High speed analysis of complex indoor VOC mixtures by vacuum-outlet GC with air carrier gas and programmable retention

A pressure-tunable, series-coupled column ensemble was used with atmospheric pressure air as carrier gas for the vacuum-outlet GC analysis of 42 volatile and semivolatile organic compounds commonly encountered as indoor air pollutants. Separation strategies applicable to a field-portable instrument that will employ a dual-stage preconcentrator and a microsensor array as the detector were developed, where coelution of certain analytes can be tolerated. The capillary column ensemble consists of a 4.5-m segment of nonpolar dimethyl polysiloxane followed by a 7.5-m segment of polar trifluoropropylmethyl polysiloxane. Good long-term thermal stability of the column ensemble was observed for continuous operation in air at temperatures up to 210 degreesC. A computer-driven pressure controller at the column junction point is used to adjust vapor retention for specified sets of target compounds. The compounds were divided into two groups according to retention order, and high-speed analysis conditions were determined for the two groups individually as well as for the entire mixture. The earlier eluting group of 21 compounds was analyzed isothermally at 30 degreesC in about 160 s using a single, on-the-fly junction; point pressure change during the separation. The later eluting group of 21 compounds was analyzed in about 200 s with temperature programming and a constant (tuned) junction-point pressure. The entire mixture was analyzed in about 400 s using a two-step temperature program and a three-step pressure program, with minimal overlap in eluting peaks. Separations are adequate for analysis by a sensor array capable of discriminating among small groups of coeluting vapors on the basis of their response patterns.