The accuracy of the sample pre-treatment is also related to the accuracy of the subsequent analysis. Size reduction is a key step in sample pretreatment. To choose a suitable grinding instrument, we need to consider the experiment and choose a suitable grinding instrument:

1. Sample type

- Is the sample hard or soft? There is simple way to judge: if the sample can be cut with scissors, we can classify it as a soft sample; if the sample need to be smashed with a stone, we can categorize it as a hard sample.

- Sticky, sugary, watery and oily? These samples are mostly food samples, for example, meat products containing water, oil and fat, fruits and vegetables containing water, candies and preserved fruit containing sugar with viscosity.

- With shell or not? For example, shelled grain, shelled seafood.

- Are they temperature sensitive? At room temperature, some samples are difficult to be crushed, such as plastic particles; some biological samples also need to be processed at low temperature.

2. Sample feed size

Different mill works in different principle and allows different feed size. And for some sample with bigger initial size, pretreatment to smaller piece before feeding is required.

3. Sample final fineness

It needs to meet the requirement of subsequent physical and chemical analysis, not the finer the better.

4. Single crushing capacity

Some mills are of high handling capacity up to 200KG/hour, for example Jaw Crusher JC7 in mineral application, some can process up to 192 sample each time but each is less than a few gram, such as Micro Ball Mill GT300, in bio application.

5. Material of grinding set

If subsequent analysis of the grinded sample is heavy metal determination, stainless steel material grinding set is not suitable, because stainless steel my bring trace contamination into sample grinded. In such cases, grinding set of agate, Zirconium oxide or Tungsten carbide is recommended.