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 atmospheri c pressure air as carrier gas for the vacuum-outlet GC analysis of 42 volat ile and semivolatile organic compounds commonly encountered as indoor air p ollutants. Separation strategies applicable to a field-portable instrument that will employ a dual-stage preconcentrator and a microsensor array as th e detector were developed, where coelution of certain analytes can be toler ated. The capillary column ensemble consists of a 4.5-m segment of nonpolar dimethyl polysiloxane followed by a 7.5-m segment of polar trifluoropropyl methyl polysiloxane. Good long-term thermal stability of the column ensembl e was observed for continuous operation in air at temperatures up to 210 de greesC. A computer-driven pressure controller at the column junction point is used to adjust vapor retention for specified sets of target compounds. T he compounds were divided into two groups according to retention order, and high-speed analysis conditions were determined for the two groups individu ally as well as for the entire mixture. The earlier eluting group of 21 com pounds was analyzed isothermally at 30 degreesC in about 160 s using a sing le, on-the-fly junction; point pressure change during the separation. The l ater eluting group of 21 compounds was analyzed in about 200 s with tempera ture programming and a constant (tuned) junction-point pressure. The entire mixture was analyzed in about 400 s using a two-step temperature program a nd a three-step pressure program, with minimal overlap in eluting peaks. Se parations are adequate for analysis by a sensor array capable of discrimina ting among small groups of coeluting vapors on the basis of their response patterns.