Principles of Sampling
A carefully designed sampling plan is ordinarily required to provide reliable samples. Persons engaged in sampling hazardous sites may need initial and periodic medical examinations to ensure that they have not contracted medical problems related to the materials with which they are involved, and consideration of possible liabilities due to mishandling is recommended when developing sampling plans and strategies for hazardous materials. In many cases, training of sampling personnel may be required. This is true especially when new sampling operations are undertaken or when new personnel are involved. A sample custodian may be required to ensure orderly management of samples with provision for safeguarding samples at all times. Stratification, when possible, is an insidious source of error in analytical samples. Samples that were initially well-mixed may separate, partially or fully, over a period of time. If the holding time is considered to be inconveniently short, conditions of storage and stabilization must be modified necessitating a new determination of holding time.