Detection of Nitro-Compounds by Organic Semiconductor Sensors

A sensor-based instrument for determination of the composition and concentrations of vapours of organic nitro compounds and nitrogen dioxide in the atmosphere is described. Four organic semiconductor sensors based on fluoroaluminium phthalocyanine (AlpcF), chlorogallium phthalocyanine, chloroaluminium naphthalocyanine and the copper complex of tetraazadibenzo-14-annulene are used in conjunction with platinized platinum preconcentrators. The sensors and preconcentrators are located in separate concentric annular sections of a sample chamber. These sections are rotated by a microprocessor-controlled stepper motor to permit loading of the preconcentrator, relocation to a position directly opposite a sensor, evacuation, and preconcentrator triggering and sensor-response measurement. The importance of the evacuation stage for obtaining fast response, and the need to energize the preconcentrator throughout the measurement stage to prevent readsorption problems, have been demonstrated. The performance of the AlpcF sensor has been evaluated, showing sensitivity to ppm levels of nitrobenzene.