Chlorides potentiometric titration

The indicator electrode employed in a potentiometric titration will, of course, be dependent upon the type of reaction which is under investigation. Thus, for an acid-base titration, the indicator electrode is usually a glass electrode (Section 15.6) for a precipitation titration (halide with silver nitrate, or silver with chloride) a silver electrode will be used, and for a redox titration [e.g. iron(II) with dichromate] a plain platinum wire is used as the redox electrode. 

The chlorine content can be determined by either chlorine elemental analysis or a potentiometric titration using a chloride-ion electrode. For titration, about 0.2 g. of polymer is heated in 3 ml. of pyridine at 100° for 2 hours. This suspension is then transferred to a 50-mi. beaker containing 30 ml. of aqueous 50% acetic acid and 5 ini. of concentrated nitric acid, and the resulting mixture is titrated against aqueous 0.1 N silver nitrate. 

It was found that chlorides, chlorates, and nitrates interfere by forming in sol ppts (Ref 6). Later it was found that w sol perchlorates could be analyzed gravimetrically by pptn of the perchlorate ion as tetraphenylarsonium perchlorate (Ksp at 20° = 2.60 0.14 x 10"9). The ppt can be (Tried at 105° and weighed directly (Ref 16). Still more recently a specific perchlorate ion electrode has been developed (Ref 17) which can be used for the potentiometric titration of the perchlorate ion using a soln of tetraphenylarsonium chloride as the titrant (Ref 15). Tetra-phenylphosphonium chloride has been similarly used, but the corresponding Sb compd is too insol in w for practical use (Ref 8), For routine assay of perchlorates for use by the armed forces, a Na carbonate fusion procedure is described in Mil Specs MlL-A-23946 (19 Aug 1964) MIL-A-23948 (19 Aug 1964) (see also under Ammonium Perchlorate). The tetraphenylarsonium chloride procedure has also been proposed for use in Mil Specs (Ref 11)... 

Chloride can be determined in AOS by potentiometric titration of a sample with silver nitrate after acidification with nitric acid. A silver/glass electrode system is used. 

Less complex techniques have been reported to be useful to study the acidic and alkaline treatment processes of biosorbents and the role of carboxyl and carboxylate groups in metal adsorption. Rakhshaee and coworkers101 used potentiometric titration curves to assess the content of such groups in L. minor biomass treated with NaOH and HC1. The results showed an increase (up to 25%) in the adsorption of Hg(II), Cr(III), Cr(VI), and Cu(II) with NaOH-treated biomass as a consequence of an increase of -COO- groups (0.92-2.42 mmol/g). On the contrary, the -COOH groups increase observed (1.50-2.41 mmol/g) due to the acidic treatment led to a decrease in the metal ions uptake (up to 33%) despite activation by the chloride salts. 

The methods most commonly used to detect hydrogen sulfide in environmental samples include GC/FPD, gas chromatography with electrochemical detection (GC/ECD), iodometric methods, the methylene blue colorimetric or spectrophotometric method, the spot method using paper or tiles impregnated with lead acetate or mercuric chloride, ion chromatography with conductivity, and potentiometric titration with a sulfide ion-selective electrode. Details of commonly used analytical methods for several types of environmental samples are presented in Table 6-2. 

The products of the reactions of picryl chloride with isomeric 4- and 5-aminobenzofurazans in dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) were studied by means of nonaqueous potentiometric titration. The effect of the position of the furazan fragment in 4- and 5-picrylaminobenzofurazans on the NH acidity is considered. The electron-acceptor properties of the furazan fragment were evaluated via inclusion of the resulting data into the pK -cr correlation for 2,4,6-trinitrodiphenylamines <2005RJC933>. 

Chloride can also be estimated by potentiometric titration using standard silver nitrate [27]. The results are recorded directly and evaluated by means of a computer program based on the Gran extrapolation method. The determinations have a precision of 0.02% and since many samples can be titrated simultaneously, the time for a single determination can be reduced to less than 5 min. 

The secondary amine function of dobutamine hydrochloride may be determined by potentiometric titration with perchloric acid using glacial acetic acid as a nonaqueous solvent. Mercuric acetate is used to tie up the chloride ion. 

Valproic acid can be potentiometrically titrated with standardized 0.1 N tetra-n-butylammonium hydroxide in chlorobenzene using a modified glass-calomel electrode system, in which 1.0 M aqueous tetra-n-butylammonium chloride has been substituted for potassium chloride, and employing acetone as the sample solvent. 

Metrohm Herisau Prazisions-pH meter E 510 and combined electrode were used for the potentiometric titrations and electrode was filled with saturated solution of potassium chloride in water free methanol instead of aqueous potassium chloride. 

The potentiometric titrations were performed in a three necked vessel equipped with electrode, drying tube filled with calcium chloride, semi-microburette and a magnetic stirrer. Burette had an adaptor which connected with a drying tube and the 0.12 M HCl solution bottle, and filled with the solution by means of nitrogen gas flow dried over calcium chloride. 

Figure 4.3 Potentiometric titration curve obtained by dissolving 200 mg of dishwashing fluid in water and titrating against hexadecylpyridinium chloride solution, employing a zeolite-polydimethylsiloxane (NaY-PDMS) modified electrode (cf. SAQ 4.3). From Matysik, S Matysik, F.-M., Mattusch, J. and Einicke, W.-D., Electroanalysis, 10, 98-102, (1998), Wiley-VCH, 1998. Reproduced by permission of Wiley-VCH.

How is the solubility product of silver chloride determined via a potentiometric titration ... 

The chloride ion in the hydrochloride anion of chlorpromazine can be obtained with high precision using potentiometric titration with Ag(I) [65]. 05 M Ce(S04)2 was used for the determination of chlorpromazine in dilute H2SO4 solution to a colorless end-point [66]. 

Shoukry et al. have prepared plastic membrane ion-selective electrodes for the determination of procaine and other anaesthetic compounds [69]. The electrode selective for procaine was prepared with the use of a membrane containing 15% of the procaine tetraphenylborate ion pair with 40% of dioctyl phthalate and 45% of poly vinyl chloride (PVC). The membrane was attached as a disc (12 mm diameter, 0.3 mm thick) to the polished PVC cap of the electrode tube, which contained an internal solution of 0.1 M sodium chloride made 1 mM in the same drug, and in contact with a Ag-AgCl wire. Linear response ranges were determined to be 20.0 pM to 16 mM for procaine over the pH range of 3.1 to 7.9. The electrodes could also be used in the potentiometric titration of the drug with 0.01 M sodium tetraphenylborate. 

For incorporation of crown ethers and cryptates into the RTV encapsulant system as sodium and potassium ion scavengers, the total ionic contaminants must first precisely be determined. Atomic absorption is used to measure these ions in commercial silicone RTVs and silicone fluids. Values of "10 ppm for sodium and potassium were obtained in the best samples. Chloride level was determined by potentiometric titration of the silicone with AgN03. A quantity of ion trap (either crown ethers or cryptates) was then added to the RTV silicone encapsulant, and its molar concentration was equal to the combined sodium and potassium contaminant levels. 

Other methods have been described which depend on reduction of the tellurium compound by means of titanous chloride, but these generally are not trustworthy owing to the formation of hydrogen telluride. Potentiometric titration with titanous chloride in the presence of hydrochloric acid has been recommended.1... 

Quadrivalent cerium salts may be volumetrically determined by arsenious acid in aqueous sulphuric acid solution using a manganese salt as catalyst, with potassium iodate present as a promoter.2 Excess of arsenious acid is used and back-titrated with permanganate. If nitric acid is present in place of sulphuric acid, an alkali chloride and a trace of iodine are used to promote the action of the manganese salt. Direct potentiometric titration with arsenious acid may also be employed. 

Table 5), and several are now being used, or are potentially useful, for measuring key ocean elements. The most common use of direct potentiometry (as compared with potentiometric titrations) is for measurement of pH (Culberson, 1981). Most other cation electrodes are subject to some degree of interference from other major ions. Electrodes for sodium, potassium, calcium, and magnesium have been used successfully. Copper, cadmium, and lead electrodes in seawater have been tested, with variable success. Anion-selective electrodes for chloride, bromide, fluoride, sulfate, sulfide, and silver ions have also been tested but have not yet found wide application. 

ISO (2006a). Cheese and Processed Cheese Products—Determination of Chloride Content— Potentiometric Titration Method (Standard ISO 5943/IDF 88). International Organization... 

Chen, Y. Wang, T. Helmy, R. Zhou, G.X. etal., Concentration determination of methyl magnesium chloride and other Grignard reagents by potentiometric titration with in-line characterization of reaction species by FTIR spectroscopy /. Pharm. Biomed. Anal. 2002, 29, 393 04. 

A modification of the oxygen bomb combustion method (ASTM D-2361) for the determination of chlorine consisted of acidifying a solution of the adsorbed combustion products and titrating the chlorine potentiometrically. A potentio-metric titration was also tried for the determination of chlorine by the oxygen flask method. Combustion products, including chlorine, were absorbed in sodium hydroxide (NaOH), and the chloride was measured using silver-silver chloride electrodes. Although there was no statistical difference in results obtained from potentiometric titration and the Eschka procedure, the latter was more precise. 

The following procedures were reported for the assay of Melphalan Tablets (a) hydrolysis with aqueous potassium hydroxide under reflux and potentiometric titration of the liberated chloride ions with silver nitrate in the presence of nitric acid. (Corrections for "ionisable chlorine" are made by titrating under the same conditions a sample that is not subjected to hydrolysis [25,46].) (b)... 

The assay is performed by potentiometric titration of the chloride ions liberated by alkaline hydrolysis, as described under 9.1 Assay (a). 

Titrimetric measurements alkalinity titration for carbonate and bicarbonate ion determinations, argentometric and potentiometric titrations for determining chloride, and iodo-metric titration for sulfite, chlorine, and dissolved oxygen. 

Other examples of potentiometric titrations include acid-base titrations, in which an indicator electrode provides a response to hydronium ions, such as the glass electrode, quinhydione electrode, or antimony electrode. In precipitation and complexation titrations the indicator electrode should provide the response to the active species in the solution. Thus, during the titration of chloride ions by silver nitrate, a silver electrode is an effective indicator electrode. 

Until recently, the most popular reference half-cell for potentiometric titrations, polarography, and even kinetic studies has been the saturated aqueous calomel electrode (SCE), connected by means of a nonaqueous salt bridge (e.g., Et4NC104) to the electrolyte under study. The choice of this particular bridge electrolyte in conjunction with the SCE is not a good one because potassium perchlorate and potassium chloride have a limited solubility in many aprotic solvents. The junction is readily clogged, which leads to erratic junction potentials. For these practical reasons, a calomel or silver-silver chloride reference electrode with an aqueous lithium chloride or quaternary ammonium chloride fill solution is preferable if an aqueous electrode is used. 

The chloride content of the same aliquot used for total acidity was determined by potentiometric titration with 0.1N silver nitrate solution. 

Nakazawa and Tanaka described a potentiometric titration of salts of organic bases in non-aqueous solvents with the addition of bismuth nitrate [16], The base halide or hydrohalide (0.7 mequiv.) is dissolved in 40 mL of anhydrous acetic acid, and then 40 mL of 1,4-dioxane and 2.5 mL of 5% Bi(N03)3 solution in acetic acid are added. The Bi(N03)3 prevents interference by the halide. The solution is titrated to a potentiometric endpoint with 0.1 M HC104 (a blank titration is also carried out). Results of purity assays of acetylcholine chloride and other compounds were tabulated, and it was found that the coefficient of variation was 0.18%. 

Figure 12.3. Potentiometric titration of various metal-chloride solutions (from Evangelou, 1997, unpublished data, with permission).

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