Analysis of an antibiotic

[shashank_03]

Hi All,
I am in a process to analyze an antibiotic in human plasma using lc-ms/ms system.i have found that the response of my drug drops continuosly.I am using Reverse phase chromatography,i have even changed the mobile phase and columns and still the same thing is occuring?
Does anybody have the solution for this?

Thanks in advance

[Don_Hilton]

A bit more information could be helpful.

Are you runnign a calibration standard (that does not go through sample prep /extraction steps)?

[kerri]

Could depend on the antibiotic used (rapidly degrades, storage issue, etc). Could be due to a method that isn't robust. Could be a instrumental situation (N2 gas unstable, etc). There are more potential problems areas that can be at fault. So as Don said, if you give us some more detailed information...

[krickos]

Could depend on the antibiotic used (rapidly degrades, storage issue, etc). Could be due to a method that isn't robust. Could be a instrumental situation (N2 gas unstable, etc). There are more potential problems areas that can be at fault. So as Don said, if you give us some more detailed information...

Agreed. The sometimes very poor stability penicillins due to pH can be a huge factor.

To give an example drug substance X stored at pH 3 degrades with 10% in 22 hours, at pH 7 10% degradation is achevied in only 1 hour (room temperature).

When we worked a pencilline similar to what described above we cooled all standard/sample solutions and set the LC autosampler comparment to 4-8°C.