why the peak goes -ve initially

[shullur]

inj temp=270 degrees
fid temp=270 degrees
oven temp=100 degrees
with the above conditions on a gc i inject the methanol. the peak goes initially in the negative side before going +ve.

what may be the reason

[Bruce Hamilton]

What carrier gas, detector, split injection ratios, how much injection etc etc.

Assuming FID, one likely cause is a large injection volume disturbing the FID, which can usually be fixed by adjusting detector gas flows, split vent, or injection volume.

Bruce Hamilton