ABSTRACT
Noradrenaline is a catecholamine which has been largely recognised to play a very important role in biological systems. In view of the neurotransmitter's alleged importance, this work aimed at showing the influence of time on its spectral behaviour using different analytical methods and determining its acidity constants through spectrophotometric titration and by the so-called point-by-point analysis, where the samples are freshly prepared for each pH value investigated at the instant required. Because the catecholamines are light-sensitive and likely to react with the oxygen in the surrounding air, both methods used preclude its incidence onto the samples being analysed under the presence of a nitrogen atmosphere maintained over the solutions. The constants obtained through point-by-point analysis were log beta1 = 30.71+/-0.16, log beta2 = 22.00+/-0.15 and log beta3 = 11.69+/-0.16.
Subject(s)
Acids/chemistry , Norepinephrine/chemistry , Chromatography, High Pressure Liquid , Electrochemistry , Molecular Structure , Spectrum Analysis , Time Factors , TitrimetryABSTRACT
The present work aimed at describing the spectral behaviour of the serotonin and to evaluate its acidity constants using three different methods, using two spectrophotometry titrations and a third method that involved point-by-point analysis, which permitted to monitor closely and determine the evolution of the serotonin species in solution as a function of time. The three methods allowed estimation of three acidity constants associated to the same number of functional groups that form part of the molecule. The results given by the point-by-point analysis were: log(beta1) = 24.95 +/- 0.12; log(beta2) = 20.20 +/- 0.10; log(beta3) = 10.89 +/- 0.018.
Subject(s)
Chemistry, Physical/methods , Serotonin/chemistry , Spectrophotometry/methods , Copper/chemistry , Humans , Hydrogen-Ion Concentration , Light , Models, Chemical , Nitrogen/chemistry , Serotonin/analysis , Software , Time Factors , Zinc/chemistryABSTRACT
In this work, the results are presented concerning the influence of time on the spectral behaviour of adrenaline (C(9)H(13)NO(3)) (AD) and of the determination of its acidity constants by means of spectrophotometry titrations and point-by-point analysis, using for the latter freshly prepared samples for each analysis at every single pH. As the catecholamines are sensitive to light, all samples were protected against it during the course of the experiments. Each method rendered four acidity constants corresponding each to the four acid protons belonging to the functional groups present in the molecule; for the point-by-point analysis the values found were: log beta(1) = 38.25 +/- 0.21, log beta(2) = 29.65 +/- 0.17, log beta (3) = 21.01 +/- 0.14, log beta(4) = 11.34 +/- 0.071.
Subject(s)
Epinephrine/chemistry , Absorption , Hydrogen-Ion Concentration , Molecular Structure , Spectrum Analysis , Time FactorsABSTRACT
The time stability of the azomethine-H species was determined not to be better than 10 min in the absence of oxygen and light, however under phosphate buffered conditions the azomethine-H species remained stable for longer periods, as indicated by the spectrophotometric behaviour. Nevertheless, the analysis time still exceeded the stability allowance. Therefore, the determination of the acidity constants of the Azomethine-H species was studied by means of UV-vis spectrophotometry in buffered media by means of the point-by-point analysis and data processing with SQUAD to refine the resulting constants, which were: pK(a1) = 3.39, pK(a2) 7.36 and pK(a3) 8.73. The latter were associated to the corresponding acid-base equilibria of the amine and hydroxy groups constituting the molecule.
Subject(s)
Naphthalenesulfonates/chemistry , Thiosemicarbazones/chemistry , Buffers , Hydrogen-Ion Concentration , Molecular Structure , Phosphates/chemistry , Spectrophotometry , TitrimetryABSTRACT
The interest in determining the acidity constants of the catecholamines stems from the fact that they play rather an important biological role. The present work reveals the effect of different parameters such as oxygen, light, analysis time and pH on the dopamine oxidation process, where oxygen has an effect on the dopamine oxidation of 40% and up to 20% is attributed to exposure to light as a function of the pH. The application of adequate control on the said parameters (which ensured stability of the dopamine) facilitated the determination of the corresponding three acidity constants, 9.046+/-0.147, 10.579+/-0.148 and 12.071+/-0.069.
Subject(s)
Dopamine/chemistry , Hydrogen-Ion Concentration , Drug Stability , Kinetics , Oxidation-Reduction , Spectrophotometry/methodsABSTRACT
This work reports the use of alpha and beta-cyclodextrin-modified carbon paste electrodes (CPE(alpha-CD) and CPE(beta-CD)) to determine simultaneously Pb(II) and Cd(II) by means of the electrochemical technique known as anodic stripping voltammetry (ASV). Both modified electrodes displayed good resolution of the oxidation peaks of the said metals. Statistic analysis of the results strongly suggests that the CPE(beta-CD )exhibited a better analytical response that the CPE(alpha-CD), while the detection limits obtained for Pb(II) were 6.3 x 10(-7) M for the CPE(alpha-CD) and 7.14 x 10(-7) M for the CPE(beta-CD), whereas for Cd(II) they were 2.51 x 10(-6) M for the CPE(alpha-CD) and 2.03 x 10(-6) M for the CPE(beta-CD).
