An unexpected Griess reaction on the important anti-malarial drug primaquine and its application for drug determination.

•An unexpected Griess reaction on the important antimalarial drug primaquine has been studied.•The absorption of azo products varied due different electron contributing effects of substituents.•An optimized Griess reaction was developed for colorimetric determination of PMQ with promising sensitivity and selectivity.•This method has been successfully used to quantity PMQ in serum within clinically relevant concentrations.