New Knife Mill Sets Standards - The GM 300 Produces Homogeneous Samples Within Seconds - Dr Andreas Theisen

Retsch’s knife mill GRINDOMIX GM 300 is ideal for the gentle size reduction and homogenisation of food and feed. It processes sample volumes of up to 4,500ml quickly and reproducibly. With its four sharp and robust blades and a powerful drive with temporary peaks of up to 3kW it is ideally suited to homogenise substances with a high water, oil or fat content as well as dry, soft, medium-hard and fibrous products.

The so-called QuEChERS method (‘quick, easy, cheap, effective, rugged and safe’) has been developed to make sample preparation to pesticide analysis more efficient. Serial tests have proved that the analysis results obtained with the QuEChERS method can easily bear comparison with more common methods, such as DFG S19.

For a test according to QuEChERS, 10g of homogenised sample material are extracted with 10ml acetonitrile. After that the organic phase is dried and tested for pesticides with chromatographic analysis. To guarantee reproducible analysis results, it is essential to completely homogenise the sample. Food often occurs in rather inhomogeneous forms (such as, fruit, flesh, peel, pit), and the 10g have to be representative of the entire initial material.

To make sure the sample preparation is reproducible, the homogenisation process needs to be carried out with a laboratory mill. Care must be taken that the sample is not warmed during the grinding process, as pesticides are partly volatile substances. This effect can be avoided by cooling the sample with dry ice, for example. Moreover, a finer grind size and greater homogeneity are obtained with frozen material because the embrittlement improves the breaking properties of the sample. Therefore, it is recommendable to grind food samples mixed with dry ice at -80°C.