Curcumin Electrochemistry-Antioxidant Activity Assessment, Voltammetric Behavior and Quantitative Determination, Applications as Electrode Modifier.

Curcumin (CU) is a polyphenolic compound extracted from turmeric, a well-known dietary spice. Since it has been shown that CU exerts beneficial effects on human health, interest has increased in its use but also in its analysis in different matrices. CU has an antioxidant character and is electroactive due to the presence of phenolic groups in its molecule. This paper reviews the data reported in the literature regarding the use of electrochemical techniques for the assessment of CU antioxidant activity and the investigation of the voltammetric behavior at different electrodes of free or loaded CU on various carriers. The performance characteristics and the analytical applications of the electrochemical methods developed for CU analysis are compared and critically discussed. Examples of voltammetric investigations of CU interaction with different metallic ions or of CU or CU complexes with DNA as well as the CU applications as electrode modifiers for the enhanced detection of various chemical species are also shown.

Past and Present of Electrochemical Sensors and Methods for Amphenicol Antibiotic Analysis.

Amphenicols are broad-spectrum antibiotics. Despite their benefits, they also present toxic effects and therefore their presence in animal-derived food was regulated. Various analytical methods have been reported for their trace analysis in food and environmental samples, as well as in the quality control of pharmaceuticals. Among these methods, the electrochemical ones are simpler, more rapid and cost-effective. The working electrode is the core of any electroanalytical method because the selectivity and sensitivity of the determination depend on its surface activity. Therefore, this review offers a comprehensive overview of the electrochemical sensors and methods along with their performance characteristics for chloramphenicol, thiamphenicol and florfenicol detection, with a focus on those reported in the last five years. Electrode modification procedures and analytical applications of the recently described devices for amphenicol electroanalysis in various matrices (pharmaceuticals, environmental, foods), together with the sample preparation methods were discussed. Therefore, the information and the concepts contained in this review can be a starting point for future new findings in the field of amphenicol electrochemical detection.

Rapid voltammetric method for quinine determination in soft drinks.

A novel voltammetric assay for quinine (QN) determination using an electrochemically pretreated pencil graphite electrode is described. The detection limit of QN was 2 × 10-7 M. The method possesses some obvious advantages including extreme simplicity, rapid response, and low cost.

Alternative sample diluents in bioanalytical LC-MS.

The problem of sample diluent in bioanalytical LC-MS is reviewed with a special focus on large-volume injections and non-miscible solvents with mobile phase components. These issues are related to the sample preparation approach, which in many instances provides the sample diluent before injecting this into the chromatographic column. The sample volume influences the quantitation limit of the chromatographic method, while its nature may influence the retention process of the injected analytes. The literature reports a few papers that are focused on alternative sample diluents in bioanalytical LC-MS that are generally non-miscible with mobile phase. The principle of this approach and some of its current bioanalytical applications from literature are discussed. However, more applications and more publications from HPLC users and vendors are expected in this field, which could prove its analytical importance and potential in bioanalysis.

Greener bioanalytical approach for LC/MS-MS assay of enalapril and enalaprilat in human plasma with total replacement of acetonitrile throughout all analytical stages.

Green bioanalytical approaches are oriented toward minimization or elimination of hazardous chemicals associated to bioanalytical applications. LC/MS-MS assay of enalapril and enalaprilat in human plasma was achieved by elimination of acetonitrile from both sample preparation and chromatographic separation stages. Protein precipitation (PP) by acetonitrile addition was replaced by liquid-liquid extraction (LLE) in 1-octanol followed by direct large volume injection of the organic layer in the chromatographic column operated under reversed phase (RP) separation mechanism. At the mean time, acetonitrile used as organic modifier in the mobile phase was successfully replaced by a mixture of propylene carbonate/ethanol (7/3, v/v). Three analytical alternatives ((I) acetonitrile PP+acetonitrile based chromatographic elution; (II) 1-octanol LLE+acetonitrile based chromatographic elution; (III) 1-octanol LLE+propylene carbonate/ethanol based chromatographic elution) were validated and the quality characteristics were compared. Comparison between these alternative analytical approaches was also based on results obtained on incurred samples taken during a bioequivalence study, through application of the Bland-Altman procedure.

Retention studies for large volume injection of aromatic solvents on phenyl-silica based stationary phase in RP-LC.

The use of a large volume injection of hydrophobic solvents as diluents for less hydrophobic solutes has already been proven for C18 and C8 stationary phases in reversed-phase liquid chromatography. The same possibility is investigated for a phenyl-hexyl stationary phase using aromatic solvents (benzene, toluene, ethylbenzene and propylbenzene) as diluents for several model analytes also containing aromatic rings. Both hydrophobic interaction and π-π stacking account for the competitive interaction of both the diluent and model analytes with the phenyl-hexyl phase. A linear decrease in analyte retention factor was observed with an increase of injection volume in the range of 1-100 µL. A moderate peak efficiency decrease was also observed, but peaks of model analytes remained undistorted with minimum band broadening up to 100 µL injection volume. A very small retention decrease was observed when changing the sample diluent in the homologous series: benzene, toluene, ethylbenzene and propylbenzene. The critical conditions for a successful large volume injection of analytes dissolved in studied hydrophobic solvents are for the analyte to have lower hydrophobicity and for the specified solutes to have proper solubility.

Total antioxidant capacity of some commercial fruit juices: electrochemical and spectrophotometrical approaches.

The aim of this paper was to assess the total antioxidant capacity of some commercial fruit juices (namely citrus), spectrophotometrically and by the biamperometric method, using the redox couple DPPH. (2,2-diphenyl-1-picrylhydrazyl)/DPPH (2,2-diphenyl-1-picrylhydrazine). Trolox was chosen as a standard antioxidant. In the case of the spectrophometric method, the absorbance decrease of the DPPH. solution was followed. For the biamperometric method, the influence of some parameters like the potential difference, DeltaE, DPPH. concentration, and Trolox concentration was investigated. The calibration graph obtained for Trolox presents linearity between 5 and 30 microM, (y=0.059 x + 0.0564, where y represents the value of current intensity, expressed as microA and x the value of Trolox concentration, expressed as muM; r(2)=0.9944). The R.S.D. value for the biamperometric method was 1.29% (n=10, c=15 microM Trolox). In the case of the spectrophotometric method, the calibration graph obtained for Trolox presents linearity between 0.01 and 0.125 mM (y= -9.5789 x+1.4533, where y represents the value of absorbance and x, the value of Trolox concentration, expressed as mM; r(2)=0.9963). The R.S.D. value for the spectrophotometric method was 2.05%. Both methods were applied to total antioxidant activity determination in real samples (natural juices and soft drinks) and the results were in good agreement.