A new analytical system, based on an acoustic wave sensor, for halitosis evaluation

A new inexpensive analytical system to analyze H2S in the exhaled breath is presented. The system is based on an acoustic wave sensor, employing a piezoelectric quartz crystal with a chemical coating sensitive to the analyte (triethanolamine). The paper addresses the choice of the quartz crystal coating and of the adsorbent used in the preconcentration column, as well as the optimization of the crystal cell design, oscillator and frequency counter. It includes also an extensive study on possible interferences and on its elimination. The analytical system composed of the H2S sensor, the preconcentration column and water absorbents, allowed the injection of sample volumes of 400 mL, which made possible to reaching detection limits of 50 ppb (v/v). This low detection limit, allied to a sensitivity of 85.6 Hz/ppm, was effective in discriminating healthy individuals from patients with periodontal disease. H2S levels from 170 ppb (v/v) to 1625 ppm (v/v) were found in breath samples. All healthy individuals showed levels of H2S lower than 255 ppb (v/v). Patients known to suffer to some kind of gum pathology presented a wide range of H2S concentrations in the exhaled air, which could only be explained after more extensive clinical evaluation.