Equilibrium distribution sampling device for preparation of calibration mixtures for gas chromatography-mass spectrometry†
A simple approach for preparing standard mixtures of volatile and semi-volatile organic compounds is reported. When placed in a closed container, standard mixture components partition between a polymeric material such as poly(dimethylsiloxane) (PDMS) and headspace to provide constant vapor concentrations. The granular form of heat-conditioned PDMS provides rapid equilibration with the headspace vapor and serves as a standard reservoir. Solid phase micro extraction (SPME) or gas-tight syringe can be used to deliver sample from the headspace to the analytical instrument. Quantitative calibration can be achieved with either active temperature control or by using a previously constructed look-up table. The effects of PDMS form and temperature on equilibrium distribution, initial equilibrium time, and re-equilibrium time after sampling were investigated. With respect to long term use and stability, analytes introduced onto 2.0 g of PDMS in a 7.4 mL vial were sampled more than 114 times during a test period of 43 days, giving chromatographic peak area %RSD values below 4.5% for all compounds. This device was designed to be solventless, quantitative, reproducible, environmentally friendly, and robust for routine evaluation and calibration of gas chromatography-mass spectrometry (GC-MS) systems.