Cell Matching in Spectrophotometer
What is the definition of matching?
The degree to which absorption cells will produce a similar absorbance or transmission value when empty or filled with water is referred to as cell matching. When spectrophotometer cells were not properly produced and most absorption instruments were single beam, the practice began (no ability to automatically adjust for the blank). The concept of matching has grown less significant as high-quality cells from big manufacturers like Qvarz have become the standard and instruments have improved. Because measuring a cell without a sample does not assess the accuracy of the path length or the dimensional quality of the windows, a bad cell might appear to be matched. The most significant aspects of cell quality are described below, along with the requirements that Qvarz brand cells should meet.
Parallelism in Windows
The windows must be parallel in order for the route length to stay constant across the cell window. Windows parallelism is better than 3 minutes of arc.
Flatness of Windows
Light must not be concentrated, reflected, or refracted through the windows, therefore they must be as flat as possible. Window flatness is less than 4 Newton Fringes.
Polish of Windows
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.
Pathlength with a high tolerance
The pathlength (the distance between the interior of the cell’s windows) must be kept within a tight tolerance. The maximum tolerance for a Starna brand cell is listed in the table below. The tolerances for each material vary according to the features of each material.
| Window Material | Pathlength Range | Pathlength Tolerance |
|---|---|---|
| Glass | less than 10 mm | +/- 0.02 mm |
| Glass | 10 to 20 mm | +/- 0.1 mm |
| Glass | 20 to 100 mm | +/- 0.2 mm |
| Special Optical Glass | up to 20mm | +/- 0.01 mm |
| Special Optical Glass | 20 to 100 mm | +/- 0.02 mm |
| Quartz | up to 0.05 mm | +/- 0.002 mm |
| Quartz | 0.1 to 0.4 mm | +/- 0.005 mm |
| Quartz | 0.5 to 20 mm | +/- 0.01 mm |
| Quartz | 20 to 100 mm | +/- 0.02 mm |
What impact do specifications have on matching?
A spectrophotometer and a fluorometer cell’s performance is dependent on all of the following parameters. When these parameters are kept to a high standard, the cell is said to be “matched” since no two cells with the same physical configuration, material, or path length are alike. We produce cells with such tight tolerances that they are “better than matched.”
Is it possible to match Fluorometer Cells?
Matching, by definition, is the measurement of absorption straight across a cell’s path length and does not take into account any fluorometry characteristics. It’s far more necessary to use a high-quality cell made of “background fluorescence-free” quartz. Our fused quartz is an amazing fluorescence material.