Chromatographic Methods for Environmental Analysis - Fundamentals of Environmental Sampling and Analysis - page 282

when sample run is finished because a regular UV lamp can only last certain hours
without substantial decrease in output energy. If HPLC instrument should be idle for
an extended period, add some methanol in water. This will avoid potential bacterial
growth in tubing and reservoirs.
GC Maintenance The key to GC maintenance is probably to follow
manufacterer's recommended maintenance schedule for gas purifier, sample
introduction syringe, inlet septum, inlet liner, column, and detector (refer to
Fig. 10.3). High purity carrier gases are always required. For instance, oxygen causes
rapid column degradation at elevated temperatures, hydrocarbons impurities give
high noise to FID detectors, and water and oxygen are detrimental to ECD detectors.
Sometimes, do not overlook the obvious-make sure the carrier gas is turned on at all
times when the column oven is on.
Replace non-indicating gas trap every 6-12 month or when indicating traps start
to change color. Change inlet septum every 50 or so samples or when signs of
deterioration are visible (gaping holes, fragments in inlet liner, low column
pressure). Replace inlet liner regularly or when dirt is visible in the liner or if
chromatography is degraded. For the GC column, the best practice is the weekly-
monthly trimming off 1/2-1 meter column front if a large load of sample is routinely
analyzed. Columns should not exceed their maximum allowable temperature.
Samples with very high or low pH levels, salts and buffers, strong acids, and excess
derivatizing reagents will greatly shorten column life, and should be avoided. GC
detectors need to be checked on an average of 6-12 month or as needed when a
problem occurs.
FID detectors require little maintenance other than occasionally calibrating gas
flow rates. Clean FID jet as needed when dirty deposits are present, which cause
chromatographic noise and spikes. The primary maintenance for a TCD involves
the thermal ''bake-out'' or replacement of the filaments when wandering baseline,
increased noise, or a change in response is present. Thermal cleaning should also be
performed for ECD when similar chromatographic problems exist. Cleaning
procedures other than thermal, however, should be performed only by licensed
personnel who can handle radioactive 63 Ni in the ECD detector.
General Guidelines on Troubleshooting
A general troubleshooting strategy is presented here first. This includes the
following: (a) take your system apart and think logically. Do not just immediately
reach for your toolbox; (b) look at the symptoms as to when and how the patterns
change; (c) consider the possibilities and determine the potential cause(s); and
(d) do one thing at a time, and eliminate one possibility at a time. Changing too many
parameters at one time will make it hard to diagnose the problem.
As introduced in Section 10.1.5, the chromatogram is the basis for all the
qualitative and particularly quantitative analysis. Likewise, chromatograms are also
the key to diagnose the problem. Since similarities exist between GC and HPLC, we
discuss them together for convenience. When chromatographic interpretation is