PHASE-SELECTIVE ALTERNATING-CURRENT ADSORPTIVE STRIPPING VOLTAMMETRY OF AMINOPTERIN ON A MERCURY THIN-FILM CARBON-FIBER ULTRAMICROELECTRODE

The electrodeposition of mercury thin films onto carbon fibres for the determination of aminopterin and its analogues has been optimized fol lowing an investigation of the electrochemical reduction processes of aminopterin obtained at a static mercury drop electrode. The advantage ous characteristics of ultramicroelectrodes combined with adsorptive p reconcentration and phase-selective a.c. stripping voltammetry were fo und to yield a very sensitive and reproducible method. By using this e lectrode, accumulation was performed at five different concentrations of aminopterin ranging from 5 x 10(-10) to 5 x 10(-8) mol dm-3. The el ectrode yielded a calibration graph from 2 x 10(-10) to 8 x 10(-9) mol dm-3 (r = 0.994) with a limit of detection [signal-to-noise ratio (S/ N) = 31 of 1 x 10(-10) mol dm-3 aminopterin in aqueous solutions. The reproducibility of the signal was evaluated at three different concent rations of aminopterin producing relative standard deviations ranging from 3.57% at the 5 x 10(-10) mol dm-3 level to 2.49% at the 1 X 10(-8 ) mol dm-3 level (n = 10). The electrode was applied to the determinat ion of aminopterin in urine resulting in a limit of detection (S/N = 3 ) of 2.5 x 10(-7) mol dm-3 without the employment of any pre-treatment of the urine.