ABSTRACT
A capacitively coupled contactless conductivity detector for high performance liquid chromatography was developed. The detector was consisted of a signal generator, a signal amplifier, and a pair of tubular electrodes. A plastic connecting tube following the separation column was threaded through the two tubular electrodes. When the separated components passed the region between two tubular electrodes, they would be sensed. The instrumental parameters of this detector were investigated, including the internal diameter of connecting tube,the frequency and voltage of excitation signal, electrodes length, and the gap between two electrodes. The 0.5 mm of internal diameter of connecting tube, 70 kHz of excitation frequency, 60 V of excitation voltage,10 mm of electrodes length and 1.5 mm of gap between two electrodes were finally found to be the best working conditions for the detector. This HPLC-C4D(capacitively coupled contactless conductivity detector) was applied to the analysis of oleic and linoleic acids in Brucea javanica oil. The chromatographic peak area was linear with concentration for oleic and linoleic acids in 5-1000 μg/mL, and the limit of detection reached 2.5 μg/mL and 1.0 μg/mL,respectively. The results demonstrate that the present method is sensitive and accurate, proving this homemade contactless conductivity detector has a great application potential for pharmaceutical analysis in future development.