disapperance of peak

[joyce]

There were supposed to be 3 peaks on my standard, 1 internal standard and 2 other isomer, cis I and cis II. These 3 peaks appearded on my first run at 235C. However the third peak did not appear after the column oven temperature (230C) as well as when i set back to 235C.
Please help. Thank you.

[k66]

Give more details. what kind of substance. Did you make overheat befor right injetion?

[joyce]

Sorry for the brief statement.
My sample contains Cis I and Cis II isomer. Together with the internal standard, there are supposed to be 3 peaks, in which the retention time windows for the internal standard is apprximately 14 min; cis I- approximately 29 min; and cis II-approximately 27 min.

Most of the time when i only managed to get my cis I but never cis II. I have tried to adjust the oven temperature as well as the flow rate but it just doesn't seem to work.

I am using an autosampler with splitless injector and DB-1 capillary column.

Please help.

[chromatographer1]

Joyce,

Your information is still too sparse for the forum to help you.

Please try to clarify with more details: the analytes involved, the solvent used for injection, how much you are injecting, the injector and detector temperatures, the detector used, and the levels you are trying to detect.

Thanks,

Rod

[joyce]

I will try to explain as detail as possible.

I am using a 30m/0.25mm (id) with DB-1 of 0.25um film thickness coated with dimethyl polysiloxane packing.
The column temperature is between 225 to 235C, isothermal, injection prt is 260C and detector-300C, FID as rate is 0.8mL/min with the injection valume of 1uL.

I am using tetrahydrofuran as my solvent for my sample with dioctyl phthalate as my internal standard. I am supposed to test the percentage of the active ingredient in my sample, which would be around 10% (w/w).

Hopefully these details will be able to help me to solve this problem.