SummaryWhen ionic surfactants are used as mobile phases in micellar liquid chromatography, MLC, the retention of compounds is governed by hydrophobic and electrostatic forces. In the absence of electrostatic effects, the hydrophobicity of a compound is the predominant factor affecting its retention and its interaction with micelles. Because both interactions should be considered for ionic compounds, a novel retention model is proposed which includes the hydrophobicity of a compound and the molar fraction of its charged form. High correlations between the logarithm of the capacity factors and structural parameters were obtained for ionic compounds with different degrees of ionization. The effect of the nature and composition of the mobile phase (pH, concentration of surfactant and modifier) was studied. The modelling of the retention of compounds as a function of physico-chemical parameters and experimental variables was established by means of multivariate regression methods (MLR, PLS). In addition, a predictive model for estimating the hydrophobicity of catecholamines is proposed. Finally, quantitative retentionactivity relationships in MLC were also investigated for catecholamines.
A spectrophotometric procedure is proposed for the assay of N-acetylcysteine (NAC) in the range 0.5-49 pg ml-I, based o n the reaction of the thiol group with o-phthalaldehyde and isoleucine at pH 9.5 (Amax. = 335 nm). The procedure was applied successfully to the determination of NAC in several pharmaceutical formulations. The recoveries ranged from 98 t o 106%, with relative standard deviations of less than 1.5%. The method is free from interferences and is simple, rapid and easy t o automate.
A direct and simple procedure for the determination of naproxen and propranolol in pharmaceutical preparations was developed. The procedure was based on the measurement of the room-temperature phosphorescence of sodium dodecyl sulfate micellar solutions of the drugs. The appropriate experimental conditions to obtain a reproducible and maximum phosphorescence signal, when sulfite is used to eliminate the oxygen from the micellar solutions, were studied. The results of the analysis of several pharmaceutical preparations were satisfactory. The presence of hydralazine in pharmaceuticals containing propranolol gave low values owing to quenching of the phosphorescence signal.
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