the size of a sample depends on the test being carried out
samples need to be representative - enough of the sampleto give a picture of the whole item
Preservation of Samples:
its important for the sample to stay the same and not deteriorate etc. For this reason some need to be analysed immediatly whilst others can be stored in the appropriate conditions
Avoiding Contamination:
crime scene investigators wear protective clothing so as to avoid contaminating samples
they put samples in sealed bags
sometimes have to give evidence in court about possible routes of contamination
Avoiding Tampering:
Tamper-proof seals to ensure there's no swapping of samples - shows exactly had access to the samples
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