Optimization of a Thermal Desorption Method for a Mixture of Volatile Organic Compounds (C1–C10): Comparison of Two Types of Cold‐Traps

Abstract

This study concerns the optimization of the desorption of 42 volatile organic compounds (nonhalogenated and halogenated aliphatic hydrocarbons, alkylated and chlorinated monoaromatic compounds, and terpenes) from a sorbent trap that contains 140 mg of Tenax‐GR and 60 mg of Chromosorb‐106. Gaseous standards were used for this purpose and were prepared using the packed column injector method. Generation conditions were optimized by means of a centered factorial experimental design and fixed at 125°C of injector temperature, 50 mL/min of carrier gas flow rate, and 40 sec of injection time. After tube desorption, analytes were focused on a cold‐trap. The type of cold‐trap determines the load of analytes on the system and, therefore, the method sensitivity. The influence of some variables (times, flows, and temperatures of desorption for tube and cold‐trap) on the whole desorption process was studied using two types of traps: a standard packed cold‐trap, and a low‐flow one. In the case of the standard cold‐trap, no variables have a significant effect on the process, and therefore, tube desorption was carried out at 190°C for 4 min with a helium flow of 100 mL/min. For cold‐trap desorption, values were 275°C, 3 min, and 3.9 mL/min. But in the case of the low‐flow trap, the flow that desorbs adsorption tube and cold‐trap was significant and was classically optimized. The final values were 190°C, 4 min, and 60 mL/min of desorb flow for tube desorption and 275°C, 3 min, and 1 mL/min of outlet split flow for cold‐trap desorption. An important improvement (ca 50%) on method detection limits was observed using the low‐flow cold‐trap.