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11/6/2015 by mdc
http://labauto.flsmidth.com/blog/how-to-combat-contamination
Dave Coler reports that one of the key challenges to good XRF sample preparation is contamination. Contamination comes from two main sources ... the sample preparation device and sample to sample cross contamination.

Sample pulverizers are usually the sample preparation device that has the potential to contribute the most contamination to a sample. Pulverizers usually use a ring and puck style grinding bowl to grind samples from coarse chips to a fine powder. This grinding action can add various elements contained in the grinding vessel to a sample which is why one should be careful about choosing the grinding medium.

Steel, tungsten carbide and ceramics such as alumina and zirconia are the most common choices. Steel can add Fe, Ni and Cr, tungsten carbide will add W and alumina and zirconia will add Al and Zr respectively. Think about what elements you are interested in analyzing and make your choice accordingly. Tungsten carbide is often a default choice because of its hardness and because W is usually not a key element for analysis for many applications. The downside is that tungsten carbide is often the most expensive option.

Sample-to-sample cross contamination in the sample preparation process is by far the biggest contributor to sample contamination. This is particularly true if one is working in an environment where one is analyzing a wide range of sample types

There are three main ways to reduce sample-to-sample cross contamination... Bowl Cleaning, Pre-Contamination, and Cleaning Media. All three approaches to reducing cross contamination are valid depending on the needs of a particular laboratory. These methods are not mutually exclusive and can be combined for particularly challenging samples. The choice of an approach should be based on the types of samples to be analyzed, your analytical goals, and the speed required for the overall analysis.


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