Optimizing the Analysis of Volatile Organic Compounds

28
Ultra-High-Purity Brass
Line Regulator
Use wherever you
need to reduce the
line pressure by
20psi or more.
Same purity level
as high-pressure
cylinder regulators.
Fitting qty. cat.#
1 /4" female NPT ports* ea. 21666
* Please order appropriate male connector,
pipe-to-tube fittings; see our catalog.
www.restekcorp.com
Figure 25.
Electrolytic conductivity detector: propanol tank with pump.
Drain from Cell
To Pump
To Cell
Out of Pump
Propanol
Pump
Figure 26.
With any detector, always be sure that gas flows are adjusted properly.
PID Makeup
H2
PID Purge
ELCD Maintenance and Troubleshooting: ELCD performance depends on the reactor temperature,
the volume of the conductivity cell, the propanol flow rate, the hydrogen gas flow
(Figure 26), and the purity of the solvent system. The goal is to minimize tailing as much as
possible without losing sensitivity. Depending on the amount of use and the types of samples
analyzed, the nickel reaction tube – the reaction catalyst – should be replaced as often
as monthly. Hydrocarbons and certain other compounds can “poison” the reaction tube and
reduce its catalytic activity. Oxygen and moisture can oxidize the reaction tube, affecting
sensitivity. High-purity hydrogen gas is critical for a stable baseline. Use gas regulators with
stainless steel diaphragms and the proper purifiers for reaction gases.
A drop in sensitivity (particularly for brominated compounds), baseline instability, or
appearance of unknown peaks indicate it might be necessary to replace the reaction tube.
Reconditioning the reaction tube might restore baseline stability: disconnect the PTFE
transfer line, then increase the reactor temperature to 1000°C for one hour, then reset the
reaction temperature to 900°C for re-calibration.