What is the standard path length of a cuvet in most spectrophotometers?

• A. 0.5 cm
• B. 1 cm
• C. 2 cm
• D. 5 cm

Answer: (B)

In spectrophotometry, absorbance follows the equation A = εlc, where l is the path length—the distance light travels through the sample. Using a standard path length helps keep measurements comparable and within a practical, linear range for most samples. A path length of 1 cm provides a good balance: for typical concentrations and molar absorptivities, the resulting absorbance values fall in a range that detectors measure accurately (neither too low nor too high). If the path length were shorter, the absorbance would be smaller, reducing sensitivity; if longer, absorbance could become too high and cause saturation or require dilutions. While other cuvettes with 0.5 cm or larger 2 cm (and even 5 cm) path lengths exist for specific needs, the conventional standard used in most spectrophotometers is 1 cm.