What type of analytical method is typically used to determine the concentration of an ion based on its mass?

The correct answer is gravimetry. Gravimetry is an analytical method that involves the measurement of mass to determine the concentration of an ion or compound in a sample. In gravimetric analysis, a target ion is usually converted into a precipitate, which is then filtered, dried, and weighed. The mass of the precipitate is correlated to the amount of the ion present in the original sample, allowing for the calculation of its concentration. This method is highly accurate and precise because it relies on direct measurements of mass, which are less susceptible to systematic errors that may occur in methods reliant on indirect measurements.

Gravimetry is particularly effective for determining the concentrations of metals and other inorganic species. The thoroughness of the method ensures that all relevant species can be accounted for, making it a reliable choice when mass measurements can be performed with high precision.

In contrast, other methods such as spectroscopy and chromatography rely on different principles — for instance, spectroscopy measures the interaction of electromagnetic radiation with matter, and chromatography separates components in a mixture based on their movement through a stationary phase. Volumetry involves measuring the volume of a solution to determine concentration, typically through titration. These methods serve their own purposes but do not fundamentally measure concentration based on mass in