M. A. Herrador

Estimation of pH and autoprotolysis constants in mixtures of aliphatic amides with water: Medium effect on the 4-aminoazobenzene system

Correction factors to the glass electrode and autoprotolysis constants of mixtures of aliphatic amides with water: N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), N-methylformamide (NMF), N-methylacetamide (NMA), formamide (F) and acetamide (A), have been determined. The acidity constants of 4-aminoazobenzene referred to the standard state of the mixtures of these aliphatic amides with water as well as the medium effect on the 4-aminoazobenzene system have been evaluated from spectrophotometric measurements.

Spectrophotometric determination of zinc in potable waters and insulin with methylglyoxal bis(4-phenyl-3-thiosemicarbazone)

This paper describes the interaction of methylglyoxal bis(4-phenyl-3-thiosemicarbazone)(MGBPT) with a range of cations in aqueous dimethylformamide. A spectrophotometric method is proposed for the determination of zinc in potable waters and insulin. The method is based on the reaction of MGBPT with zinc, which produces an intense yellow MGBPT-Zn (1 : 1) complex that has an absorption maximum at 455 nm at pH 6.4 and obeys Beers law in the concentration range 0.2–4 p.p.m. The method is compared with the other proposed thiosemicarbazone procedures for the spectrophotometric determination of zinc.

Spectrophotometric determination of palladium in catalysts with glyoxal bis(4-phenyl-3-thiosemicarbazone)

The behaviour of glyoxal bis(4-phenyl-3-thiosemicarbazone)(GBPT) with a variety of metal ions has been studied by spectrophotometry in a medium containing 60% of dimethylformamide and its potential as an analytical reagent has been assessed. A method for the spectrophotometric determination of palladium is proposed. The green 1 : 1 palladium(II)-GBPT complex (Iµ= 3.2 × 103 l mol–1 cm–1 at 635 nm and 1.5 × 103 l mol–1 cm–1 at 700 nm) is formed at pH 9.6–1 N acidity. The spectrophotometric method has been applied to the determination of palladium in several sample catalysts.

Spectrophotometric evaluation of acidity constants of isonicotinic acid

Abstract The acid-base equilibria of isonicotinic acid in aqueous media with a constant ionic strength 0.1 at 20 ± 1°C have been spectrophotometrically studied in detail. A new numerical method applicable to the evaluation of overlapping acidity constants has been described.

NEUTIT: a computer program for evaluating equivalence volumes and ionization constants in polar non-aqueous or partially aqueous media

Abstract A modified version of the EUTIT program, called NEUTIT, which accounts for potentiometric titrations in polar non-aqueous or partially aqueous media is developed. The program was applied to the titration data of several substances in three mixed solvents. The output of the program gives consistent and unbiased estimations of equivalence volumes and acidity constants. Good agreement between acidity constants evaluated from NEUTIT and the reported literature values is found in all cases. The program utilizes all titration data pairs which may be acquired from an automatic titrator unit.

Numerical evaluation of overlapping acidity constants from the ratio of absorbances at two wavelengths

A numerical method for the evaluation of overlapping acidity constants is proposed in this paper. The method is based on the ratio of absorbances measured at two wavelengths and is rather simpler than the successive approximation methods described by others. The method has been applied to evaluation of the acidity constants of isonicotinic acid.

Spectrophotometric Study of the Complexation of Indium(III) With the α-Diketone Bis(4-Phenyl-3-Thiosemicarbazones) Derived From Glyoxal, Biacetyl and Methylglyoxal

Abstract Indium(III) reacts with α-diketone bisphenylthiosemicarbazones derived from glyoxal, biacetyl and methylglyoxal to form 1:1 and 1:2 (In: reagent) complexes in acid and basic medium, respectively. The effect of experimental variables was studied in detail on the acid site, and a new method for the spectrophotometric determination of indium(III) with meth-ylglyoxal bis(4-phenyl-3-thiosemicarbazone) (MGBPT) is proposed. The yellow 1:1 In-MGBPT complex is formed at pH 3.5–6 in a solution containing a 60 % V/V of dimethylforrnamide. The nature of the complex (∊ = 27,100 1 mol−1 cm−1 at 465 mm) and the effect of interferences were studied.

Spectrophotometric determinationof zinc in cooking salts, tap and mineral waters with phenylglyoxal mono(2-pyridyl)hydrazone

Abstract The behaviour of phynylglyoxal mono(2-pyridyl)hydrazone (PGMPH) with various metal ions was studied by spectrophotometry. The reaction of zinc with PGMPH provides a sensitive and precise method for the determination of zinc in tap and mineral waters and in cooking salts. Zinc ion reacts with PGMPH at pH 7.2—8.5 in solutions containing 40% (v/v) ethanol to form a yellow-orange complex with maximum absorbance at 464—470 nm. The molar absorptivity of the 1:2 ZnPGMPH complex is 71 300 1 mol −1 cm −1 . Interferences are considered in detail.

A Three Equation Method for the Numerical Evaluation of Acidity Constants of Single Equilibria from Spectrophotometric Data

Abstract In this paper we devise a numerical method for the evaluation of acidity constants of single equilibria suitable for use when the limit absorbance of the pure species are unavailable since these species cannot be obtained pure in solutions. The method has been applied to the evaluation of the first acidity constant of methylglyoxal bis (4-pheny1-3-thiosemicarbazone) (MGBPT).