Chromatography Forum

Can anyone tell me why USP Resolution is calculated using "lines drawn tangent to the peak at 50% height", but the USP plate count is determined by drawing lines tangent to the peak at 61% peak height. I think that if a peak is assumed to be Gaussian in shape, the inflection points would be at ~61%. So why the difference for resolution vs. plate count?
thanks for any help!

LaDeneVerda

Historical reasons I think. Before they made the resolution setting available to users it was at 50%. Now it can be set either way, or if you use Apex track it ignores it and used the true inflection point of the peak. Note USP's "relatively straight sides of the peak" leaves a lot of room for changes wither way.