The HI84430-50 is a 100 mL bottle of alkaline titrant solution that is used for low range (15 to 500 mg/L as CaCO₃) determination of acidity in water.

The determination of water acidity is based on the neutralization of all acidic species contained in water samples by titration with a basic titrant solution:

H⁺ + OH^- → H₂O

The endpoint of an acid base titration corresponds stoichiometrically to the complete neutralization of the acids present. Water acidity results from strong and weak acids as well as from the hydrolysis of salts. Due to these more complex mixtures, endpoints for water acidity are arbitrarily fixed on practical considerations. Unpolluted surface waters contain carbon dioxide as the main acidic component, and titration of these samples corresponds to the stoichiometric neutralization of carbonic acid with sodium hydroxide. The titration to pH 8.3 represents total acidity. The titration to pH 3.7 represents strong acidity from polluted water.  If the samples are suspected to contain hydrolyzable salts or polyvalent cations (such as chromium, iron, manganese), it is necessary to pretreat the samples with HI84430-58 reagent.

The HI84430 mini titrator is designed to determine the acidity of waters by potentiometric titration in both a low range (15 to 500 mg/L as CaCO₃) and high range (400 to 4000 mg/L as CaCO₃). Both total and strong acidity can be determined by the HI84430. If the measured pH is lower than 3.7 both total and strong acidity can be determined. If the sample is greater than pH 3.7 then only total acidity can be determined.

Replacement reagents required to operate the HI84430: