Decrease of sensitivity at low concentration ethambutol.

[areeya]

Dear All,

I have question about dramatical decreasing of peak area at low concentration.

I developed the LC/MS method to analyse ethambutol. I use Atlantis HILIC column elute with 75% acetonitrile (0.2% formic acid); isocratic system.

Peak area of ethambutol standard 1 mcg/ml is 4,000,000. Thus, I expect the peak area at 0.1 mcg/ml should be 400,000. However, the result is difference. The peak area at 0.1 mcg/ml is about 120,000.

Does anybody have suggestion?

Thank you,
Areeya

[pliva]

Dear All,

I have question about dramatical decreasing of peak area at low concentration.

I developed the LC/MS method to analyse ethambutol. I use Atlantis HILIC column elute with 75% acetonitrile (0.2% formic acid); isocratic system.

Peak area of ethambutol standard 1 mcg/ml is 4,000,000. Thus, I expect the peak area at 0.1 mcg/ml should be 400,000. However, the result is difference. The peak area at 0.1 mcg/ml is about 120,000.

Does anybody have suggestion?



i think 0.1 mcg/ml is out of your linearity range. try to optimise the chromatographic condition. you can predict the probable area but its not necessary to get the exact. may be the sensitivity of your method is low.





Thank you,
Areeya

[Uwe Neue]

Please tell us if your sample is a standard, or if it is in a biological matrix or any other matrix. If in the presnece of a matrix, the cause of this could be ion-suppression from the matrix.

[Kostas Petritis]

Also, does your peak is symmetrical or does it tails? Sometimes tailing peaks in low concentrations are not intergrated correctly...

What about the intermediate dilutions? Some compounds also when diluted too much you get losses due to adsorption to the vial