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5 months ago

Progressive reduction of signal

We have two Varian CP-3800 GC units. In the analysis* with TSD (GC1) and TSD or FID (GC2) both chromatographs show a progressive reduction of signal in the detection of nicotine during the day (for example, using TSD in a day the initial ABC is 1000 in the morning and the final ABC is 800-900 in the afternoon). Because both chromatographs are showing the same problem and share the main gas supply lines, we verify and there are no gas leaks.*Using very similar methods: same capillary column type, program temperature, standard solution (fresh or old), solvent, etc.

Does anyone know why this is happening?



5 months agoReply from Dan Ste.Marie
Luz SorianoCan you give the details of your method? Temperatures , gas flows, column, etc? Dan
5 months agoReply from Luz Soriano
avatar placemark Thank you. I have only been using blank (solvent) and satandard solution and during the analysis of this solution is where I have found as a resulta progressive reduction of signal.

5 months agoReply from Dan Ste.Marie
Luz SorianoIt is likely the result of your sample matrix. It is likely something in the matrix is adversely affect the TSD response and then it is able to re-equilibrate overnight. What happens if you run a blank or two.prior to your last standard? Dan

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Varian - CP-3800
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