Flow Injection Determination of Glutamate in Human Serum and Rat Brain Samples with Immobilized Glutamate Oxidase and Glutamate Dehydrogenase Reactors

Peer Reviewe

Stalikas, “Study of the behavior of water-soluble vitamins in HILIC on a diol column

Abstract An effort has been made to investigate the chromatographic behavior and to understand the basic mechanisms in HILIC-based separation of water-soluble vitamins with highly varied properties on a diol column. The water content of the mobile phase is of utmost importance because it directly affects the type and extent of interactions of the solutes with the stationary phase and with the buffered mobile phase. A mixed-mode partitioning-surface adsorption mechanism enables most precise description of their chromatographic retention and separation. The point at which surface adsorption becomes apparent, however, depends on the properties of the solutes on the given stationary phase, and on the presence of buffer salt ions. Adjustment of mobile phase pH and use of different buffer salts can be used to modify electrostatic interactions among the solutes, active silanols, and counter-ions. The role of hydrogen bonding was clarified by substitution of ACN by solvents with moderate to strong hydrogen bonding potential. Analytes which are neutral at the working pH start to interact with the stationary phase when the ACN content is increased to 80%. Negatively charged analytes are adsorbed on the stationary phase when the ACN content is approximately 86%, because augmentation of the counter-ions weakens electrostatic repulsion by the active silanol groups. On the other hand, the electrostatic attraction of thiamine contributes significantly to its retention even when using mobile phases with high water content

Stalikas, “Study of the behavior of water-soluble vitamins in HILIC on a diol column

Abstract An effort has been made to investigate the chromatographic behavior and to understand the basic mechanisms in HILIC-based separation of water-soluble vitamins with highly varied properties on a diol column. The water content of the mobile phase is of utmost importance because it directly affects the type and extent of interactions of the solutes with the stationary phase and with the buffered mobile phase. A mixed-mode partitioning-surface adsorption mechanism enables most precise description of their chromatographic retention and separation. The point at which surface adsorption becomes apparent, however, depends on the properties of the solutes on the given stationary phase, and on the presence of buffer salt ions. Adjustment of mobile phase pH and use of different buffer salts can be used to modify electrostatic interactions among the solutes, active silanols, and counter-ions. The role of hydrogen bonding was clarified by substitution of ACN by solvents with moderate to strong hydrogen bonding potential. Analytes which are neutral at the working pH start to interact with the stationary phase when the ACN content is increased to 80%. Negatively charged analytes are adsorbed on the stationary phase when the ACN content is approximately 86%, because augmentation of the counter-ions weakens electrostatic repulsion by the active silanol groups. On the other hand, the electrostatic attraction of thiamine contributes significantly to its retention even when using mobile phases with high water content

Nanometer-sized ceria-coated silica-iron oxide for the reagentless microextraction/preconcentration of heavy metals in environmental and biological samples followed by slurry introduction to ICP-OES

A slurry suspension sampling technique is developed and optimized for the rapid microextraction of heavy metals and analysis using nanometer-sized ceria-coated silica-iron oxide particles and inductively coupled plasma optical emission spectrometry (ICP-OES). Magnetic-silica material is synthesized by a co-precipitation and sol-gel method followed by ceria coating through a precipitation. The large particles are removed using a sedimentation-fractionation procedure and a magnetic homogeneous colloidal suspension of ceria-modified iron oxide-silica is produced for microextraction. The nanometer-sized particles are separated from the sample solution magnetically and analyzed with ICP-OES using a slurry suspension sampling approach. The ceria-modified iron oxide-silica does not contain any organic matter and this probably justifies the absence of matrix effect on plasma atomization capacity, when increased concentrations of slurries are aspirated. The As, Be, Mo, Cr, Cu, Pb, Hg, Sb, Se and V can be preconcentrated by the proposed method at pH 6.0 while Mn, Cd, Co and Ni require a pH ≥ 8.0. Satisfactory values are obtained for the relative standard deviations (2-6%), recoveries (88-102%), enrichment factors (14-19) and regression correlation coefficients as well as detectability, at sub-μg L(-1) levels. The applicability of magnetic ceria for the microextraction of metal ions in combination with the slurry introduction technique using ICP is substantiated by the analysis of environmental water and urine samples

Detection of microcystins in Pamvotis lake water and assessment of cyanobacterial bloom toxicity

Lake Pamvotis is a shallow, eutrophic Mediterranean lake with ecological significance. This paper deals with the evaluation of cyanobacterial toxicity in Lake Pamvotis. ELISA and HPLC revealed the presence of significant amounts of MCYST-LR. Danio rerio bioassay confirmed the toxic nature of the bloom. Cyanobacterial extracts had adverse toxic effects on development of D. rerio. Also, it was shown that cyanobacterial extracts containing environmentally detected concentrations of MCYST can cause reduced survival rate of fish species. The results clearly indicate that cyanobacterial blooms in Lake Pamvotis may be regarded as human and fish health hazard. Continuous monitoring of the lake is suggested, in order to prevent future possible intoxications