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Detection system titration

Several experimental techniques may be used, such as acid/base titration, electrical conductivity measurement, temperature measurement, or measurement of optical properties such as refractive index, light absorption, and so on. In each case, it is necessary to specify the manner of tracer addition, the position and number of recording stations, the sample volume of the detection system, and the criteria used in locating the end-point. Each of these factors will influence the measured value of mixing time, and therefore care must be exercised in comparing results from different investigations. [Pg.299]

At point E, the system is in the third buffer region and pH = pXa3. When this reaction is complete, the primary species in solution are phosphate ions and sodium ions, which form a solution of Na,P04(aq). To reach this stoichiometric point (F in the plot), we have to add another mole of OH for each mole of H3P04 initially present. At this point, a total of 3 mol OH has been added for each mole of H,P04. Notice that the third stoichiometric point (point F) is indistinct, largely because Ka3 is comparable to Kn.. As a result, it is not detected in titrations. [Pg.585]

It is certainly clear that a coulometric titration, like any other type of titration, needs an end-point detection system in principle any detection method that chemically fits in can be used, be it electrometric, colorimetric, photoabsorptionmetric, etc. for instance, in a few cases the colour change of the reagent generated (e.g., I2) may be observed visually, or after the addition of a redox, metal or pH indicator the titration end-point can be detected photoabsorptiometrically by means of a light source and photocell combination. Concerning the aforementioned coulometric titration of Fe(II), it is... [Pg.236]

Christian, G. D. A Sensitive Amperometric Endpoint Detection System for Microcoulometric Titrations. Microchem. J. 9, 484 (1965). [Pg.103]

With any endpoint detection system several practical considerations are important for reliable results. For example, the indicator electrode should be placed in close proximity to the flow pattern from the burette, so that a degree of anticipation is provided to avoid overrunning the endpoint. Another important factor is that the indicator electrode be as inert and nonreactive as possible to avoid contamination and erratic response from attack by the titration solution. A third and frequently overlooked consideration is the makeup of the reference electrode and, in particular, its salt bridge. For example, a salt-bridge system that contains potassium chloride can cause extremely erratic behavior of any electrochemical system if the titrant solution contains perchlorate ion (because of the precipitation of potassium perchlorate at the salt-bridge titrant-solution interface). Likewise, a potassium chloride salt bridge in a potentiometric titra-... [Pg.141]

For this titration the dual-polarized amperometric endpoint detection system provides good sensitivity and rapid response. [Pg.156]

Because the generator electrodes must have a significant voltage applied across them to produce a constant current, the placement of the indicator electrodes (especially if a potentiometric detection system is to be used) is critical to avoid induced responses from the generator electrodes. Their placement should be adjusted such that both the indicator electrode and the reference electrode occupy positions on an equal potential contour. When dual-polarized amperometric electrodes are used, similar care is desirable in their placement to avoid interference from the electrolysis electrodes. These two considerations have prompted the use of visual or spectrophotometric endpoint detection in some applications of coulometric titrations. [Pg.157]

The nature of the tracer dictates the detection system. For the liquid phase, quite often the tracers (e.g., NaCl, H2S04, etc.) are such that the detection probe is directly inserted into the reactor and continuous monitoring of the concentration at any fixed position is obtained by means of an electrical conductivity cell and a recorder. In this case, no external sampling of liquid is necessary. If the tracer concentration measurement requires an analytical procedure such as titration, etc., sampling of the liquid is required. For the solid phase, a magnetic tracer is sometimes used. The concentration of a solid-phase tracer can also be measured by a capacitance probe if the tracer material has a different dielectric constant than the solid phase. In general, however, for solid and sometimes gas phases, some suitable radioactive tracer is convenient to use. The detection systems for a radioactive tracer (which include scintillation counters, a recorder, etc.) can be expensive. Some of the tracers for the gas, liquid, and solid phases reported in the literature are summarized in Table 3-1. [Pg.62]

The solution conditions and the end-point detection system are usually chosen based on the same criteria used for an ordinary titration (e.g., fast, definite, single, complete titration reaction and sensitive end-point detection). The current density range for... [Pg.433]

Nicholson proposed a differential potentiometric tltrator involving two indicator electrodes for the automatic control of processes in industrial plants [35]. As can be seen from Fig. 7.20, the sample and reagent streams are split and led to two half-cells via capillary tubes adjusted to provide slightly different titrated fractions. The potential difference (AE) between the two indicator electrodes Is transmitted to a control and detection system (D) which regulates the flow of titrant in an automatic fashion by means of valve V, thereby maintaining the preselected AE between the two ends of the cell. The speed of titrant addition, reflected by the flow meter (M), is a measure of the sample composition. An evaluation of the instrument carried out by the titration of dichromate with iron(II) revealed that the conditions to be used must be carefully selected. Thus, stable electrode responses are only obtained in the zone where Fe(II) prevails, and not in that where dichromate prevails over the former as the process determining the potential obtained in such a zone is irreversible. This method therefore has limited application in the control of slow reactions. [Pg.224]

Fig. 7.21 (a) Detail of automatic titrator with photometric detection system (b) general configuration of the titrator. (Reproduced from [36] wlh permission of Elsevier). [Pg.225]

Assuming impurities can be satisfactorily pretitrated, the lower limit of the amount of sample that can be titrated is governed primarily by the sensitivity of the available endpoint detection system. Very small currents, such as 0.1 /xA, can be measured accurately (actually, currents smaller than 60 electrons per second have been measured and the time of electrogeneration can be measured accurately. With conventional amperometric and potentiometric endpoint indication, coulometric titrations in typical solution volumes cannot be accurately made at generating currents of less than about 100 A. [Pg.107]

Titration of mAbs as capture and detection systems against dilutions of 146S, 12S, TTV, and DNV. [Pg.277]

Titration of 146S in the presence of a constant amount of 12S using mAh capture and detection systems. [Pg.279]

Figure 5 Cell arrangement for coulometric titration in the constant current mode. The counter-electrode is isolated from the sample solution by a liquid junction formed, for example, with a glass frit. The indicator electrodes may belong to a potentiomet-ric, amperometric, or conductometric detection system. Figure 5 Cell arrangement for coulometric titration in the constant current mode. The counter-electrode is isolated from the sample solution by a liquid junction formed, for example, with a glass frit. The indicator electrodes may belong to a potentiomet-ric, amperometric, or conductometric detection system.
Figure 5.79 Influence of chelators on hydrolysis (detected by titration of the phthalic acid formed) of various plasticizers at 70 °C without buffer system (200 ml water, 10 ml plasticizer, 0.3 ml chelator) [202]... Figure 5.79 Influence of chelators on hydrolysis (detected by titration of the phthalic acid formed) of various plasticizers at 70 °C without buffer system (200 ml water, 10 ml plasticizer, 0.3 ml chelator) [202]...

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See also in sourсe #XX -- [ Pg.11 , Pg.12 ]




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