ABSTRACT
An ion chromatography-electrospray mass spectrometry (IC-MS) method was developed 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 attained. 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)2CO3, 9.7 mM NH4OH, and 4% (v/v) methanol and had a pH 9.9. Even though eluant suppressed IC-MS degraded detection limits by a factor of 4 over the nonsuppressed system, using the retention 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 intact 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(III), Ca, MgEDTA, and EDTA itself were not detected. Detection limits for the various complexes ranged from 0.1 to 1 microM.
Subject(s)
Chelating Agents/chemistry , Edetic Acid/chemistry , Metals, Heavy/analysis , Plants/chemistry , Chromatography, Ion Exchange , Environmental Monitoring/methods , Metals, Heavy/chemistry , Sensitivity and Specificity , Spectrometry, Mass, Electrospray IonizationABSTRACT
The metabolism of cycloate, a thiocarbamate herbicide, was investigated in mature radish leaf. Twelve new metabolites were identified by liquid chromatographic/mass spectrometric analysis using fast atom bombardment and packed capillary liquid chromatography columns. Full-scan and tandem mass spectrometric methods were employed. Application of the on-column focusing technique resulted in identifications with injections of as little as 15 ng of metabolite (20 ppb in radish). This injection technique allows the practical use of packed capillary liquid chromatography/mass spectrometry in sample-limited applications. Cycloate is oxidized to several ring-hydroxylated isomers that are subsequently glucosylated and esterified with malonic acid. Cycloate is also conjugated with glutathione. Metabolic hydrolysis of the glutathione conjugate formed a cysteine conjugate that is further metabolized by amidation with either malonic or acetic acid. Transamination of the cysteine conjugate gave a thiolactic acid derivative. Metabolites were also identified that were the result of both ring-hydroxylation and conjugation with glutathione. One of these, an N-acetylcysteine conjugate, is the first report of a mercapturic acid in plants. The structures of two of the new metabolites were confirmed by chemical synthesis.
