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In our first blog article on increasing the sensitivity in case of limit of detection (LOD) / limit of quantitation (LOQ) problems in HPLC methods, we addressed the increase in sensitivity primarily by reducing baseline noise. Now we will look on the same topic from another perspective – with the eyes of “method optimization”. What can be optimized to increase the peak size and thus the overall signal to noise ratio (S/R)?

In any quantification method of a drug or its active ingredient, the linearity of the calibration line is a crucial criterion for the correctness of the values. The measured values should, in the best case, be directly proportional to the concentration of the analyte in the sample. Most methods have their limits; therefore, you often narrow the measurable range (linear range).

During validation of purity testing methods of drugs or their active ingredients, sooner or later a point comes when the detection and quantification limits are needed to be determined. The limit of detection or LOD is defined as the lowest amount of an analyte in a sample that can still be detected. This is different from quantification - since the limit of quantitation (LOQ) is the lowest amount of an analyte in a sample that can still be reliably quantified.