Alkalinity determination by potentiometry: intercalibration using three different methods

• Main Authors: Mintrop, L., Pérez, Fiz F., González-Dávila, Melchor, Santana-Casiano, Magdalena, Körtzinger, Arne
• Format: Article in Journal/Newspaper
• Language: Spanish; English
• Published: Universidad Autónoma de Baja California 2000
• Subjects: Alkalinity; Potentiometry; Seawater; Certified reference materials; Alcalinidad; Potenciometría; Agua de mar; Material certificado de referencia; Doble; Referencia; North Atlantic
• Online Access: http://hdl.handle.net/10261/25136

16 pages, 1 figure, 3 tables. [EN] Seawater was sampled from different depths in the North Atlantic Ocean (Canary Islands region) and distributed among three different labs for the determination of titration alkalinity. Analysis was performed by potentiometric methods, involving titration in a closed cell, titration in an open cell and a two end-point acid addition method. The precision, which is the sample reproducibility taken from the mean standard deviation for replicate measurements, was between 0.45 and 0.90 µmol kg(-1) for the individual labs. Accuracy, here taken as the deviation for the values of a lab from the mean of all three, was mostly below 1 µmol kg(-1) and never exceeded 0.1% of the sample value. Mean standard deviation for all labs and all samples was 0.87 µmol kg(-1), once the individual methods were calibrated using certified reference material (CRM). Without CRM calibration, the mean standard deviation would increase to 2.8 µmol k(-1). The conclusion is that current high precision methods for alkalinity measurements calibrated with CRMs are able to reach similar accuracy as the measurement of total dissolved inorganic carbon by coulometry and therefore allow for the precise determination of the oceanic carbon dioxide system by using the two measured parameters. [ES] Se determinó la alcalinidad de muestras de agua de mar recogidas a diferentes profundidades en el Océano Atlántico Norte y distribuidas entre tres laboratorios, utilizando tres variantes potenciométricas: valoración en cubeta cerrada, valoración en cubeta abierta y un método de adición a doble punto final. La precisión, la reproducibilidad de la muestra obtenida a partir de la desviación estándar media para medidas replicadas, fue entre 0.45 y 0.90 µmol . kg(-1) para cada laboratorio. La exactitud, tomada como la desviación de los valores de un laboratorio respecto de la media de los tres, fue mayoritariamente menor que 1 µmol . kg(-1) y nunca excedió 0.1% del valor de la muestra. La desviación media estándar para todos los ...