Error titration method

The comparison of more than two means is a situation that often arises in analytical chemistry. It may be useful, for example, to compare (a) the mean results obtained from different spectrophotometers all using the same analytical sample (b) the performance of a number of analysts using the same titration method. In the latter example assume that three analysts, using the same solutions, each perform four replicate titrations. In this case there are two possible sources of error (a) the random error associated with replicate measurements and (b) the variation that may arise between the individual analysts. These variations may be calculated and their effects estimated by a statistical method known as the Analysis of Variance (ANOVA), where the... 

Active matter (anionic surfactant) in AOS consists of alkene- and hydroxy-alkanemonosulfonates, as well as small amounts of disulfonates. Active matter (AM) content is usually expressed as milliequivalents per 100 grams, or as weight percent. Three methods are available for the determination of AM in AOS calculation by difference, the two-phase titration such as methylene blue-active substances (MBAS) and by potentiometric titration with cationic. The calculation method has a number of inherent error factors. The two-phase titration methods may not be completely quantitative and can yield values differing by several percent from those obtained from the total sulfur content. These methods employ trichloromethane, the effects from which the analyst must be protected. The best method for routine use is probably the potentiometric titration method but this requires the availability of more expensive equipment. 

Isaeva [181] described a phosphomolybdate method for the determination of phosphate in turbid seawater. Molybdenum titration methods are subject to extensive interferences and are not considered to be reliable when compared with more recently developed methods based on solvent extraction [182-187], such as solvent-extraction spectrophotometric determination of phosphate using molybdate and malachite green [188]. In this method the ion pair formed between malachite green and phosphomolybdate is extracted from the seawater sample with an organic solvent. This extraction achieves a useful 20-fold increase in the concentration of the phosphate in the extract. The detection limit is about 0.1 ig/l, standard deviation 0.05 ng-1 (4.3 xg/l in tap water), and relative standard deviation 1.1%. Most cations and anions found in non-saline waters do not interfere, but arsenic (V) causes large positive errors. 

Direct titration method offers a serious limitation for the assay of aluminium and bismuth containing pharmaceutical inorganic substances because of the precipitation of the metal as their corresponding hydroxides in alkaline media thereby introducing undesirable errors. 

The residues of the organic portion of (he molecule remaining could be oxidized by the potassium dichromate used in (he back titration method and so introduce errors. The dead stop method or the colorimetric method (below) might be preferred in such cases... 

This review updates a classic and influential review by Halevi.3 What makes the current review timely is the recent development of a nuclear magnetic resonance (NMR) titration method capable of exquisite accuracy and not subject to the systematic error associated with possible impurities in one of the samples and not in the other. New values can now be compared with previous ones. 

Should any iron(II) reach the anode, it also would be oxidized and thus not require the chemical reaction of Eq. (4.13) to bring about oxidation, but this would not in any way cause an error in the titration. This method is equivalent to the constant-rate addition of titrants from a burette. However, in place of a burette the titrant is electrochemically generated in the solution at a constant rate that is directly proportional to the constant current. For accurate results to be obtained the electrode reaction must occur with 100% current efficiency (i.e., without any side reactions that involve solvent or other materials that would not be effective in the secondary reaction). In the method of coulometric titrations the material that chemically reacts with the sample system is referred to as an electrochemical intermediate [the cerium(III)/cerium(IV) couple is the electrochemical intermediate for the titration of iron(II)]. Because one faraday of electrolysis current is equivalent to one gram-equivalent (g-equiv) of titrant, the coulometric titration method is extremely sensitive relative to conventional titration procedures. This becomes obvious when it is recognized that there are 96,485 coulombs (C) per faraday. Thus, 1 mA of current flowing for 1 second represents approximately 10-8 g-equiv of titrant. 

While the redox titration method is potentiometric, the spectroelectrochemistry method is potentiostatic [99]. In this method, the protein solution is introduced into an optically transparent thin layer electrochemical cell. The potential of the transparent electrode is held constant until the ratio of the oxidized to reduced forms of the protein attains equilibrium, according to the Nemst equation. The oxidation-reduction state of the protein is determined by directly measuring the spectra through the tranparent electrode. In this method, as in the redox titration method, the spectral characterization of redox species is required. A series of potentials are sequentially potentiostated so that different oxidized/reduced ratios are obtained. The data is then adjusted to the Nemst equation in order to calculate the standard redox potential of the proteic species. Errors in redox potentials estimated with this method may be in the order of 3 mV. 

Calibration is the largest source of error in the measurements. N0a permeation rates were determined by the rate of weight loss. Neighing errors amount to + 2%. The uncertainty in the NO/Oa titration method used to check the weight loss method is about 5%. Additional calibration errors of + 2% are caused by temperature variations of the permeation devices. 

Standard titration techniques, using indicators [4,5,13] with 2-butanol as the titrant, have greater error (3 standard deviations = 1-5% of value), but usually this is still acceptable. The real advantage of these indicator methods is that virtually no capital investment is required for the equipment. The equipment for the more accurate potentiometric titration method can cost upward of 15,000 dollars. This is why titrations using 2,2 -bipyridyl or 1,10-phenanthroline are more prevalent in the literature. 

In classical potentiometric titration, soluble species produced by dissolution of the solid may contribute to the consumption of an acid or base and induce an error in the calculated Oq. This error is not corrected for in back titrations of an inert electrolyte (Figure 2.6). The back-titration method was designed to avoid the error induced by the dissolution of the solid phase, and it has been used for solids that show appreciable solubility. For solids that are practically insoluble, the... 

It must be remarked, however, that the curves shown in Fig. 3 are hardly typical. Two definite points of inflection are observed for a dibasic acid only if the two ionization constants are of quite different orders of magnitude, Auerbach and Smolczyk7 have shown, theoretically, that the two points of inflection will not appear unless the ratio Ki/E2 is greater than 16. However, it is safe to say that the ratio must be considerably greater than that if the inflection points are to be obtained experimentally with any accuracy. Also, if the two ionization constants are not quite different the values of the constants determined by the potentiometric titration method described above may be somewhat in error, as is shown by the authors just mentioned and by Simms. ... 

The results are given in Table 11.8. The table gives silica particle diameter calculated from the specific surface area obtained by the Sears titration method after soluble silica correction. Values obtained at 0.3% SiOa are subject to more error due to higher amount of silica monomer present relative to colloidal silica. Results obtained by electrodialysis nucleation and by acidification with H2SO4 are included for comparison. 

An advantage of this system over the conventional BOD system (Winkler titration method) and the DO probe is that it can be used to monitor changes in DO levels with time. The procediues for ensuring that sufficient nutrients are available for the 5 days of the tests are not as rigorous as with the standard procedures, however, and this could lead to low BOD results. Additionally, air could leak into the manometer system, causing errors. 

To derive Eq. (3-1), Knudsen and co-workers mainly used samples from the Baltic and from the Mediterranean and the Red Sea. The offset of 0.03 in Eq. (3-1) reflects that the salt composition especially in the Baltic Sea is not exactly constant (Millero and Kremling, 1976) and thus contradicts the basic assumption of constancy that led to Eq. (3-1). However, the proposed titration method also had advantages it could be performed in reasonable time onboard a ship, and for salinity measurements in open ocean areas where S is close to 35 %o, the error induced by the non-constancy is less than that from titration (0.02 %o in salinity). Therefore, the so-called Mohr-Knudsen titration method (Mohr, 1856 see Chapter 11) and the Knudsen formula (3-1) served oceanographers for more than 60 years to determine salinity from chlorinity. 

It should be noted that value Vg strongly depends on the experimental techniques used in measurement. The time-consuming, error-causing ways should be avoided (such as the surface titration method), and instead a much simpler way i.e. pulse technology could be used. When the measurement of chemisorption is carried out by the pulse technology at room temperature, the nature of the support does not relate to the fraction of the metal. Because it provides a more precise measurement for turnover frequency, this approach has opened up a new prospect for fundamental research. 

A commonly used method for determining acid content is alkali titration using an appropriate indicator [1-4], However, in this method, there is the possibility of error due to an inability to detect a subtle color change of the indicator in the transition range, especially in cases of colored samples. In addition, the titration method is not sufficiently sensitive to detect low acid content, and it requires large sample amounts and a great deal of time. Potentiometric titration is commonly recommended as an alternative method. 

The results obtained by the present FIA method were compared with those obtained using conventional titration (using KOFF) methods (Table 36.2). In the titration methods, the end points were determined based on the color change of phenolphthalein and potentiometry. In Table 36.2, the values of the RSD of the data by the present FIA-ECD method are less than 2.0%, the best of the three methods. The RSD was greatest in conventional titration with phenolphthalein. Such a decreased reproducibility is considered to be due to an indicator error. FFowever, no marked differences in RSD could be detected between the present and potentiometric titration methods. Potentiometric titration does not show any indicator error [13]. 

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