What are the two units of measurement typically used on a spectrophotometer?

Spectrophotometers are instruments used to measure how much light a substance absorbs or transmits at a given wavelength. The two key units of measurement typically utilized in this context are absorbance and percent transmittance.

Absorbance quantifies how much light is absorbed by the sample as it passes through. It is a logarithmic measure of the ratio of incident light to transmitted light, where a higher absorbance indicates that more light is absorbed by the analyte in the sample.

On the other hand, percent transmittance represents the percentage of light that passes through the sample compared to the incident light. It is calculated as the ratio of transmitted light to incident light, expressed as a percentage. This measure gives an immediate sense of how opaque or transparent the sample is.

Combining these two measurements allows laboratory analysts to interpret the concentration of substances in the sample, as both values are related through Beer-Lambert Law, which connects absorbance to concentration, making this pair essential in various analytical applications in water testing and other chemistry fields.