Method for determining the path length of a sample and validating the measurement obtained

A method for traceably determining an unknown optical path length of a sample in an optical measuring device, which optical measuring device is validated using a certified reference material having a specified nominal absorbance, the sample being dissolved or suspended in a solvent, which solvent is also the solvent of the certified reference material, wherein the certified reference material is contained in first and second closed cuvettes, which cuvettes have a first and second specified path length and a specified accuracy, the method comprising the steps of:

• measuring absorbance of the certified reference material to obtain a first absorbance measurement for the first specified path length;
• measuring absorbance of the certified reference material for a second path length to obtain a second absorbance measurement;
• using a dropper to drop a specified volume of the solvent on the optical measuring device so that the path length of the specified volume can be determined by reference to the first and second absorbance measurement;
• and
• using the dropper to drop the sample on the optical measuring device, which sample has the same volume as the specified volume, thereby enabling a traceable absorbance measurement of the sample.