Potentiometric signal functions

Signal Functions of Potentiometric Sensors with Oxide-Ion-Conducting... 

Signal Functions of Potentiometric Oxygen Sensors with Oxoanionic Solid... 

Most potentiometric electrodes are selective for only the free, uncomplexed analyte and do not respond to complexed forms of the analyte. Solution conditions, therefore, must be carefully controlled if the purpose of the analysis is to determine the analyte s total concentration. On the other hand, this selectivity provides a significant advantage over other quantitative methods of analysis when it is necessary to determine the concentration of free ions. For example, calcium is present in urine both as free Ca + ions and as protein-bound Ca + ions. If a urine sample is analyzed by atomic absorption spectroscopy, the signal is proportional to the total concentration of Ca +, since both free and bound calcium are atomized. Analysis with a Ca + ISE, however, gives a signal that is a function of only free Ca + ions since the protein-bound ions cannot interact with the electrode s membrane. 

When measuring a signal, one records the magnitude of the output or the response of a measurement device as a function of an independent variable. For instance, in chromatography the signal of a Flame Ionization Detector (FID) is measured as a function of time. In spectrometry the signal of a photomultiplier or diode array is measured as a function of the wavelength. In a potentiometric titration the current of an electrode is measured as a function of the added volume of titrant. 

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. 

In general, the signal from a gas chromatograph is recorded continuously as a function of time by means of a potentiometric device. Most frequently, a recorder of 1-10 mV full-scale deflection ( 10 inches) and having a response time 1 second or less is quite adequate. 

The signal emerging from the detector of a HPLC is recorded continuously as function of time most commonly with the help of a potentiometric recorder. Invariably, a recorder of 1 to 10 mV full-scale deflec-... 

The reference electrode is used as a potentiometric (always zero-current) probe to monitor A< >w relative to its own A< >r. This value is compared with Ea and if a difference (i.e., an error signal) exists, the potential impressed across the cell by the potentiometer is adjusted until balance (i.e., no error signal) is achieved. A device that accomplishes this control function automatically is called a potentiostat for obvious reasons. Such behavior can be mimicked by the experimenter. Although this is assuredly almost never done these days, it is useful to think about a manual potentiostat as a pedagogical device. 

The amperometric approach to endpoint detection provides considerable latitude in the selection of the best conditions for the most specific and sensitive endpoint response. Furthermore, the response signal is directly proportional to the concentration of the observed species, whereas potentiometric responses are a logarithmic function of the concentration. Another attractive feature of amperometric endpoint detection is that the most important data are obtained prior to and after the equivalence point, whereas in potentiometric titrations the most important data occur at the equivalence point, which is the most unstable condition of the titration. With amperometric titrations an extrapolation of the straight-line portion of the curve, either prior to or after the equivalence point, to an intercept will provide an accurate measure of the equivalence point. 

Acoustic spectroscopy has several characteristics that make it useful. One clear advantage over light-scattering techniques is the ability to stir, pump, or otherwise physically agitate the sample during analysis, making the technique well suited to potentiometric titration and analysis of unstable suspensions. When the acoustic signal is measured as a function of the transmitter-receiver gap, it requires no... 

Sometimes, particularly when the detectability of various methods is being compared, the units of mass fraction are expressed in the logarithmic scale. Thus, instead of mass fractions 0.000001 or 0.000005, their negative logarithms, 6.00 or 5.30 respectively, are given. This is particularly convenient when the analytical signal is a logarithmic function of concentration, as occurs in potentiometric measurements. 

It would be necessary to decouple the radio frequency to prevent it interfering with the function of the potentiometric recorder (or signal processing amplifier). The resistance capacity decoupling shown in their circuit appears hardly sufficient to achieve this in a satisfactory manner and consequently, the circuit shown in figure 11 may be only schematic. The column was connected directly to the sensor and the eluent passed through the annular channel between the central electrode and the sensor wall. 

The use of a UV spectrophotometric procedure can thus be proposed as an alternative method for the determination of inorganic sulphide in water and wastewater. A first method, based on the use of a multiwavelength procedure has been proposed for natural water [35], The interferences are modelled from an exponential function and the simultaneous determination of total sulphide and iodide is possible. A second method integrates the semi-deterministic deconvolution procedure [36]. The potentiometric method will be chosen as reference for the validation of this last procedure. The UV quantification is carried out by deconvolution (see Chapter 2) between 205 nm and 320 nm. Raw samples were diluted four times to prevent the UV signal saturation for a 10-mm quartz cell. Sulphide (HS ) concentration is given by the product of the contribution coefficient of sulphide reference spectrum (replacing nitrate in the previous set) and the corresponding concentration, affected by the dilution factor. 

Another research team has successfully applied WT in voltammetric studies. Specifically, WT was applied to process DPV signals [32], potentiometric-titration- [33], and oscillographic chronopotentiometric signals [34,35]. Chen et al. [32] proposed a new type of wavelet function, the difference of... 

Some automatic potentiometric titrators (continuous titrators) carry out the analysis continuously. The flow rate of the titrant varies according to the signal obtained from the electrode. Once a steady state has been attained, the flow rate of the titrant becomes the measure of the concentration of the analyte in the sample. If the potential of the indicator electrode and the flow rate of the titrant are recorded as function of time one obtains the record of the variation of analyte concentration with time. 

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