THE IMPORTANCE OF APPROPRIATE SAMPLING FOR analytical work cannot be overemphasized. Unfortunately, this topic is often not given sufficient thought, and there is often not enough training on the subject. A clear understanding of the nature of the problem or the reason analysis is needed must be established prior to obtaining a sample. It is extremely important to know the compositional makeup of the bulk material from which the sample is being taken. Without this knowledge, improper sampling can very easily occur. The homogeneity or heterogeneity of the sample along with its stability is very important to consider. The composition of a sample may change once it is removed from its natural matrix or environment due to interactions with a container, ultraviolet light, or air, for example. One should also know in advance what level of precision is required of the analysis and what compositional information is required. Development of a sampling plan is one of the most important steps in providing reliable samples and consequently accurate and reliable data. The types of samples usually encountered are as follows: Representative Sample: A sample considered to be typical of the bulk material and whose composition can be used to characterize the bulk with respect to the parameter measured. Systematic Sample: a sample taken according to a systematic plan with the objective of investigating systematic variability of the bulk. Systematic effects due to time or temperature are typical matters of concern. Random Sample: A sample selected by a random process to eliminate questions of bias in selection and/or to provide a basis for statistical interpretation of measurement data. Composite Sample: A sample composed of two or more increments that are combined to reduce the number of individual samples needed to average compositional variability .