ABSTRACT
A new flow-injection (FI) and high performance liquid chromatography (HPLC) with chemiluminescence detection method has been proposed for the determination of α-lipoic acid (LA). The assay is based on the measurement of chemiluminescence (CL) produced during the reaction of α-lipoic acid with potassium permanganate in a sodium hexametaphosphate medium (pH 3). This reaction is accompanied by a weak CL, which is greatly increased in the presence of a formaldehyde solution. The proposed FI method allows the determination of LA over the range: 0.5-20µgmL(-1) with LOD 4×10(-3)µgmL(-1). An introduction of HPLC into the flow manifold improves selectivity of the method and allows the determination of LA in a complex sample. The chromatographic linear range is 2.5-30µgmL(-1) with LOD 1.774µgmL(-1). Chromatographic separation was achieved by isocratic elution (acetonitrile/potassium dihydrogen phosphate, pH 3, adjusted with phosphoric acid): 30/70 using a Cosmosil 5C(18)-MS-II (4.6mm×150mm I.D.) column at a flow rate of 1.0mLmin(-1). The presented methods were utilized to determine the α-lipoic acid content in "Alfa-lipoic acid" capsules and in food products.
Subject(s)
Chromatography, High Pressure Liquid/methods , Flow Injection Analysis/methods , Luminescent Measurements/methods , Thioctic Acid/analysis , Thioctic Acid/chemistry , Food Analysis , Formaldehyde/chemistry , Oxidants/chemistry , Oxidation-Reduction , Phosphates/chemistry , Potassium Permanganate/chemistry , Thioctic Acid/isolation & purificationABSTRACT
Hydrogen peroxide, potassium permanganate, potassium dichromate, potassium hexacyanoferrate(III), cerium(IV) sulphate and sodium peroxidisulphate have been tested as potential reagents for chemiluminescence generation from the oxidation of phenothiazine derivatives. Only with potassium permanganate in acidic medium were satisfying results achieved. A total of 13 different phenothiazine derivatives produce luminescence of different intensities on oxidation. Thioridazine hydrochloride was chosen to develop a rapid and simple method for its determination in pharmaceutical formulations. The limit of detection is 1.2 x 10(-6) mol l(-1), and 110 samples per hour can be determined.
Subject(s)
Antipsychotic Agents/analysis , Thioridazine/analysis , Flow Injection Analysis , Indicators and Reagents , Luminescent Measurements , Oxidants , Potassium Permanganate , TemperatureABSTRACT
A method for the spectrophotometric determination of promazine by flow injection analysis is reported. The procedure is based on the reaction of promazine with molybdophosphoric acid. Concentrations of promazine in the range 1-25 ppm have been determined with a relative standard deviation of 1.8% at 10 ppm (n = 20). The method was applied to the determination of promazine in injections and compared favourably with an independent reference method based on spectrophotometry.
