Development of a compact sample pre-concentration system for the detection of a trace amount of volatile organic compounds (VOCs)

Abstract

A new pre-concentration system was developed for a trace detection of VOCs by adopting a ceramic heater, a dc power supply, a three-way solenoid valve, a micro-diaphragm pump, and a programmable logic control system. The adopted ceramic heater was made by coating carbon powder onto the inner wall of a ceramic tube and by additional coating of silver paste both on the inside as well as outside of the rims of a ceramic tube to create electrical connection with dc power supply. Various adsorbing materials, such as charcoal powder, molecular sieve, and Tenax-TA, were packed inside the ceramic heater for pre-concentration of VOCs from a sample reservoir. The ceramic heaters were prepared to have a resistance ranging from 10 to 25 Ω, and the heating time was optimized from 8 to 16 s in order to maximize the thermal desorption of the adsorbed VOCs while avoiding any possible damage to the ceramic heater. The performance of the developed system was estimated by measuring the enhancement of ion signals for VOCs by using the pre-concentration system and the laser photoionization mass spectrometry. The signal enhancement was identified to be better than 40 when compared to the signals measured without the pre-concentration device.