Nevin Öztekin

Simultaneous determination of nitrite and nitrate in meat products and vegetables by capillary electrophoresis

Abstract A capillary electrophoresis method for the simultaneous analysis of nitrite and nitrate in meat products and vegetables using direct UV detection is reported. The method is based on the separation of two anions in a capillary coated with polyethyleneimine (PEI). Since PEI is a cationic polymer, the electroosmotic flow is reversed over a wide pH range and the fast separation of anions is achieved without the addition of any electroosmotic modifier to the separation buffer. The detection limit of the method is sufficiently low for food products. Good reproducibility and recovery results were obtained using thiocyanate as internal standard.

Adsorption of polyethyleneimine from aqueous solutions on bentonite clays

The adsorption of the cationic polymer, polyethyleneimine (PEI), on bentonite clay particles was investigated. The adsorption rates for the bentonite suspensions are very fast. The high affinity type of interactions between PEI and bentonite samples is attributed to the electrostatic interaction between the clay particles in ambient basic suspensions and the positively charged high molecular weight polyelectrolyte. The adsorption capacity and the influence of the polyelectrolyte on the rheological behavior change with the exchangeable ions, i.e. Na and Ca ions of the bentonite samples.

Voltammetric determination of nitrite in meat products using polyvinylimidazole modified carbon paste electrode

A simple and sensitive voltammetric method was developed to determine the amount of nitrite by using Carbon Paste Electrode (CPE) which is modified with polyvinylimidazole (PVI). A buffer solution of phosphate with a pH 4 value was used in the experiments. The amount of the nitrite-ion was determined by cyclic voltammetry (CV). The electro-chemical behaviour of nitrite-ion was investigated by using CV on the PVI modified CPE. A well-defined oxidation peak was obtained at 0.83 V against a reference Ag/AgCl electrode. Differential pulse voltammetry (DPV) was applied for the calibration plot and for the detection limit. The optimisation procedure was done in two steps: using a two-level factorial design for preliminary evaluation of the contributing factors, and the Box-Behnken Design (BBD) to assess the optimal experimental conditions. These are done with the analysis of 3 different factors in 15 runs of DPV. The optimum conditions are obtained within a linear response range of 5×10(-7)-1×10(-4) mol L(-1). Regression analysis is performed within this range showed the linear equation of y=0.028x+3.93×10(-7) with r(2)=0.9982, and for n=7. Limit of Detection (LOD) was 9×10(-8) mol L(-1) with S/N=3, and Limit of Quantification (LOQ) was 3×10(-7) mol L(-1) with S/N=10. The procedure was used successfully to detect the amount of nitrite in meat products.

Determination of amino acids in pomegranate juices and fingerprint for adulteration with apple juices

A new chiral micellar electrokinetic chromatography-laser induced fluorescence (MEKC-LIF) method was developed using sodium dodecylbenzene sulphonate (SDBS) as surfactant for the determination of chiral amino acids in pomegranate juices. The use of SDBS as the micellar medium enhanced the fluorescence intensities of amino acids derivatised with fluorescein isothiocyanate (FITC). The amino acid profile of pomegranate juices was compared to apple amino acids and l-Asn was proposed as a marker for the adulteration of pomegranate juices with apple juices.

Separation and direct UV detection of lanthanides complexed with cupferron by capillary electrophoresis.

Separation and detection of lanthanides by capillary zone electrophoresis in the presence of cupferron (N-nitroso-N-phenylhydroxylamine) as UV absorbing complexing agent were investigated. The resolution of partially complexed positively charged cupferron complexes is improved by using a buffer ligand competing with cupferron for metal ions. When hydroxyisobutyric acid (HIBA) is used as buffer and competing ligand, it provides complete separation of all 14 lanthanides with good peak shapes. An on-column separation of 14 lanthanides was achieved in only 7 min using 0.1 mmol/l cupferron, 15 mmol/1 HIBA at pH 4.9. The separation efficiencies for the optimum separation condition are between 77,000 and 208,000 theoretical plates. Determination of lanthanide complexes was performed by direct UV detection at 210 nm. Detection limits (signal-to-noise ratio=3) are ca. 0.24-0.47 microg/ml for lanthanides. Under optimum conditions, the complete separation of thorium and uranium from mixed lanthanides was achieved.

Effect of the adsorption of cetylpyridinium bromide on the flow behaviour of bentonite dispersions

Abstract The adsorption of the cationic surfactant, cetylpyridinium bromide (CPBr), and the rheological behaviours of the CPBr-coated bentonite dispersions (0.1% w/v) are investigated in the concentration range of 0.01–10 mmol/l CPBr. The adsorption capacity and the influence of the cationic surfactant on the flow behaviours change with the nature of the exchangeable cations, i.e. Na+ and Ca2+, of the bentonite samples.

Separation and direct UV detection of lanthanides complexed with pyridine-2-carboxylic acid by capillary electrophoresis

Separation and detection of lanthanides by capillary zone electrophoresis in the presence of pyridine-2-carboxylic acid (picolinic acid) as UV-absorbing complexing agent were investigated. The resolution of partially complexed positively charged complexes is improved by using two buffer ligands competing with picolinic acid for metal ions. When hydroxyisobutyric acid (HIBA) and formic acid are used together as competing ligands, this provides complete separation of all 14 lanthanides with good peak shapes. An on-column separation of 14 lanthanides was achieved in only 9 min using 0.8 mmol/l picolinic acid, 10 mmol/l HIBA and 25 mmol/l formic acid at pH 4.7. Determination of lanthanide complexes was performed by direct detection at 210 nm. Detection limits (signal-to-noise ratio=3) are ca. 0.53-0.96 microg/ml.

Non-ionic micellar electrokinetic chromatography with laser-induced fluorescence: a new method tested with biogenic amines in brined and dry-salted fish.

A non‐ionic micellar electrokinetic chromatography method coupled to laser‐induced fluorescence detection was developed for the quantitative determination of biogenic amines. Complete resolution of six biogenic amines – FITC derivatives – was achieved in less than 10 min, employing 10 mM Brij 35 in 75 mM borate buffer and at pH 9.7 as the running electrolyte. Relative fluorescence intensities of biogenic amines enhanched considerably and separation time decreased considerably when Brij 35 was substituted for SDS in the same buffer. The detection limits of the method for biogenic amines were found between 0.416 and 1.26 nM. The precisions for the corrected peak areas were calculated as between 1.63 and 3.24 %RSD. The applicability of the method was demonstrated by analyzing biogenic amines in the processed, brined, and dry‐salted fish samples. The method is simple and rapid, and widely applicable for the determination of biogenic amines in food samples.

Effects of polyethyleneimine adsorption on rheology of bentonite suspensions

The influence of the cationic polymer, polyethyleneimine polymer (PEI) on the flow behaviour of bentonite suspensions (2%, w/w), was studied. XRD, zeta potential and adsorption studies were done together with rheological measurements. The addition of PEI at concentration ranges of 10-5-4.5 g/l and their rheological properties and stability of bentonite suspensions were studied. The adsorption rates for the bentonite suspensions are very fast. The XRD results showed that the PEG molecules did not intercalate into the layers of the clay.

Isolation and analysis of bioactive diterpenoids in Salvia species (Salvia chionantha and Salvia kronenburgiii) by micellar electrokinetic capillary chromatography.

In the present work, we isolated two bioactive diterpenoids, horminone and 7-O-acetylhorminone and developed a micellar electrokinetic chromatography (MEKC) method for the simultaneous quantitative analysis of them in Turkish Salvia species. The optimal separation electrolyte was 50 mmol/L SDS and 25% methanol at pH 11.5. The limits of detection (S/N=3) were 3.269 and 4.518 microg/mL for horminone and 7-O-acetylhorminone, respectively. The method has been applied successfully to analyze these two components in Salvia chionantha and Salvia kronenburgii acetone extracts.