Chromatography Forum

I am using Chemstation software and in the Extended Performance report it list 4 different calculations for Theoretical Plates

1.Tangent Method
2. Halfwidth Method
3. 5 Sigma Method
4.Statistical

Which of the four above is equivalent to the USP formula for calculation Theoretical Plates. I have tried to look it up but have been unable to get a clear answer.

Thanks for your help

The USP method is 16*(tR/BW)^2 where tR is retention time and BW is baseline width. BW is calculated from the tangents at the inflection points on the leading and trailing edges of the peak.

The EP method is 5.54*(tR/W50)^2 where tR is retention time and W50 is width at 50% of maximum.

If you assume a Gaussian peak shape, they give the same numbers. Of course, real peaks are usually not Gaussian.

i am almost completely sure its the halfwidth method.. thats the figure i used with chemstation.... and as far as i can remember that was the USP one!

No Chellie. Mark is correct. The USP method is the tangent method.

I was able to confirm that it is indeed the Tangent method.

Thanks for your help