Gradient Step-Test Calculations

[Sallybeetle]

In the recent Gradient Performance Checks Article of LC/GC magazine (10/2004 issue), the Step-Test was calculated using the "theoretical (programmed) value." But, if the data acquisition software output is in absorbance units and the programmed value is in % A and % B, what is the theoretical value? Is the maximum absorbance of 100% B taken into account? Is the acetone level in line B adjusted to obtain close to a 1 AUFS?

I am writing an IQ/OQ that will be used as a model for future HPLC calibrations, and I am incorporating the methods outlined in this article.

I am sure this is just easy math, but it does not make sense to me.

Any help would be appreciated.

[tom jupille]

In theory, each step will generate the same percentage change in absorbance.

[JA]

mathematically, the article indicates you want:
|Bp – Be| ≤ 1

where:
Bp = programmed %B
Be = experimental %B

Be = 100 He / H0+H100

He = step height at Bp
H0 = height at 0 %B
H100 = height at 100 %B

following on from what Tom said, perhaps you could look at the consistency of the step height change (%RSD). For method validations or transfer I think this test is important in terms of accuracy, hence the criterion chosen.

HTH = hope that helps

[Sallybeetle]

Thanks for your help. I basically figured it out once I sat down with pen and paper and graphed it out.

The only difference is that I interpreted the end result wrong. I was calculating it as 1-(Be/Bp).