Small Volume Cells and Z Dimension

Posted by airekacells 10/01/2015 0 Comment(s) About Aireka Cells,


What does Z Dimension mean?


The Z-dimension (center height) is the height from the bottom of the cuvette to the center of its sample chamber. In cases where the cuvette's polished window is very small (where usually the entire cuvette is black aside from the aperture window), it is critical that the Z-dimenion of the cuvette be the same as the height of the instrument's light beam. Generally speaking, Z-dimension can be either 8.5, 15, or 20 mm depending on the instruments manufacturer.


Why Z Dimension is Important?


Each instrument manufacturer makes engineering decisions for the design of their instrument to assure that it performs optimally. The height, width, focus and placement of the light beam in any instrument is based on the engineering decisions to assure that the instrument performs to their published specifications. It is important to you, as the instrument user, only when you are attempting to use a small sample volume. You must assure 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



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:

Cut a piece of dense paper 12mm wide and 100mm long.
Make a hole in the center of the paper about 3mm in diameter (you can just push a ballpoint pen through the paper) 8.5mm from the bottom of one end and 15mm from the bottom of the other end.
Turn on your spectrophotometer in %T mode and set to any reasonable wavelength.
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.
If neither works then make up another piece of paper with holes placed at different dimensions and determine which works best.