New Spectrophotometric Method for Determination of Cadmium

The reagent 2-hydroxy-4-n-butoxy-5-bromopropiophenone thiosemicarbazone (HBBrPT) has been used for the determination of Cd(II) by using spectrophotometric method. The reagent HBBrPT gave an intense yellow colour with Cd(II) solution in basic medium. The maximum absorbance was observed at 440 nm, in basic buffer solution (pH 10.00). The molor absorptivity and Sandell's sensitivity of Cd(II)-HBBrPT complex were 4035 mol -1 cm -1 and 0.02765 µg cm -2 respectively. The stability constant of 1:2 Cd(II)-HBBrPT complex was 8.46 x10 6 .The effect of various iron was also studied.


Introduction
Thiosemicarbazone are known as analytical reagents [1][2][3][4][5][6] . The reagents is formed by the condensation of thiosemicarbazide carbonyl compound. Thiosemicarbazones are also found to have biological activity. These compounds contain an azomethine for their reactivity with number of transition metal ions, which from coloured complexes. Further the metal complexes formed with these reagents are of great medicinal value in the treatment of diseases like influenza, protozoa, small pox and certain kinds of tumor 7 . These compounds are known for their antitubercular activity 8 .Metal chelate of there reagent inhibit tumor growth and increase the activity of some drugs 9 . In the treatment of cancer the active species is the metal chelate of thiosemicarbazone 10 . Metal chelates of these compounds are used as pesticides 11 and fungicidea 12,13 in agriculture.

Solution preparation
Buffer solutions were prepared using HCl, CH 3 COOH and CH 3 COONa in acidic medium and NH 4 OH, NH 4 Cl in basic medium.

Preparation of metal solution and reagent solution
Cd(II) solution was prepared using analytical reagent grade cadmium nitrate. The amount of Cd(II) in this solution was determined volumetrically using EDTA 14 . Appropriate quantity of 2-hydroxy-4-n-butoxy-5-bromopropiophenone thiosemicarbazone was dissolved in benzene for making 0.0005 M reagent solution.
An aliquot of the solution containing 5.62-16.86 µg/mL of Cd(II), 10 mL of basic buffer solution of the pH 10 and 1 mL 0.0005M 2-hydroxy-4-n-butoxy-5-bromopropiophenone thiosemicarbazone was taken in 25 mL volumetric flask were made upto the mark with distilled water. The absorbance of this solution was measured at 440 nm against reagent blank.
Shimadzu 160A UV-visible spectrophotometer (Japan) equipped with 1 cm quartz cell was used in these investigations for making absorbance measurements. A pH meter ELICO L 1-120 (ELICO, Hyderabad) was used to make pH measurements.

Results and Discussion
Cd(II) reacts with 2-hydroxy-4-n-butoxy-5-bromopropiophenone thiosemicarbazone in basic pH to give yellow coloured species. The colour reaction of Cd(II) with the reagent is instantaneous even at room temperature. The absorbance of yellow coloured species at a wavelength corresponding to maximum absorbance i.e. 440 nm remains constant at least one hour. Studies on the effect of pH on the absorbance revealed that the maximum colour was formed in a solution of pH 10.00. A ten-fold excess of the reagent was adequate for the complete colour development. Addition of excess of the reagent has no adverse effect on absorbance. The order of addition of various components shows on effect on absorbance values. Physicochemical and analytical characteristic of Cd(II)-HBBrPT data shown in Table1.The studies relating to the effect of Cd(II) related that a linear relationship exists between metal ion concentration and absorbance in the range 5.62-16.86 µg/mL, the molorabsorptivity and sandell's sensitivity are 4035 mol -1 cm -1 and 0.02765 µg cm -2 respectively. As the metal ion Cd(II) forms the coloured complex with the reagent, an attempt was made to determine the composition and the stability constant of the complex. The method of Vosburgh and Cooper's 15 showed that only one complex is formed. To determine the stoichiometry of complex, Job's method 16 related data is shown in Figure 1 and mole ratio method 15 is shown in Figure 2 were conducted to make these determinations. . It is noticed that Cd(II) forms a stable yellow colored 1:2 (metal: ligand) complex with 2-hydroxy-4-n-butoxy-5-bromopropiophenone thiosemicarbazone. The stability constant of the complex was found to be 8.46 X10 6 .
The effect of various ions on the determination of Cd(II) was studied to find the tolerance levels of this foreign iron the present method the results are presented in Table 2.

Applications
The complex formed between cadmium and 2-hydroxy-4-n-butoxy-5-bromopropiophenone thiosemicarbazone is stable and can be used for analysis. The method has been applied for the analysis of synthesized mixtures containing Cd(II). The related data is shown in Table 3. Table 3. Analysis of synthetic mixture.

Conclusions
Cd(II) forms a 1:2 stable yellow colored complex with 2-hydroxy-4-n-butoxy-5bromopropiophenone thiosemicarbazone. This complex was used for the determination of cadmium in microgram quantities. The stability constant of the complex is 8.46X10 6 . The molar absorptivity and Sandell's sensitivity are 4035 mol -1 cm -1 and 0.02765 µg cm -2 respectively. The method has been applied for the analysis of cadmium in synthesized mixtures and also in alloys.