Determination of carbonate and hydrogencarbonate by titration using sequential injection analysis Original Research Article

A fully automated spectrophotometric sequential injection titration system has been developed for the determination of carbonate and hydrogencarbonate in water samples. The sample is titrated against hydrochloric acid using phenolphthalein and methyl orange as indicators; the absorbance is measured at 430 nm. A logarithmic relationship is obtained between the peak width and the absorbance. The logarithmic range for carbonate is 0.0008–0.01 M, and for hydrogencarbonate is 0.001–0.01 M. Reproducibility is good (<2% for carbonate and <1.5% for hydrogencarbonate) and the results obtained agree well with those obtained using a potentiometric titration. The sample throughput is 12 samples h−1.