Ideally, the assay control sample and reference standard should be as similar as possible to the test samples in excipient formulation, concentration, aliquot volume, container, and so on. The assay control sample, reference standard, and test samples should be prepared and tested in exactly the same way. However, an initial step such as reconstitution of a lyophilized reference standard or dilution of a more concentrated solution may be necessary. Commonly, the reference standard may be presented in a formulation buffer different from that of the test samples to permit its storage as a frozen solution. It then requires dilution (concentration permitting) in the formulation buffer of the test samples to render it as similar as possible to the test samples. Similarly, the formulation of the assay control sample and other control samples should be brought as close as possible to that of the test samples.