Effects of sample collection

Biological contamination of the sample can occur where sampling devices have not been sterilised. External bacterial contamination and microbial activity present in the sample could combine to degrade existing macromolecules. Chemical transformations such as methylation, cleavage of the carbon-metal bond, and reduction of the metal have occurred in the presence of micro-organisms (Thayer and Brinkman, 1984 Thayer, 1984 Krishnamurthy, 1992) as shown by the following equations  

Introduction of external chemical contamination from the sampling devices into the sample should be avoided because binding of metals to biological molecules is possible in vitro, and this can change the distribution of metal-containing species in the sample. Heavy metal contaminants could cause protein precipitation as well as irreversible deactivation of enzymes. 

Approaches to minimising sampling errors (Guder and Wahlefeld, 1983) and preventing the introduction of chemical contamination (Versieck et al., 1982 Heydorn, 1984 Aitio and Jarvisalo, 1994) have been published. To reduce the risks of introducing errors during sampling, metal-free and sterile devices, and standardised procedures should be used. 

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