Development of a gas chromatographic method for the simultaneous determination of trace amounts of ethylenediaminetetraacetic acid and diethylenetriaminepentaacetic acid in natural waters

Abstract

A GC method for the simultaneous determination of ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA) in natural waters is described. The method was studied with spiked samples of distilled water, sea-water (2 matrices) and humic-containing lake water. An acidified 5–10 ml sample was evaporated and esterified with C2H5OH, containing H2SO4 and CH3COOH catalysts and CH3(CH2)15CN as an internal standard. The esterified sample was extracted with C6H5CH3, neutralized with KHCO3, dried with anhydrous Na2SO4 and analysed by GC with nitrogen–phosphorus selective detection. The best recoveries were obtained by the esterification in 100 °C for 3 h. The tetraethyl ester of EDTA and pentaethyl ester of DTPA were further identified by mass spectrometry. In the sea- and lake water matrices, the recoveries of EDTA and DTPA were 80–110%. High concentrations (above 50 mg l–1) of iron (Fe3+) interfered considerably in the determination of DTPA. For EDTA the interference was insignificant with iron concentrations below 500 mg l–1.