Spectrophotometric pH measurements of freshwater

被引：38

作者：

French, CR ^{[1
]}

Carr, JJ ^{[1
]}

Dougherty, EM ^{[1
]}

Eidson, LAK ^{[1
]}

Reynolds, JC ^{[1
]}

DeGrandpre, MD ^{[1
]}

机构：

[1] Univ Montana, Dept Chem, Missoula, MT 59812 USA

来源：

ANALYTICA CHIMICA ACTA | 2002年 / 453卷 / 01期

关键词：

spectrophotometric pH; cresol red; freshwater; low ionic strength;

D O I：

10.1016/S0003-2670(01)01509-4

中图分类号：

O65 [分析化学];

学科分类号：

070302 ; 081704 ;

摘要：

The use of cresol red (CR) indicator for determination of freshwater pH is evaluated. Ionic strength effects and indicator pH perturbation are discussed and quantified using theoretical and empirical approaches. Spectrophotometric and potentiometric methods are directly compared by repeated analyses of a low ionic strength pH buffer. The mean and standard deviation of the two methods were 7.618 +/- 0.008 (spectrophotometric) and 7.484 +/- 0.040 (potentiometric) (N = 18) with systematic errors of 0.003 and 0.137 pH units relative to the true pH (7.621). Field data from an alkaline river (pH similar to 7.8-8.8) show that measurement reproducibility is better than 0.01 pH units, making it possible to resolve very small spatial and temporal changes in riverine pH. Uncertainty in the indicator apparent dissociation constant limits the accuracy of the pH measurement to similar to0.05 pH units. An alternative method for estimating the dissociation constant, based on calculation of pH from two other carbonate parameters, is proposed. (C) 2002 Elsevier Science B.V. All rights reserved.

引用

页码：13 / 20

页数：8

共 27 条

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