What is the primary purpose of both UV and visible spectrophotometers?

The primary purpose of both UV and visible spectrophotometers is to determine the concentration of a sample. These instruments operate on the principle that different substances absorb specific wavelengths of light. By measuring the intensity of light that passes through a sample at particular wavelengths, a spectrophotometer can quantify how much light is absorbed by the sample, which is directly related to the concentration of the absorbing species present.

Typically, this measurement is defined by Beer-Lambert’s law, which states that absorbance is proportional to concentration. Therefore, if you know the absorptive characteristics of a compound and measure its absorbance, you can calculate the concentration of that compound in a solution accurately. This capability makes UV and visible spectrophotometers essential in fields such as biochemistry, chemistry, and environmental science for analyzing solutions.

The other choices do not align with the primary function of these instruments; they are not designed to measure pH, detect mass loss, or analyze gas concentrations directly.