Experimental comparison of the different approaches to estimate LOD and LOQ of an HPLC method

Detection and quantification limits (LOD and LOQ) are two fundamental eleme nts of method validation, Rigorous statistical definitions exist, but in HP LC they could not be implemented. Nevertheless there are several estimation methods for these limits, The most commonly used is the signal-to-noise ra tio criterion. Others are based on the dispersion characteristics of the re gression line, either simple or weighted. For LOQ, Eurachem proposed an alt ernate approach based on the use of a target value for the area RSD, Since official guidelines imposed no particular modus operandi, an experimental m ethodology was set up to investigate the compatibility of the different app roaches and their respective reliabilities. Several samples prepared in a c oncentration range close to the limits were analyzed. It appeared that, bot h for values and their reliabilities, the different approaches were far fro m equivalent. In our opinion, the best way to handle the problem of detecti on and quantification limits was a methodology based on the use of the resi dual standard deviation of a weighted regression for LOD and on a Eurachem approach for LOQ. Values obtained by these means had the advantage of being reliable, i.e., with a small dispersion, and were still compatible with th ose obtained with the usual signal-to-noise ratio approach.