Search

A relatively simple, rapid extraction technique based on acetonitrile was combined with the use of screen-printed electrodes bearing cholinesterases to detect organo-phosphate pesticides from an otherwise intractable matrix, sheep wool. It proved possible to separate, for convenience, the exposure of the electrodes from measurement of their (inhibited) activity. The electrodes were used once and then discarded. Estimation of the extent of inhibition is dependent on reference to the activity of control electrodes. The presence of pesticides in the extracts could be detected with any of three commonly available cholinesterases but the most sensitive enzyme was butyryl cholinesterase from horse serum.

Amperometric sensors based on lactate oxidase and platinized carbon were constructed entirely by screen-printing. They were used to estimate the lactate concentration in diluted samples of yoghurt and buttermilk. Estimates made in untreated (apart from dilution) solutions were subject to bias, relative to values obtained from spectrophotometric assays. Removal of cations improved the accuracy of the estimates. Calcium may have made a small contribution to the bias but the nature of the inhibition is otherwise unknown. With untreated samples, determinations of any accuracy require sufficient dilution to avoid such bias, although the smaller signals resulting from dilution place more demands on calibration and manufacturing standards. The relative standard deviations of estimates, based on variation among sensors, of the most dilute samples were generally too high for practical use. The errors of estimates at lower dilutions approached those of screen-printed sensors made under industrial conditions.