Chromatographic Troubleshooting
Baseline symptoms
2.Baseline is erratic, moves up and down (wander):
C Suspect a leak in the system: Check septum condition and replace if necessary. Check column connections.
If the leak is at the detector end of the column, retention times are stable from run to run, but sensitivity is reduced. If it is at the inlet end, sensitivity is reduced and retention times are delayed.
Noise
Noise is rapid vertical baseline fluctuations, broadening the baseline and giving it a hairy appearance. Noise is different from spiking; spikes are isolated events, rather than almost continuous, and are described on the next page.
Some noise is inevitable with any detector. At high attenuation it is invisible but appears as attenuation is decreased. Noise limits useful detector sensitivity; thus, it should be minimized.
1.Noise appears suddenly on a previously clean baseline:
C Consider all changes made recently in the system: Reduced attenuation, for example, makes noise more apparent, though the absolute noise level is unchanged.
C New septa may contribute noise from bleed of low molecular weight material. If noise decreases when inlet temperature is lowered, this is a likely cause. Only highest quality septa should be used.
C Contaminated carrier gas: If a tank was replaced recently, and the old one is available and has some gas left in it, try the older tank to determine if noise decreases.
If the new gas is so badly contaminated it saturates traps, changing to the old gas may not show improvement until traps are regenerated. This problem is most common with N1 carrier gas, since suppliers may exercise less care than with other common carrier gases.
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