Martina Medvidović-Kosanović

Determination of anti-oxidative histidine dipeptides in poultry by microchip capillary electrophoresis with contactless conductivity detection

A home-made microchip electrophoresis (MCE) device was used to quantitate two biologically important histidine dipeptides, carnosine and anserine, using capacitively coupled contactless conductivity detection (C4D), at pH 2.7. The C4D detector exhibited a linear response to both carnosine and anserine in the range of 0-200μM for the individual dipeptides and in the range of 0-100μM for each dipeptide when both were present as a mixture. The limit of detections (LOD) for the dipeptides in the mixture were 0.10μM for carnosine and 0.16μM for anserine. Standard addition was used to detemine the accuracy of the method. For carnosine and anserine the recoveries were in the range of 96.7±4.9-106.0±7.5% and 95.3±4.5-105.0±5.1% in thigh muscle and 97.5±5.1-105.0±7.5% and 95.3±5.4-97.3±5.6% in breast muscle, respectively.

Determination of anionic surfactants in real samples using a low-cost and high sensitive solid contact surfactant sensor with MWCNTs as the ion-to-electron transducer

Multi-walled carbon nanotubes (MWCNTs) were used as a conducting substrate for construction of an all solid contact anionic surfactant sensor, which used the 1,3-didecyl-2-methylimidazolium–tetraphenylborate (DMI–TPB) ion pair as the sensing element implemented in PVC membranes. Scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS) were used for morphological and electrochemical characterisation of the sensor. The investigated sensor showed a Nernstian response for lauryl sulfate (LS), 57.1 mV per decade of activity between 2.0 × 10−7 and 1.1 × 10−3 M; and a sub-Nernstian response for dodecylbenzenesulfonate (DBS), 51.1 mV per decade of activity between 3.6 × 10−7 and 6.6 × 10−4 M. For each ten-fold concentration change, the response time was 7 s (in the range from 1 × 10−6 M to 5 × 10−4 M). The detection limits for LS and DBS in water were 1.2 × 10−7 and 2.6 × 10−7 M, respectively. The sensor revealed a stable potentiometric response at pH 3–13 with a signal drift of 1.9 mV h−1 and exhibited outstanding selectivity performances for LS toward the majority of organic and inorganic anions that are most frequently employed in commercial formulations based on surfactants. The new sensor was applied for end-point location at potentiometric anionic surfactant titrations. Cetyltrimethylammonium bromide (CTAB) was used as a standard cationic titrant in all titrations. Ethoxylated non-ionic surfactants (EONSs) with a higher content of ethoxylated groups in the molecule and higher concentrations of EONSs reduce the magnitude of inflexion of titration curves and may cause a remarkable distortion during anionic surfactant (AS) determination. The sensor was tested by determination of ASs in commercial detergent products. The standard two-phase titration method and a conventional PVC liquid membrane surfactant sensor (PVCSS) showed satisfactory mutual agreement. The low-cost surfactant sensor developed had an operational lifetime of ca. six months.

Potentiometric, electrochemical and UV/VIS investigation of a copper (II) complex with beta-alanyl-L-histidine

The main goal of this study was to investigate complexation of L-carnosine and its constituent amino acids beta-alanine and L-histidine with copper (II) in a buffer at pH = 10. For this study the following methods were used: potentiometry, cyclic and differential pulse voltammetry and UV/VIS spectroscopy. The results have shown that L-histidine and L- carnosine formed a complex with copper in a 1:1 ratio, while no complexation with beta-alanine was observed.