Instrumentation potentiometric techniques

Potentiometric techniques are prevalent for instrumental titration processes. Often the typical sigmoidal (S shaped) potentiometric titration curve is used as a synonym for the term titration curve as a whole, although curves with linear branches are found also. Titration curves are recorded by plotting the results of potentiometric measurement (the voltage differences between reference and indicator electrodes) vs. the amount of titrant used. A typical example for titration of a strong acid by means of a strong base is shown in Fig. 9.2. The equivalence point (the point where the amount of titrant added would just correspond to 100% reaction degree) in this case is reached at... 

The experimental approaches used to characterize ion-pair partitioning are cyclic voltammetry and potentiometric titration. Cyclic voltammetry is overall more powerful, but requires special instrumentation which is not commercially available as a ready-to-use set-up. For this reason the potentiometric titration technique has been more widely used. 

Before considering instrumentation in some detail in later chapters, it will be helpful to outline the kinds of experiments that we wish to implement electronically. It is useful to characterize electroanalytical techniques as either static or dynamic. Static methods are philosophically akin to the passive observation mentioned earlier. They entail measurements of potential difference at zero current such that the system defined by the solid-solution interphase is not disturbed and Nernstian equilibrium is maintained. Although such potentiometric measurements (e.g., pH, pM) are of great practical importance, our focus here will be on the dynamic techniques, in which a system is intentionally disturbed from equilibrium by excitation signals consisting of a wide variety of potential and current programs. 

Potentiometric titration is a commonly used technique determination (Albert and Serjeant, 1984). The PCA101 chemical analyzer, developed and manufactured by Sirius Analytical Instruments Ltd., is the rst commercial instrument designed specilly to determine ionization constants (Avdeef, 1993). The theory and applications of the method have been discussed byAvdeef (Avdeef, 1993), and the reader is directed to that excellent review for a detailed discussion. 

Table II summarizes the most often used techniques. The methods are grouped according to categories of archaeological artifacts for which they are considered most appropriate. Colorimetry, potentiometric titrations, UV, and visible range spectrophotometry are used whenever possible, primarily because the instruments are usually available and...

Electrochemical biosensors have some advantages over other analytical transducing systems, such as the possibility to operate in turbid media, comparable instrumental sensitivity, and possibility of miniaturization. As a consequence of miniaturization, small sample volume can be required. Modern electroanalytical techniques (i.e., square wave voltammetry, chronopotentiometry, chronoamperometry, differential pulse voltammetry) have very low detection limit (1(T7-10 9 M). In-situ or on-line measurements are both allowed. Furthermore, the equipments required for electrochemical analysis are simple and cheap when compared with most other analytical techniques (2). Basically electrochemical biosensor can be based on amperometric and potentiometric transducers, even if some examples of conductimetric as well as impedimetric biosensor are reported in literature (3-5). 

There are a variety of analytical methods commonly used for the characterization of neat soap and bar soaps. Many of these methods have been published as official methods by the American Oil Chemists Society (29). Additionally, many analysts choose United States Pharmacopoeia (USP), British Pharmacopoeia (BP), or Pood Chemical Codex (FCC) methods. These methods tend to be colorimetric, potentiometric, or titrametric procedures. However, a variety of instrumental techniques are also frequendy utilized, eg, gas chromatography, high performance liquid chromatography, nuclear magnetic resonance spectroscopy, infrared spectroscopy, and mass spectrometry. 

Different electrochemical sensors have been developed for cell concentration measurement. The most promising of these sensors are based on impedimetric measurements. A commercial version of a sensor that measures the frequency-dependent i)ermittivity is available from Aber Instruments Ltd [137-139]. Another type of electrochemical probe measures the potential changes in the cell suspension caused by the production of electroactive substances during cell growth [140-143]. To date, no on-line applications of these potentiometric sensors under real cultivation conditions have been reported. Other types of probes, such as amperometric and fuel-cell sensors, measure the current produced during the oxidation of certain compounds in the cell membrane. Mediators are often used to increase the sensitivity of the technique [143-145]. 

The quartz crystal nanobalance (QCN) can be combined with practically any electrochemical methods, such as cyclic voltammetry, chronoamperometry, chronocoulometry, potentiostatic, galvanostatic, rotating disc electrode [11], or potentiometric measurements. The EQCN can be further combined with other techniques, e.g., with UV-Vis spectroscopy [12], probe beam deflection (PBD) [13], radiotracer [14], atomic force microscopy (AEM) [15], and scanning electrochemical microscopy (SECM) [16]. The concept and the instrumentation of... 

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