I am doing RS force degradation study, As per methodology, if RS conc is 1000ppm ,then what conc. should I use for FD study? Do we have to use 1000ppm (as per methodology) or adjust the conc. of main peak, in such a way to get respone 0.1 to 1.0 . or use both, i.e stressed on target conc.(as per method) and inject stress sample as well as sample with low volume( to adjust response0.1 to 1.0 AU).
Note: most of the method have main peak response is more than 1.0AU
Hi Sachin,
It's better to use a conc. that gives sufficient enough response that its e.g. 0.1% area is well above LOQ for an RS method. If this conc. is too high to give peak purity for main peak (drug) even with pure drug sample then peak purity (co-elution) can be checked using an appropriately diluted sample of the stressed sample (sufficiently high response without detector response saturation and thus distortion of its UV scan at peak apex). The final conc. will depend on the chromophoric properties of the drug in case and the wavelength of detection. A drug peak may show sharp peak and moderate response at wavelength of detection but the same may reveal detector saturation (flat top or distorted top peak at a wavelength of maximum response and at cut off values of UV e.g. ~200-220 nm).
I hope this answers to your query.
Question: What is RS (ref. standard???); The concentration of the main analyte should be adjusted to give you approx. 1-1.5 AU; then, you may expect a 0.1% impurity to yield a 1-1.5 mAU level response (approx.).
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