Determination of transition metal ions in tobacco as their 2-(2-quinolinylazo)-5-dimethylaminophenol derivatives using reversed-phase liquid chromatography with UV–VIS detection

This paper reports the utilization of solid-phase extraction and the reversed-phase high-performance liquid chromatography for the determination of six important transition metal ions: iron, cobalt, nickel, copper, zinc and manganese in tobacco with 2-(2-quinolinylazo)-5-dimethylaminophenol (QADMAP) as chelating reagent. Iron, cobalt, nickel, copper, zinc and manganese ions react with QADMAP to form colored chelates in the medium of acetic acid–sodium acetate buffer solution (pH 4.0). These chelates can be enriched by solid-phase extraction with Waters Sep-Pak-C18 cartridge, and eluted the retained chelates from cartridge with tetrahydrofuran. The chelates were separated on a Waters Nova-Pak-C18 column (150×3.9 mm, 5 μm) by gradient elution with methanol (containing 0.5% of acetic acid) and 0.05 mol/l pH 4.0 acetic acid–sodium acetate buffer solution as mobile phase at a flow-rate of 0.5 ml/min. The detection limits of iron, cobalt, nickel, copper, zinc and manganese are 10, 12, 8, 13, 17 and 22 ng/l, respectively. This method had been applied to the determination of iron, cobalt, nickel, copper, zinc and manganese in tobacco with good results.