Loss Of Sensitivity Or Excessive Drift; Loss Of Peaks In Specific Areas Of The Chromatogram; Extraneous Peaks - Agilent Technologies 7820A Service Manual

Agilent 7820 GC Service
253

Loss of sensitivity or excessive drift

Several possible causes exist for overall deterioration of the
chromatogram.

Contamination in the valve requires a thorough cleaning.

Internal leakage requires a complete disassembly and
inspection of the mating surfaces.

Poor temperature control may require a full check of
electronic and thermal components.

Lack of proper conditioning techniques, columns, etc.

Failure or deterioration of other components (columns,
detectors, etc.).
Loss of peaks in specific areas of the
chromatogram
Entire sections of chromatographic data can be lost due to a
valve that does not rotate or one that rotates improperly. Other
than obvious component failures (solenoid, actuator, etc.),
improper adjustments and misalignments cause most problems.

Check that adequate air (about 482 kPa or 70 psi) is
supplied.

Check the valve. Is it rotating?

If the valve rotates, check for proper alignment of the
actuator, mechanical binding or slippage of connecting parts.

Check for blocked flow paths with valve in both positions.

Extraneous peaks

Air peaks are sometimes seen in a chromatogram when leakage
occurs because the valve rotor does not seal properly. These
leaks may not be detectable using the soap-bubble method.
If a leak is suspected but cannot be located with soap bubbles, a
pressure check will determine definitely if a leak exists.
Extraneous peaks can occur due to contamination or improper
conditioning of the valve. If leaks are not apparent, clean or