Reference materials for oceanic CO2 analysis: a method for the certification of total alkalinity

This paper describes a method used to certify reference materials based on seawater for total alkalinity. The technique employs a two-stage, potentiometric, open-cell titration using coulometrically analyzed hydrochloric acid. The equivalence point is evaluated from titration points in the pH region 3.0–3.5 using a least-squares procedure that corrects for the reactions with sulfate and fluoride ions. The reproducibility (one standard deviation) of this technique is less than 1 μmol kg−1; the accuracy is within 2 μmol kg−1.