Deg (PAP) % Ratio DHP: PAR Concentration (μg ML-1) 1D method (PAR) Recovery % 1DD method (DPH) Recovery % DPH PAR PAP 0.00 *1:20 8 10 0.00 100.00 98.75 10 *1:20 8 9 1 101.11 98.50 20 *1:20 8 8 2 100.48 98.37 30 *1:20 8 7 3 98.42 98.62 40 *1:20 8 6 4 98.33 98.75 50 *1:20 8 5 5 100.80 98.50 60 *1:20 8 4 6 102.50 98.87 Mean ± SD 100.48±1.486 98.62±0.176 * The ratio present in Panadol night® tablets prepared by spiking technique where 8μg/mL of DPH is (7.5 μg/mL + 0.5 μg/mL) [17].

Table 2: Determination of Paracetamol and Diphenhydramine Hydrochloride in presence of P-aminophenol in laboratory prepared mixtures by the proposed derivative and first derivative of ratio spectra spectrophotometric methods.