Troubleshooting
HPLC System Troubleshooting _____________________________________________________________
UV Detector Problems
Temperature, wavelength selection, and the detector time constant affect
noise and drift. If the environmental temperature varies greatly, baseline
drift can occur.
Wavelength selection can influence background noise and signal-to-noise
ratios. In general, lower wavelengths result in increased signal for the
sample as well as the background noise. Balance the gain in signal against
the increase in noise when selecting lower wavelengths.
The detector time constant acts as an electronic filter to reduce baseline
noise. Set the time constant to 1/10th of the peak width (10 points per peak).
Solvent selection is influenced by the wavelength to be monitored; for
example, methanol is good for gradient work at 254 nm, but creates
unacceptable baseline drift at 215 nm. Acetonitrile has much lower
absorbance at low wavelengths, and is suitable down to 200 nm.
Contaminated solvents can cause high background.
Deuterium lamps should last for ~ 1000 hours. Noise spikes in the detector
can arise from lamp filament flicker.
Detector cells are prone to trapping air bubbles from the mobile phase or
micro-particulate matter from the column. The windows can also become
clouded by polymerized organic material with long-term use. Solve bubble
problems in the cell by using a thoroughly degassed mobile phase, assuring
that the fittings are leak-free, and applying a slight backpressure with a
detector backpressure device. The cell should be flushed daily with the rest
of the system.
Noise spikes can arise from lamp problems, air bubbles, or external
electrical interference. Setting the flow to zero and observing the baseline
can help to identify the cause. If the baseline is constant, a bubble is likely,
but if the noise persists, a failed lamp or external electrical problem is more
likely.
Testing UV Detectors
Test a UV detector by monitoring the output either via the analog inputs
(check output voltage) or by viewing the UV detector display.
Injecting a solution of erythromycin, for example, should give a good
response at a wavelength setting of 280 nm.
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___________________________ MSQ Hardware Manual ____________________________
