Borate determination

A similar example represents the determination of borate that is usually analyzed with ion-exclusion chromatography. However, when borate is converted into tetrafluoro-borate by reacting with hydrofluoric acid [107], upon application of an anion exchanger indirect borate determination together with other inorganic anions becomes possible. Tetrafluoroborate is a polarizable anion therefore, when using the suppressor technique some p-cyanophenol is added to the carbonate/bicarbonate eluent to improve the peak shape of the ion that elutes after sulfate. 

Caffeine in tea and coffee is determined by CZE using nicotine as an internal standard. The buffer solution is 50 mM sodium borate adjusted to pH 8.5 with H3PO4. A UV detector set to 214 nm is used to record the electropherograms. 

Students determine the concentrations of caffeine, acetaminophen, acetylsalicylic acid, and salicylic acid in several analgesic preparations using both CZE (70 mM borate buffer solution, UV detection at 210 nm) and HPLC (C18 column with 3% v/v acetic acid mixed with methanol as a mobile phase, UV detection at 254 nm). 

Weber, P. L. Buck, D. R. Capillary Electrophoresis A Past and Simple Method for the Determination of the Amino Acid Composition of Proteins, /. Chem. Educ. 1994, 71, 609-612. This experiment describes a method for determining the amino acid composition of cyctochrome c and lysozyme. The proteins are hydrolyzed in acid, and an internal standard of a-aminoadipic acid is added. Derivatization with naphthalene-2,3-dicarboxaldehyde gives derivatives that absorb at 420 nm. Separation is by MEKC using a buffer solution of 50 mM SDS in 20 mM sodium borate. 

Glass-forming systems other than siUca have been examined. The fraction of three- and four-coordinated boron in borate glasses can be determined by nmr (29). Both nmr and x-ray diffraction (30) results led to the suggestion that the boroxyl ring is the stmctural unit of vitreous The... 

Analysis. The abiUty of silver ion to form sparingly soluble precipitates with many anions has been appHed to their quantitative deterrnination. Bromide, chloride, iodide, thiocyanate, and borate are determined by the titration of solutions containing these anions using standardized silver nitrate solutions in the presence of a suitable indicator. These titrations use fluorescein, tartrazine, rhodamine 6-G, and phenosafranine as indicators (50). 

Alkalinity. The alkalinity of a water sample is its acid-neutrali2ing capacity. Bicarbonate and carbonate ions are the predominant contributors to alkalinity in most waters, and their chemical equiUbria generally maintain the pH of 5—9. The presence of enough hydroxide ion to affect the alkalinity determination in natural waters is rare. SiUca, borate, or phosphate do contribute to the overall alkalinity if present in large enough quantities. 

A single-crystal x-ray stmcture determination has shown that the borate ion in the pentahydrate and in borax are identical (77). 

Borate reacts with curcumin [458-37-7] C2 H2qO, in the presence of a mineral acid to give a colored 1 2 bore acid curcumin complex that has been used to determine microamounts of boron. Carrninic acid [1260-17-9J, C22H2QO23, (98) and azomethine-H (99) also form a colored complex usehil for low level detection of borates. Boron compounds give a characteristic green color when burned in a flame. 

For the most part boric acid esters are quantitated by hydrolysis in hot water followed by determination of the amount of boron by the mannitol titration (see Boron compounds, boric oxide, boric acid and borates). Separation of and measuring mixtures of borate esters can be difficult. Any water present causes hydrolysis and in mixtures, as a result of transesterification, it is possible to have a number of borate esters present. For some borate esters, such as triethanolamine borate, hydrolysis is sufftciendy slow that quantitation by hydrolysis and titration cannot be done. In these cases, a sodium carbonate fusion is necessary. 

Catechin and epicatechin are two flavanols of the catechin family. They are enantiomers. The capillary zone electrophoresis (CE) methods with UV-detection were developed for quantitative determination of this flavanols in green tea extracts. For this purpose following conditions were varied mnning buffers, pH and concentration of chiral additive (P-cyclodextrin was chosen as a chiral selector). Borate buffers improve selectivity of separation because borate can make complexes with ortho-dihydroxy groups on the flavanoid nucleus. 

Cerium is one of the most widely used activators, which improve the working characteristics of many scintillators. Determination of the valence state of cerium in single crystals of alkaline and rare-earth borates allows to establish the nature of activator centers for purposeful influence on the scintillation efficiency of the matrix. 

Investigated is the influence of the purity degree and concentration of sulfuric acid used for samples dissolution, on the analysis precision. Chosen are optimum conditions of sample preparation for the analysis excluding loss of Ce(IV) due to its interaction with organic impurities-reducers present in sulfuric acid. The photometric technique for Ce(IV) 0.002 - 0.1 % determination in alkaline and rare-earth borates is worked out. The technique based on o-tolidine oxidation by Ce(IV). The relative standard deviation is 0.02-0.1. 

The weakness of the ri -coordination follows from the general stmcture determination of tetrakis(2-thienyl)borate, 44 (96IC7095). Counterions of potassium are ri -coordinated, one cation per two thienyl substituents belonging to the neighboring anions. 

Table 5-1. Enantioselectivities determined for several drugs. All experiments were performed at room temperature, except those marked with, which were performed at 4 °C. In some cases a lipophilic anion was used to facilitate the solubilization of the drug in the organic phases (PFj = hexafluorophosphate BPh = tetraphenyl borate). DHT = dihexyl tartrate DBT = dibenzoyl tartrate PLA = poly (lactic acid). ...

Poloxamers are used primarily in aqueous solution and may be quantified in the aqueous phase by the use of compleximetric methods. However, a major limitation is that these techniques are essentially only capable of quantifying alkylene oxide groups and are by no means selective for poloxamers. The basis of these methods is the formation of a complex between a metal ion and the oxygen atoms that form the ether linkages. Reaction of this complex with an anion leads to the formation of a salt that, after precipitation or extraction, may be used for quantitation. A method reported to be rapid, simple, and consistently reproducible [18] involves a two-phase titration, which eliminates interferences from anionic surfactants. The poloxamer is complexed with potassium ions in an alkaline aqueous solution and extracted into dichloromethane as an ion pair with the titrant, tet-rakis (4-fluorophenyl) borate. The end point is defined by a color change resulting from the complexation of the indicator, Victoria Blue B, with excess titrant. The Wickbold [19] method, widely used to determine nonionic surfactants, has been applied to poloxamer type surfactants 120]. Essentially the method involves the formation in the presence of barium ions of a complex be-... 

Discussion. Potassium may be precipitated with excess of sodium tetraphenyl-borate solution as potassium tetraphenylborate. The excess of reagent is determined by titration with mercury(II) nitrate solution. The indicator consists of a mixture of iron(III) nitrate and dilute sodium thiocyanate solution. The end-point is revealed by the decolorisation of the iron(III)-thiocyanate complex due to the formation of the colourless mercury(II) thiocyanate. The reaction between mercury( II) nitrate and sodium tetraphenylborate under the experimental conditions used is not quite stoichiometric hence it is necessary to determine the volume in mL of Hg(N03)2 solution equivalent to 1 mL of a NaB(C6H5)4 solution. Halides must be absent. 

Determination of borate as nitron tetrafluoroborate Discussion. Boric acid (100-250 mg) in aqueous solution may be determined by conversion into tetrafluoroboric acid and precipitation of the latter with a large excess of nitron [see Section 11.11(E)] as nitron tetrafluoroborate, which is weighed after drying at 110°C. The accuracy is about 1 per cent. 

Phosphate, arsenate, and vanadate interfere. Borate, fluoride, and large amounts of aluminium, calcium, magnesium, and the alkali metals have no effect in the determination, but large amounts of iron (> 5 per cent) appear to produce slightly low results. 

Small amounts of lithium phenolate or dilithium-2,2 biphenyldiolate, whose anodic decomposition starts at about 3.2 V versus Li and thus before anodic decomposition of the borates begins, prevent the anodic decomposition of benzenediolatoborate anions in PC. The behavior of the solution is then determined by the additive. 

Solutions of 7.5 g (40 mmol) of triisopropyl borate in 10 mL of dry diethyl ether and 40 mmol of 0.87 M allylmagnesium bromide in diethyl ether arc added dropwisc separately to 10 mL of diethyl ether at — 78 °C. This mixture is stirred for 0.5 h at —78 JC, then is allowed to warm to r.t. and stirred for 3 h. The slurry is recooled to 0 C. and then 40 mmol or 1 N aq hydrochloric acid saturated with NaCl are added dropwise over 15 min. The mixture is warmed to r.t., and stirring is continued for 10 min. The organic layer is separated and directly treated with 9.4 g (40 mmol) of diisopropyl (/ ,/ )-tartrate (DIPT). The aqueous phase is extracted with three 50-mL portions of diethyl elher/CH.CI, 5 1. The combined organic layers are dried over anhyd MgS04 for 2.5 h, then filtered under argon. The filtrate is concentrated in vacuo and toluene is added to give a final volume of 50 mL. The concentration of reactive allylboronate is determined by treatment of a 1 mL aliquot of this solution with a known excess of cyclohexanecarboxaldehyde. This... 

Controlled potential electrolysis was carried out for 4 h by applying a definite potential difference, iiappb at the stationary interface between W containing 10 M NADH and 0.01 M borate buffer and DCE containing 10 M CQ, and the concentration of NADH in W after the electrolysis was determined spectrophotometrically. Ratios of concentrations of NADH reacted (and hence decreased) by the electrolysis are plotted as curve 1 in Fig. 6 as the function of itappi-... 

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