The adequacy (inadequacy) of samples to each other and reference materials to test samples is an important notion in the metrology of chemical analysis. However, the literature gives no strict definition for this notion. In this paper, it was proposed to determine adequacy based on the measure of inadequacy. For the case of two samples, the measure of inadequacy is the absolute value of the difference between the systematic errors of the results of analyses of the samples; it depends on the difference in the composition and properties of the samples. The measure of inadequacy of a standard reference material to a series of test samples is the maximum distance between the systematic error of the reference material and one of the quantiles of the systematic error distribution of the test samples Q(0.025); Q(0.975); the errors in this case are due to the composition and the properties of the test samples. The samples are considered adequate if the measure of inadequacy can be neglected compared to the normalized error of the analysis. Using the determination of total cholesterol in the blood serum of humans as an example, it was shown that the standard reference material in the analysis of samples of complex composition is often inadequate to test samples.