HP 5890 Series II, Reference Manual

Page: 204 / 244

Chromatographic Troubleshooting
Baseline symptoms
204
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 N
1
carrier gas,
since suppliers may exercise less care than with other common
carrier gases.