Chromatography Forum

Hallo

I have a doubt regarding the definition of disregard limit in HPLC methods for related substances in European Pharmacopoeia. For example in one of the methods the limits are described as follows:
Limits:
— impurities D, G: for each impurity, maximum 0.3 per cent,
— impurities A, B, C, E, F, H, I: for each impurity, maximum 0.2 per cent,
— impurity with relative retention at about 1.23: maximum 0.2 per cent,
— any other impurity: maximum 0.1 per cent,
— total: maximum 1.2 per cent,
— disregard limit: 0.05 per cent.
Should I disregard all the peaks below 0,05% including those specified (A, B,…I) and report them as “not detectedâ€

you should always keep in mind that HPLC analyses has it's limitation.
not all that looks like a peak can be considered a peak let alone be quantified.
this is why you have the S/N ratio. a peak that has a Singnal to Noise ratio of <3>10 is considered qualitative. you can say that the substance is being detected that is generally your LOD (limit of detection). a peak with a S/N of more the 10 is considered quantitative, LOQ.

what ever is less then 3 might be your substance but it is also most defenetly as well noise. therefore you do not report it has being detected let alone quantitate.
the EP method defenetly tells you that you do not need to report any peak with less then 0,05%.
i can even say that you can calculate how this 0,05% translate into an area value compare to your STD area and put that value has a minimum area thresold. that way those noise peak will not even show on your chromatogram. make sure that you report the procedure correctly.

if you think that the total amount of disregard peaks is too high then first check the way you perform the integration. maybe you are using parameters which are too sensitive. If not then maybe you should check the drift and noise of your HPLC.

We use the phrase "below reporting limits" for peaks that are less than 0.05% (API) or 0.10% (drug product).