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Z Dimension of Spectrophotometer Cells
What does Z Dimension mean?
Z Dimension is defined as the distance from the bottom of the cell compartment in your instrument to the centre of the light beam.

Why is Z Dimension Important?
Each instrument manufacturer makes engineering decisions for the design of their instrument to ensure optimum performance. The height, width, focus and placement of the light beam in any instrument is based on these engineering decisions to ensure that the instrument performs to their published specifications. It is important to you, as the instrument user, when you are attempting to use a small sample volume. You must ensure that your smaller volume is placed in the centre of the light beam and that any light which does not pass through your sample is blocked (or masked) by black material. If the cell is not properly masked then the sensitivity will be eroded.

Z Dimension of various manufacturers
We have compiled this list of Z Dimensions from some of the instrument manufacturers. If you find a discrepancy in this list, please let us know and we will investigate.

Manufacturer Z Dimension
Beckman® 8.5 mm
Bio-Rad 8.5 mm
Hewlett Packard® 15 mm
Hitachi® 8.5 or 12 mm
Perkin-Elmer® 15 mm
Pharmacia 15 mm
Shimadzu® 15 mm
Spectronics® 8.5 mm
Thermo spectronic 8.5 or 15 mm
Unicam 8.5 mm
Varian® 15 or 20 mm
GBC® 15 mm
Z height

How can I determine the Z Dimension of my instrument?
You can test for the Z dimension of your instrument very easily.
Simply follow these steps:
  1. Cut a piece of dense paper 12mm wide and 100mm long.
  2. Make a hole in the centre of the paper about 3mm in diameter (you can just push a ballpoint pen through the paper) 8.5mm from the bottom of one side and 15mm from the bottom of the other.
  3. Turn on your spectrophotometer in %T mode and set to any reasonable wavelength.
  4. Place the piece of paper with the hole in the end into the cell holder as if it were a cell. Whichever end (either 8.5mm or 15mm) transmits light will tell you the Z dimension of your instrument.
  5. If neither works then make up another piece of paper with holes placed at different dimensions and determine which works best or contact us for the "Lab Coat Trick"!
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