YAMAMOTO CO., LTD.

Outline of Measuring Method

Clean-up Operation

Samples of chemical residues and mycotoxin are natural substances of agricultural produce and animals, and contain a large amount of various organic compounds. There are approximately 600 kinds of agricultural chemical and more than 100 kinds of mycotoxin, which must be measured in the concentration of ppm or ppb. To successfully extract agricultural chemicals and mycotoxin from the sample, therefore, substances that interfere with the analysis such as color materials, fat, protein and sugars have to be removed. This operation is called clean-up. Clean-up is an important operation and there are several clean-up methods, such as liquid phase partition method, distillation method, coagulating method and chromatography (adsorption, distribution, ion-exchange, gel filtration, thin layer).
A fully-automated clean-up machine using gel-filtration chromatography is commercially available.

Quantitative Analysis

After clean-up, a quantitative analysis is done. The method is highly discriminating and must be highly sensitive.
It, therefore, uses a detector such as the gas chromatograph and the high-performance liquid chromatograph.
Analyzing of chemical residues and mycotoxin is related to micro-measurement, and requires the special reagent for analyzing of chemical residues or a reagent of a highly purified type. All glass equipment must be carefully cleaned.
Especially when electron capture detector gas chromatograph (ECD) is used, all glass receptacles must be cleaned with the solvent to remove chemical residues.
In the actual analysis, it is necessary to do a recovery test and confirm the detection limit using a reagent from the same lot as that used for the analysis.

Preparing a Sample

When storing an analysis sample of chemical residues, make sure to store it in a freezer or a refrigerator to prevent the sample from volatiling or being decomposed. Residual chemical content varies depending on the portions of agricultural products, therefore, the sample should be taken from a predesignated portion. Take 500~2,000g of the sample, homogenize it, and use 20~100g each for the analysis. Vegetables and fruits are homogenized by adding water as necessary. Care should be taken as some chemical residues might be decomposed by enzymes included in vegetables and fruits or under certain pH conditions. Cereals are crushed to 40 mesh by a milling machine for analysis. The mycotoxin sample represents local pollution. It is important that the whole of more than 1kg of sample grains be crushed and homogenized from which the sample is taken.