Enikö Tatár

Effect of lead, nickel and vanadium contamination on organic acid transport in xylem sap of cucumber

Abstract Three organic acids (citric, fumaric and malic) of the Krebs cycle were measured by the reversed-phase high performance liquid chromatography (RP-HPLC) technique in the xylem saps of cucumber plants grown in (i) control nutrient solutions containing iron as Fe(III)-ethylene-diamine-tetraacetate (Fe(III)-EDTA), Fe(III)-citrate or FeCl 3 and (ii) in nutrient solutions contaminated with nickel, lead or vanadium in a concentration of 10 −5 M. Simultaneously, the heavy metal content of the xylem sap samples was determined by total reflection X-ray fluorescence spectrometry (TXRF). In the presence of lead or nickel contamination the transport of the organic acids became higher by factor 1.1–2.3 compared to the control plants when Fe(III)-citrate or Fe(III)-chloride was added to the nutrient solutions. In the case of plants growing in Fe(III)-EDTA containing solutions, however, the transport of the organic acids decreased by 30–40%. The effect of vanadium on the transport of organic acids was considerably smaller. Generally, the deviation in the organic acid transport between the contaminated and the control plants was proportional to the heavy metal transport in the xylem in the sequence Ni>Pb>V.

Determination of organic acids and their role in nickel transport within cucumber plants

Reversed-phase (RP) and ion-pair (IP) high performance liquid chromatographic (HPLC) methods were developed for the direct analysis of the organic acids (citric, malic and fumaric) present in xylem sap samples of cucumber plants grown in ‘nickel free’ and nickel contaminated nutrient solutions. Both methods were developed using Nucleosil C18 RP columns and phosphate buffers with organic additives (2.5 v/v% acetonitrile for the RP and 10 v/v% methanol for the IP method) as mobile phases. The main advantage of the RP method over the IP method is in its easiness and rapidity of separation. The IP method that uses tetrabutylammonium hydrogen sulfate (TBAHSO4) in a concentration of 5 mmol/dm3 dissolved in the eluent, ensured better separation for malic acid. For the elucidation of the role of organic acids in nickel transport in xylem vessels, size exclusion chromatography (SEC) methods — using a silica Macrosphere column and acetate buffer – were elaborated. Analyzing the model solutions of citric or malic acids containing nickel(II) sulfate with the aid of an ‘off-line’ SEC-graphite-furnace atomic absorption spectrometer (SEC-GF-AAS) system, the implication of citric acid in the transport of nickel may be justified. However, neither the separation of the acids nor their identification in the real samples could be carried out with this method because of the following reasons: their similar molecular size and the presence of small inorganic ions in the saps in high concentrations like nitrate ions.

Microwave assisted dissolution of aluminium oxide samples

The dependence on time of the efficiency of microwave assisted digestion of Al2O3 samples with various physico-chemical properties in H2SO4 solution (1 + 1) at a temperature of 170 °C and a pressure of 207 kPa has been investigated. Therefore, the concentrations of Al and that of the impurities in the solutions obtained, as well as the masses of residues after different times have been measured. The efficiency of the dissolution was shown to depend on the specific surface area and on the phase-state of the Al2O3. The time demand for total dissolution of the samples ranged from 0.1 to 7 hours.

Application of total-reflection X-ray fluorescence spectrometry and high-performance liquid chromatography for the chemical characterization of xylem saps of nickel contaminated cucumber plants

Abstract Total-reflection X-ray fluorescence (TXRF) spectrometry, reversed-phase (RP) and size–exclusion (SE) high-performance liquid chromatography (HPLC) methods were applied for the characterization of low-volume xylem sap of control and nickel contaminated cucumber plants growing in hydroponics containing urea as the sole nitrogen source. In these saps collected for 1 h, Ca, K, Fe, Mn, Ni, Zn, as well as malic, citric and fumaric acids were determined. The SEC measurements showed that macromolecules were not detectable in the samples. Nickel contamination had minimum impact on the organic acid transport, however, the transport of Zn, K and Fe was reduced by 50, 22 and 11%, respectively. This observation supports the results of our earlier experiments when nitrate ions were used as the sole nitrogen form. At the same time, the fresh root weight and the volume of the collected xylem sap increased by 36 and 85%, respectively. Therefore, nickel addition seemed to decrease the urea toxicity of the plants. By pooling the eluting fractions of the SEC column, which were 10-fold concentrated by freeze-drying, the series of the resulted samples were analyzed by the TXRF spectrometry and RP-HPLC. The three organic acids could be identified in only one of the fractions, which contained Fe and, in the case of the contaminated plants, Ni in detectable concentration. However, considerable parts of these two elements and Mn, as well as practically the total amounts of Cu may be transported by unidentified organic compounds in the xylem.

Comparison of the recovery of amino acids in vapour-phase hydrolysates of proteins performed in a Pico Tag work station and in a microwave hydrolysis system☆

Abstract An exhaustive study was made to determine the amino acid composition of lysozyme in hydroysates performed in a CEM microwave oven under various conditions [0.621–0.827 MPa (90–120 p.s.i.g.) for 5, 10, 20 and 40 min], determined by HPLC as their phenylthiocarbamyl derivatives. The results showed that the CEM microwave hydrolysis system works reproducibly up to 0.689 MPa (100 p.s.i.g.) pressure only. Uniformly optimum parameters for all components present in hydrolysates were not found. The recoveries of the components at 0.621 MPa (90 p.s.i.g.) (after 20 and 40 min) and at 0.689 MPa (100 p.s.i.g.) (after 10 20 and 40 min) varied from 63 to 111%. The reproducibility of the measurements was

Hyphenated technique for investigation of nickel complexation by citric acid in xylem sap of cucumber plants

Abstract A size-exclusion high performance liquid chromatographic-inductively coupled atomic emission spectrometric (SE-HPLC-ICP-AES) method was developed in order to elucidate the role of citric acid in the complexation of nickel in xylem saps of cucumber plants. The complexation of nickel by citric acid was modeled by preparing standard solutions of nickel(II) nitrate or sulfate whose Ni concentration was 2 μg/cm3 and citric acid whose concentration ranged between 100 and 500 μg/cm3. By passing these model solutions through the column, the higher the concentration of the citric acid, the greater was the shift of the Ni peak toward the retention time of the citric acid molecules detected with UV spectrometry. This may be evidence for the complexation capability of citric acid. The method was employed for xylem saps originating from nickel-contaminated cucumber plants previously grown in nitrate or urea-containing nutrient solutions. The obtained results for those real and spiked samples with citric acid showed similarity to that of the solutions containing citric acid and nickel.