Marker Compound Standardization: HPTLC and HPLC Approaches

Marker compound standardisation formalises the chromatographic identification and quantification methods introduced in Phase 3 into a validated, routinely applied quality-control procedure. HPTLC standardisation, now recognised as a mandatory identification test under the 2022 edition of the Indian Pharmacopoeia, requires the use of a certified reference standard of at least ninety-eight percent purity, a calibration curve constructed from five to seven standard concentrations applied on the same plate as the test sample, and a linear response (correlation coefficient of at least 0.999) across the working range; marker compound content is then calculated from the ratio of sample peak area to the calibration curve slope, with system suitability additionally confirmed through retention factor reproducibility within ±0.02 and adequate resolution between adjacent chromatographic bands.

HPLC standardisation follows the more extensive validation framework specified by ICH Q2(R1), addressing linearity across six concentration levels spanning fifty to two hundred percent of the target marker concentration (with a required correlation coefficient of at least 0.9999 and a y-intercept within two percent of the total response), repeatability precision (six replicate injections at the target concentration, with a relative standard deviation of peak area and retention time not exceeding two percent), intermediate precision (assessed across multiple days and multiple analysts to capture realistic inter-day variability), accuracy (assessed by spiked recovery at eighty, one hundred, and one hundred twenty percent of target, with acceptable recovery in the range of ninety-eight to one hundred two percent), specificity (confirmed by the absence of co-eluting peaks in blank and placebo samples, ideally supported by photodiode-array peak purity analysis), and the limits of detection and quantification, conventionally defined at signal-to-noise ratios of three and ten respectively.