Page 1 of 1
caliberation curve slop keep on decrease
Posted: Wed Nov 16, 2005 7:33 pm
by 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.
Posted: Thu Nov 17, 2005 3:11 am
by james little
i would suspect that it is the mass spec. Possibly need to clean the source?
Posted: Thu Nov 17, 2005 5:08 pm
by meillid
Thanks. I have clearned the MS, problem still there. Any other suggestions?
Posted: Fri Nov 18, 2005 4:37 pm
by 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?
Posted: Fri Nov 18, 2005 5:35 pm
by 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.
Posted: Fri Nov 18, 2005 6:00 pm
by MG
What is your matrix? Also, what about QC standards interspersed with your samples: are they generally lower than the theoretical value?
Posted: Sat Nov 19, 2005 10:49 am
by 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
Posted: Mon Nov 21, 2005 6:40 pm
by 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.