Application of solid adsorbent-coated quartz crystal sensor

Though activated carbon is well known for its capability to adsorb most organic substances, it lacks selectivity on the adsorbates. Keeping the ruggedness and stability of the activated carbon, molecular sieve has the selectivity which gives different adsorptivity depending on the molecular size of the adsorbates. The molecular sieve is coated onto one electrode of a quartz crystal oscillator to fabricate a gas sensor in this study. The detection performance of the sensors with two different pore sizes of the molecular sieve is examined from their implement in the determination of methanol, ethanol and n-hexane concentration in air. From the performance test, the ruggedness, sensitivity and selectivity of the sensor are investigated. From the variation of oscillation frequency of the sensor, it is found that the variation is proportional to the concentration of the organic vapors. The sensors show good recovery to the initial state when fresh air is provided. While the activated carbon coated sensor doesn't show selectivity among different organic materials, the molecular sieve coated sensor gives selective detection from methanol and ethanol mixed vapor.