Once the sample has been split, a coin toss (heads indicates the right half, tails the left half) or throw of a die (even indicates the right half, odd the left half) is used to randomly select half of the sample. If the sample being processed is an elutriate sample, then the half of the sample selected is retained for analysis and the other half is discarded. If the sample being processed is a main-body sample, then the half of the sample selected is designated as the main-body component and the other half is designated as the "split" sample component. The split-sample component is retained for QA/QC purposes and shipped to the BQAU. All sample components must be labeled and preserved properly.
Some particularly large samples may require repeated splitting to obtain suitable volumes (less than or equal to 0.75 L) of main-body, split, and elutriate sample components. These samples may also be larger than the capacity of the sieve used for splitt ing the sample. In these circumstances, manageable portions of the sample are split until the entire sample has been split into halves. The multiple portions of split sample that are produced are assigned to their component halves in an unbiased manner (that is, by coin toss or roll of the die). If the resulting split-sample component (elutriate, split, or main-body) exceeds 0.75 L, it is split again. Careful records of the number of splits performed and the portion of the original sample retained for analysis are kept and entered on the appropriate field data sheet.
A flow chart showing how the various sample components are split and reduced to one-fourth of their original volume is illustrated in figure 9. In actual field situations further sample splitting may be necessary. Each time the elutriate sample component is split, a portion of it is discarded. In contrast, when the main-body sample component is initially split (one-half split), an additional sample component is generated (split) and no sample material is discarded. When subsequent splits are necessary , they are applied to the "split" and "main-body" sample components and portions of each are discarded (for example, the one-fourth split). The main-body and split-sample components are processed in parallel so that the split-sample component sent to the BQAU is, in theory, identical to the main-body sample component sent to the contract laboratory. Consequently, the split samples can be processed and used to evaluate the performance of contract laboratories.