The methods talk about different kinds of “batches” and tie the frequencies of QC samples to various batches. Is there a single definition of a “batch?
Yes and no. Chapter One defines a “batch” as A group of samples which behave similarly with respect to the sampling or testing procedures being employed and which are processed as a unit…” Because of the many sample processing steps that can be involved in a given analysis, there are a number of types of batches, each of which may drive the frequency of QC operations. For example: Extraction or digestion batch – A group of up to 20 samples extracted together (organics) or digested together (metals) using the same techniques. In order to demonstrate that the extraction or digestion equipment used for these samples does not result in contamination of the samples, you need to prepare a method blank with each batch of samples extracted or digested together. In order to demonstrate that you could perform the sample preparation procedures in a clean matrix, you also need to prepare one laboratory control sample (LCS) with each such batch. The method blank, LCS, and any spiked samples (MS)
