An extractive spectrophotometric method for the determination of the trace amounts of tin has been carried out by employing 6-chloro-3-hydroxy-2-(2′-thienyl)-4-oxo-4
Tin does not occur free in nature and is found almost exclusively as tin oxide known as cassiterite or tin stone. Tin although a toxic metal, still it is being widely employed in manufacturing important alloys [
A model-140-02, Shimadzu with 10 mm matched cells was used for the routine absorbance measurements and spectral studies.
The standard stock solution (250 mL) of Sn(II) containing 1 mg mL−1 of the metal ion was prepared by dissolving an accurately weighed amount (0.475 g) of SnCl2·2H2O (RANBAXY) in 20 mL of concentrated hydrochloric acid, diluting with deionized water up to the mark and standardized by the SnO2 method gravimetrically [
6-Chloro-3-hydroxy-2-(2′-thienyl)-4-oxo-4
Dichloromethane (Ranbaxy) was used for extraction as such.
Synthetic samples were prepared by mixing tin solution with solutions of various metal ions in suitable proportions so as to give the composition as shown in Table
The analysis of various samples with the proposed method.
Sample composition | ||
---|---|---|
Matrix* | Sn added, |
Sn found**, |
Zn(0.02), Pb(0.01), Cu(0.001)a | 10.0 | 10.03 ± 0.85 |
Cu(0.070), Co(0.014)b | 8.0 | 7.89 ± 0.71 |
Co(1), Ba(2), U(0.01), Mo(0.020)c | 7.0 | 6.83 ± 0.58 |
Cd(2), Fe(0.1), V(0.1)d | 12.0 | 11.96 ± 0.71 |
Cr(0.1), Sr(1), Ag(0.5), Zr(0.01)e | 12.0 | 11.99 ± 0.62 |
Pb (2), Nb(0.1), Th(0.05) f | 5.0 | 5.13 ± 1.63 |
As(2), Se(3), Ti(0.1)e | 8.0 | 7.92 ± 0.56 |
Re(0.01), Ta(0.05), Bi(1)g | 5.0 | 5.03 ± 0.82 |
Be(2), Pt(0.01), Ir(0.01) | 10.0 | 9.85 ± 0.41 |
Gun metal | 4.9%h | 4.48% ± 0.72 |
Tin can | — | 0.15%i |
*Amount of metal ion shown in parentheses is in mg. **Average of triplicate analyses; mean ± % RSD. a,bCorrespond to kneiss metal and argental, respectively. cIn presence of 0.5 mg dithionite. dIn presence of 100 mg ascorbic acid. eIn presence of 7 mg phosphate. fIn presence of 4 mg oxalate. gIn presence of 100 mg iodide. hCertified value. iConfirmed by SnO2 method.
A weighed sample of gun metal (0.2 g) was dissolved in 10 mL of concentrated hydrochloric acid and 2–4 mL of concentrated nitric acid on heating and the volume was made up to 100 mL in a volumetric flask. 10 ML of this solution was diluted to 100 mL to get a working solution of low concentration. An aliquot (0.25 mL) of this solution was analyzed by the proposed method.
A weighed sample (0.6 g) of tin taken in a 10 mL beaker was heated gently with 5 mL of concentrated hydrochloric acid. The sample was dissolved completely by adding 5–10 mL of distilled water and heating until the volume was reduced to 2–5 mL. After cooling, the volume of the solution was made up to 25 mL and suitable portions of the sample solution were analyzed for tin content.
To 1 mL aliquot of the sample solution containing ≤13
Modifications of the method for V, Fe, Nb, Zr, W, Mo, Bi, and Ti: in the sample when Ti(IV), Zr(IV), and W(VI) were masked with sodium phosphate, Fe(III) and V(V) with ascorbic acid, Bi(III) with potassium iodide, Mo(VI) with sodium dithionite, and Nb(V) with sodium oxalate added prior to the addition of reagent and solvent. The respective amount of the masking agents used was mentioned in the effect of diverse ions.
Tin(II) reacted with 6-chloro-3-hydroxy-2-(2′-thienyl)-4-oxo-4
Effect of various parameters on the absorbance of Sn(II)-CHTB complex.
HCla (M) | 0.043 | 0.044 | 0.045 | 0.046–0.060 | 0.065 |
Absorbance | 0.370 | 0.420 | 0.460 | 0.490 | 0.450 |
CHTBb (mL) | 0.2 | 0.3 | 0.4 | 0.5–2.2 | 2.5 |
Absorbance | 0.310 | 0.375 | 0.440 | 0.490 | 0.430 |
Equilibration timec (sec) | 0.0 | 2 | 4 | 5–300 | — |
Absorbance | 0.100 | 0.320 | 0.480 | 0.490 | — |
Conditions: (a) Sn(II) = 10
Absorption spectrum of Sn(II)-CHTB complex in dichloromethane. Curve A: 1
The absorbance of the complex was found maximum in HCl medium, where as it was observed to be low in H2SO4, CH3COOH, and HClO4. Since the Sn(II)-CHTB complex showed maximum absorbance in 0.046–0.05 mol L−1 HCl, so 0.05 mol L−1 HCl was chosen to provide suitable acidity. Portions 0.5–2.2 mL of 0.1% CHTB solution in acetone resulting in maximum absorbance to the complex under all the conditions were stated in Table
Out of the number of the solvents studied for extraction of the Sn(II)-CHTB complex, dichloromethane was found to be most suitable because it provides a high absorbance value and stability of the complex. The absorbance showed a downward trend in the case of dichloromethane, 1,2-dichloroethane, benzene, toluene, ethyl acetate, carbon tetrachloride, isoamyl acetate, isobutyl methyl ketone, chloroform, cyclohexane, and isoamyl alcohol. So the dichloromethane was selected for the extraction of the Sn(II)-CHTB complex from the aqueous phase.
From a study of the above variables, the optimum conditions for the system have been laid down, as already stated in the procedure. The metal complex obeys Beer’s law in the range 0–1.3
Job’s method of continuous variations of Sn(II) and CHTB. Curve A: 435 nm, Curve B: 410 nm, and Curve C: 450 nm.
Mole ratio method of CHTB and Sn(II). Curve A: 435 nm, Curve B: 410 nm, and Curve C: 450 nm.
Chemical Structure of CHTB.
Chemical Structure of Sn(II)-CHTB complex.
Under optimum conditions of the procedure, the effect of different anions and cations has been studied on the absorbance of the Sn(II)-CHTB complex. The amount of diverse ions which caused a ≤1% error in the absorbance was taken as the tolerance limit. The tolerance limit of foreign ions tested is given in Table
Tolerance limit of different ions in the determination of 10
Ions | Tolerance limit |
---|---|
(concentration mg/10 mL) | |
Thiourea, sulphite, ascorbic acid, and iodide | 100.0 |
Sulphate, nitrate | 80.0 |
Bromide, sulfosalicylic acid | 75.0 |
Chloride, tartrate | 50.0 |
Acetate | 40.0 |
Carbonate, citrate | 20.0 |
Thiocyanate | 10.0 |
Phosphate | 7.0 |
Dithionite | 5.0 |
Oxalate | 4.0 |
EDTA “disodium salt” | 2.0 |
Glycerol | 1.0a |
H2O2 (30%, m/v) | 0.5a |
Zn(II), Pb(II), and Se(II) | 10.0 |
Cd(II) | 8.0 |
Ba(II), Ni(II), Co(II), and Hg(II) | 5.0 |
Be(II), Ce(IV), As(II), Mg(II) Mn(II), Sr(II), Al(III), and Os(VIII) | 3.0 |
Ag(I), Cu(II) | 2.0 |
U(VI) | 1.0 |
Ta(V) | 0.7 |
Cr(VI) | 0.5 |
Th(IV) | 0.3 |
Ru(III), Ir(III) | 0.1 |
aValue given in mL.
Among the study of cations it was found that cations like Fe(III), Zr(IV), Nb(V), V(V), Mo(VI), W(VI), and Ti(IV) did influence the absorbance of the Sn(II)-CHTB complex. However the interference of these metals could be prevented by making use of suitable masking agents, that is, for 1 mg of Fe(III), 100 mg ascorbic acid; for 1 mg of Nb(V), 4 mg sodium oxalate; for 1 mg of V(V), 100 mg ascorbic acid; for 0.1 mg of Mo(VI), 5 mg of sodium dithionite; for 1 mg of W(VI), 7 mg sodium phosphate; for 1.5 mg Zr(IV), 7 mg sodium phosphate; for 0.3 mg of Ti(IV), 7 mg sodium phosphate; and for 5 mg of Bi(III), 100 mg iodide added prior to the addition of CHTB in 10 mL aqueous volume under optimum condition of the procedure.
For the determination of microamounts of tin, the proposed method is simple, rapid, sensitive, and selective and free from the interference of a large number of metal ions. The wide applicability of the method is tested by the analysis of several synthetic samples, tin can, and gun metal sample with satisfactory results. The high reproducibility of the method is tested by performing several sets of experiments while keeping the same amount of tin metal ions in each set; the relative standard deviation of the method is 0.98%.
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors’ sincere thanks are due to Kurukshetra University, Kurukshetra, and Panjab University, Chandigarh, for providing the necessary facilities.