The use of surrogate reference standards in quantitative HPLC: A case study of the analysis of Ibuprofen tablets and Promethazine Hydrochloride tablets

The use of readily available drug molecules as surrogate reference standards to replace the use of chemical reference standards in quantitative hplc analysis was investigated. This involved the development of a simple, rapid and sensitive reverse phase hplc method for the analysis of Ibuprofen tablets and Promethazine Hydrochloride tablets. A proportionality constant, K was determined that made it possible for Ibuprofen tablets and Promethazine Hydrochloride tablets to be assayed without the use of their chemical reference standards. The chromatographic condition for the assay of Ibuprofen tablets consisted of Shimadzu LC-10AD Liquid Chromatography pump, ZORBAX SB C18 5µm 4.6 × 250mm column, PERKLIN ELMER 785A programmable Absorbance Detector at 222nm and eDAQPowerChrom 280 -Integrator. The elution was isocratic with mobile phase consisting of methanol; water; Orthophosphoric Acid in the ratio 750; 247; 3. The mean retention times for the analyte and its surrogates were; Ibuprofen (6.46±0.050 min), Benzoic Acid (2.19±0.008 min), Aspirin (1.95±0.005 min) and the average K values obtained for the surrogate reference standards were Benzoic Acid (0.4516±0.0076) and Aspirin (0.5427±0.0943). The K value obtained when Benzoic Acid was used as surrogate reference standard was used to analyse three brands of Ibuprofen tablets and obtained percentage contents of 100.81±1.890, 101.26±1.035, 101.53±0.696 for Brands IN, IE and ID respectively. Also, the K value obtained when Aspirin was used as surrogate reference standard was used to analyse the three brands of Ibuprofen tablets and obtained percentage contents of 99.42±1.011, 103.12±1.441, 104.03±2.049 for Brands IN, IE and ID respectively. The standard method for the assay of Ibuprofen tablets gave percentage contents of 99.22% ± 0.826, 97.89% ± 1.008, 97.41% ± 0.634 for Brands ID, IE and IN respectively. The method developed and the standard method gave percentage contents that were significantly different at 95% confidence intervals. The two methods however showed no significant difference in their precision at 95% confidence intervals. The assay of Promethazine hydrochloride also employed a microbore column packed with a C8 reversed-phase material (Phenomenex C8 5µm 150 × 4.60mm column) with an isocratic mixture of methanol and 1% Triethylamine in a ratio 9:1 as the mobile phase. The chromatographic separation was monitored by a UV/VIS detector at a wavelength of 250 nm and the mean retention times were Promethazine hydrochloride (4.01±0.023 min), Caffeine (2.34±0.029 min), Metronidazole (2.26±0.047 min) and Indometacin (1.58±0.037 min). When Caffeine was used as surrogate reference standard, the K value obtained was 5.3787±0.0880 with percentage content of 103.16%±0.294, 101.12%±0.587, and 103.49%±0.925 for brands PZ, PG, PS respectively. With Metronidazole as surrogate standard, the K value obtained was 6.1014±0.1189 with percentage content of 99.36%±0.500, 100.31%±0.745, 102.35%±0.596 for the three brands PZ, PG and PS respectively. When Indometacin was used as surrogate reference standard the K value was 1.7051±0.0255 with assays of 97.29%±0.627, 97.79%±0.741 and 96.22%±0.647 respectively for brands PZ, PG and PS. The standard method from the BP also showed results of 100.7%±0.641, 100.7%±0.360 and 102.3%±0.468 respectively for brands PZ, PG and PS of Promethazine hydrochloride tablets. The methods were statistically comparable to the Standard BP method at the 95% confidence except for the accuracy. The assays for all the brands of Ibuprofen tablets and Promethazine hydrochloride tablets using the developed methods however fell within the permissible range of the British Pharmacopoeia Benzoic acid and Aspirin can be used as surrogate reference standards for the assay of Ibuprofen using the K values obtained. Also, Promethazine hydrochloride tablets can be assayed using Caffeine, Metronidazole and Indometacin as surrogate reference standards.

Source: KNUST