Method validation: selectivity, limit of detection, limit of quantification, linearity range and sensitivity-
The selectivity of the method was checked by spotting 50μg x μl –1 of pseudoephedine HCl (a structurally related drug) individually and as a mixture (in 1:1 proportion) on a plate. Rest of the procedure followed was a described above under, “preparation of calibration curve”. The limit of detection, limit of quantification, linearity range of the calibration curve and sensitivity (which is the slope of the calibration curve) were also determined.
Accuracy of the assay was determined following standard procedure; the results obtained by spotting known amount of drug applied on the plate were compared with the experimental values. The accuracy was expressed in terms of % basis using the following equation-
% Bias = Observed value – Original concentration
-------------------------------------------------------------------------- x 100
The inter- day assay variability was calculated for all concentrations in the linearity range (35,70,105 and 140 μg). The intra- day variation was determined on six replicate samples of a low (35 μg) and a high (140 μg) of the concentration curve.
Ruggedness of the analytical method was determined by the analysis of the same sample of pseudoephedrine HCl in two separate laboratories having similar equipments by three different analysts on consecutive days for a week. The coefficient of variation (%CV) amongst the results obtained was calculated.
Comparison of HPTLC with HPLC-
The accuracy of the proposed HPTLC method was compared with a reported HPLC method of estimation of pseudoephedrine HCl (detected at 210 nm) using Partisil SCX (10μm) HPLC column (25cm x 4.6 mm). The mobile phase comprised of 24 mM phosphate buffer (pH=2.3) in 50 % aqueous acetonitrile solution (1.5 ml per min.).
Applicability to stability studies-
The proposed HPTLC technique was applied in evaluating the stability of pseudoephedrine HCl samples stored under exaggerated conditions of temperature (40,50 and 60 + 1 deg.C) with relative humidity of 58,75 and 90 %. The standard samples (70 μg /ul) during the analysis were spotted after every 10 tests samples during the analysis. The method was also applied in the analysis of aged pseudoephedrine sulphate samples stored under similar conditions; the details of the stability studies are being published elsewhere.
In the next post, we shall take up discussion on results and discussion of these experiments.
To be continued in Part 4 ...