Gross and Laboratory size Samples


Irespective of the state of materials to be sampled, the level of heterogeneity, the size , nature and volume of the sample and configuration of the site , the interest of the analyst is to develop a gross sample of which laboratory size sample will be obtained for investigation

Gross sample

Perfectly, gross sample is a miniature replica of the whole population of the materials to be analysed. It must corresponds to the whole population both in chemical composition and in particle size distribution. A certain portion of the whole must be removed through any of the sampling methods earlier discussed. The sample may be grab or composite depending on the judgement of the analyst. The competence and expertise required for obtaining the gross sample vary and depend on the situation at hand. This range from sampling homogeneous situation of liquid and gases, to sampling particulate solids, to sampling of metal and alloys.

The size of the gross sample needs not to be larger than necessary. The size is determined by the following factors

  1. the uncertainty that can be tolerated between the composition of the samples as a whole

  2. the degree of heterogeneity of materials being sampled

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3.the level of particle size at which heterogeneity begins.

Laboratory size sample

This is the ultimate sample on which analysis is carried out from non homogeneous material. The gross sample may weigh several hundreds of kg or more. A laboratory size that is almost one over thousands or less is obtained. Diminutions in particles size is essential as the weight of the sample is decreased to ensure that the sample composition continue to be representative of the original materials. The sample obtained upon arrival at the laboratory received further treatment before it is eventually analysed. The integrity of sample to maintain chains of a custody procedure must be ensured.

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