The sample is the most critical element of the analytical process. The quality of any data produced primarily depends on the sample analyzed. A sample must be representative of the whole so that the final result represents the entire system that it is intended to represent. A sampling program must be planned to satisfy the objectives of the study and yet remain within the limitations of available manpower, time, and money. Samples collected at a particular time and place are called grab or individual samples. This type of sample represents conditions at the time it was collected. The material of which the sample container is made should be chosen so that it will not react with the sample. It should be resistant to leakage and breakage and should have the proper volume necessary for the analyte(s) of interest. Caution must be taken to prevent contaminating the sample with fingers, gloves, or other materials.