How to fix the concentration for RS by HPLC

Answer Posted / dhilip anand

To determine the sample concentration that gives an
acceptable LOQ
(Signal to Noise ratio, S/N) in low level spike
concentrations. The sample concentration should
be low enough to maintain linearity and precision, but high
enough to achieve the desired LOQ.
For example, if the ICH reporting limit for this drug
product is 0.1%, the LOQ of the method
should be less than 0.05% (i.e., desired LOQ, in %). By
using spike sample solutions of very
diluted concentrations for the significant related
substances, estimate the concentrations that give
a S/N of about 10 for the significant related substances.
This estimated concentration is the
approximate LOQ concentration (i.e., estimated LOQ
concentration, in µg/mL).
The following equation can be used to estimate the target
sample concentration for the method:
Target sample concentration =
estimated LOQ concentration (µg/mL) x 1/desired LOQ (%) x 100
Hi this above answer probably worksout since most of the
drug's TDI(dose) will be <1g so desired LOQ % is regarded as
0.05% for reporting threshold with 0.1% and anybody suggest
what will be the desired LOQ % when reporting threshold is
0.05% i.e., if TDI is >1g as per ICH??? Can correct the
above answer if m wrong???

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