Abstract
Quartz crystal sensors for the analysis of carbaryl, 1-naphthol, catechol and 4-aminophenol were developed. The analysis was based on the reaction of the analyte of interest with a phenolic compound to produce an analyte specific product that precipitates out and deposits on the surface of the quartz crystal producing a signal. Carbaryl was first converted to 1-naphthol by alkaline hydrolysis and then detected by a phenolic reaction. The speed of the phenolic reaction and precipitate formation was enhanced by using either potassium periodate or ammonium persulfate initiators. The latter was proved to be more efficient in decreasing the analysis time and increasing the magnitude of the signal. Ammonium persulfate decomposed with time. The effect of ‘aged’ ammonium persulfate on the reaction of 4-aminophenol with o-cresol produced a fast (less than 3 min) and very stable signal. An investigation of the mechanisms of ammonium persulfate decomposition and action on the phenolic reactions was performed. In order to improve the response size, the effect of the presence of organic solvents in the reaction of 1-naphthol with 4-aminophenol was investigated. From the solvents tested (methanol, isopropyl alcohol, dimethyl formamide and acetone) acetone and DMF were more efficient in increasing the magnitude of the crystal response. Large signals that have never reported before in the literature were obtained. The quartz crystal sensors developed, had the required short analysis times but lacked the required lower detection limits. Dry reagent chemistry was incorporated into the quartz crystal sensors to solve this problem. The use of water-soluble polymers (PVA) showed promising results in that direction. Electrochemical quartz crystal microbalance sensors were used for the detection of 4-AP, catechol (an enzymatic product of salicylate) and paracetamol in an effort to improve the detection limit of analgesic compounds and decrease the number of steps of analysis. Large signals (-1000 Hz) in a short time (3 min) were obtained from the electropolymerisation of the analytes on the surface of the quartz crystal. This was performed in the absence of ammonium persulfate demonstrating the great promise held in the use of E-QCM sensors for the detection of these analytes. Key words: quartz crystal, precipitation reactions, 4-aminophenol, E-QCM, phenols analgesic drugs.