Voltammetric determination of trace quantities of 6-thioguanine based on the interaction with DNA at a mercury electrode

Herein, a sensitive square wave voltammetric (SWV) method is described for the quantitative determination of an anticancer drug, 6-thioguanine (6-TG). The interaction of 6-TG with double stranded DNA (ds-DNA) in the solution phase resulted in a well amplified SWV response at the surface of hanging mercury dropping electrode (HMDE). Accumulation and stripping steps were made in the sample medium conditioned with acetate buffer (pH 4.8). Optimized conditions for the accumulation step included the deposition potential at −0.10 V, a deposition time of 30 s, a frequency of 50 Hz, a pulse amplitude of 20 mV, and a step potential of 7 mV. In the solution containing 2.0 mg L−1 ds-DNA, determination was performed within a wide concentration range of 2.4 × 10−9 to 1.8 × 10−5 mol L−1, and a detection limit of 2.1 nmol L−1 6-TG. An overall conclusion was that the intercalation of 6-TG into ds-DNA in a solution medium of the acetate buffer is a possible reason for the observed behavior. The method was applied for the determination of 6-TG in 6-thioguanine tablets and spiked blood serum samples. No statistically significant differences were observed between the expected and obtained concentrations. The new method is sufficiently sensitive to detect ultra trace amounts of 6-TG content.