Which analytical method measures the amount of light scattered by particles in solution at a 90° angle?

The correct answer is based on the principle of nephelometry, which specifically measures the amount of light scattered by particles in a solution at a 90° angle. This method is particularly useful for analyzing solutions containing suspended particles, as it determines the concentration of these particles by quantifying the scattered light.

When light is directed into a sample, particles in suspension will scatter the light. In nephelometry, detectors are positioned at a 90° angle to the path of the incident light, allowing the device to measure only the light that is scattered by the particles rather than the light that passes directly through the sample. This configuration enhances the sensitivity of the measurement, making it particularly suitable for low-concentration samples.

In contrast, turbidimetry measures the decrease in transmitted light intensity through a sample, and it does not involve measuring the scattered light at an angle. Therefore, it is not applicable here. Other options, such as hydroelectric focusing and chemiluminescence, do not pertain to light scattering measurements and are used for entirely different purposes in analytical chemistry. This reinforces the distinction of nephelometry as the suitable method for the scenario presented in the question.