Single-point titration

An interesting method is single-point titration, in which a certain amount of reagent is added to the sample and the ISE potential is measured in the resultant solution [6, 7, 28,62, 64, 66, 77). The authors claim that the precision is similar to that of a classical titration (a relative standard deviation of 0.1 to 1.3%). Time is saved and the method is readily applicable to automated measuring systems. 

F. Albertus, B. Horstkotte, A. Cladera, V. Cerda, A robust multisyringe system for process flow analysis. Part I. On-line dilution and single point titration of protolytes, Analyst 124 (1999) 1373. 

Very low C /Co ratios are efficiently attained because the chamber and sample volumes are usually not restricted. The multi-syringe flow system for single-point titrations [75] can be used to demonstrate this. Precise... 

O. Astrom, Single-Point Titrations. Part 4. Determination of Acids and Bases with Flow Injection Analysis. AnaL Chim. Acta, 105 (1979) 67. 

Anfalt and Jagner [57] measured total fluoride ion concentration by means of a single-crystal fluoride selective electrode (Orion, model 94-09). Samples of seawater were adjusted to pH 6.6 with hydrochloric acid and were titrated with 0.01 M sodium fluoride with use of the semi-automatic titrator described by Jagner [28]. Equations for the graphical or computer treatment of the results are given. Calibration of the electrode for single-point potentiometric measurements at different seawater salinities is discussed. 

At this point I want to emphasize that the procedure I am about to describe bears no relation to the previous titration method, though confusingly similar. The latter is a single-phase titration in octanol, while this is an aqueous-phase titration in the presence of octanol. 

Surface areas (SBET) were measured with a Micromeritics Flowsorb II using the single point approximation of the BET equation for the adsorption of N2 at 77 K. Carbon deposits on the catalyst were quantified by elemental analysis involving combustion to CO2, absorption in a Ba(C104)2 solution and coulometric titration. 

In principle one could use the break points in the titration curve as approximations of the equivalence points, although these points do not quite coincide with the true equivalence points moreover, co-precipitation (if not suppressed) often leads to a blurring of those points. At any rate, it is usually a better practice to avoid reliance on single points in a titration curves for the precise determination of the equivalence volumes, because such single readings are inherently rather vulnerable to experimental uncertainty. 

Tab. 11.1. Host-guest interaction of molecular tweezers 2 and 3 with aromatic guests 4, 5 and 6. Experimental results of H-NMR titration at 294 K, variable-temperature (VT) single-point NMR analysis, and high-pressure (HP) NMR study at 298 K.

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... 

The equation curve equations developed earlier can be used for single points as well as for entire curves. If only a few separate points are needed, however, calculations designed for each point might be simpler than the titration curve equation. Such calculations involve (a) stoichiometry of the A/B reaction, (b) recognition of the type of pH situation results from this, and finally, (c) using the appropriate, simple formula (see Problem 4-1) and making the necessary substitutions. 

Most uses of flow techniques involve the quantitative determination of some target species. This chapter describes various ways of using flow techniques with quantitative purposes, such as calibration curves, based on peak height or peak area, and titrations, based on distance between equivalence points or single-point method. Stopped-flow technique can be used for both, quantitative approach, for example in kinetic methods, or for qualitative determinations inasmuch as it allows spectral and potential scans to be performed. Multiparameter analysis is presented in two forms to be carried out, by multivariate chemometric techniques or by applying sandwich technique. Finally, smart systems are presented as a step forward in automation, commonly used in multiparameter analysis. 

E. Alberttis, 1. Cortes, M. Alvarez, V. Cerd Non-linear calibration in single point flow titration of pro-tolytes. A comparison of model options by using delta Test, Anal. Chim. Acta 414 (2000) 221—237. 

Compounds having an EC50 around 3-30 pM are probed in the steep part of their EC50 curves. In a single-point experiment, small concentration shifts inside the well due to titration can lead to big changes in the observed effect in a retest. 

The objective of the titration is to determine the point at which reaction is complete, called the equivalence point. This is reached when the number of moles of OH- added is exactly equal to the number of moles of acetic acid, HC O originally present To determine this point, a single drop of an acid-base indicator such as phenolphthalein is used. It should change color (colorless to pink) at the equivalence point. 

The formation of a single complex species rather than the stepwise production of such species will clearly simplify complexometric titrations and facilitate the detection of end points. Schwarzenbach2 realised that the acetate ion is able to form acetato complexes of low stability with nearly all polyvalent cations, and that if this property could be reinforced by the chelate effect, then much stronger complexes would be formed by most metal cations. He found that the aminopolycarboxylic acids are excellent complexing agents the most important of these is 1,2-diaminoethanetetra-aceticacid (ethylenediaminetetra-acetic acid). The formula (I) is preferred to (II), since it has been shown from measurements of the dissociation constants that two hydrogen atoms are probably held in the form of zwitterions. The values of pK are respectively pK, = 2.0, pK2 = 2.7,... 

C04-0144. Vitamin C (also called ascorbic acid) is an acid whose formula is HCg H7 Og. When treated with strong base, it undergoes the following reaction HCg H7 0(5 + OH H7 Og + H2 O A pharmacist suspects that the vitamin C tablets received in a recent shipment are not pure. When a single 500.0-mg tablet is dissolved in 200.0 mL of water and titrated with a standard base that is 0.1045 M, it takes 24.45 mL to reach the stoichiometric point. Are the tablets pure If not, what is the mass percentage of impurities (Assume no impurity is either an acid or a base.)... 

The above system of directly sensing a process stream without more is often not sufficiently accurate for process control so, robot titration is preferred in that case by means of for instance the microcomputerized (64K) Titro-Analyzer ADI 2015 (see Fig. 5.28) or its more flexible type ADI 2020 (handling even four sample streams) recently developed by Applikon Dependable Instruments20. These analyzers take a sample directly from process line(s), size it, run the complete analysis and transmit the calculated result(s) to process operation (or control) they allow for a wide range of analyses (potentiometric, amperometric and colorimetric) by means of titrations to a fixed end-point or to a full curve with either single or multiple equivalent points direct measurements with or without (standard) addition of auxiliary reagents can be presented in any units (pH, mV, temperature, etc.) required. 

In an ideally designed experiment, only a single titration is needed to determine the solubility constant and the aqueous pKa. This is possible when the amount of sample, such as a weak base, added to solution is such that from the start of an alkalimetric titration (pH [Pg.104]

In a typical titration with the autotitrator a significant fraction of the equivalence volume is added in a single aliquot and allowed to equilibrate before further titrant is added. The end point is detected by comparing changes in the millivolt output of the light source (Figure 1) ( ). 

To invoke our geothermometer, we need to recombine the vapor and fluid phases and then heat the mixture to determine saturation indices as functions of temperature. We could do this in two steps, first titrating the vapor phase into the liquid and then picking up the results as the starting point for a polythermal path. We will employ a small trick, however, to accomplish these steps in a single reaction path. The trick is to add the vapor phase quickly during the first part of the reaction path but use the cutoff option to prevent mass transfer over the remainder of the path. The commands to set the mass transfer are... 

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