Z-Dimensions Are Not Created Equal

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.

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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