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Polarographic determination of indium(III) after salting-out extraction of the bromide complex into acetonitrile
Tulonru. Vol. 26, pp. 987 10 990 0 Pergamon Press Ltd 1979. Prmted in Great Britain
0039-9140/79/l
1014987102.00/0
POLAROGRAPHIC DETERMINATION OF INDIUM(II1) AFTER SALTING-OUT EXTRACTION OF THE BROMIDE COMPLEX INTO ACETONITRILE Y. NAGAOSA Faculty of Engineering, Fukui University, 3-chome, Bunkyo, Fukui, 910 Japan (Received 7 February
1979. Accepted 16 May 1979)
Summary-A simple and sensitive method has been developed for the polarographic determination of indium(II1) after solvent extraction into acetonitrile, salted-out from aqueous solution with sodium bromide. The extracted indium(III)-bromide complex gives a well-defined d.c. wave with E,,2 = -0.69 V vs. SCE. The wave-height is directly proportional to the concentration of indium(II1) from 1.6 x lO-6 to 3.0 x 10-4M with respect to the original aqueous solution. In the a.c. polarographic method, a linear calibration curve is obtained for indium(II1) over the concentration range from 1.6 x 10e6 to 1.5 x 10-‘M, and interference from most foreign ions can be eliminated. In particular, 10.0 mg of Fe(II1) and 2.5 mg of Tl(II1) are tolerated when 1.0 g of ascorbic acid is added. The lower limit of determination is 8 x 10e8M indium(II1) by the square-wave polarographic method.
in aqueous solution can be determined polarographically with good sensitivity, as it undergoes a reversible three-electron reduction at a drop ping mercury electrode.’ Interference from Cd(II), Tl(II1) and Pb(I1) is avoided by adding a suitable complexing agent such as potassium iodide’ or potassium chloride.’ A solvent-extraction procedure has been used for the removal of major constituents such as Tl(II1) and Fe(III), before polarographic determination of indium(III).4 Several studies have been reported on the direct polarographic determination of indium(II1) after solvent extraction with oxine,’ DDTC6 or acetylacetone.’ Although these extraction-polarographic methods are sensitive and selective, they are troublesome to use because the extract has to be mixed with other solvents for the polar@ graphic measurement. It was the aim of the present study to develop a simple and selective procedure for the extraction-polarographic determination of indium(II1). In a previous investigation,* acetonitrile (AN) was exploited as the solvent for an extraction-polarographic determination of cadmium(I1) based on the fact that the solvent can be separated from its aqueous solution by salting-out with ammonium sulphate. In the present study, this polarographic method of analysis has been applied to the direct determination of indium(II1) in the AN extract, in which the ion is isolated and concentrated from aqueous solution. Sodium bromide is used as both the salting-out agent for the phase separation and the complexing ligand for the indium, and tetrabutylammonium bromide (TBAB) as both the counter-ion in the extracted ion-pair and the supporting electrolyte in the polarographic measurement. The proposed method is simple, selective and sensitive.
EXPERIMENTAL
Indium(II1)
TAL. 2611I-A
Apparatus
A Yanagimoto polarograph, Model PA-202, was used or square-wave (swf polarography. Other instiuments used were the same as described previouslv.” The DME had the following characteristics: m = 0.783 &/sec, t = 4.70 s&z in AN at a mercury head of 6O:Ocm. Standard indium(lZ1) solution. Indium sulphate (0.339 g) was dissolved in 1 litre of water containing a small amount of shlphuric acid, to give an approximately 10e3M solution which was then standardized by complexometric titration. Sodium bromide (Wako Junyaku Chemicals) and TBAB (Tokyo Kasei Chemicals) were used without further purification. AN was purified by distillation once from phosphorus pentoxide to remove reducible impurities.’ Other reagents were of guaranteed reagent grade. Procedure
To 25.0 ml of acidic aqueous solution containing indium: (III), 20.0 ml of 0.05M TBAB solution in AN were added, ‘followed by IS.0 g of sodium bromide as the salting-out agent. The mixture was shaken for 1 min. then allowed to stand for 1 min. A portion of the extract was transferred into a polarographic cell, deaerated with nitrogen gas for 3 min, and the polarogram was recorded (us. S.C.E.) at 25 + 0.1”. RESULTS AND DISCUSSION
Ternary
phase diagram
Acetonitrile is separated from aqueous solutions by salting-out with sodium bromide. In this investigation the volumes of the resulting phases were measured when different amounts of sodium bromide were added to water-AN mixtures. The results are shown in Fig. 1. The ternary diagram obtained is expressed in terms of percentage by weight and represents the
Y.
988
NAGAOSA Table 1. Effect of tetrabutylammonium bromide (TBAB) concentration on the d.c. wave- and a.c. peak-heights for IO-‘M In(III)
100
TBAB, M
id, IAA
i,
0.005 0.010 0.025 0.040 0.050 0.060 0.075 0.100
0.276 0.252 0.255 0.248 0.240 0.240 0.211
218 222 215 210 204 196 190 169
Volume of AN recovered, ml
El/z, V
10.0 10.0
-0.68
10.1 10.2 10.3 10.5 10.8
-0.69 -0.69 -0.69 -0.70 -0.71
11.0
-0.73
NaBr
Fig. I. Phase diagram of acetonitrile/water/sodium hromide 1, VW/V,= I; 2, VW/V,= 2; 3, VW/V,= 5; 4. VW/V, = 10; 5 represents the compositions producing a homogeneous solution on dilution with water.
of water, AN and sodium bromide mixtures. The dotted line indicates the compositions from which a homogeneous solution is produced on addition of an excess of water, while the solid lines represent the compositions for which the volume-ratios of the two phases (VW/V,)are 1, 2, 5 and 10 after phase separation. The volume-ratio was 3.9 under the conditions of the procedure described. composition
Polarograms
Figure 2 illustrates the d.c. and a.c. polarograms of several metal bromides observed under the conditions described. The available potential range is from -0.36 to - 1.45 V us. SCE. The extracted In(M) complex gave a well-defined d.c. wave with E 1,2 = -0.69 V and a sharp a.c. peak at the same potential. The d.c. wave of In(II1) was diffusion controlled, and represented a three-electron reaction. The polarographic determination of the In(II1) is considered to be reasonably selective since the E,,, is In(m) 2
O.~JIA
0.15 V or more apart from those of the other metal complexes. The Tl(II1) complex gave two d.c. waves with Elj2 = -0.35 and -0.54 V. The second wave, which corresponds to T&I) 4 Tl(0) exhibited a maximum and the a.c. peak was distorted. The Pb(I1) complex gave a dc. wave with maxima and a fair a.c. peak at -0.45 V. An ill-defined d.c. wave and no a.c. peak were observed in the caSe of the Cd(I1) complex. Effect of TBAB concentration
Table 1 shows the effect of increasing TBAB con-’ centration on the dc. and a.c. polarographic waves for an initial concentration of 10-‘M In(II1). It was noted that the d.c. polarogram became well-defined at TBAB concentration above O.OlM. As the concentration of TBAB is increased, the dc. wave-height (id) and a.c. peak-height (i,) decrease and the half-wave potential shifts towards more negative potentials. The decrease in the heights is probably ascribable to increase in the final volume and the viscosity of the AN phase and a salting-in effect due to TBAB. The shift of the E,,Z is mainly correlated with the increase in the TBAB concentration of the AN phase, where In(m)
f40 Tl(Ill
scale units
!+ Tl(m)
E
vs
SCE, V
Fig 2. Polarograms (d.c. and ac.) of various metal bromides after extraction into acetonitrile. [Tl(III) 1 2.55 x 10e5M, [Pb(II)] 2.41 x IO-‘M, [In( III)] __ 1.44 x 10v5M, fCd(II)] 4.46 x 10e5M. The broken line is the d.c. polarogram of 1.44 x 10F5M In@I) in.i.C IM NaBr.
Polarographic
determination
989
of indium(II1)
0 10
5
Fig 3. Effect of sodium bromide concentration
25
20
15
NaBr ,
g
on d.c. wave-height and a.c. peak-height for 10-5M In(II1).
TBAB acts as both the counter-ion in the complex extracted and the supporting electrolyte. The 10.0 ml of extract obtained by following the recommended procedure had an electrolytic conductivity of 1.73 x lo-’ ohm-‘.cm-‘, a water content of 14.70/ a viscosity of 0.463 cP, and a sodium bromide content of 68.0 mg (0.066/M).A concentration of O.OSMTBAB in AN was chosen as being most suitable for the reagent. Effect of sodium bromide concentration The amount of sodium bromide taken was varied between 7.0 and 25.0 g. The results are shown in Fig. 3, from which it can be seen that i, and i, were approximately constant for the addition of amounts between 10 and 20 g. The volume of AN phase recovered increased with increasing amounts of sodium bromide up to 10 g, and became constant for amounts between 10 and 25 g. The half-wave potential shifted towards more negative potentials with increasing amounts of the salt, probably because of increase in
the sodium bromide concentration in the AN phase, since the TBAB concentration in the AN phase remained constant. Hence 15 g was the amount of sodium bromide chosen for use in the standard procedure. Effect of volume of aqueous phase
Values of i, and i, were obtained for extractions from different volumes of the original aqueous phase from 15 to 35 ml, as shown in Fig. 4. The heights increased greatly with increasing volume of the aqueous phase, because of the high degree of extraction and the decrease in volume of the AN phase. The volume of original aqueous phase taken must therefore be kept constant (25.0 ml). Efict of pH
Extractions were carried out at different pH-values, by addition of l.OM sulphuric acid or 1.0~ sodium hydroxide. Figure 5 shows the plots of i, and
adjusted
200
0.3
300
4 5 - 0.2 .P
200
100
a .r
p. .r
100
0.1
0
0 15 Initial
20 volume
25
30 of
aqueous
35
012 ~0117..
ml
Fig. 4. Effect of initial volume of aqueous phase on d.c. wave-height and a.c. peak-height for lo-‘A4 In(II1).
3
4
5
6
PH
Fig. 5. Effect of pH on d.c. wave-height and a.~. peakheight for IO-‘A4 In(II1).
Y. NAGAOSA
990 Table 2. Effect of diverse ions on the determination 27.7 pg of indium(III)
Species added Cu(II)’
Fe(III)* Fe + ascorbic acid, 1 g Pb(II)* Cd(H) Tl(III)* Tl + ascorbic acid, 1 g Hg(II)* Bi(III)* Ca(I1) Al(II1) NiIII)
ZniIi) Co(II)
AidI) FPO:SCN -
Amount of indium(II1) added, found, mg &I 0.5 0.5 10.0
2.5
IO.0 0.5 2.5 0.5 0.5
116.0 100.0 100.0 100.0 100.0 1.0 12.9 13.2 11.4 12.9 116.0 10.2 1.0 1.0 1.0
27.9 27.1 29.7 28.0 27.4 28.5 28.6 26.8 28.2 28.7 27.5 27.8 28.0 26.8 26.2 26.5 27.1 27.9 27.3 26.1 27.5 27.4 25.5 27.3
of
Error,? % +0.9 -2.1 +0.9 +1.4 -0.9 +3.1 +3.3 -3.2 +1.9 +3.8 -0.7 +0.2 +1.3 -3.2 -5.3 -4.3 -2.0 +0.9 -1.4 -5.8 -0.5 -0.8 -8.0 -1.4
* Denotes maximum amount tolerable within an error of +‘4%. t Based on mean of three determinations. i, against pH of the aqueous phase after extraction. It was found that the heights were approximately constant over the pH range 0.4-4.6. Over this pH range,
the volume of AN phase recovered was constant (10.3 ml) and 99.5% of the In(II1) complex was extracted in a single extraction. Calibration curves
On the basis of these results, the procedure for the polarogrrfphic determination of In(II1) was established. The d.c. and a.c. polarograms were recorded at various concentrations of In(W), while other conditions were kept constant. The calibration curves obtained were linear over the concentration ranges 1.6 x 10m6-3.0 x 10e4M In(III) for d.c. and 1.6 x 10-6-l.5 x 10-5A4 for a.c. polarography. The diffusion current constant of In(W) in the AN extract was 9.50 @. 1.mmole-’ . mg-2’3. se~‘/~, about 4
times that obtained in 1M aqueous sodium bromide, as shown in Fig. 2. The relative standard deviation was 2.1% for 27.7 pg of indium(II1) (10 determinations by a.c. polarography). E$ect of diverse ions
Possible interferences were investigated by a.c. polarography, which gave considerably better resolu, tion for substances reduced at potentials close to each other. The results are summarized in Table 2. Cu(II), Fe(III), Pb(II), Cd(H), Tl(III), H&II) and Bi(III) were found to be tolerable at the levels tested. The interference caused by 10.0 mg of Fe(II1) and 2.5 mg of Tl(III) could be eliminated by the addition of 1.0 g of ascorbic acid before the extraction step. Other cations such as Al(W), Ni(II), Zn(I1) and Mn(I1) showed no effect on the determination. Among the anions tested, MnO;, CrO:- and EDTA interfere seriously even in small amounts and must be excluded. Thiosulphate and tungstate were tolerable at levels up to 1 mg. Square-wave polarography
Since the extract had a high electrical conductivity, an attempt was made to use square-wave polarography. It was found that a sharp peak for In(II1) was observed at -0.69 V and that the lower limit of determination was 8 x IO-‘M (9 ppM) with respect to the original aqueous phase. Acknowledgements-The author wishes to express his sincere thanks to Professor Taitiro Fujinaga of Kyoto University and to Dr. Masatada Satake of Fukui University for their valuable advice and discussion during the research. REFERENCES 1. L. Meites, Polurographic Techniques, 2nd Ed., Interscience, New York, 1967. 2. H. Uehara, Rev. Polarog. (Kyoto), 1959,7, 81. 3. B. Breyer, F. Getmann and S. Hacobian, Australian J. Chem., 1950, A3, 567. 4. F. A. Pohl and W. Bensels, Z. Anal. Chem., 1958, 161, 108. .5 T. Fujinaga and B: K. Puri, Talanta, 1975, 22, 71. 6. T. Fujinaga, H. A. Brodowsky, T. Nagai and K. Yamashita, Rev, Polurog. (Kyoto), 1963, 11, 217. 7. B. K. Afghan, R. M. Dagnall and K. C. Thompson, Talanta, 1967, 14, 715. 8. T. Fujinaga and Y. Nagaosa, Chem. Mt., 1978, 587. 9. J. F. Coetzee, G. P. Cunningham, D. K. McGuire and G. R. Padmanabhan, Anal. Chem.. 1962, 34, 1139.
0039-9140/79/l
1014987102.00/0
POLAROGRAPHIC DETERMINATION OF INDIUM(II1) AFTER SALTING-OUT EXTRACTION OF THE BROMIDE COMPLEX INTO ACETONITRILE Y. NAGAOSA Faculty of Engineering, Fukui University, 3-chome, Bunkyo, Fukui, 910 Japan (Received 7 February
1979. Accepted 16 May 1979)
Summary-A simple and sensitive method has been developed for the polarographic determination of indium(II1) after solvent extraction into acetonitrile, salted-out from aqueous solution with sodium bromide. The extracted indium(III)-bromide complex gives a well-defined d.c. wave with E,,2 = -0.69 V vs. SCE. The wave-height is directly proportional to the concentration of indium(II1) from 1.6 x lO-6 to 3.0 x 10-4M with respect to the original aqueous solution. In the a.c. polarographic method, a linear calibration curve is obtained for indium(II1) over the concentration range from 1.6 x 10e6 to 1.5 x 10-‘M, and interference from most foreign ions can be eliminated. In particular, 10.0 mg of Fe(II1) and 2.5 mg of Tl(II1) are tolerated when 1.0 g of ascorbic acid is added. The lower limit of determination is 8 x 10e8M indium(II1) by the square-wave polarographic method.
in aqueous solution can be determined polarographically with good sensitivity, as it undergoes a reversible three-electron reduction at a drop ping mercury electrode.’ Interference from Cd(II), Tl(II1) and Pb(I1) is avoided by adding a suitable complexing agent such as potassium iodide’ or potassium chloride.’ A solvent-extraction procedure has been used for the removal of major constituents such as Tl(II1) and Fe(III), before polarographic determination of indium(III).4 Several studies have been reported on the direct polarographic determination of indium(II1) after solvent extraction with oxine,’ DDTC6 or acetylacetone.’ Although these extraction-polarographic methods are sensitive and selective, they are troublesome to use because the extract has to be mixed with other solvents for the polar@ graphic measurement. It was the aim of the present study to develop a simple and selective procedure for the extraction-polarographic determination of indium(II1). In a previous investigation,* acetonitrile (AN) was exploited as the solvent for an extraction-polarographic determination of cadmium(I1) based on the fact that the solvent can be separated from its aqueous solution by salting-out with ammonium sulphate. In the present study, this polarographic method of analysis has been applied to the direct determination of indium(II1) in the AN extract, in which the ion is isolated and concentrated from aqueous solution. Sodium bromide is used as both the salting-out agent for the phase separation and the complexing ligand for the indium, and tetrabutylammonium bromide (TBAB) as both the counter-ion in the extracted ion-pair and the supporting electrolyte in the polarographic measurement. The proposed method is simple, selective and sensitive.
EXPERIMENTAL
Indium(II1)
TAL. 2611I-A
Apparatus
A Yanagimoto polarograph, Model PA-202, was used or square-wave (swf polarography. Other instiuments used were the same as described previouslv.” The DME had the following characteristics: m = 0.783 &/sec, t = 4.70 s&z in AN at a mercury head of 6O:Ocm. Standard indium(lZ1) solution. Indium sulphate (0.339 g) was dissolved in 1 litre of water containing a small amount of shlphuric acid, to give an approximately 10e3M solution which was then standardized by complexometric titration. Sodium bromide (Wako Junyaku Chemicals) and TBAB (Tokyo Kasei Chemicals) were used without further purification. AN was purified by distillation once from phosphorus pentoxide to remove reducible impurities.’ Other reagents were of guaranteed reagent grade. Procedure
To 25.0 ml of acidic aqueous solution containing indium: (III), 20.0 ml of 0.05M TBAB solution in AN were added, ‘followed by IS.0 g of sodium bromide as the salting-out agent. The mixture was shaken for 1 min. then allowed to stand for 1 min. A portion of the extract was transferred into a polarographic cell, deaerated with nitrogen gas for 3 min, and the polarogram was recorded (us. S.C.E.) at 25 + 0.1”. RESULTS AND DISCUSSION
Ternary
phase diagram
Acetonitrile is separated from aqueous solutions by salting-out with sodium bromide. In this investigation the volumes of the resulting phases were measured when different amounts of sodium bromide were added to water-AN mixtures. The results are shown in Fig. 1. The ternary diagram obtained is expressed in terms of percentage by weight and represents the
Y.
988
NAGAOSA Table 1. Effect of tetrabutylammonium bromide (TBAB) concentration on the d.c. wave- and a.c. peak-heights for IO-‘M In(III)
100
TBAB, M
id, IAA
i,
0.005 0.010 0.025 0.040 0.050 0.060 0.075 0.100
0.276 0.252 0.255 0.248 0.240 0.240 0.211
218 222 215 210 204 196 190 169
Volume of AN recovered, ml
El/z, V
10.0 10.0
-0.68
10.1 10.2 10.3 10.5 10.8
-0.69 -0.69 -0.69 -0.70 -0.71
11.0
-0.73
NaBr
Fig. I. Phase diagram of acetonitrile/water/sodium hromide 1, VW/V,= I; 2, VW/V,= 2; 3, VW/V,= 5; 4. VW/V, = 10; 5 represents the compositions producing a homogeneous solution on dilution with water.
of water, AN and sodium bromide mixtures. The dotted line indicates the compositions from which a homogeneous solution is produced on addition of an excess of water, while the solid lines represent the compositions for which the volume-ratios of the two phases (VW/V,)are 1, 2, 5 and 10 after phase separation. The volume-ratio was 3.9 under the conditions of the procedure described. composition
Polarograms
Figure 2 illustrates the d.c. and a.c. polarograms of several metal bromides observed under the conditions described. The available potential range is from -0.36 to - 1.45 V us. SCE. The extracted In(M) complex gave a well-defined d.c. wave with E 1,2 = -0.69 V and a sharp a.c. peak at the same potential. The d.c. wave of In(II1) was diffusion controlled, and represented a three-electron reaction. The polarographic determination of the In(II1) is considered to be reasonably selective since the E,,, is In(m) 2
O.~JIA
0.15 V or more apart from those of the other metal complexes. The Tl(II1) complex gave two d.c. waves with Elj2 = -0.35 and -0.54 V. The second wave, which corresponds to T&I) 4 Tl(0) exhibited a maximum and the a.c. peak was distorted. The Pb(I1) complex gave a dc. wave with maxima and a fair a.c. peak at -0.45 V. An ill-defined d.c. wave and no a.c. peak were observed in the caSe of the Cd(I1) complex. Effect of TBAB concentration
Table 1 shows the effect of increasing TBAB con-’ centration on the dc. and a.c. polarographic waves for an initial concentration of 10-‘M In(II1). It was noted that the d.c. polarogram became well-defined at TBAB concentration above O.OlM. As the concentration of TBAB is increased, the dc. wave-height (id) and a.c. peak-height (i,) decrease and the half-wave potential shifts towards more negative potentials. The decrease in the heights is probably ascribable to increase in the final volume and the viscosity of the AN phase and a salting-in effect due to TBAB. The shift of the E,,Z is mainly correlated with the increase in the TBAB concentration of the AN phase, where In(m)
f40 Tl(Ill
scale units
!+ Tl(m)
E
vs
SCE, V
Fig 2. Polarograms (d.c. and ac.) of various metal bromides after extraction into acetonitrile. [Tl(III) 1 2.55 x 10e5M, [Pb(II)] 2.41 x IO-‘M, [In( III)] __ 1.44 x 10v5M, fCd(II)] 4.46 x 10e5M. The broken line is the d.c. polarogram of 1.44 x 10F5M In@I) in.i.C IM NaBr.
Polarographic
determination
989
of indium(II1)
0 10
5
Fig 3. Effect of sodium bromide concentration
25
20
15
NaBr ,
g
on d.c. wave-height and a.c. peak-height for 10-5M In(II1).
TBAB acts as both the counter-ion in the complex extracted and the supporting electrolyte. The 10.0 ml of extract obtained by following the recommended procedure had an electrolytic conductivity of 1.73 x lo-’ ohm-‘.cm-‘, a water content of 14.70/ a viscosity of 0.463 cP, and a sodium bromide content of 68.0 mg (0.066/M).A concentration of O.OSMTBAB in AN was chosen as being most suitable for the reagent. Effect of sodium bromide concentration The amount of sodium bromide taken was varied between 7.0 and 25.0 g. The results are shown in Fig. 3, from which it can be seen that i, and i, were approximately constant for the addition of amounts between 10 and 20 g. The volume of AN phase recovered increased with increasing amounts of sodium bromide up to 10 g, and became constant for amounts between 10 and 25 g. The half-wave potential shifted towards more negative potentials with increasing amounts of the salt, probably because of increase in
the sodium bromide concentration in the AN phase, since the TBAB concentration in the AN phase remained constant. Hence 15 g was the amount of sodium bromide chosen for use in the standard procedure. Effect of volume of aqueous phase
Values of i, and i, were obtained for extractions from different volumes of the original aqueous phase from 15 to 35 ml, as shown in Fig. 4. The heights increased greatly with increasing volume of the aqueous phase, because of the high degree of extraction and the decrease in volume of the AN phase. The volume of original aqueous phase taken must therefore be kept constant (25.0 ml). Efict of pH
Extractions were carried out at different pH-values, by addition of l.OM sulphuric acid or 1.0~ sodium hydroxide. Figure 5 shows the plots of i, and
adjusted
200
0.3
300
4 5 - 0.2 .P
200
100
a .r
p. .r
100
0.1
0
0 15 Initial
20 volume
25
30 of
aqueous
35
012 ~0117..
ml
Fig. 4. Effect of initial volume of aqueous phase on d.c. wave-height and a.c. peak-height for lo-‘A4 In(II1).
3
4
5
6
PH
Fig. 5. Effect of pH on d.c. wave-height and a.~. peakheight for IO-‘A4 In(II1).
Y. NAGAOSA
990 Table 2. Effect of diverse ions on the determination 27.7 pg of indium(III)
Species added Cu(II)’
Fe(III)* Fe + ascorbic acid, 1 g Pb(II)* Cd(H) Tl(III)* Tl + ascorbic acid, 1 g Hg(II)* Bi(III)* Ca(I1) Al(II1) NiIII)
ZniIi) Co(II)
AidI) FPO:SCN -
Amount of indium(II1) added, found, mg &I 0.5 0.5 10.0
2.5
IO.0 0.5 2.5 0.5 0.5
116.0 100.0 100.0 100.0 100.0 1.0 12.9 13.2 11.4 12.9 116.0 10.2 1.0 1.0 1.0
27.9 27.1 29.7 28.0 27.4 28.5 28.6 26.8 28.2 28.7 27.5 27.8 28.0 26.8 26.2 26.5 27.1 27.9 27.3 26.1 27.5 27.4 25.5 27.3
of
Error,? % +0.9 -2.1 +0.9 +1.4 -0.9 +3.1 +3.3 -3.2 +1.9 +3.8 -0.7 +0.2 +1.3 -3.2 -5.3 -4.3 -2.0 +0.9 -1.4 -5.8 -0.5 -0.8 -8.0 -1.4
* Denotes maximum amount tolerable within an error of +‘4%. t Based on mean of three determinations. i, against pH of the aqueous phase after extraction. It was found that the heights were approximately constant over the pH range 0.4-4.6. Over this pH range,
the volume of AN phase recovered was constant (10.3 ml) and 99.5% of the In(II1) complex was extracted in a single extraction. Calibration curves
On the basis of these results, the procedure for the polarogrrfphic determination of In(II1) was established. The d.c. and a.c. polarograms were recorded at various concentrations of In(W), while other conditions were kept constant. The calibration curves obtained were linear over the concentration ranges 1.6 x 10m6-3.0 x 10e4M In(III) for d.c. and 1.6 x 10-6-l.5 x 10-5A4 for a.c. polarography. The diffusion current constant of In(W) in the AN extract was 9.50 @. 1.mmole-’ . mg-2’3. se~‘/~, about 4
times that obtained in 1M aqueous sodium bromide, as shown in Fig. 2. The relative standard deviation was 2.1% for 27.7 pg of indium(II1) (10 determinations by a.c. polarography). E$ect of diverse ions
Possible interferences were investigated by a.c. polarography, which gave considerably better resolu, tion for substances reduced at potentials close to each other. The results are summarized in Table 2. Cu(II), Fe(III), Pb(II), Cd(H), Tl(III), H&II) and Bi(III) were found to be tolerable at the levels tested. The interference caused by 10.0 mg of Fe(II1) and 2.5 mg of Tl(III) could be eliminated by the addition of 1.0 g of ascorbic acid before the extraction step. Other cations such as Al(W), Ni(II), Zn(I1) and Mn(I1) showed no effect on the determination. Among the anions tested, MnO;, CrO:- and EDTA interfere seriously even in small amounts and must be excluded. Thiosulphate and tungstate were tolerable at levels up to 1 mg. Square-wave polarography
Since the extract had a high electrical conductivity, an attempt was made to use square-wave polarography. It was found that a sharp peak for In(II1) was observed at -0.69 V and that the lower limit of determination was 8 x IO-‘M (9 ppM) with respect to the original aqueous phase. Acknowledgements-The author wishes to express his sincere thanks to Professor Taitiro Fujinaga of Kyoto University and to Dr. Masatada Satake of Fukui University for their valuable advice and discussion during the research. REFERENCES 1. L. Meites, Polurographic Techniques, 2nd Ed., Interscience, New York, 1967. 2. H. Uehara, Rev. Polarog. (Kyoto), 1959,7, 81. 3. B. Breyer, F. Getmann and S. Hacobian, Australian J. Chem., 1950, A3, 567. 4. F. A. Pohl and W. Bensels, Z. Anal. Chem., 1958, 161, 108. .5 T. Fujinaga and B: K. Puri, Talanta, 1975, 22, 71. 6. T. Fujinaga, H. A. Brodowsky, T. Nagai and K. Yamashita, Rev, Polurog. (Kyoto), 1963, 11, 217. 7. B. K. Afghan, R. M. Dagnall and K. C. Thompson, Talanta, 1967, 14, 715. 8. T. Fujinaga and Y. Nagaosa, Chem. Mt., 1978, 587. 9. J. F. Coetzee, G. P. Cunningham, D. K. McGuire and G. R. Padmanabhan, Anal. Chem.. 1962, 34, 1139.