Understanding Cell Matching for Spectrophotometer Cuvettes

What is meant by cell matching?

Matching of cells refers to the degree to which absorbtion cells will produce comparable absorbance or transmission readings while empty or full of water. The technique began during a time when spectrophotometer cells were of poor quality and the majority of absorbtion instruments were single-beam instruments (no ability to automatically adjust for the blank). 

As high-quality cells from large manufacturers such as Qvarz have become the norm and as technologies have advanced, the concept of matching has become less significant. A poor cell may appear matched because measuring a cell without a sample does not evaluate the accuracy of the path length or the dimensional quality of the windows. The parameters you can anticipate from Qvarz brand cells are outlined here, along with the essential factors of cell quality.

Parallelism of Windows

The windows must be parallel so that the path length remains constant across the entirety of the cell window. Windows parallelism exceeds three minutes of arc

Window Flatness

To prevent light from being concentrated, reflected, or refracted, the windows must be as flat as possible. Less than 4 Newton Fringes for Window Flatness.

Window Polish 

To maintain light dispersion to a minimum, the windows must be polished to a high tolerance. The scratch/dig ratio for Window Polish is 60/40.

High tolerance Pathlength

The distance between the cell’s internal windows (the pathlength) must be maintained with a high tolerance. The maximum tolerance for a Qvarz brand cell is detailed in the table below. Due to the qualities of each material, each material’s tolerances are unique.