Gas-phase reactions of mono-, di-, and trimethylamine with various metal salts: The use of piezoelectric crystals in a vacuum system
✍ Scribed by George G. Guilbault; A. Lopez-Roman; S.M. Billedeau
- Publisher
- Elsevier Science
- Year
- 1972
- Tongue
- English
- Weight
- 330 KB
- Volume
- 58
- Category
- Article
- ISSN
- 0003-2670
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✦ Synopsis
For the past thirty years, most studies of gas-solid interactions have been carried out by chemists seeking to learn more about the structure of gases adsorbed on catalytic surfaces. Infrared spectroscopy has proven to be very useful in studying directly these chemisorption reactions and many review articles have been written on this topic 1-3. Recently, Guilbault and Billedeau 4'5 have shown by infrared techniques that the methylamines form chemisorption products with many transition metal salts.
Piezoelectric quartz crystals are currently used for frequency control in communications equipment, selective filters in electronic equipment, measurement of the temperature and the dew point of gases, and in very accurate clocks. King 6 demonstrated that quartz crystals could also be used as sorption detectors by coating the crystals with appropriate compounds. In these applications advantages are taken of the very high sensitivities of the vibrating crystal to the adsorption of materials on the crystal surface.
The presence of a solid on the crystal surface will alter the frequency of vibration, but the amplitude is hardly affected. A film of liquid or solid on the surface, however, reduces the amplitude of the vibration, and if a gas dissolves into the liquid or solid, the amplitude is reduced further.
The change in frequency of the oscillating quartz crystal according to the Sauerbrey's equation 7 :
where AF is the frequency change due t ° the coating in Hz, F is the frequency of the quartz plate in MHz, A is the area of the coated electrode in cm 2, T is the thickness of the plate in cm, and AW is the weight of the deposited film in g. For common crystals this equation is reduced to AF = -2.3.106. F:.AW/A
(2)
This equation predicts that commercially available 15-MHz crystals having electrodes 5 mm in diameter will have a mass sensitivity of 2600 Hz per #g of material adsorbed by the 6rystal. A detection limit of about 10-1 e g can be calculated, indicating that the piezoelectric crystal detector has the potential to be one of the most sensitive of all detectors.