Automated dynamic headspace organic solvent film microextraction for benzene, toluene, ethylbenzene and xylene: Renewable liquid film as a sampler by a programmable motor

A simple, fast and efficient dynamic headspace-organic solvent film microextraction (DHS-OSFME) method using a new automatic device was developed. The renewable organic films were formed inside a microsyringe barrel using the uniform and repeated movement of the syringe plunger enabled by programmable stirring motor. The plunger speed, number of extraction cycles, and dwell time (stop time after each half round) were controlled by a computer software, which was written by C++ Builder. A theoretical treatment of the DHS-OSFME based on the consecutive first-order process is proposed in this report. A mathematical solution for the dynamic process of the mass transfer was obtained by correlating the variation of analyte concentration in the syringe volume with the plunger speed and the amount of analyte extracted to the OSF. Benzene, toluene, ethylbenzene, and o-xylene (BTEX) were employed as model compounds to assess the extraction procedure and were determined by gas chromatography-flame ionization detection. Of the three organic solvents (1-octanol, benzyl alcohol and n-dodecane) studied as extractants, n-dodecane proved to be the most sensitive solvent for the extraction of these analytes. Several parameters, including the syringe withdrawal rate, dwelling time, number of extraction cycles, sampling volume, sample temperature, and ionic strength of the solution, were investigated for their effects on the extraction performance. The calibration graphs were linear in the range of 0.5–200 ng ml−1, with the detection limits between 0.18 and 0.35 ng ml−1. Wastewater samples were extracted by the optimized method, and determined using the standard addition method.