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  • Author or Editor: W. O'Hare x
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Abstract  

Headspace analysis by means of sensor arrays has been successfully applied to a wide range of qualitative applications. In this study, a six element array of coated Quartz Crystal Microbalance (QCM) sensors was used for the headspace analysis of milk volatiles. The sensors were exposed to uncontaminated samples of milk and samples contaminated with Pseudomonas fragi (Ps. fragi) or Escherichia coli (E. coli). Principal component analysis (PCA) was used to analyse the sensor array responses. No discrimination between uncontaminated milk samples and those contaminated with Ps. fragi was observed. This can be explained by Ps. fragi being a poor fermenter of milk. However, encouraging results were found for the discrimination between the milk samples and those contaminated with E. coli.

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Abstract  

Quartz crystal microbalances have high mass sensitivities. Their application in gas sensing has been limited because they are required to have both high selectivity and reversibility. Yet by the inherent nature of their operation these properties are mutually exclusive. One approach to this problem is to use an array of quartz crystal microbalances. We have used an array of six coated quartz crystal microbalances for the classification of methanol, propan-1-ol, butan-1-ol, hexane, heptane and toluene. A novel classification scheme using fuzzy membership functions was found to be highly efficient.

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Abstract  

An electronic nose utilising an array of six-bulk acoustic wave polymer coated Piezoelectric Quartz (PZQ) sensors has been developed. The nose was presented with 346 samples of fresh edible oil headspace volatiles, generated at 45°C. Extra virgin olive (EVO), Non-virgin olive oil (OI) and Sunflower oil (SFO), were used over a period of 30 days. The sensor responses were then analysed producing an architecture for the Radial Basis Function Artificial Neural Network (RBF). It was found that the RBF results were excellent, giving classifications of above 99% for the vegetable oil test samples.

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Abstract  

The effect of different relative humidity (RH) on the response of a six-polymer coated Quartz Crystal Microbalance (QCM) sensor based electronic nose (EN) was investigated, RH 30 and 50% respectively. Increases in the sensor responses were observed for an increase in RH. A stainless steel pre-concentration tube (PCT) containing Porapak-S and a nichrome heating element was developed to minimise the effect and allow for chromatographic pre-separation. Breakthrough times of chemical compounds through the PCT were experimentally determined and used to select a mixture of water and toluene as a suitable sample for pre-separation. The PCT was capable of separating the water from the toluene and the EN was competent at evaluating the concentration of toluene in the solution.

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