Determination of lead by hydride generation inductively coupled plasma mass spectrometry (HG-ICP-MS): On-line generation of plumbane using potassium hexacyanomanganate(III)

A hydride generation (HG) procedure has been described for determination of Pb by ICP-MS using potassium hexacyanomanganate(III), K₃Mn(CN)₆, as an additive to facilitate the generation of plumbane (PbH₄). Potassium hexacyanomanganate(III) was prepared in acidic medium as it was unstable in water. The stability of hexacyanomanganate(III) was examined in dilute solutions of HCl, HNO₃ and H₂SO₄. The solutions prepared in 1% v/v H₂SO₄ were found to be stable for over a period of 24 h. The least suitable medium was 1% v/v HNO₃. For generation of plumbane, acidic hexacyanomanganate(III) and sample solutions were mixed on-line along a 5-cm long tygon tubing (1.14 mm i.d.) and then reacted with 2% m/v sodium borohydride (NaBH₄). A concentration of 0.5% m/v K₃Mn(CN)₆ facilitated the generation of PbH₄ remarkably. In comparison to H₂SO₄, HCl provided broader working range for which optimum concentration was 1% v/v. No significant interferences were noted from transition metals and hydride forming elements, up to 0.5 μg mL⁻¹ levels, except Cu which depressed the signals severely. The depressive effects in the presence of 0.1 μg mL⁻¹ Cu were alleviated by increasing the concentration of K₃Mn(CN)₆ to 2% m/v. Under these conditions, the sensitivity was enhanced by a factor of at least 42 to 48. The detection limit (3 s) was 0.008 μg L⁻¹ for ²⁰⁸Pb isotope. Average signal-to-noise ratio (S/N) ranged between 18 and 20 for 1.0 μg mL⁻¹ Pb solution. The accuracy of the method was verified by analysis of several certified reference materials, including Nearshore seawater (CASS-4), Bone ash (SRM 1400), and Mussel tissue (SRM 2976). The procedure was also successfully applied to the determination of Pb in coastal seawater samples by ICP-MS.