SPE sample pre-treatment using a mixed-mode sorbent of reverse-phase and ionic exchange for determination of ALMWOAs in waters

Abstract

Studies concerning the role of aliphatic low molecular weight organic acids (ALMWOAs) in physical, chemical and biological processes occurring in rhizosphere have been carried out over the last decades. However, the analytical determination of ALMWOAs concentrations in nature is difficult owing to their considerably low levels and the interference of most environmental matrices, which demands pre-concentration steps. For these reasons, a pre-treatment of the sample prior to its analysis is usually required. Herein, a solid phase extraction (SPE) method is given as a sample pre-treatment step for ALMWOAs determination in solutions with plant exudates. A SPE sorbent, with characteristics different from those used until now, was used to overcome matrix interference. High-performance liquid chromatography (HPLC) coupled with a diode array detector (DAD) was used for analysis.Acceptable ALMWOAs recovery percentages were achieved for freshwater matrices and interference of trace metals (Cu, Cd and Ni) was not observed. The developed method was applied to identify and estimate the levels of ALMWOAs released in the solution (freshwater enriched with 10 mg/L Cu, 5 mg/L Ni and 1 mg/L Cd) where roots of Halimione portulacoides and Phragmites australis specimens have been exposed, for 2 hours. Both plants liberated measurable amounts of oxalic acid and P. australis also released into the solution citric and maleic acids.