Pre analytical related to procedure before we take the sample for processing. The sample may be looks very simple but it eat our brains when we start to quantify what we need.
Samples are not simple as it looks. Characteristic changes with time, temperature, moisture and also the matrix.
1. Sample collection and transportation
How we collect the specimen from the bulk is very important. Most of the real samples are not homogeneous. So, it is important to identify the sampling location, position and quantity. The way the sample collected ensures that there is no cross contamination. Once collected, the preservation is important to ensure that the sample integrity are there till it reach to laboratory for further process. Many times, need to add preservatives or to be frozen or to be kept in vacuum, etc., depends on the sample type, matrix and target molecules.
2. Sample labeling
The sample should be labeled with enough information to identify. It is not possible to write all the technical information, so need to do codification. The document forwarded with samples will contain as much as information to select technology in minimum time, and also to store in proper condition till taken it into process. Very simple example is H2O2. When the saline tube to be tested for the presence of H2O2, the sample can be sent in normal condition, but if the H2O2 comes in pure form, need to be in ice box - always till transferred into headspace vial for calibration.
3. Planning for analysis
Decide when the sample to be taken for analysis, means, how long the sample can be kept on hold, is important. It depends again on matrix and target molecules. Biological samples cannot hold for a longer time as so many by products will start to develop due to degradation. This degradation cannot be identified from smell or appearance initially. But that is enough to misguide you in interpretation.