Chromatography Forum

I use an OI 4450 tandem PID/FID to analyze volatiles by GC. I am having trouble with peaks topping out and looking rounded instead of nice and sharp. This all started when the bulb went bad and had to be replaced.

The lamp power supply is set to the lowest setting.

The strange thing is, I changed the power supply with another one we had laying around and the lamp is no longer maxing out the detector, but this power supply will not stay lit. Am I looking at 2 defective power supplies here? Has anyone else had any trouble like this?

Thank-you for your time.

omaejel,

Do you have make up flow on the PID side of the detector. Often these units use this to sweep the PID and feed the FID the hydrogen flow. If you turned this off, it would cause a significant increase in sensitivity and degrade the peak shape.

What do the peaks look like on the FID anyway, normal?

Best regards.

Thank-you for your response.

I will double check the make up flow to ensure that it has not been turned off by the analyst that normally runs this instrument, but i do not think it has.

The FID peaks look wonderful and this instrument runs every day for analysis of Gasoline Range Organics.