Z-Dimensions Are Not Created Equal
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.
|Hewlett – Packard®||15 mm|
|J & M®||8.5 mm|
|Ocean Optics®||15 mm|
|Perkin – Elmer®||15 mm|
|Varian ®||20 mm|
To determine the Z-dimension of a cuvette holder:
- 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.
- 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.
- 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.