Chromatography Forum

Dear all,
please help me with interpretation of requirements given in a USP monograph:
a) "the tailing factor is not more than 1.5"
b) "the column efficiency is not less than 2000 theoretical plates"

On the report from HPLC instrument I have values for
a) Symmetry and USP Tailing - what is their relation to the tailing factor?
b) For column efficiency the results are reported by four methods (tangent, half width, 5 sigma and statistical) - which results should I look to comply with USP?

Thanks!
Marijana

If you're using a USP monograph's suitability requirements, USP Tailing is what you need to look at in the report. Symmetry provides the same type of information but not necessarily via the same calculation.

Also - with USP tailing, that is supposed to be checked at 5% of peak height. Despite this, at least one enterprise data system out there allows for calculation of it at 10% of peak height.

For column efficiendy, there is a USP formula for that that you can probably get the data system to use

N=16(t/W)^2 or N=5.54(t/Whalf)^2
t is time from injection to peak max height,
W is baseline peak width as defined by tangents drawn on either side of the peak (tangent method) and Whalf is peak width at half the height of the peak (so use either one, but note what you used as their results will differ some).

To clarify: for the USP you can either use the tangent method or the half-height method. I recommend the tangent method.

The USP tailing factor is the ratio of the peak width at 5% of the height of the peak divided by 2 times the front of the peak. Your machine will usually calculate this for you.

Thanks for all the information!
I have managed to find formula that the instrument uses when calculating USP tailing factor and column effieciency, and thanks to your answers the things are much more clear now!

Marijana