What is the primary instrument used for quantitative measurement of absorbance in a solution?

The primary instrument used for quantitative measurement of absorbance in a solution is a spectrophotometer. This device operates on the principle of light absorption by a sample solution. When a beam of light passes through the solution, certain wavelengths are absorbed while others are transmitted. The spectrophotometer measures the intensity of the transmitted light relative to the intensity of the incident light, allowing for the calculation of absorbance according to Beer’s Law. This quantitative measurement is essential in various biological and chemical analyses, such as determining the concentration of a substance in a solution.

Other instruments listed, like the refractometer and fluorometer, serve different purposes. A refractometer measures the refractive index of a solution, which can provide information about its concentration but does so differently than absorbance measurement. The fluorometer measures the fluorescent properties of a solution rather than its absorbance. Lastly, a pH meter is designed to measure the acidity or alkalinity of a solution, which is unrelated to absorbance. Each of these instruments has specialized applications but does not replace the function of a spectrophotometer in measuring absorbance.