an absorbance < 0.002, in presence of masking agent, if any. !Added after reduction by sodium dithionite unless otherwise stated; cyanide were added as potassium salts and tartrate as the sodium salt. t SSA = sulphosahcylic acid. ’ TGA = thioglycollic acid added before reduction. $ Precipitates formed after dithiomte reduction were filtered off before extraction.
-
and
citrate
V-a)
0.8,
598
SHORT
COMMUNICATIONS
On reduction with sodrum dithionite at pH 3-7, mercury and lead give black, arsenic brown and cadmium yellow sulphlde precipitates; strontium and barium give white precipitates of their sulphates. These precipitates need not be filtered off as they do not affect the extraction of vanadium. Any slight emulsion appearing at the interface is removed in the filtration of the organic phase. Bismuth and copper form black sulphide precipitates which should be filtered off before the extraction. Even then, some copper seems to be left, giving a yellow solution after extraction with oxine m carbon tetrachlorlde. This can be prevented by masking with sulphosalicyhc acid after the reduction. Other elements, such as alummium, zinc, uranium, iron, cobalt, mckel, titanium, antimony, tin and chromium give yellow or yellowish green solutions because of extraction of their oxinates. This can be prevented (up to the tolerance limit) by using the masking agents shown in Table 3. Addition of sulphosalicylic and thioglycollic acids lowers the pH but the same maximum extraction 1s obtained by increasing the time of equilibration to 4 min in the first extraction. When the vanadium sample solution IS brought to the desired pH, some of the hydrolysable ions precipitate. Dithiomte is added without filtration of these precipitates as they do not interfere with the process of extraction. Only m the case of tin and antimony is thioglycolhc acid to be added to the neutral solution before the reduction. Under these conditions, tin does not give any precipitate but antimony gives the orange-red sulphide which remains at the Interface. If thioglycollic acid is not added, tm and antimony sulphldes are precipitated and give an emulsion on shaking with the solvent. The thioglycollic acid also prevents the extraction of oxinates of these elements. In the case of titanium, the vanadium is adsorbed on the hydrolytic precipitate and hence the tolerance is very low. Molybdenum gives a brown precipitate on shaking with oxme m carbon tetrachlonde, forming unbreakable emulsions and being partly extracted. Therefore, molybdenum must be separated. The tolerance limits cannot be raised because of the upper limits of masking agents for vanadium extraction. Applications The sensitivity of the method is double that obtained by usmg oxine or its derivatives with vanadium(V) and 1s rarely exceeded by other photometric methods for vanadium. With the masking agents suggested, the limits of tolerance of interfermg elements are much higher than in the other methods. Only molybdenum interferes seriously. The reduction of V(V) to V(III) by dithlonite is very convement and rapid. The method uses ordinary reagents and takes 10 min or less m series. The use of a single heavier solvent is also an advantage.
Table 4. Analysis
of samples
Sample
composition
by the proposed
V added, ,u9
Matrix* Fe(l.7) Cr(0.24) Co(O.OlS)t Fe(l.5) Cr(O.12) W(O.35)$ Sn(40) Sb(15) Ce(5) Th(30) W(50) Rutile (V = 0.125x)$ Ilmenite (V = 0.0911%)$
* The number of mg of the element for analysis is given in brackets. t Analogous to Crocar. $ Analogous to High Speed Steel. $ By ferron method
15 6 40 40 30
method
V found, p(9 15.0 5.9, 6.0 40.3 40.0 30.0, 30.1 0.125% 0.0912%
m the ahquot
The scope and apphcabdlty of the method the satisfactory analysis of different synthetic of rutile and ilmenite (Table 4).
taken
is shown by samples and
Acknowledgements-The authors sincerely thank Prof. S. M. Mukherji, Head of the Chemistry Department, for facdities and S.P.A. is also grateful to the U.G.C., New Delhi, for a Junior Research Fellowship. REFERENCES
1. H. Goto and S. Ekeda, Nippon Kagaku Zasshl, 1958, 79, 152. 2. Y. V. Karyakin and A. V. Zaval’skaya, Zh. Anaht. Khim., 1968, 23, 1742. 3. I. A. Tserkovmtskaya and V. V. Perevoshchikova, rbfd., 1972, 27, 1111. 4. T. T. Lai and S. N. Chen, J. Chinese Chem. SK, 1962, Ser. II, 9, 249. 5 G. G. Rao and P. K. Rao, Talanta, 1966, 13, 1336. 6. V. S. Syrokomski and Y. V. Klimenko, Vanadometry (in Russian), Metallurglzdat, Moscow, 1950). 7. K. Kodama, Methods of Quantitative lnorganlc Analysis, p. 291 Interscience, New York, 1963. 8. G. Charlot and D. Bezier, Quantltatwe Inorgamc Analysis, p. 306. Methuen, London, 1957. 9. L. S. A. Dlkshltulu and D. Satyanarayana, Indian J Chem., 1974, 12, 180. 10. Gmelin, Handbuch Der Anorganischen Chenae, Vanadium, Teil B- Lieferung 2, p. 705,. Verlag Chemie, Weinheim/Bergstr., 1968.
Summary-Vanadium(V) is rapidly reduced by dithionite to V(II1) which is extracted as the oxinate mto carbon tetrachloride. Vanadium is determined by measuring absorbance of the complex at nn,rx = 42c-425 nm with a sensitivity of 0.004 pg/cm* and Beer’s law range of O-7 pg/ml. Several mg of some important elements can be tolerated if they are masked. Molybdenum Interferes seriously The method has been applied to synthetic samples, rutile and ilmenite with satisfactory results. Using ordinary reagents and taking 10 mm or less in series for a determmation, the method has a sensltivlty rarely exceeded by others with a much higher tolerance for other elements.
SHORT COMMUNICATIONS Vol 23,pp 596598 PergamonPress. 1976Prmtedm GreatBr~tam
SP~CTROPHOTO~ETRIC
V. Department
of Chemistry,
D~TER~I~ATIO~ V(II1) OXINATE YATIRAJAM
Kurukshetra
OF VANADIUM
and S. P. ARYA
University,
Kurukshetra
132119, Haryana,
(Receiaed 22 October 1975. Accepted 13 January
Almost all the numerous photometric methods for vanadium determmatmn are based on vanadium(V) complexes. Only a few are based on vanadmm(IV) complexes. There are even fewer methodslm4 based on vanadium(II1). Although some of them are highly sensitive, it would be advantageous to have methods with higher tolerance limits to anafyttcally important elements to avoid prehminary separations. The limitation in usmg vanadium(III) appears to be its production and the stability of tts complexes amalgam6 or stannous chloride4 reduction Electrolytic,’ IS frequently used for producmg vanadium(II1). A greater choice of reagents and condittons should be posstble if introduction of metal tons can be avoided in the reduction. Accordmgly, we present below a method of producing vanadium(II1) by sodium dithionite reduction and its extraction by oxine for its spectrophotometric determination.
EXPERIMENTAL
Reagents and solutzons Vanadium solution. A stock solution (10 mg of V/ml) was prepared from sodium metavanadate and standardized by suitable dilution gave lOO- and the oxine method;7 lo-flgcglml solutions. 8-Hydroxyqutnoline. A 2% solution in carbon tetrachloride. Solutions of’ other elements. Prepared by dissolvmg suitable salts in water or dilute sulphunc acid to give 10 or 1 mg of element per ml. Samples. Synthetic samples were prepared by mixing solutions of the ions to give the required compositions (see Table 4). Rutile and Yemenite Finely powdered sample (1.0 g) was fused’ with 5 g of fusion mixture in a platinum crucible for nearly 30 mm. The melt was cooled and taken up m hot water. The msoluble restdue was filtered off on Whatman No. 41 paper and washed 4 times with 5 ml of hot water each time. The filtrate was just acidified to htmus wtth dilute sulphurtc acid and boiled to expel carbon dioxide. Any precipitate was filtered off, and washed twice with 5-ml portions of hot water. The filtrate and washings were cooled and made up to 5 ml. Aliquots of this solution were then used for the determinatton of vanadium by the procedure. Determination procedure To 20 ml of solution containing < 175 pg of vanadium at pH 3-10, in a 150-ml separatory funnel, solid sodium dithiomte (05-2.Og) was added. After wattmg for 2 mm the funnel was stoppered and shaken gently for 2 min with lOm1 of the oxine solution in carbon tetrachloride, can bemg taken to release the pressure occasionally. After tht. layers had separated, the solvent phase was removed and passed through Whatman No. 41 paper (moistened with carbon tetrachlortde) into a 25-ml volumetric flask. The extraction was repeated wtth another 1Oml of the oxine
AS
India
1976)
solution. Any complex sticking to the filter paper was washed mto the flask, with oxine solution added dropwise. The solutton was made up to the mark with carbon tetrachloride and mixed. The absorbance of the yellow complex was measured in l-cm cells at 420 nm with a Beckman DU sp~trophotometer~ against a stmdarly treated reagent blank. The latter gave an absorbance of 0.006 against oxme in carbon tetrachloride. Samples containing other elements. Masking agents were added after the reduction to vanadium(III), as shown m Table 3. In the case of tungsten, the tartrate was added to the solution at pH 8.5-10, before reduction. RESULTS AND DISCUSSION
When sodmm dtthionite is added to mg amounts of vanadium(V) in slightly alkaline or acid solution, the pH decreases gradually, depending upon the amount of the reductant. The green solution obtained shows an absorption spectrum similar to the one obtamed for vanadium(II1) prepared by electrolyttc reduction’ or mercury reductor.’ When the solutton is shaken with oxine m carbon tetrachloride a yellow complex is extracted quantitatively, showing an absorption peak at 420nm. An initial pH of 3-10 before addition of dtthionite gives a constant absorbance; the absorbance is lower if the inittal pH is outside this range. Carbon tetrachloride is found to be the best solvent (Table l), giving the highest absorbance. A single extraction with 10ml of solvent was made from 20ml of aqueous phase. The colour 1s not stable m other solvents except benzene, and in it has lower absorbance at the same L,X. The effect of vartous parameters on the V(III)-oxmate absorbance in carbon tetrachloride is shown in Table 2. the other conditions in each study being kept at the lower end of the optimum range. The optimum condittons for maximum absorbance are, inmal pH of the aqueous phase 3-10, reduction with 0.552.0 g of sodium dithtonite, 2 mm waiting after mtxing and 2-3 min equtlibration with l-4”,; oxine solution in carbon tetrachloride. A single extractton with oxme m carbon tetrachloride removes more than 99’%; of the vanadmm but a second extraction with 10 ml of the solvent ts recommended for 100% recovery On the basis of Job’s curves. the extracted specres has a 3: I hgand:metal composition.” The species has an Table 1. Absorbance different solvents
of vanadium(III)-oxmate complex (V 5 pg/ml m the aqueous phase)
Solvent Carbon tetrachlorlde Benzene Chloroform Methyl isobutyl ketone Amy1 acetate Amy1 alcohol
Absorbance 103 0.995 0.858 0.940 0.920 0.662
in
SHORT
Table 2. Dependence
Oxine/CCl,, Absorbance
of the V(III)-oxinate
%
Sodium dlthionite, Absorbance Time of contact, Absorbance
g
min
extraction on different phase)
0.02 0.70
0.05 0.96
0.1 0.98
0.1 0.7
0.2 0.98
0.5-2.0 1.03
0.25 0.93
0.5 1.00
1.0 1.01
absorption maximum at 42@425 nm, with sensitivity for vanadium of 0.004 pg/cm2 (Fig. 1). At wavelengths shorter than 370nm, the blank absorbs highly. There 1s no other peak at wavelengths up to 850 nm even at 0.8 mg/ml vanadium concentration. Beer’s law is obeyed up 7 pg of V per ml of solvent phase. The absorbance remains constant for 45 min Eflect of diverse
ions
Sodium chloride (5 g), sulphate (5 g), tartrate (2 g), acetate (3 g), thiourea (1 g) and ascorbic acid (1 g) have no effect on the extraction of vanadium. Only limited amounts of sulphosalicylic acid (0.4 g), thioglycollic acid (0.6 ml) and potassium cyamde (0.2g) can be tolerated. Nitrate can be tolerated up to 5 mg/ml. Phosphate (2 g of the sodium salt) decreases the extractlon. Fluoride and oxalate in > 50 mg/ml and EDTA m > 5 mg/ml concentrations mask the vanadium extraction completely. Table
3. Extraction
Tolerance hmit mg/20 ml*
Element Al(II1) Zn( II) Cu(II)f WI) Fe(III) Co(I1)
100 100 20 10 2 15
WVI)
80
Th(IV)
30
Ti(IV)
1
Sn(I1) Sb(II1) Ni(I1)
100 30 15
Cr(V1)
50
Cr(VI), Ca(II), Bi(V)f As(V) PbUI) Hg(II), Mg(II), Ba( II)
Ce(IV) Cd(I1)
Mn(II), SrUI),
597
COMMUNICATIONS
5 20 20 40 50 100
parameters
(V 5 pg/ml in the aqueous
0.2 0.99
0.5 1.005
2.0-3.0 1.03
5.0 1.01
1.0 1.016
2.0-4.0 1.03
020
s 46 $ 2
010
0 400
350
450
500
550
x, “rn Fig. 1. Absorption spectrum of V(III)-oxinate; (b) 0.4 pg/ml of solvent phase. of diverse elements Colour of extract Yellowish green Yellow Yellow Yellow Blackish brown Yellow
Faintly
yellow
Faintly
yellow
Yellow Yellow Greenish Yellow
yellow
Masking
agent9
SSAt(0.4 g) SSAt(0.4 g) SSAt(0.4 g) SSAt(0.4 g) SSAt(0.4 g) SSAt(0.4 g) or cyanide (0.2 g) Tartrate (0.5 g) Citrate (0.05 g) Tartrate (2.0 g) TGAI(0.6 ml) TGAI(0.6 ml) Cyanide (0.2 g) Ascorbic acid (l.Og)
Colourless Colourless Colourless Colourless Colourless Colourless
* For an absorbance < 0.002, in presence of masking agent, if any. !Added after reduction by sodium dithionite unless otherwise stated; cyanide were added as potassium salts and tartrate as the sodium salt. t SSA = sulphosahcylic acid. ’ TGA = thioglycollic acid added before reduction. $ Precipitates formed after dithiomte reduction were filtered off before extraction.
-
and
citrate
V-a)
0.8,
598
SHORT
COMMUNICATIONS
On reduction with sodrum dithionite at pH 3-7, mercury and lead give black, arsenic brown and cadmium yellow sulphlde precipitates; strontium and barium give white precipitates of their sulphates. These precipitates need not be filtered off as they do not affect the extraction of vanadium. Any slight emulsion appearing at the interface is removed in the filtration of the organic phase. Bismuth and copper form black sulphide precipitates which should be filtered off before the extraction. Even then, some copper seems to be left, giving a yellow solution after extraction with oxine m carbon tetrachlorlde. This can be prevented by masking with sulphosalicyhc acid after the reduction. Other elements, such as alummium, zinc, uranium, iron, cobalt, mckel, titanium, antimony, tin and chromium give yellow or yellowish green solutions because of extraction of their oxinates. This can be prevented (up to the tolerance limit) by using the masking agents shown in Table 3. Addition of sulphosalicylic and thioglycollic acids lowers the pH but the same maximum extraction 1s obtained by increasing the time of equilibration to 4 min in the first extraction. When the vanadium sample solution IS brought to the desired pH, some of the hydrolysable ions precipitate. Dithiomte is added without filtration of these precipitates as they do not interfere with the process of extraction. Only m the case of tin and antimony is thioglycolhc acid to be added to the neutral solution before the reduction. Under these conditions, tin does not give any precipitate but antimony gives the orange-red sulphide which remains at the Interface. If thioglycollic acid is not added, tm and antimony sulphldes are precipitated and give an emulsion on shaking with the solvent. The thioglycollic acid also prevents the extraction of oxinates of these elements. In the case of titanium, the vanadium is adsorbed on the hydrolytic precipitate and hence the tolerance is very low. Molybdenum gives a brown precipitate on shaking with oxme m carbon tetrachlonde, forming unbreakable emulsions and being partly extracted. Therefore, molybdenum must be separated. The tolerance limits cannot be raised because of the upper limits of masking agents for vanadium extraction. Applications The sensitivity of the method is double that obtained by usmg oxine or its derivatives with vanadium(V) and 1s rarely exceeded by other photometric methods for vanadium. With the masking agents suggested, the limits of tolerance of interfermg elements are much higher than in the other methods. Only molybdenum interferes seriously. The reduction of V(V) to V(III) by dithlonite is very convement and rapid. The method uses ordinary reagents and takes 10 min or less m series. The use of a single heavier solvent is also an advantage.
Table 4. Analysis
of samples
Sample
composition
by the proposed
V added, ,u9
Matrix* Fe(l.7) Cr(0.24) Co(O.OlS)t Fe(l.5) Cr(O.12) W(O.35)$ Sn(40) Sb(15) Ce(5) Th(30) W(50) Rutile (V = 0.125x)$ Ilmenite (V = 0.0911%)$
* The number of mg of the element for analysis is given in brackets. t Analogous to Crocar. $ Analogous to High Speed Steel. $ By ferron method
15 6 40 40 30
method
V found, p(9 15.0 5.9, 6.0 40.3 40.0 30.0, 30.1 0.125% 0.0912%
m the ahquot
The scope and apphcabdlty of the method the satisfactory analysis of different synthetic of rutile and ilmenite (Table 4).
taken
is shown by samples and
Acknowledgements-The authors sincerely thank Prof. S. M. Mukherji, Head of the Chemistry Department, for facdities and S.P.A. is also grateful to the U.G.C., New Delhi, for a Junior Research Fellowship. REFERENCES
1. H. Goto and S. Ekeda, Nippon Kagaku Zasshl, 1958, 79, 152. 2. Y. V. Karyakin and A. V. Zaval’skaya, Zh. Anaht. Khim., 1968, 23, 1742. 3. I. A. Tserkovmtskaya and V. V. Perevoshchikova, rbfd., 1972, 27, 1111. 4. T. T. Lai and S. N. Chen, J. Chinese Chem. SK, 1962, Ser. II, 9, 249. 5 G. G. Rao and P. K. Rao, Talanta, 1966, 13, 1336. 6. V. S. Syrokomski and Y. V. Klimenko, Vanadometry (in Russian), Metallurglzdat, Moscow, 1950). 7. K. Kodama, Methods of Quantitative lnorganlc Analysis, p. 291 Interscience, New York, 1963. 8. G. Charlot and D. Bezier, Quantltatwe Inorgamc Analysis, p. 306. Methuen, London, 1957. 9. L. S. A. Dlkshltulu and D. Satyanarayana, Indian J Chem., 1974, 12, 180. 10. Gmelin, Handbuch Der Anorganischen Chenae, Vanadium, Teil B- Lieferung 2, p. 705,. Verlag Chemie, Weinheim/Bergstr., 1968.
Summary-Vanadium(V) is rapidly reduced by dithionite to V(II1) which is extracted as the oxinate mto carbon tetrachloride. Vanadium is determined by measuring absorbance of the complex at nn,rx = 42c-425 nm with a sensitivity of 0.004 pg/cm* and Beer’s law range of O-7 pg/ml. Several mg of some important elements can be tolerated if they are masked. Molybdenum Interferes seriously The method has been applied to synthetic samples, rutile and ilmenite with satisfactory results. Using ordinary reagents and taking 10 mm or less in series for a determmation, the method has a sensltivlty rarely exceeded by others with a much higher tolerance for other elements.