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An Exercise To Illustrate the Importance of Sample Preparation in Chemical Analysis
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Abstract
The results of chemical analyses can only be as good as the sampling and sample preparation. Chemists need to recognise this problem and ensure that the analytical sample is representative and free from contamination. This paper gives a brief description of the equipment and methods necessary for sample preparation, but concentrates more on the data obtained by students and the conclusions that may be drawn from such data. This exercise may be used by class instructors when introducing students to the pitfalls in sampling and the power of statistics. Two series of five sieved samples in the size fractions <63 µm, <125µm, <710µm, <2000µm and >2000µm are discussed. The first series of samples have been ground prior to being reduced using a sample splitter. The other series of samples are unground having only been passed through a sample splitter to reduce the sample size. Bias in sampling has deliberately been introduced to second sample series. Hence the selection of any one fraction over another will inevitably lead to a biased result. For particles of about 2000µm it only takes 2-3 particles to make the required analytical sample. Hence the sampling process is highly speculative, and the three particles chosen might have a very different composition to any other three particles. The students will then realise that there a many more particles in the other fractions, making them likely to be more representative.
Keywords (Audience):
Second-Year UndergraduateKeywords (Domain):
Analytical ChemistryKeywords (Pedagogy):
Hands-On Learning / ManipulativesKeywords (Subject):
Laboratory Equipment / ApparatusCiting Articles
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- Received: August 03, 2009
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