Just wondering if anyone has had any unusual experiences with reproducibility of caffeine. The method is quite simple and works well for about 15-10 injections after that injection accuracy deteriorates?? It doesn't appear to be a carryover issue but any advice on better caffeine determinations is much appreciated.

Thanks in advance

Mr. Bunsen Burner

Hello Mr Bunsen Burner


1 - What is your caffeine matrix? Is there any degradant caffeine compound in your sample?
Is it possible extract the caffeine of the sample before the injections?

2 - What is the pH of the caffeine solutions and the pH of the mobile phase?

3 - Is the loss of the reproducibility accompaned
by caffeine degration? Are there news peaks in the
chromatograms? Is there variations on the caffeine
time retention?

Hi Carlos

The mobile phase is buffered and pH to 4 and the standards are made up in the mobile. (samples are diluted soft drinks). There does not seem to be any degradation peaks. The Autoinjector is cooled to 4oC and the column oven is 30oC.
There does seem to be slight retention time shifts occationally. Of the two standards (80 and 120ppm) the 80 seems to give better %RSD's more consistantly than the 120ppm??

Any ideas or help is much appreciated.

BB.

Helo Ms B.B.

1 - Can your method garantee the Accuracy and Precision on 80 and 120ppm? What is the range of your method?

2 - What is your criteria of acceptance to your minim %RSD? What is the %RSD for standard 80ppm and 120ppm?

3 - It is not concordant with the literature but
a method can to have better %RSD for 80ppm.

Happyness,

Carlos Teixeira

What is your buffer?