Detector problems fall into two categories — electrical and mechanical/optical. For electrical problems, you should contact the instrument manufacturer. Mechanical or optical problems usually can be traced to the flow cell. Detector-related problems include leaks, air bubbles, and cell contamination. These usually produce spikes or baseline noise on the chromatograms or low sensitivity.
Some cells especially those used in refractive index detectors are sensitive to pressure. Flow rates or back pressures that exceed the manufacturer’s recommendation will break the cell window. Old or defective lamps as well as incorrect detector rise time, gain, or attenuation will reduce sensitivity and peak height. Faulty or reversed cable connections can also be the source of problems.
Baseline Spikes
- Eliminate bubbles that pass through the flow cell by degassing solvents.
- Check fittings for a leak in the system, and repair as needed.
- Voltage transients on a single circuit may interfere with detector output.
- ensure that the detector and recorder are connected to the same outlet
- to eliminate voltage transients by connecting the detector and recorder power lines to a constant voltage transformer or line filter
- Reduce pump noise by changing the compensation settings on the pump and by examining check valves.
Baseline Noise
- Allow the lamp to warm up.
- Check flow cell for contamination.
- If you see baseline deflection when back pressure is exerted on the flow cell, you probably have bubbles trapped in the cell. Try one of these methods to eliminate bubbles:
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- increase back pressure on the cell by connecting pressure regulator tubing to the flow cell outlet
- flush flow cell using a syringe filled with fresh solvent
- to raise the collector vial to a level higher than the cell
- Check the grounds on all instruments; eliminate ground loops by plugging the detector and recorder into the same outlet.
- Eliminate drafty air currents.
- Eliminate smoke from the environment.
- A lamp may be weak.
- A filter may be defective.
Baseline Drift
- Eliminate changes in ambient temperature. If drift is dependent on temperature, eliminate drafts and avoid areas of direct sunlight.
- Check flow cell for contamination.
- Check for contaminated or bleeding, columns. If drift disappears after you stop the flow, then check the solvents and regenerate or replace the column.
- If you see baseline deflection when back pressure is exerted on the flow cell, you probably have bubbles trapped in the cell. Try one of these methods to eliminate bubbles:
- increase back pressure on the cell by connecting pressure regulator tubing to the flow cell outlet
- flush flow cell using a syringe filled with fresh solvent
- raise the collector vial to a level higher than the cell
- Check the pump or delivery system to determine that the flow rate is constant.
- The lamp may be weak.
- The filter may be defective.
- Check the flow cell for the leak.
Unable to Zero
- Check connections to the recorder.
- Check purity and UV cutoff of solvents. Use only HPLC-grade solvents.
- Eliminate bubbles trapped in the flow cell. Increase the flow rate and apply back pressure by using a syringe or septum to momentarily block the exit stream.
- Check flow cell for contamination.
- Check for contaminated columns. If necessary, regenerate or replace the column.
- Check the flow cell for the leak. Tighten flow cell connections.
No UV Illumination
- The fuse may be blown.
- The 4-pin power supply connector and/or 6-pin lamp connector may be loose.
- The lamp may be defective.
Decreased Response to Known Sample Concentration
- The lamp may be weak.
- The filter may be defective.
- Check connections to a recorder.
- Verify sample concentration and solvent.
Unit not functioning
- Check the cord and power connection.
- The fuse may be blown.
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HPLC
