Indirect potentiometry

One of the most fruitful uses of potentiometry in analytical chemistry is its application to titrimetry. Prior to this application, most titrations were carried out using colour-change indicators to signal the titration endpoint. A potentiometric titration (or indirect potentiometry) involves measurement of the potential of a suitable indicator electrode as a function of titrant volume. The information provided by a potentiometric titration is not the same as that obtained from a direct potentiometric measurement. As pointed out by Dick [473], there are advantages to potentiometric titration over direct potentiometry, despite the fact that the two techniques very often use the same type of electrodes. Potentiometric titrations provide data that are more reliable than data from titrations that use chemical indicators, but potentiometric titrations are more time-consuming. 

Flame photometry Atomic absorption spectrometry Amperometry/coulometry Indirect potentiometry... 

The measurement of pK for bases as weak as thiazoles can be undertaken in two ways by potentiometric titration and by absorption spectrophotometry. In the cases of thiazoles, the second method has been used (140, 148-150). A certain number of anomalies in the results obtained by potentiometry in aqueous medium using Henderson s classical equation directly have led to the development of an indirect method of treatment of the experimental results, while keeping the Henderson equation (144). 

Ion-selective electrodes allow the measurement of ionic activity in diluted or undiluted whole blood, plasma or rum. The direct (undiluted) measurement may be preferred, since no sample pretreatment is necessary and the assay values are independent of hematocrit and amount of solids present. However, direct potentiometry by its very nature does not provide total concentration values similar to those obtained by flame photometry and indirect (diluted) potentiometry... 

In analytical practice, some methods using definitive measurements, in principle, are also calibrated by indirect reference measurements using least squares estimating to provide reliable estimates of b (spectrophotometry, potentiometry, ISE, polarography). 

The potential of an electrode is related directly to the activities, and thus indirectly to the concentrations, of the chemical species involved in the equilibria that establish the potential. The main virtues of potentiometry are simplicity, very low power requirements, and the possibly small size of the sensors. The main drawback is that an unwanted reaction may enter into determination of the potential and sensitivity may be poor. Potentio-metric sensing, as a transducing technique, can be coupled with an infinite... 

For monitoring catalytic (enzymatic) products, various techniques, such as spectrophotometry [32], potentiometry [33,34], coulometry [35,36] and amperometry [37,38], have been proposed. An advantage of these sensors is their high selectivity. However, time and thermal instability of the enzyme, the need of a substrate use and indirect determination of urea (logarithmic dependence of a signal upon concentration while measuring pH) cause difficulties in the use and storage of sensors. 

The first estimate of the Bk(IV)-Bk(III) potential was made in 1950, only a short time after the discovery of the element. A value of 1.6 V was reported, based on tracer experiments (3). Later, in 1959, a refined value of 1.62 0.01 V was reported for the couple, based on the results of experiments with microgram quantities of berkelium (4). The potential of the Bk(IV)-Bk(III) couple has subsequently been determined by several workers using direct potentiometry (220-224) or indirect methods (218, 225, 226). All of the above-mentioned determinations were performed in media of relatively low complexing capability. The formal potential of the Bk(IV)—Bk(III) couple is significantly shifted to less positive values in media containing anions that strongly complex Bk(IV), such as PCV- and CO32- ions (227). This behavior closely parallels that of the Ce(IV)-Ce(III) couple (228). In fact, the Bk(IV)-Bk(III) couple markedly resembles the Ce(IV)-Ce(III) couple in its oxidation-reduction chemistry. 

Detected ions Potentiometry with mebr. ISE Amperom. Condr Suppr. ictivity SC Direct uv Indirect... 

A theoretically predicted positive bias of 6.7% for direct potentiometry (total ion molality in plasma water) versus indirect assay (total ion concentration in the whole sample volume) is generally accepted for normal situations and is compensated by calibration. 

In potentiometry, all ions present in the solution principally contribute to the potential of the working electrode. As the ratio between the analyte concentration and that of other species in the solution generally is rather low, the analyte contribution to the detector signal is often low, which results in relatively poor detection limits. To circumvent this problem, ion-selective membranes (ISM), which permit only some ions to pass through the membranes, are commonly employed. In this way, detection limits down to 10 mol/L can be achieved. The ISM also reduces the influence from matrix components, which allows measurements in complex matrices such as blood or seram without interferences. The long-term stability of these electrode may, however, be a problem, as the electrodes might have to be replaced after a few hours or days. Common analytes are inorganic anions and cations, especially alkali and alkaline earth metals ions. A further application is the indirect detection of amino acids, where the... 

Ion-selective electrodes (ISEs) are commercially available for many anions and cations, as indicated in Tables 4-7. Other analytes can be determined using ISEs in an indirect way. Chapter 28.3 deals with various types of jx>tentio-metiic biosensors. A special advantage of ion-selective potentiometry is the possibility of carrying out measurements even in microliter volumes without any loss of analyte. 

Potentiometry-FIA Orthophosphate + tripolyphosphate 310 10 Indirect detection using Pb(II) electrode—better selectivity for S04 [116]... 

Taking advantage of the relative simplicity, ease of miniaturization, possibility of in situ measurements, low cost, and high sensitivity of electroanalytical techniques, various electrochemical detection approaches have been coupled to FIA for the multiplexed determination of target analytes, with either direct or indirect detection. Commonly used electroanalytical techniques include potentiometry, conductometry, voltammetry, and amperometry, among others. Although amperometry has been the preferred option in most applications, potentiometry (Lee et al., 2001, 2002 Suwansa-Ard et al., 2005) and conductometry (Suwansa-Ard et al., 2005) have also been employed (Llorent-Martinez et al., 2011). 

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