Spectrophotometric Accuracy, Linearity and Adherence to Beer's Law

The distinction between the terms photometric accuracy, photometric linearity, and adherence to Beer's Law is discussed. To describe the last, a new term “analytical linearity” is suggested. Some instrument response functions which exhibit acceptable analytical linearity are shown, nevertheless, to be photometrically inaccurate. Methods of measuring true photometric accuracy, the search for absolute photometric standards, and the ultimate limitations of such standards are reviewed.