Application of ion chromatography to the analysis of lead–acid battery electrolyte

Abstract

Stringent specifications are laid down for the sulfuric acid used as battery electrolyte. In the present work ion chromatography (IC) was applied to the determination of several species in sulfuric acid and it proved possible to separate impurities in the presence of large amounts of sulfate ion without the need for a preconcentration or pre-separation step. Fluoride, chloride, bromide, nitrate, phosphate, sodium, potassium, magnesium, calcium, iron, copper, nickel, zinc and cadmium can easily be determined by diluting the lead–acid battery electrolyte (usually 38% H₂SO₄) 40-fold. Most of the species to be determined were found to be adversely affected by sample pre-treatments, such as sulfate precipitation or ion-exchange resin separation. The pH of the analyte strongly affects the analytical response and hence the optimum pH range was established for anions, alkali and alkaline earth metals, and transition metals. In the presence of organic compounds, oxidative UV photolysis of the sample permits determinations to be performed without any interference. The proposed procedure involves the IC determination of fluoride, chloride, bromide, nitrate, and phosphate using a carbonate–hydrogencarbonate eluent with suppressed conductivity detection, that of sodium, potassium, magnesium and calcium using a hydrochloric acid–2,3-diaminopropionic acid hydrochloride eluent with suppressed conductivity detection and that of iron, copper, nickel, zinc and cadmium using pyridine-2,6-dicarboxylic acid as eluent with visible absorbance detection. Detection limits ranged between 0.2 and 1.3 ppm and the linearity of the calibration graphs was found to be extended by up to two orders of magnitude.