Chromatography Forum

Hi All,

An example of an injection sequence:

std-1
sample-1
sample-2
sample-3
sample-4
sample-5
sample-6
std-2
sample-7
sample-8
sample-9
sample-10
sample-11
sample-12
std-3

This would normally be quantified by calculating samples 1-6 based on std-1 and std-2 average and samples 7-12 based on std-2 and std-3 average?

I'm working on a method with a slight trend/drift and started to think of following alternative: samples 1 and 2 based on std-1 only, samples 3 and 4 based on std-1 and std-2 average, samples 5, 6, 7 and 8 based on std-2 only, samples 9 and 10 based on std-2 and std-3 average and samples 11 and 12 based on std-3 only.

The idea was that the two samples before and after a standard (samples 5-8) would have closest conditions to the standard in the middle (std-2). The two samples in the middle of the bracket (samples 9 and 10) would represent "average conditions" etc.

Any comments? Someone using a similar method?

thanks
MK

this asumes that the respons from standard 1 and standard 2 are realy different. if that is the case you have a bigger problem then your bracketing-scheme. i think it would be wise in that case to inject mere standards.

I agree with aldij. Injecting your standards more frequently is certainly a better option.

If your method is stable ie no drift then in your example I would always average all of your standards and calc all samples relative to this one average value. If you have a method where you are seeing drift then like the other respondents I would use standards at least after every other sample and average the standards in pairs. A good check is to put a sample in at the beginning and again at the end of your sequence and if the bracketing is working you should get the same answer.

Like many things in chromatography, if you can show that using this technique gives answers that are no different than what you get using a more tradition approach, then it is valid. If you can validate the method using this exact technique, then the technique is valid. Simple.