Güler Somer

A direct method for the determination of selenium and lead in cow's milk by differential pulse stripping voltammetry

The selenium and lead contents in milk samples from Turkey were determined using a hanging mercury drop electrode ( HMDE ) and differential pulse cathodic stripping voltammetry ( DPCSV ) and differential pulse anodic stripping voltammetry ( DPASV ), respectively. In this method, the milk samples were digested in HNO3 : HClO4 ( 1:1 ) mixture by a wet digestion procedure. The DPCSV of milk samples in 0.1 M HCl solution showed a peak for selenium at −0.56 V , and DPASV for lead showed a peak at -0.35 V. A deposition potential of -0.2 V for selenium, and −0.5 V for lead were suitable. The standard addition method was used to determine selenium and lead in the sample. The linear domain range was 75–1.2 μg/l for selenium with a correlation coefficient of 0.9981 and 185–8.7 μg/l for lead with a correlation coefficient of 0.9945. The proposed method provides a simple and suitable procedure for the determination of trace amounts of selenium and lead. In this method, there is no need for sophisticated instruments and tedious separation procedure. Selenium and lead contents of milk samples from three distinct regions of Turkey were obtained between 21.5–69.4 and 22.1–59.2 μg/l (n=4–5), with the relative standard deviations of 10.3–10.7 and 6.8–9.9% , respectively.

Polarographic and voltammetric behavior of selenious acid and its use in analysis

Solution chemistry of Se(IV), in particular the acid-base properties, salt and complex formation, chemical reduction and reaction of Se(IV) with organic and inorganic sulfur compounds are briefly summarized. The electrochemical reduction of Se(IV) on dropping and stationary mercury electrodes is dealt with in some detail. The effects of antecedent acid-base equilibria and of consecutive reactions of the reduction product, Se(2-), adsorption of their products, and effects of added metal ions are discussed. The principles and applications of stripping analyses for determination of ultratraces of Se(IV) are summarized. The behavior on unreactive (Au, Pt, carbon) and reactive (Hg, Ag, Cu) electrodes are compared.

Simultaneous determination of selenium and lead in whole blood samples by differential pulse polarography.

The polarographic reduction of lead in the presence of selenite gives rise to an additional peak corresponding to the reduction of lead (Pb) on adsorbed selenium (Se) on mercury at -0.33 V. The selenium and lead content can be determined using this peak by the addition of a known amount of one of these ions first and then the second ion. The linear domain range of lead is 5.0x10(-7)-2.0x10(-5) M and for selenium 5.0x10(-7)-1.0x10(-5) M. Using this method 4.90x10(-7) M Se(IV) and 1.47x10(-6) M Pb(II) in a synthetic sample could be determined with a relative error of +2.0% and 1.8%, respectively (n=4). A recovery test after acid digestion for a synthetic sample was 97% for selenium and 96.5% for lead. The method was applied to 1 ml of digested blood, and 328+/-23 mug l(-1) Se(IV) and 850+/-62 mug l(-1) Pb(II) could be determined with a 90% (n=5) confidence interval.

Determination of selenium in garlic by cathodic stripping voltammetry

Abstract The selenium content in a garlic sample was determined on hanging mercury drop electrode (HMDE) using cathodic stripping voltammetry (CSV). In this method the dried garlic sample was digested in HNO3:HClO4 (1:1) by wet-digestion procedure. The CSV voltammogram in 0.1 M HCl solution showed a peak for Se at −0.56 V. Effect of deposition potential, deposition time and sweep rate on this peak were tried to determine the optimum experimental conditions. A deposition potential of −0.2 V was applied for 120 s while stirring the solution by passing nitrogen and followed a potential scan of 50 mV/s in a negative direction. The standard addition method was used to determine selenium in the sample. The linear domain range of Se (IV) was 2.0×10−8–6.0×10−7 M with a correlation coefficient of 0.9985. This method was used for the first time for the determination of selenium in garlic sample without any separation procedure and preconcentration techniques such as ion exchange, solvent extraction or hydride generation. The amount of selenium determined in three different samples from three different regions were 370±26 (n=5), 485±35 (n=4) and 365±46 (n=4) ng/g (dry-weight) with relative standard deviations of 7.0, 7.2 and 12.6%, respectively.

Preparation and application of a new glucose sensor based on iodide ion selective electrode

An electrode for glucose has been prepared by using an iodide selective electrode with the glucose oxidase enzyme. The iodide selective electrode used was prepared from 10% TDMAI and PVC according our previous study. The enzyme was immobilized on the iodide electrode by holding it at pH 7 phosphate buffer for 10min at room temperature. The H(2)O(2) formed from the reaction of glucose was determined from the decrease of iodide concentration that was present in the reaction cell. The iodide concentration was followed from the change of potential of iodide selective electrode. The potential change was linear in the 4x10(-4) to 4x10(-3)M glucose concentration (75-650mg glucose/100ml blood) range. The slope of the linear portion was about 79mV per decade change in glucose concentration. Glucose contents of some blood samples were determined with the new electrode and consistency was obtained with a colorimetric method. The effects of pH, iodide concentration, the amount of enzyme immobilized and the operating temperature were studied. No interference of ascorbic acid, uric acid, iron(III) and Cu(II) was observed. Since the iodide electrode used was not an AgI-Ag(2)S electrode, there was no interference of common ions such as chloride present in biological fluids. The slope of the electrode did not change for about 65 days when used 3 times a day.

Determination of ascorbic acid in fruit and vegetables using normal polarography

Abstract The ascorbic acid content of fruit and vegetables was determined by normal polarography. It was found that oxalic acid and EDTA protected the vitamin during the sample preparation procedure but oxalic acid was preferred to be used for polarographic analysis. Citrate buffer was used as the supporting electrolyte since it was already present in fruit and vegetables and resisted the change in pH upon the addition of the fruit extract. The most suitable pH of the supporting electrolyte was determined to be 4.5. A procedure is suggested for the determination of ascorbic acid in fruit and vegetables. The standard deviation for the method based upon the pooled precision data was found to be 1.0 for tomatoes and 3.1 for oranges.

A new and direct method for the trace element determination in cauliflower by differential pulse polarography.

Using the DPP polarograms of wet digested cauliflower sample in acetate buffer at pH values of 2, 4 and 6, Fe, Zn, Mo, Se, Cr, Cd, Pb, Ti and Cu quantities were determined. The best separation and determination conditions for Zn, Se and Mo was pH 2; for Cr, Zn, Mo and As was pH 4; for Pb pH 6, for Ti, Cu and Fe was pH 6-7 EDTA, for Cd pH 2 EDTA and for lead pH 6, all in acetate buffer. The trace element ranges for cauliflowers from two different seasons were (first figure for winter, the second for summer) for Se 120-250mugg(-1), Fe 70-85mugg(-1), Cu 320-150mugg(-1), Ti 90-120mugg(-1), Cr 130-630mugg(-1), Zn 90-550mugg(-1), Mo 170-230mugg(-1), Cd 20mugg(-1) (in winter) and Pb 130-300mugg(-1) in dry sample. Cd was under the detection limit in summer. The length of digestion time had no effect on the recovery of copper, iron, molybdenum and zinc between 15 and 3h of digestion.

Photosensitized decomposition of ascorbic acid in the presence of riboflavin

Abstract We studied the riboflavin-sensitized photodecomposition of ascorbic acid by visible light using the polarographic technique. The reaction was carried out at 25°C in the pH range 2.5–6.0 under anaerobic and aerobic conditions and the reaction rate was found to depend on the pH in both cases. Oxygen was consumed during photooxidation and the rate was limited by the riboflavin concentration. Formation of hydrogen peroxide appeared under both aerobic and anaerobic conditions. Reaction steps related to the formation of hydrogen peroxide were included in the reaction mechanisms.

Preparation of a new solid state fluoride ion selective electrode and application.

A new solid state fluoride ion selective electrode composed of 70% Ag(2)S, 10% Cu(2)S and 20% CaF(2) has been developed. An analytically useful potential change occurred, from 1x10(-6) to 1x10(-1)M fluoride ion. The slope of the linear portion (1x10(-1)-1x10(-5)M) was about 26+/-2mV/10-fold concentration changes in fluoride. It was found that pH change between 1 and 8 had no effect on the potential of the electrode. There was no interference of most common cations such as K(+,) Na(+), Ca(2+) and Mg(2+) and anions such as Cl(-), NO(3)(-), SO(4)(2-) and PO(4)(3-). The lifetime of the electrode was more than 2 years, when used at least 4-5 times a day, and the response time was about 60s. The measurements were made at constant ionic strength (0.1M NaNO(3)) and at room temperature. This electrode has been used for the determination of fluoride ion in Ankara city tap water and in bottled spring water using standard addition method. The validation of the electrode has been made with a commercial fluoride ion selective electrode (Orion) and high consistency was obtained.

Binuclear manganese (III) complexes as electron donors in D1/D2/cytochrome b559 preparations isolated from spinach photosystem II membrane fragments.

Abstract The capability of different manganese complexes to act as PS II electron donors in D1/D2/ cytochrome b 559 complexes has been analyzed by measuring actinic light-induced absorption changes at 680 nm (650 nm) and 340 nm, reflecting the photoaccumulation of Pheophytin- (Pheo-) and the reduction of NADP+ respectively. The data obtained reveal: a) the donor capacity of synthetic binuclear Mn(III)2 complexes containing aromatic ligands significantly exceeds that for MnCl2 in both cases, i.e. Pheo- photoaccumulation and NADP+ reduction; b) manganese complexes can serve as suitable electron donors for light-induced NADP+ reduction catalyzed by D1/D2/cytochrome b559 complexes and ferredoxin plus ferredoxin- NADP+ reductase under anaerobic conditions and c) the specific turnover rate of the system leading to NADP+ reduction is extremely small. The implications of these findings are briefly discussed.