Optimization of a Flow Injection Differential Potentiometric System with Two Identical Electrodes for the Determination of Calcium Ion in Water With Improved Sensitivity

Abstract

An experimental optimization by the modified simplex method of a flow injection analysis (FIA) system for the differential potentiometric determination of calcium ion in water is reported. The performances of the optimized system and of an equivalent conventional potentiometric FIA system are compared. The most important features of the proposed system are a substantial increase in sensitivity (from about 28 to about 50 mV per decade) in the linear response range (10 24 -10 22 mol l 21 in both cases) and better repeatability (0.5 and 0.8% versus 1.7 and 1.9%, respectively, at 1 3 10 23 and 6.2 3 10 24 mol l 21 calcium ion). The influence of the ionic strength is discussed, showing that it significantly affects the accuracy of the results. The relative accuracy of the differential system was demonstrated by the determination of the calcium content of drinking waters in parallel with an ASTM certified method.

Optimization of a bipotentiometric flow injection analysis system for simultaneous determination of calcium and chloride ions in natural waters

“…The system described in this paper uses electrodes selective to calcium and chloride placed in series, to allow the simultaneous determination of both species in natural waters. As in the previous case, 8 the shape of the signal was found to depend on the geometric and hydrodynamic parameters of the system, owing to the comparatively slow response of the calcium electrode. Therefore, the system had to be optimized to find the best conditions in which the electrodes work alternatively as indicator and reference electrodes.…”

“…Flow injection analysis (FIA) with potentiometric detection allows the assembly of devices in which both electrodes contribute to the signal, thus providing full utilization of the capacity of the potentiometric cell to generate information. [1][2][3][4][5][6][7][8] We recently described a system where two calcium ion selective electrodes (ISEs) are placed in series in the manifold, one connected to the reference input and the other to the electrode input of one voltmeter. 8 If the flow and manifold parameters are adequately chosen, the second ISE keeps a constant potential (fixed by the background concentration in the carrier solution of the species to which this ISE is sensible) while the sample is flowing through the first electrode and provides signal, and vice versa.…”

“…[1][2][3][4][5][6][7][8] We recently described a system where two calcium ion selective electrodes (ISEs) are placed in series in the manifold, one connected to the reference input and the other to the electrode input of one voltmeter. 8 If the flow and manifold parameters are adequately chosen, the second ISE keeps a constant potential (fixed by the background concentration in the carrier solution of the species to which this ISE is sensible) while the sample is flowing through the first electrode and provides signal, and vice versa. This system allows the detection of calcium ion with increased sensitivity, i.e., produces information with increased quality.…”

Detectores potenciométricos para sistemas de análise por injecção em fluxo, evolução e aplicação

“…O primeiro sistema FIA com detecção multiparamétrica deve-se a Hansen 127 , que incorporou, em série, um eléctrodo sensível a cálcio e outro de pH para detecção simultânea dos respectivos iões. Este procedimento pode ser atingido utilizando-se vários 14,42,56,67,69,97,109,127,152,160,174,175,177,182,184,196,198,203,207,220,224,226,273,301 , ou um só detector, com a ajuda de diferentes configurações FIA 331 . As montagens para determinações multiparamétricas podem ser baseadas na colocação de detectores em série, desde que o primeiro detector não seja destrutivo da amostra, ou na divisão de fluxo após a injecção da mesma.…”

“…A utilização frequente destes sistemas, nos quais numa mesma análise se procede à monitorização de dois ou mais parâmetros, tem sido muito explorada, particularmente nesta última década, sobretudo porque, dada a utilização de unidades de configuração tubular, o fluxo de amostra mantém as suas características hidrodinâmicas inalteradas. Encontramse descritos inúmeros sistemas de fluxo empregando dois ou mais detectores potenciométricos 14,42,56,67,69,97,109,127,152,160,174,175,177,182,184,196,198,203,207,220,224,226,273,301 , mas também dois tipos distintos de processos de detecção 7,21,25,34,73,75,79,80,120,141,152,156,187,189,197,219,232,233,287,290,304,312,318 . Como exemplos destacam-se,...…”