Calibration for On-Site Analysis of Hydrocarbons in Aqueous and Gaseous Samples Using Solid-Phase Microextraction

Rapid sampling and sample preparation methodology was investigated using adsorptive poly(dimethylsiloxane)/divinylbenzene and Carboxen/poly(dimethylsiloxane) solidphase microextraction (SPME) fiber coatings and volatile aromatic hydrocarbons (BTEX: benzene, toluene, ethylbenzene, and o-xylene). Aflow-through system was used to generate a standard aqueous solution of BTEX as model sample with known linear velocity. Parameters that affect the extraction process, including sampling time, concentration, water velocity, and temperature, were investigated. Very short sampling times from 10 s and sorbents with strong affinity and large capacity were used to ensure the effect of "zero sink" and to calibrate the extraction process in the initial linear extraction region. Several different concentrations were investigated, and it was found that mass uptake changes with concentration linearly. The increase of water velocity increases mass uptake, though the increase is not linear. Temperature does not affect mass uptake significantly under typical field sampling conditions. To further accurately describe rapid SPME analysis of aqueous samples, a new model translated from heat transfer to a circular cylinder in cross-flow was used. An empirical correlation to this model was used to predict the mass-transfer coefficient. Findings indicate that predicted mass uptake compares well with experimental mass uptake. The new model was tested for rapid air sampling, and it was found that this new model also predicted rapid air sampling accurately. Findings presented in this study extend the existing fundamental knowledge related to rapid sampling/sample preparation with SPME.