Determination of metal-EDTA complexes in soil solution and plant xylem by ion chromatography-electrospray mass spectrometry

An ion chromatography-electrospray mass spectrometry (IC-MS) method was dev eloped to quantify the metal complexes of ethylenediaminetetraacetic acid ( EDTA) in soil solution and plant xylem exudate. Suitable separation of the metal-EDTA complexes was achieved on a Dionex AS5 column using 2 mM Na2CO3 as the eluant. However, satisfactory detection by eluant suppressed IC-MS, in either the positive or negative ion detection mode, could not be attaine d. A new eluant that still attained suitable separation and produced ionic species that could be detected by MS in the negative ion mode was developed . The eluant consisted of 2.5 mM (NH4)(2)CO3, 9.7 mM NH4OH, and 4% (v/v) me thanol acid had a pH 9.9. Even though eluant suppressed IC-MS degraded dete ction limits by a factor of 4 over the nonsuppressed system, using the rete ntion time and not the m/z (mass-to-charge ratio) of the intact chelate for identification, the latter allowed the metal complexes to be detected inta ct and was optimized for the analysis of environmental samples. The number of metal-EDTA species that could be detected was limited by the eluant used for ion chromatography (i.e. only those complexes that were stable at high pH), with metal-EDTA complexes of Al, Cd, Cu, Co, Mn, Ni, Pb, and Zn being adequately resolved. Iron(lll), Ca, MgEDTA, and EDTA itself were not detec ted. Detection limits for the various complexes ranged from 0.1 to 1 muM.