A new and very simple procedure for the differential pulse polarographic determination of ultra trace quantities of tungsten using catalytic hydrogen wave and application to tobacco sample

In this work a new and very simple differential pulse polarographic method is established for the trace determination of tungsten using catalytic hydrogen peak. For its determination, polarograms have been taken in various electrolytes including Britton–Robinson buffer (pH = 2.0, pH = 4.0, pH = 5.0 and pH = 6.0), nitric acid, hydrochloric acid, perchloric acid and phosphoric acid. The highest peak was obtained in the presence of 0.01 M H3PO4 + 0.1 M KCl (pH = 2.0–2.5) which appeared at −1.1 V. The effects of pH, phosphate concentration, type of electrolyte on this peak have been studied. The height of the hydrogen catalytic peak was increasing with the addition of Mo(VI). Formation of a heteropoly acid was responsible of the catalytic hydrogen peak. The best condition for the determination of 5 × 10−8 M W(VI) was found to be 1 × 10−5 M Mo(VI) and 1 × 10−2 M H3PO4 + 0.1 M KCl (pH = 2.0–2.5). terference effect of Cu(II), Pb(II), Sn(IV), Mo(VI), Se(IV), As(III) and Zn(II) have also been studied. Among these ions only in the presence of As(III), the catalytic hydrogen peak of tungsten (shown as Mo–W) overlapped with the hydrogen catalytic peak of arsenic (Mo–As). This interference could be eliminated by oxidizing As(III) into As(V) using HNO3. With the newly established method the limit of detection (LOD) was 1.3 × 10−9 M (S/N = 3). This method was applied successfully for the determination of tungsten in digested tobacco sample.