Table III.
Common causes of excessive peak tailing from anELCD.
Contaminated conductivity cell
Contaminated reaction tube
Contaminated resin cartridge
Contaminated Teflon
®
transfer line
Dead volume between detectors in series
Leak at the base of the reaction tube
Lowmakeup gas flow
Low propanol flow
Low reaction gas flow (hydrogen)
Low reaction temperature (below 850°C)
Unpure gas (carrier / makeup / reaction)
29
Figure 27.
ELCD reactor removed from detector
assembly, reaction tube exposed.
Always
CheckHere
for Leaks.
Nickel
Reaction
Tube
Similarly, theTeflon
®
transfer line between the reactor and the conductivity cell requires fre-
quent cleaningor replacement. Flushing the transfer line should removemost of the contamina-
tion. Todo this, disconnect the line from the reaction tube andplug the drain line leading from
the reaction cell. Thiswill force propanol through the transfer line, flushing contaminationout.
If this does not improve response andpeak shape, replace the transfer line (cat#20121, page27).
Use only high-purity solvents in theELCD (onlyHPLC-grade for halogenmode). The solvent
intake line is equippedwith a scrubber resin cartridge that removes contaminants from the sol-
vent. Tomaintain solvent purity and a stable baseline, change this cartridge every sixmonths.
ELCD:MinimizingPeakTailing:
Peak tailing is a characteristic of the ELCD – the key to
successful ELCD operation is regularmaintenance tominimize the tailing.Most tailing
problems are caused by contamination or leaks in the system. Peak tailing also can be
caused by contamination in theTeflon
®
transfer line from the reaction tube to the conductivi-
ty cell. Table III lists factors that can contribute to tailing peaks. Reaction tube deterioration
can be due towater and/or oxygen corroding the tube surface over time, or to carbon
deposits left by the organic solvent. In purge and trap applications, watermanagement can
help slow this corrosion.
Poor responses for brominated compounds indicate active sites in the pathway. Isolate the
purge and trap system bymaking amanual injection. If responses for brominated com-
pounds still are poor, the reaction tube probably is deteriorating.A combination of tailing
peaks and poor responses for brominated compounds also is an indication that the reaction
tubemust be replaced.Maintain detailed notes on instrument maintenance tominimize trou-
bleshooting problems in the future.
ELCD performance also depends on the internal volume of the conductivity cell. Older
ELCDs have larger cell volumes that causemore tailing. Smaller cells in newer ELCDs sig-
nificantly reduce peak tailing.
Replacement Nickel Reaction Tubes
• Pretreated formaximum sensitivity.
• Quality-controlled for reliability.
• Available for different models.
To replace these instrument part numbers:
Order these
Restek part
numbers:
ELCDModel # Tremetrics
Varian PerkinElmer Shimadzu O.I. Analytical qty.
cat.#
Hall 700A 115439-0003 00-996724-14 0330-2675
—
— 2-pk.
21580
Hall 1000
117459-0003 00-997625-12 N660-1072 220-90435-00
— 2-pk.
21581
O.I. 4420
—
— —
—
183780
2-pk.
21582
