Jm. Hernandez-ayon et al., pH, alkalinity and total CO2 in coastal seawater by potentiometric titration with a difference derivative readout, ANALYT CHIM, 394(1), 1999, pp. 101-108
A method for measuring three components of the CO2 system, pH, alkalinity (
A(t)) and total CO2 (TCO2) in coastal seawater is presented. The measuremen
ts are sufficiently precise to register CO2 changes of biological origin in
surficial and coastal waters or in culture media. The method is based on a
modified potentiometric titration of seawater with acid in a custom-built
cell with the data plotted as a difference derivative, giving two peaks fro
m which total carbonate and alkalinity can be computed. pH is calculated di
rectly from the initial millivolt reading of the sample. One important aspe
ct of this technique is that, unlike a Gran titration, the measured values
of pH, A(t) and TCO2 are independent of any pre-conceived seawater model. I
n this work we demonstrate that the relative position of the two peaks (use
d for determining TCO2) is relatively insensitive to interferences from dis
solved organic matter to about 1 x 10(-4) M, while peak height is sensitive
to it. This last observation permits the detection of organic bases which
might be included in the measurement of alkalinity. (C) 1999 Elsevier Scien
ce B.V. All rights reserved.