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

Reversed-phase (RP) and ion-pair (IP) high performance liquid chromatograph ic (HPLC) methods were developed for the direct analysis of the organic aci ds (citric, malic and fumaric) present in xylem sap samples of cucumber pla nts grown in 'nickel free' and nickel contaminated nutrient solutions. Both methods were developed using Nucleosil C18 RP columns and phosphate buffer s with organic additives (2.5 v/v% acetonitrile for the RP and 10 v/v% meth anol for the IP method) as mobile phases. The main advantage of the RP meth od over the IP method is in its easiness and rapidity of separation. The IP method that uses tetrabutylammonium hydrogen sulfate (TBAHSO(4)) in a conc entration of 5 mmol/dm(3) dissolved in the eluent, ensured better separatio n for melic acid. For the elucidation of the role of organic acids in nicke l transport in xylem vessels, size exclusion chromatography (SEC) methods - using a silica Macrosphere column and acetate buffer - were elaborated. An alyzing the model solutions of citric or malic acids containing nickel(II) sulfate with the aid of an 'off-line' SEC-graphite-furnace atomic absorptio n spectrometer (SEC-GF-AAS) system, the implication of citric acid in the t ransport of nickel may be justified. However, neither the separation of the acids nor their identification in the real samples could be carried out wi th this method because of the following reasons: their similar molecular si ze and the presence of small inorganic ions in the saps in high concentrati ons like nitrate ions. (C) 2000 Elsevier Science B.V. All rights reserved.