Impurity Calculator with Relative Response Factor

Quantify an impurity against the API standard and see which ICH Q3B threshold it crosses.

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Impurity peak area

Standard peak area

Standard conc. (API) mg/mL

Sample conc. mg/mL

Relative response factor

Maximum daily dose mg

Example: API standard at 0.1% of the sample concentration, sample at 1 mg/mL, RRF 0.85, maximum daily dose 200 mg. Thresholds per ICH Q3B(R2) for drug products.

Impurity–

Reporting threshold–

Identification threshold–

Qualification threshold–

Impurity % = (A_imp/A_std)·(C_std/C_sample)·(1/RRF)·100 · RRF = response of impurity / response of API at equal concentration

How it works

Most related-substances methods quantify impurities against a dilute API standard, typically at the specification or reporting level. Because an impurity rarely gives exactly the same detector response as the API, a relative response factor corrects the result: RRF below 1 means the impurity responds less than the API, so its true content is higher than the uncorrected area ratio suggests.

ICH Q3B(R2) sets thresholds for degradation products in new drug products that depend on the maximum daily dose, expressed either as a percentage or as a total daily intake, whichever is lower. Results here use those rules; your specification and regional guidance take precedence.