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An in vitro assay for the acaricidal effect of ivermectin is described. The test is based on the migration ability and survival of Sarcoptes scabiei var. suis mites on the surface of agar gels containing the acaricide. The effect of a given concentration of ivermectin is expressed as an activity index (AI) for the mites, calculated from observed migration and mite survival after 24 h of incubation. In order to allow a concentration-effect curve to be based on true values of the acaricide, a method for the determination of ivermectin in agar gels was developed. Employing this method, ivermectin was demonstrated to be stable in the gels at room temperature for a month, thus allowing storage of gels for later use. The test was found to be accurate, sensitive, easy to carry out and applicable for routine determinations. The lower threshold for acaricidal effect was found to be 50-100 ng ml-1 with the AI showing a reverse linear dependence on the log concentrations above this value.

An in vitro test to determine the acaricidal effect of organophosphorous insecticides (OP) is described. The effect of parathion, phoxim and phosmet against the pig mange mite Sarcoptes scabiei var. suis was evaluated. The test is based on the migration ability of mites on the surface of agar gels containing the acaricide. The mite activity is expressed as a migration index (MI) and compared with the OP concentration in the agar. Good dose-response data were obtained for all three OPs tested, although the instability of phosmet required special precautions concerning the analysis of the agar. The test was found to be accurate, sensitive, easy to carry out and applicable for routine determinations. However, the test requires that the actual concentrations of the OPs in the gel batches are determined. For the three OPs used analytical methods were developed. While the lower threshold for acaricidal effect in vitro was approximately 1-2 micrograms g-1 for all three OPs tested, a significant difference in the higher concentration range was seen between the dose-response curve for parathion and the curves for phoxim and phosmet. While the latter curves decreased only slightly at concentrations above 3-6 micrograms g-1 (corresponding to MI values around 5-10), the curve for parathion was linear down to an MI value of 1, corresponding to a parathion concentration of approximately 30 micrograms g-1. This discrepancy was ascribed to different rates of uptake through the cuticula due to differences in the lipophilicity of the OPs.

A rapid, simple and reproducible high-performance liquid chromatography procedure is described for the qualitative and quantitative analysis of mixtures of cyanogenic glycosides. The separation is achieved by means of a reversed-phase (C8) column eluted with a phosphate buffer, pH 5.0, containing either 15 or 7.5% (v/v) methanol, 7.5% being necessary for resolution of epimeric pairs of the more hydrophilic glycosides. When this separation is combined with enzymatic post-column cleavage and electrochemical detection of the cyanide formed, a highly specific and very sensitive system is obtained. The method was applied to cyanogenic glycosides in crude plant tissue extracts, and compared with both a thin-layer chromatographic method and to a traditional determination of total cyanide released after hydrolysis. Sensitivity, selectivity and accuracy were found sufficient to enable its routine use for analysis of food and fodder samples, for example. Cyanohydrins could be detected qualitatively.

Crude and partly purified extracts from Helix pomatia and linamarase from cassava were immobilized on columns packed with porous glass or silica and used as post-column reactors in the high-performance liquid chromatography of cyanogenic glycosides. Sodium hydroxide (2 M) was added to the flowstream after the enzyme-reactor resulting in the formation of cyanide, which was then detected at a silver electrode by an amperometric measurement at 0 V with reference to a silver-silver chloride electrode. The selective detection of cyanide allows measurements in a complex matrix. The response is linear and the detection limit is in the low picomole range.