Panadol night® tablets claimed to contain 25mg DPH and 500 mg PAR/tablet (Batch No 117928) Technique component Taken (μg mL-1) Found % ± SD First derivative spectrophotometric method (D1) PAR 4 98.50 ± 0.76 First derivative of ratio spectra specrophotometric method (DD1) DPH 8*(7.5pure + 0.5 dosage form) 102.00 ± 0.72 Multivariate method PAR PLS 4 99.25 ± 0.39 100.99 ± 1.47 PCR 4 98.35 ± 0.85 99.37 ± 1.40 DPG PLS 7* 101.40 ± 0. 31 99.58 ± 1.63 PCR 7* 98.20 ± 0.25 99.70 ± 1.35 Densitometric method PAR 0.4 99.00 ± 0.25 100.00 ± 1.31 DPH 5 101.60 ± 1.70 101.70 ± 1.62 * The ratio present in Panadol night® tablets prepared by spiking technique [17], where 7μg/mL of DPH is (6.5 μg/mL of pure drug + 0.5 μg/mL of dosage form)

Table 5: Determination of Paracetamol and Diphenhydramine Hydrochloride in their pharmaceutical formulation by the proposed methods and application of standard addition technique.