Environmental Engineering Reference
In-Depth Information
will make you work more efficient. This is the time to pay off what
you have learned regarding the fundamentals of separation and detection
theories.
Optimization could be a trial-and-error process sometimes depending on
what the special circumstance is. Sometimes a method can be developed
easily by just using a column of appropriate stationary phase with a few
adjustments (e.g., mobile phase compositions in HPLC, or temperature
gradient in GC). When this is completed, proceed to inject a series of
standard solutions to obtain a calibration curve and continue to run the
samples for possibly more needed adjustments.
10.5.3 Overview on Maintenance
and Troubleshooting
Many topics and monographs are available regarding the practical aspects of various
chromatographic instruments focusing on maintenance and troubleshooting. Several
of these are listed as the suggested readings suitable for readers of various levels and
skills (e.g., Agilent, 2002b; Kromidas, 2004; Sadek, 2000; Suyder, p. 997). Provided
below are some important but obviously not exhaustive lists of maintenance and
troubleshooting guidelines. Generalizations are kept at minimum in an effort to give
readers, in particular the first-time users, some specific and useful tips.
General Guidelines on Maintenance
HPLC Maintenance Generally HPLC instruments need more regular
maintenance than GC for its proper function. The use of clean mobile phase and
samples, frequent flushing and on-time replacement of instrumental parts of injector,
autosampler, pump, column, and detector (refer to Fig. 10.4) are among the most
important.
Samples and mobile phase frequently contain particles that are not visible
with naked eyes but are detrimental
to HPLC (cause clogging) and must be
removed by membrane filtration (0.25
m) or centrifugation. When salt buffer is a
part of the mobile phase, extensive flushing must be performed after the
completion of sample run to avoid accumulation of any salt residual. Several parts
in the flow path (as described in Section 10.2.2) are subjective to periodical
replacement because of possible clogging, including inlet filter, in-line filter, and
guard column. Other replaceable parts include pump seals, injector rotor seals,
syringe, and UV lamp. Recommended schedules for average usages are listed as
following: replace pump seal after 1-2 years; replace autosampler rotor seal not later
than 7000 injections or 3000 injections if salts are used; replace syringe annually;
replace UV lamp not later than 4000 h, clean detector cell after every 2 years
(Meyer, 2004).
A guard column should always be installed to extend the life of more expensive
analytical column. To extend the useful life of UV detector, turn off the UV light
m
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