Phase-selective alternating current adsorptive stripping voltammetry of aminopterin on a mercury thin film carbon fibre ultramicroelectrode
The electrodeposition of mercury thin films onto carbon fibres for the determination of aminopterin and its analogues has been optimized following an investigation of the electrochemical reduction processes of aminopterin obtained at a static mercury drop electrode. The advantageous characteristics of ultramicroelectrodes combined with adsorptive preconcentration and phase-selective a.c. stripping voltammetry were found to yield a very sensitive and reproducible method. By using this electrode, accumulation was performed at five different concentrations of aminopterin ranging from 5 × 10–10 to 5 × 10–8 mol dm–3. The electrode yielded a calibration graph from 2 × 10–10 to 8 × 10–9 mol dm–3(r= 0.994) with a limit of detection [signal-to-noise ratio (S/N)= 3] of 1 × 10–10 mol dm–3 aminopterin in aqueous solutions. The reproducibility of the signal was evaluated at three different concentrations of aminopterin producing relative standard deviations ranging from 3.57% at the 5 × 10–10 mol dm–3 level to 2.49% at the 1 × 10–8 mol dm–3 level (n= 10). The electrode was applied to the determination of aminopterin in urine resulting in a limit of detection (S/N = 3) of 2.5 × 10–7 mol dm–3 without the employment of any pre-treatment of the urine.