Spectrophotometric study of the mercury(II)-Xylenol Orange chelate

The reaction between mercury(II) and Xylenol Orange has been studied in aqueous hexamine medium. The chelate is 1:1 and has an apparent stability constant of 2.4 (+/-0.6) x 10(6) at pH 7 (2.9 M hexamine). Beer's law is obeyed over the concentration range 0.5-2.0 x 10(-5)M mercury(II) when the hexamine concentration is 2.9 M.     

Spectrophotometric study of the chelate of palladium(II) with methylthymol blue

Methylthymol blue reacts very sensitively with palladium(II) to form two complexes. The 1:1 complex has λ_max at 530 nm in acidity range 0.02 to 0.05 M with respect to perchloric acid and 1:2 (metal reagent ratio) complex at 500 nm in pH range 6.8 to 7.5. Optimum conditions including the range for adherence to Beer's law, effect of pH, effect of excess reagent and sensitivity are reported for the photometric determination of palladium using methylthymol blue.     

Spectrophotometric study of a direct determination of serum calcium

A modification of a direct manual procedure for serum calcium has been developed in which a one-piece color reagent is used. When a micro amount of serum is added to the reagent, rapid and stable color formation occurs enabling the procedure to serve either as a manual stat system of in robotized automatic instrumentation. Total color measurement is not attained in such a procedure owing to the described regressive nature of the reagent blank. However, accurate and linear reaction characteristics are effectively achieved. The use of a low dielectric solvent, EG, served well for repressing the ionization of the blank while allowing linear and reproducible calibration characteristics.     

Spectrophotometric study of the molybdenum(VI) chelate of flavon-3-ol-2'-sulfonic acid in strong acid solutions

Molybdenum(VI) reacts with flavon-3-ol-2'-sulfonic acid (HL) in strong acid solutions to form a 1:1 chelate which has a stability constant (log K) of 3.04 at 25°C and ionic strength (l) of 1.0. Beer's law is obeyed in the range 0.69–8.20μg Mo ml^-1 in 0.3 M perchloric acid; the molar absorptivity at 370 nm is 1.4 × 10⁴ l mol^-1 cm^-1.     

Spectrophotometric study of bromide interference in a cholesterol reaction

A spectrophotometric study of the interference of bromide in the ferric chloride reaction for cholesterol has been described. The interference has been shown to be primarily an enhancement of the color reaction and secondarily an additive color owing to a change in the spectrum of the reagent blank. Tested methods of eliminating the interference included removal of bromide by ion exchange, metathetical exchange using AgIO₃, addition of bromide to a reaction plateau and a change in the solvent character of the reaction medium. It was determined that the use of an ion-exchange resin and the substitution of ethanol for acetic acid along with a modified iron reagent were the simplest choices for eliminating bromide interference in this determination. Iodate was shown to depress color formation and it appears to be a detrimental solution to the problem. Further work on the mechanism of the iodate interference is presently in progress.     

Spectrophotometric determination of rifampicin through chelate formation and charge transfer complexation in pharmaceutical preparation and biological fluids

Two simple and accurate spectrophotometric methods for determination of Rifampicin (RIF) are described. The first method is based on charge transfer (CT) complex formation of the drug with three pi-electron acceptors either 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), 7,7,7,8-Tetracyanoquinodimethane (TCNQ) or 2,3,5,6-Tetrachloro-1,4-benzoquinone (p-chloranil) in acetonitrile. The method is followed spectrophotometrically by measuring the maximum absorbance at 584 nm, 761 nm (680 nm) or 560 nm for DDQ, TCNQ and p-chloranil, respectively. Under the optimized experimental conditions, the calibration curves showed a linear relationship over the concentration ranges of 5-140 microg/ml, 2-45 microg/ml (5-120 microg/ml) and 15-200 microg/ml, respectively. The second method is based on the reaction of RIF with iron(III) forming a water insoluble violet complex which is extracted into chloroform. The method determines RIF in concentration range of 10-240 microg/ml at 540 nm. The proposed methods applied to determination of RIF in capsule, human serum and urine samples with good accuracy and precision. The results were compared statistically with the official method and showed no significant different between the methods compared in terms of accuracy and precision.     

Spectrophotometric study of thiouracil interference in a serum cholesterol determination

A spectrophotometric study of the effect of thiouracil on the determination of cholesterol by FeCl₃ reaction has been described. The depression of the reaction by thiouracil was confirmed and its removal by exchange with the iodate of AgIO₃ studied. It was found that thiouracil appeared to be removed by the exchange, but the iodate that replaced both it, as well as the chloride which is always present, interfered maximally in a FeCl₃-acetic acid protein precipitating system and to a lesser extent in an alcohol-acetone extraction system. One can infer from the results obtained that it would have been more reasonable to use an uncontaminated portion of serum for the determination of cholesterol rather than to carry out an in vitro removal of an in vitro addition of what may have been an unnecessary stabilizing agent.     

Spectrophotometric titration of ionisable groups in proteins: a theoretical study

A simple theoretical model is proposed for evaluation of the optical titration behaviour of tyrosyl and carboxyl residues in proteins. The pK values involved in the model are computed using the semi-empirical method. The titration curves are calculated using the values of the molar absorption differences for tyrosyl residues in the ultraviolet (UV) region at 245 and 295 nm, and for carboxyl residues in the infrared (IR) region at 1565 and 1707 cm(-1), respectively. The theoretical tyrosyl titration curves are compared with the experimental data for lysozyme, myoglobin and chymotrypsinogen (available in the literature). This approach provides a good tool for distinguishing between the ionisation and the conformational changes in the alkaline range. The quantitative evaluation of the change of molar extinction coefficients as a function of pH in the case of carboxyl titration for lysozyme, trypsin and cytochrome c shows a good agreement with the experimental titration data.     

Thermogravimetric study of some divalent metal chelate polymers of dithiooxamide

The thermal properties of polymeric chelates of dithiooxamide with divalent copper, cobalt, zinc and nickel have been investigated. The order of thermal stability is Ni>Co～Zn>Cu, which is the same as that observed for previously studied naphthazarin and rhodizonic acid chelates. The procedural decomposition temperatures indicate that the dithiooxamide chelates, which are not aromatic, are about as stable as the aromatic naphthazarin and rhodizonic acid chelates. Several unsuccessful attempts were made to prepare beryllium and manganese (II) chelates.     

Spectrophotometric study of coverage and acid-base equilibrium of a chemically bonded base

An aniline azo dye is immobilized on glass slides by reacting an organosilane reagent with the glass surface. The immobilized dye absorption spectral characteristics closely resemble those of the analogous solution form of the dye. The coverage of the immobilized dye, 1.1·10^?10 mol cm^?2, is consistent with simple monolayer coverage. The immobilized dye is a weaker base than the soluble form by an equilibrium constant factor of about 10, consistent with an electrostatic effect.     

Spectrophotometric study of the formaldehyde-leuco-methylene blue reaction

The sensitivity of the reaction between foimaldchyde and Icuco-mcthyleno blue has been found to be increased in the presence of ethyl alcohol, acetone, dicthyl ketone and methyl ethyl ketone. Acetone has been found to be most effective. Sensitisers increase the absorption maximum and stabilise it, while the rate of development of methylene blue colour is slowed down.Sensitivity also depends upon the content of thiosulphate used to prepare the Icuco-base; a smaller amount of thiosulphate increases greater sensitivity.     

Spectrophotometric determination of fluoride a comparative study and a suggestion for evaluating photometric data

Summary Attempts were made to develop a method for fluoride determination using the demasking principle; the result was negative. Using the method of bleaching, ferric-sulfosalicylate, ferric-tiferronate, titanium-chromotropic acid and zirconium-alizarin coloured systems have been thoroughly investigated and compared for use as reagents for fluoride determination. Ferric-sulfosalicylate system has been proved to be the best. A new method of comparing photometric data has been suggested. Error in fluoride determination by ferric-sulfosalicylate method according to the method calculation suggested is between 1.80 percent and 4.60 percent, when the fluoride concentration is from 16 to 40 ppm. The method gives reproducible results when the fluoride concentration is in the range of 0.8 ppm to 4.0 ppm.     

Solvent extraction of anions with metal chelate cations-XVIII Spectrophotometric determination of maleic acid in the presence of fumaric acid by solvent extraction with tris(1,10-phenanthroline)iron(ii) chelate cations

A new colorimetric method is proposed for the determination of maleic acid. Among aliphatic dicarboxylic acids tested, maleic acid was found to be selectively extracted into nitrobenzene as the red ion-association complex (lambda(max) 516 nm) formed between the hydrogen maleate anion and the tris(1,10-phenanthroline)iron(II) cation. At least a 32-fold molar excess of tris(1,10-phenanthroline)iron(II) relative to maleic acid is needed and the optimal pH range is 3-5. A linear relationship is obtained over the concentration range 10(-5)-10(-4)M maleic acid. The relative standard deviation was 1.0 %. The colour intensity of the extract remains constant at room temperature for at least 24 hr. A large amount of fumaric acid, the trans-isomer of maleic add, is not extracted under the same conditions. This makes it possible to determine maleic acid in the presence of fumaric acid.