Victor G. Mihucz

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.

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.

Influence of different bentonites on the rare earth element concentrations of clarified Romanian wines

The rare earth element (REE) concentrations of 19 Romanian young wine samples originating from the Dealurile Moldovei viticulture area were determined by double focusing inductively coupled plasma mass spectrometry (DF-ICP-MS) after microwave-assisted digestion with nitric acid. The determination of Eu was hampered by the BaO molecular interference. Generally, the red wine samples were more concentrated for REEs than the white wine samples studied. The REE concentrations of the four bentonites (Gelbenton, Evergel, BW200, Tükrös) determined after their fusion were higher by three orders of magnitude than those of the wine samples. After a simulated wine purification process performed with these bentonite samples and a red and white pool samples, the REE concentrations of the clarified wine samples increased by 1.2-1.5 times for red, and 1.3-3 times for white wines in case of the fibrous bentonite sample (Gelbenton), by about 2-5 times in case of the bentonite containing ovalbumin, caseine and gelatine (Evergel), meanwhile this factor was about 20-25 for Na bentonite powder samples (BW200, Tükrös). On basis of the chemometric evaluation using the REE concentrations as input data, the majority of the Feteasca wines belonged to the same cluster as well as the two Cabernet Sauvignon to another subcluster. The adequate choice of the bentonite may allow the use of REEs as fingerprints for determining the wine provenance.

Determination of fulvic acids in water samples of Hungarian caverns

Abstract Water samples from the region of Beke cavern of Aggtelek and above the Jozsefhegyi and Palvolgyi caverns of Buda, Hungary were analyzed by various chromatographic techniques and fluorescence spectrometry. According to size-exclusion chromatographic (SEC) measurements, the water samples contained only low-molecular-weight components, fulvic acids, which were concentrated and separated from inorganic and non-acidic organic compounds in the water samples at pH 2 using an XAD-8 resin column. Elution from the column was performed with 0.1 M NaOH solution. UV absorbance was monitored at 254 nm and fractions were collected and subsequently separated by applying a size-exclusion high-performance liquid chromatographic (SE-HPLC) method. The mobile phase was ammonium acetate at a concentration of 50 mmol/dm 3 and a flow rate of 0.5 cm 3 /min. The SE-HPLC measurements confirmed the presence of low-molecular-weight compounds in the samples analyzed. Quantitative determination of the fulvic acid content of the concentrated samples was carried out by fluorescence spectrometry. The excitation and emission wavelengths were 325 and 440 nm, respectively. The fulvic acid concentrations of the water samples examined ranged between 2 and 112 μg/cm 3 .

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.