A Novel Spectrophotometric Method for the Determination of Isoniazid Using Cu(II) as Spectroscopic Probe Ion

A novel method to determine isoniazid with high sensitivity and good selectivity has been established by using Cu(II) as a spectroscopic probe ion. The experiment indicated that Cu(II) was reduced to Cu(I) by isoniazid at pH 6.0, then the resulting Cu(I) was precipitated with SCN⁻ to form CuSCN that could be stayed upon the surface of water phase in the presence of NaNO₃. By determining the residual amount of Cu(II) in the water phase, the indirect determination of isoniazid could be achieved. Good linear relationship between the amount of the reacted Cu(II) and the concentration of isoniazid was observed, with the linear range being 0.050–4.50 µg·mL⁻¹, and the detection limit being 0.048 µg·mL⁻¹. This method has been successfully applied to determining isoniazid among pharmaceutical samples and patient urine samples.