Backside calibration potentiometry: Ion activity measurements with selective supported liquid membranes by calibrating from the inner side of the membrane
Backside calibration potentiometry: Ion activity measurements with selective supported liquid membranes by calibrating from the inner side of the membrane
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DOI：
10.1021/ac061467g
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发表时间：
2007-01-15
影响因子：
7.4
通讯作者：
Pretsch, Ernoe
中科院分区：
文献类型：
--
作者：
Malon, Adam;Bakker, Eric;Pretsch, Ernoe
在直接电位测定中，测量电位的大小用于确定样品的成分。虽然这对相关电位测量所需的再现性提出了相当艰巨的要求（通常为微伏量级），但如今使用离子选择电极（ISE）通过直接电位测定成功地进行了血液样本的体外临床分析。不幸的是，大多数其他分析情况不允许传感器每隔几分钟重新校准一次，如在环境监测或体内测量中，并且在这些情况下，直接电位测定法通常注定无法作为准确的方法。本文介绍了电位传感的一个新方向，称为背面校准电位测定法。通过改变膜两侧的搅拌速率来确定电位漂移的方向，从而评估薄支撑液体 ISE 膜上的化学不对称性。这种漂移的消失表明膜上浓度梯度的消失，如果膜背面的溶液成分和样品中的干扰离子浓度已知，则可用于确定样品成分。对于实际测定，改变参比溶液中主要离子或干扰离子的浓度，直到搅拌效应消失。该过程通过使用 Ba2+ 作为主要干扰离子的 Ca2+ 选择性膜进行了演示。另一个例子包括测定环境样品中的 Pb2+，其中 pH 值已调整至已知水平。在 pH 4.0 时，H+ 成为主要干扰离子。该方法通过不同环境水样的实际适用性得到验证，并将新方法获得的结果与使用标准添加的传统校准获得的结果进行了比较。讨论了新方法在准确性和适用浓度范围方面的局限性。
In direct potentiometry, the magnitude of the measured potentials is used to determine the composition of the sample. While this places rather formidable demands on the required reproducibility of the associated potential measurements, typically on the order of microvolts, in vitro clinical analyses of blood samples are today successfully performed with direct potentiometry using ion-selective electrodes (ISEs). Unfortunately, most other analytical situations do not permit the sensor to be recalibrated every few minutes, as in environmental monitoring or in vivo measurements, and direct potentiometry is often bound to fail as an accurate method in these circumstances. This paper introduces a novel direction for potentiometric sensing, termed backside calibration potentiometry. Chemical asymmetries across thin supported liquid ISE membranes are assessed by determining the direction of potential drift upon changing the stirring rate on either side of the membrane. Disappearance of this drift indicates the disappearance of concentration gradients across the membrane and is used to determine the sample composition if the solution composition at the backside of the membrane and the interfering ion concentration in the sample are known. For practical determinations, the concentration of either the primary or the interfering ion is varied in the reference solution until the stirring effect disappears. The procedure is demonstrated with a Ca2+-selective membrane using Ba2+ as the dominant interfering ion. Another example includes the determination of Pb2+ in environmental samples where the pH is adjusted to a known level. At pH 4.0, H+ turns out to be the dominant interfering ion. The practical applicability of the method is shown with different environmental water samples, for which the results obtained with the novel method are compared with those obtained by traditional calibration using standard additions. The limitations of the novel method in terms of accuracy and applicable concentration ranges are discussed.