What method is typically used for iron determinations in water?

Colorimetric analysis is a widely used method for determining iron concentrations in water due to its sensitivity and simplicity. This technique involves adding a color reagent to the water sample that reacts with iron to produce a colored compound. The intensity of the color produced is proportional to the concentration of iron in the sample. This property allows for easy quantification using spectrophotometry, where the absorbance of the colored solution is measured.

The other methods listed are not typically employed for iron determinations in water. Gas chromatography is primarily used for the analysis of volatile compounds and gases, not for metal ions like iron. Thermal gravimetric analysis measures changes in weight as a function of temperature and is not suitable for quantifying dissolved metals directly. Ion chromatography, while capable of analyzing some inorganic ions, is more specialized for ions like anions and cations, rather than specifically targeting metals such as iron in water. Thus, colorimetric analysis remains the preferred and most effective method for iron determination in aqueous samples.