Cuvettes come in a variety of shapes and sizes, but one of the most important specifications of a cuvette is its Z-dimension. The Z-dimension of an instrument (cuvette holder or spectrometer) is the distance from the bottom of the cuvette chamber floor to the center of its light beam (see image). A cuvette’s Z-dimension must match the Z-dimension of the instrument with which it will be used.

Each manufacturer designs its instruments with a specific Z-dimension. Common Z-dimensions include 8.5 and 15mm, and sometimes 20mm. When purchasing small volume cuvettes, the correct Z-dimension becomes critical. Matching the Z-dimension of the cuvette to the Z-dimension of the instrument ensures that the light beam passes through the center of small samples. The table below shows the standard Z-dimension of the spectrometer sample compartments for many manufacturers.

To determine the Z-dimension of a cuvette holder:

1. Use strips of heavy paper that will fit neatly into a cuvette (for example, 12mm x 50mm) and not allow light to pass through the cuvette.
2. Poke a tiny hole in each paper “sample.” For example, one paper sample could have a hole at 8.5mm, one at 15mm, one at 20mm.
3. One at a time, insert the paper samples into the cuvette and place the cuvette into the cuvette holder. The paper sample with the pin hole at the instrument’s Z-dimension will allow light to pass. The other paper samples will not allow light to pass.

If you have an instrument that is not on the list and need to know its Z-dimension, please contact WPI at 941.371.1003 or This e-mail address is being protected from spam bots, you need JavaScript enabled to view it .