caliberation curve slop keep on decrease

[meillid]

Hi, I use API 2000 ms/ms to do a drug qutitative analysis. but the caliberation curve slop keep on decreasing although I do use a internal standard. Anyone can help? which part , LC or ms is resposible for it? Thanks.

[james little]

i would suspect that it is the mass spec. Possibly need to clean the source?

[meillid]

Thanks. I have clearned the MS, problem still there. Any other suggestions?

[MG]

Do you mean that the curve is nonlinear, with decreasing slope at higher concentrations? Or do you mean that on multiple analyses of the calibration curve, the slope of the line keeps decreasing?

[meillid]

MG, thanks for reply. It is the later one, decreasing when comparing multiple caliberation curve, the later aquired one always has a lower slop that the earlier aquied one.

[MG]

What is your matrix? Also, what about QC standards interspersed with your samples: are they generally lower than the theoretical value?

[alealbor]

Hi Meillid,
Is it an old or new MS method? I need more information about the condition MS and LC method. Could be possible to have a MS method robust problem.





Alejandro

[meillid]

hi, Thanks all for the replies. I found out the problem. the outlet line of the injection port is gradully cloging when the pump was finally shut down by high pressure, after replace the line, caliberation curve come back to normal. Thanks again for all the discussions. I really enjoy here.