Complex-Forming Reagent determination

A similar titration curve (Fig. 50) is observed, when a suspension of lead tannate is titrated tvith dilute nitric acid in 20 per cent ethanol. By measuring the limiting current, lead can be determined in this complex. In a similar way insoluble precipitates can be analysed after the addition of complex-forming reagents, e.g. 

In titrimetric analysis (often termed volumetric analysis in certain books), the substance to be determined is allowed to react with an appropriate reagent added as a standard solution, and the volume of solution needed for complete reaction is determined. The common types of reaction which are used in titrimetry are (a) neutralisation (acid-base) reactions (b) complex-forming reactions (c) precipitation reactions (d) oxidation-reduction reactions. 

Unique methods based on new principles have been developed within the past 10 years. Threonine (27,28,249) is oxidized by lead tetraacetate or periodic acid to acetaldehyde, which is determined by photometric analysis of its p-hydroxydiphenyl complex or iodometric titration of its combined bisulfite. Serine is oxidized similarly to formaldehyde, which is determined gravimetrically (207) as its dimedon (5,5-dimethyldihydro-resorcinol) derivative or photometric analysis (31) of the complex formed with Eegriwe s reagent (l,8-dihydroxynaphthalene-3,5-disulfonic acid). It appears that the data obtained for threonine and serine in various proteins by these oxidation procedures are reasonably accurate. [Block and Bolling (26) have given data on the threonine and serine content of various proteins. ]... 

Aromatic compounds react with mercuric salts to give arylmercury compounds.69 Mercuric acetate or mercuric trifluoroacetate are the usual reagents.70 The reaction shows substituent effects that are characteristic of electrophilic aromatic substitution.71 Mercuration is one of the few electrophilic aromatic substitutions in which proton loss from the a complex is rate determining. Mercuration of benzene shows an isotope effect kB/kD = 6,72 which indicates that the [Pg.1026]

Some wet dissolution/decomposition reagents such as hydrofluoric or hydrochloric acid may have strong completing action. Very often, the complex formed may prevent the determination proper from being performed, because it is kinetically or thermodynamically very stable. In many cases the dissolution/decomposition reagents are used to destroy an organic substrate. For example, the use of nitric-perchloric or nitric-sulphuric-perchloric acid mixtures is well known. 

An ethereal solution which was 1.38ilf in methyllithium was purchased from Foote Mineral Company. The concentration of methyllithium in ethereal solutions may be conveniently determined by a procedure described elsewhere in which the lithium reagent is titrated with 5ec-butyl alcohol, utilizing the charge transfer complex formed from bipyridyl or o-phenanthro-line and the lithium reagent as an indicator. 

Diloxanide furoate was determined by Sane al. using a simple spectrophotometric method [28]. The drug was extracted from tablets with ethanol, or was filtered from a suspension and dissolved in ethanol. The resulting solution was mixed with 6% aqueous sodium hydroxide and Folin-Ciocalteu reagent, or with a 1% solution of sodium nitroprusside in aqueous 10% sodium hydroxide. The complexes formed had absorbance maxima at 650 run, or at 675 nm, respectively. 

The Falin-Ciocalteu reagent (FCR) is a complex formed in a reaction between sodium tungstate and sodium molybdenate in hydrochloric add and phosphoric acid, which turns yellow after lithium sulphate is added. The reagent reads in an alkaline environment with reducing compounds. Such a reaction gives a blue chromophore which is observed by colorimetry. The Folin-Ciocalteu method is highly sensitive - both to phenolic and non-phenolic compounds, e.g. proteins, vitamin C, vitamin Bj, folic acid, Cu(I). The method is applied most frequently to determine the total content of phenolic compounds [34,35]. If that is the case, a sample for determination should be prepared in a proper manner to minimise the effect of non-phenolic... 

Schiff s bases formed from o-hydroxyaldehydes often form reagents of service in analysis. For example, the base formed with ethylenediamine forms an insoluble complex with nickel (14) which has been used for its gravimetric determination. 2-(o-Hydroxyphenyl)benzoxazole (15a) has been... 

Electrochemical method [54] Silicate is determined in sea water by four different electrochemical methods based on the detection of the silicomolybdic complex formed in acidic media by the reaction between silicate and molybdenum salts. The first two methods are based on the addition of molybdate and protons in a seawater sample in an electrochemical cell. A semiautonomous method was developed based on the electrochemical anodic oxidation of molybdenum, the complexation of the oxidation product with silicate and the detection of the complex by cyclic voltammetry. Finally a complete reagent-less method with a precision of 2.6% is described based on the simultaneous formation of the molybdenum salt and protons in a divided electrochemical cell. 

In radioreagent methods, the radioactive product of the reaction between the substance to be determined and a radioactive reagent is separated by various methods, such as precipitation or liquid-liquid extraction. For example, Cl , Br or 1 in concentrations down to 0.5 pg/1 can be determined by addition of an excess of phe-nylmercury nitrate labelled with ° Hg. The complexes formed with the halide ions are extracted into benzene, whereas the phenylmercury nitrate stays in the aqueous phase. From the difference between the activities in the aqueous phase before and... 

The above results were confirmed subsequently by Holmes and Stevenson by determining the amino acid sequence and establishing the position of the C-labelled histidine in the peptide B obtained from E3. A reliable amino acid sequence 162 has been obtained for peptide B up to residue 30 which was in agreement with the amino acid sequence determined from the gene sequence of E3. The authors demonstrated that a histidine residue is selectively alkylated within the active site of E. coli E3 when the enzyme is a component of the PD complex. The reagent 161 functions as a unique form of an active-site-directed irreversible inhibitor. 

In the case of mixed ARSL, the phospholipid content of the liposomes is measured by the Stewart assay (21), a colorimetric technique that is widely used for phospholipid content determination. For this, a sample of the liposome dispersion (20-50 xL) is mixed with 2 mL Stewart reagent (ammonium ferrothiocyanate 0.1 M) and 2 mL chloroform. The mixture is then vortexed vigorously for at least 3 min, in order to extract the complex formed between phospholipid and Stewart reagent in the chloroform phase. After this, the samples are centrifiiged at 5,000 rpm (= 1950 X g) for 5 min, and the OD of the chloroform phase is measured at 485 nm. Finally, the lipid concentration of the samples is calculated by comparison with a standard curve (prepared from known concentrations of PC) (see Note 9). 

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