Needle electrode-based microplasma formed in a cavity chamber for optical emission spectrometric detection of volatile organic compounds through a filter paper sampling

A novel microplasma device, which generates discharge in a Poly (dimethylsiloxane) (PDMS) cavity chamber with two normal syringe needles, serving as both gas channels and electrodes, was prepared by an innovative casting technology. This microplasma device maintains a stable discharge even after working under large periods of time (4 h) and even if impurity deposition is produced on the needle electrode tips. The cavity discharge chamber of this device can also be used as a sampling compartment. 14 kinds of volatile organic compound (VOC) samples, with 6 series depending on carbon chain structures and boiling points (from 34.6 to 232.9 °C), can directly diffuse into the plasma by using a filter paper. The filter paper was placed right under the microplasma zone in the chamber. Most VOC samples could be well detected (< 20 min for each) and discriminated in this microplasma system through a portable spectrometer. Combined with the peak ratio (300-900 nm spectrometric range available) analysis, discharge parameters, specific characteristics of each sample and comparison of each homologous group could be systematically made by this device. The present work proposes a new approach for fast screening of volatile organics in water bodies or other solvents. The utility of this device was demonstrated by that BTEX-containing aqueous samples, as an example, could be detected at 50 mg/L level with detection limits of 2.5 μg/L.