Digital titrator

Wolf, S. Titroprint - ein neuartiger druckender Digital-Titrator. Chem. Rundschau (Solothurn) 22, 639-641 (1969). 

Philadelphia. PA ] (b) Digital titrator with plastic cartridge containing reagent solution is used for analyses in the field. [Courtesy Hach Co., Loveland, CO] (c) Battery-operated electronic buret with digital readout delivers 0.01-mL increments from a reagent bottle. This device can be used for accurate titrations in the field. [Courtesy Cote-Parmer Co.. Niles. ILJ... 

The digital titrator in Figure 2-6b is convenient for use in the field where samples are collected. The counter tells how much reagent has been dispensed. The precision of 1% is... 

The choice of test equipment and methods has become extremely wide and, apart from large, integrated, electronic colorimetric and spectrophotometric instrumentation, field personnel can choose from miniburettes, direct-reading titrators (modified syringes), digital titrators, drop tests, tablet tests, permanent color standard comparators, indicator papers, portable colorimeters, immunoassays, etc. Today, field-test methods tend to be tailored by equipment manufacturers to their own analytical systems, and consequently the specified use of particular standard methods for the examination of water, from any one technology or official body, is probably not realistic. Rather it is the fitness-for-purpose rule that is more relevant. 

Method (A) Using Hach digital titrator and standard acid cartridges. 

Fig. 13.14 Scheme of automatic multi-function digital titrator. (Courtesy of Ionic Inc.)-... 

A large variety of analysers such as ion chromatographs, mass spectrometers, digital titrators, calorimeters, specific ion analysers, gas and liquid chromatographs and octane number analysers are manufactured with built-in microprocessors. 

The simple electrical circuit shown in Fig. 16.15(h) is suitable for this procedure. The voltage applied to the titration cell is supplied by two 1.5 V dry cells and is controlled by the potential divider R (a 50-100 ohm variable resistance) it can be measured on the digital voltmeter V. The current flowing is read on the micro-ammeter M. 

ELECTRODEjcls Fig. 4.24 The operation of an ion-specific electrode with a slope of 59.16 mV per decade for mono-valent ions (29.58 mV/dec for di-valent ions) is simulated under the assumption that a digital volt meter with a resolution of, say, 0.1 mV is used. The sample volume and the concentration of the metered titration solution are known. Normally, one would add a few milliliters of the concentrated titration solution and do the calculation spelled out in lines 140-150 in Table 4.22 here, because the sample concentration is known, the result can be normalized to it. The operation of short-cuts (volume correction), unknowns (volume bias, deviation of true slope from theoretical), and equipment shortcomings (digitization) can be studied. 

The first question is what kind of information the chemical control can and should provide. Must it be a qualitative and/or quantitative analysis, is it based on a one- or two-dimensional measurement and should the latter consist of an analog and/or digital display The meaning of all this can be well illustrated by the example of the differential titration (see Fig. 5.1) of equivalent amounts of a strong acid (cf., Fig. 2.17, AA) and a weak acid (cf., Fig. 2.18, BA, pK, = 4). 

It may be useful to point out a few topics that go beyond a first course in control. With certain processes, we cannot take data continuously, but rather in certain selected slow intervals (c.f. titration in freshmen chemistry). These are called sampled-data systems. With computers, the analysis evolves into a new area of its own—discrete-time or digital control systems. Here, differential equations and Laplace transform do not work anymore. The mathematical techniques to handle discrete-time systems are difference equations and z-transform. Furthermore, there are multivariable and state space control, which we will encounter a brief introduction. Beyond the introductory level are optimal control, nonlinear control, adaptive control, stochastic control, and fuzzy logic control. Do not lose the perspective that control is an immense field. Classical control appears insignificant, but we have to start some where and onward we crawl. 

Potentiometric titrations are readily automated by using a motor-driven syringe or an automatic burette coupled to a chart recorder or digital printout system. This is described in more detail in Chapter 12. A micro-processor-controlled titrator is discussed in Chapter 13. 

Electronic devices such as automatic titrators and digital burets may be used in place of the traditional glass buret and manual titration. Such devices provide electronic control over the addition of titrant and thus, with proper calibration, are accurate, high-precision devices. These will be discussed in Section 4.9. 

There are also various devices that are commonly used for titrations in place of the glass burets previously described. A digital buret, for example, is an electronically controlled bottle-top dispenser that delivers 0.01-mL increments from a reagent bottle containing the titrant. There are also automatic titrators, such... 

FIGURE 4.18 An automatic titrator. A pump draws the titrant from the reagent bottle on the left and fills the reservoir in the back of the unit. Pressing a key on the keypad in the foreground delivers titrant to the titration flask on the right as the solution is automatically stirred. The volume delivered is displayed on a digital readout. 

The electrical circuit, Figure 17.2 (b), consists of two 1.5 V dry cells that provides a voltage applied to the above titration cell. It is duly controlled and monitored by the potential divider (R) and is conveniently measured with the help of a digital voltmeter (V). Finally, the current flowing through the circuit may be read out on the micro-ammeter (M) installed. 

Mg in fertilizers is based on such proceedings thereof has been applied on multiple occasions. In milk fermentation, where the samples were dried, calcined in a furnace at 600 °C, the ash was dissolved in 0.03 M HCl, the solution was centrifuged and the supernatant was thus analyzed . The complexometric method for determination of Ca(II) and Mg(II) can be carried out in a single titration with EDTA in alkaline solution, using a Ca-ISE for potentiometric determination of two endpoints. This is accomplished on digitally plotting pCa values measured by the ISE as a function of the volume V of titrant added to the aliquot of analyte the first and second inflection points of the curve mark the Ca(II) and Mg(n) equivalences, respectively. ... 

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