An apparatus for taking an accurate photometric measurement of a liquid by way of forming a specimen volume of a controlled optical path length for use with photometric measurement equipment is disclosed herein. In some embodiments, the apparatus comprises a transparent body configured for displacing a volume of a fluid and at least one support element wherein the support element is configured to maintain the transparent body at a location such that specimen fluid may enter a void volume to form a specimen volume of a controlled optical path length. In some embodiments, the apparatus comprises a plurality of transparent bodies interconnected by a web such that the transparent bodies are maintained at a spacing arrangement which allows for them to be inserted into the wells of a microplate in order to create a plurality of specimen volumes of a controlled optical path length.