another way for bracketing standards

[MK]

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

[aldij]

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.

[Ann]

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

[Ary]

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.

[AA]

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.