Z-Dimensions Are Not Created Equal
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spectroscopy cuvettes

Z-DimensionCuvettes 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.

MANUFACTURER                  
Z-DIMENSION
Agilent®15 mm
Avantes®15 mm
Beckman®8.5 mm
Bio-Rad®8.5 mm
Cecil®15 mm
Eppendorf®8.5 mm
Hewlett – Packard®15 mm
Hitachi®8.5 mm
Jasco®11 mm
J & M®8.5 mm
Ocean Optics®15 mm
Perkin – Elmer®15 mm
Pharmacia®15 mm
Shimadzu®15 mm
Spectronics®8.5 mm
Stellarnet®15 mm
Turner®8.5 mm
Varian ®20 mm
WPI 15mm


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.

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