Selection of Ultra-Micro Spectrophotometer Cuvettes

Spectrophotometers use beam light to shine through a sample in the cuvette to detect the wavelength transmission. The “Z dimension or beam height” refers to the height of the cuvette bottom to the bean source. For the beam height, three industry “standards” have been developed: 8.5mm, 15mm, and 20mm.

When working with ultra-micro and semi-micro cuvettes, the Z dimension determines the minimum volume to be filled. The cuvette must be filled to the Z dimension height of the spectrophotometer. The volume of the sample in an ultra-micro cuvette, on the other hand, is so small that the sample chamber must be lifted from the cuvette’s bottom to align the sample with the Z dimension.

Ultra-micro cuvettes are constructed with window heights that correspond with either the 8.5mm, 15mm, or 20mm Z dimensions due to conflicting spectrophotometer standards (even from the same brand). It’s crucial that the window height of your ultra-micro cuvette matches the spectrophotometer’s beam height. If the window height is incorrect, the beam will either not pass through the sample at all or will require substantially greater sample volume than the minimum given.

You must first determine the Z diemension of your spectrophotometer before selecting an ultra-micro cuvette. Check the list below if you’re not sure what your spectrophotometer’s beam height is. If your spectrophotometer isn’t mentioned, examine your instrument’s operating handbook.