Chromatography Forum

Does anyone other than the EPA use Peak Gaussian Factor to evaluate chromatography?

I have seen software that will calculate either Peak Tailing Factor or Peak Asymmetry automatically, but none that do PGF. For this we still have to print out the chromatogram and physically measure the height and width at 1/2 and 1/10 height to calculate using PGF= 1.83(W half height)/(W tenth height).

Does it really tell you anything different than either of the two other measurements will about the chromatography?

I have just always been curious about this one. Besides, with modern computer integrator software, even the area of tailing peaks is calculated quite accurately.

Is peak gaussian factor a leftover from the old days? Like 12 hour tune checks and 4 minute purges for P&T VOAs.

Is peak gaussian factor a leftover from the old days? Like 12 hour tune checks and 4 minute purges for P&T VOAs.

Probably so. It is included in methods like 508, 508A, 515, 531, ect.

These methods have not been updated in decades, and the drinking water branch of the EPA has to do things differently from waste water and RCRA so that is probably why it was included. I have just never understood the need to calculate the same thing multiple ways when one will do just fine.

EPA 625.1 and 8270 use Tailing Factor instead of PGF, which most software will automatically calculate which is simply the back half of peak width at 10% height divided by the front half of peak width.

What really doesn't make sense is that most of the tailing that would interfere with resolution or integration occurs below 5% peak height and that is ignored in all the calculations dealing with peak shapes that evaluate chromatographic performance.

Besides, with modern computer integrator software, even the area of tailing peaks is calculated quite accurately.

Was tailing ever an issue for the area integration? As far as I know there are 2 types of integrating algorithms:
1. Determine the boundaries of the peak and use Trapezoid integration or Simpson's Rule. These are probably the most popular choices and they shouldn't have issues with the tailing.
2. Model based: come up with a mathematical model for peak shape (e.g. Gaussian), then determine the parameters for the formula (e.g. amplitude, width, SD) that would minimize the difference between mathematical model and the real data. These work badly if the peak doesn't follow the mathematical model - tailing doesn't allow to accurately describe the peak with a Gaussian model.

My understanding was that the 2nd option isn't very popular. And we don't like tailing/fronting because it's impossible to tell apart a true tail and a well-hidden shoulder.

But maybe those were different times and this Peak Gaussian Factor was introduced simply because model-based approaches were more popular. And the guidelines were written for this type of algorithms. But that's just a guess.

What really doesn't make sense is that most of the tailing that would interfere with resolution or integration occurs below 5% peak height and that is ignored in all the calculations dealing with peak shapes that evaluate chromatographic performance.

But does it really matter at which height we measure tailing factor? If we measure it at 1%, we'll get a bigger value. But then the acceptable range for this value would be different.