Optimisation of the analytical detection of EDTA by HPLC in natural waters

Reversed-phase ion-pair liquid chromatography is often used to analyse trac es of EDTA in natural water samples. Some perturbations due to the presence of major anions in samples, which can compete for ion pair formation with the Fe-EDTA complex used for the detection, have been observed but never es timated and quantified. A new operational method for determining EDTA in na tural water samples is proposed by taking into account anion interactions. Qualitative and quantitative analyses of EDTA were performed with a synthet ic water at various ionic strengths. From the effect of the ionic strength controlled by CaCl2 the concentration of the counter-ion tetrabutylammonium bromide (TBA(+)Br(-)) and the methanol of the mobile phase, optimal analyt ical conditions were proposed for a better determination of EDTA concentrat ion. The limit of detection without preconcentration and the reproducibilit y defined as relative standard deviation were 5 mu g/L and 3.6% (n = 12), r espectively. This method was applied to natural samples.