Optimizing the Analysis of Volatile Organic Compounds

Similarly, the PTFE transfer line between the reactor and the conductivity cell requires fre-
quent cleaning or replacement. Flushing the transfer line should remove most of the contamination.
To do this, disconnect the line from the reaction tube and plug the drain line leading from
the reaction cell. This will force propanol through the transfer line, flushing contamination out.
If this does not improve response and peak shape, replace the transfer line (cat# 20121, page 27).
Use only high-purity solvents in the ELCD (only HPLC-grade for halogen mode). The solvent
intake line is equipped with a scrubber resin cartridge that removes contaminants from the solvent.
To maintain solvent purity and a stable baseline, change this cartridge every six months.
ELCD: Minimizing Peak Tailing: Peak tailing is a characteristic of the ELCD – the key to
successful ELCD operation is regular maintenance to minimize the tailing. Most tailing
problems are caused by contamination or leaks in the system. Peak tailing also can be
caused by contamination in the PTFE
Contaminated conductivity cell
Contaminated reaction tube
Contaminated resin cartridge
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 to water and/or oxygen corroding the tube surface over time, or to carbon
deposits left by the organic solvent. In purge and trap applications, water management can
help slow this corrosion.
Poor responses for brominated compounds indicate active sites in the pathway. Isolate the
purge and trap system by making a manual injection. If responses for brominated compounds
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
tube must be replaced. Maintain detailed notes on instrument maintenance to minimize troubleshooting
problems in the future.
ELCD performance also depends on the internal volume of the conductivity cell. Older
ELCDs have larger cell volumes that cause more tailing. Smaller cells in newer ELCDs significantly
reduce peak tailing.
Table III.
Common causes of excessive peak tailing from an ELCD.
Low makeup gas flow
Low propanol flow
Low reaction gas flow (hydrogen)
Contaminated PTFE transfer line Low reaction temperature (below 850°C)
Dead volume between detectors in series
Leak at the base of the reaction tube
Unpure gas (carrier / makeup / reaction)
Replacement Nickel Reaction Tubes
Pretreated for maximum sensitivity.
Quality-controlled for reliability.
Available for different models.
To replace these instrument part numbers:
Order these
Restek part
numbers:
ELCD Model # 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
Figure 27.
ELCD reactor removed from detector
assembly, reaction tube exposed.
Nickel
Reaction
Tube
Always
Check Here
for Leaks.
29
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