SPECIATION OF PARTS-PER-BILLION OF METAL-IONS USING SILICA AND C18-BONDED SILICA COLUMNS AND GRAPHITE-FURNACE ATOMIC-ABSORPTION SPECTROMETRY

It is demonstrated that silica gel columns will quantitatively adsorb free Cu2+ and Pb2+ ions at pH > 8. These are eluted with 0.1 M HNO3 but not with methanol. Negatively charged EDTA chelates are not adsorbed. Neutral APDC chelates are partially adsorbed on silica columns, but are quantitatively adsorbed on C18-bonded columns, and are eluted with methanol. The metal ions are partially adsorbed on C18-bonded columns, due to residual silanol groups. A microcolumn (1 mm i.d., 5 cm length) manifold system is described for automatic delivery of eluant (0.12 ml) to a heated atomic absorption graphite atomizer, using either methanol or 0.1 M HNO3 in methanol eluant, allowing speciation and measurement of parts per billion of metals. These studies demonstrate that by using a mixed column or sequential columns of silica gel and C18-bonded silica, cationic and neutral metal species could be adsorbed, followed by sequential elution and measurement using methanol and then 0.1 M HNO3. Negatively charged species could be measured directly in the sample eluant or obtained by difference from a total metal measurement.