Headspace analysis of engine oil by gas chromatography/mass spectrometry.

This study establishes the rationale necessary for determining the time to change engine oil. This is based on identifying gaseous components in new and used automobile lubricants. Key compounds, so-called "signature", are separated and identified qualitatively by coupled gas chromatography/mass spectrometry. Volatile antioxidants at zero miles and fuel contaminants at low mileage are observed in the headspace of engine oil. Several oxidative degradation components have been positively identified in the used oil, which include the following: acetaldehyde, acetone, butanal, 2-propanol, acetic acid, 2-hexanol, benzoic acid, benzaldehyde, and 1-pentanol. This study strongly suggests that the status of lubricating oil can be determined by the analysis of the gas phase above the oil. Most importantly, it opens the possibility of performing conditional maintenance of the combustion engine based on information obtained from gas sensors.

Development and calibration of field-effect transistor-based sensor array for measurement of hydrogen and ammonia gas mixtures in humid air.

A sensor array for analyzing hydrogen and ammonia gas mixtures in humid air has been developed, built into a rugged system, and calibrated for laboratory testing. The sensor array is comprised of four chemically sensitive field-effect transistors (CHEMFETs). Chemically sensitive layers for the sensors were developed and tested using a Kelvin probe. A combination of catalytic and noncatalytic thin layers (palladium and polyaniline) was selected for the four-sensor array. The work function responses of the CHEMFET sensor array to mixtures of hydrogen, ammonia, and humid air were measured. Chemometric multivariate methods, linear and nonlinear partial least squares, were used for the calibration of the sensor array using gas mixtures in the concentration range from 0 to 10 000 ppm hydrogen and ammonia in humid air. The sensor array for ammonia showed good sensitivity, selectivity, response time, and stability and is recommended for field deployment. In contrast, the sensor array for hydrogen, though highly sensitive to hydrogen, demonstrated inadequate stability, requiring further development before deployment is recommended.

Study of electrochemically deposited thin poly(N-vinylcarbazole) films.

In this paper, the influence of the water content in the acetonitrile/LiClO(4) system on the electrosynthesis and the properties of poly(N-vinylcarbazole), PNVC, films is examined. By using conventional resonant frequency and impedance measurements of an electrochemical quartz crystal microbalance (EQCM), information about the electrochemical, morphological and adhesive properties of the thin conducting films were obtained. By changing the water content of the background electrolyte, the degree of cross-linking (through the vinyl group), the doping level and the morphology of PNVC films vary simultaneously. Two limiting cases of film properties were observed: for less than 10 Vol.% water, a highly doped, porous and cross-linked polymer is synthesized. Above 10 Vol.% water content, a dense and smooth film is deposited. The growth at a constant potential was found to be limited by the diffusion of monomers to the electrode. Films grown from a system containing 20 Vol.% water exhibit better adhesive properties to the substrate than those grown from 2 Vol.% water.