@article {4921,
	title = {Characterization of dissolved tannins and their metal-ion complexes by electrospray ionization mass spectrometry},
	journal = {Analytica Chimica Acta},
	volume = {411},
	number = {1-2},
	year = {2000},
	note = {ISI Document Delivery No.: 305EYTimes Cited: 25Cited Reference Count: 51},
	month = {May},
	pages = {91-102},
	type = {Article},
	abstract = {Electrospray mass spectrometry was used to characterize metal-complexing ligands derived from tannic acid, a component of natural dissolved organic matter. Complexes formed by tannin ligands with copper and other biogeochemically important metals were identified from the mass-to-charge ratios of the corresponding deprotonated molecular ions, allowing stoichiometry and metal oxidation state to be determined. Ligand ion intensities were proportional to tannic acid concentration, with detection limits on the order of 5 nM for individual compounds in 50:50 water/acetonitrile. The relative abundance of free ligand and complex ions indicated the degree of complexation under different solution conditions (metal concentration, pH, ionic strength). Using tandem mass spectrometry, the structure and principal copper binding site for one of the tannins were also determined, providing unique information with regard to metal complexation by these polyfunctional ligands. The technique can be combined with high performance liquid chromatography for on-line separation of dissolved organic compounds. Results demonstrate the potential of this approach for characterizing the different classes of metal-complexing ligands found in natural waters. (C) 2000 Elsevier Science B.V. All rights reserved.},
	keywords = {AFFINITY-CHROMATOGRAPHY, CHROMATOGRAPHY, COMPLEXATION, copper, electrospray ionization, high performance liquid, iron, LIGANDS, MASS SPECTROMETRY, metal-ion complexes, NATURAL ORGANIC-LIGANDS, ORGANIC, PERFORMANCE, PROTEINS, REGIOSELECTIVE MONO-OXIDATION, SPECIATION, STOICHIOMETRY, tannins, TOXICITY, trace metals},
	isbn = {0003-2670},
	url = {<Go to ISI>://000086527500011},
	author = {Ross, A. R. S. and Ikonomou, M. G. and Orians, K. J.}
}
@article {4920,
	title = {Electrospray ionization of alkali and alkaline earth metal species. Electrochemical oxidation and pH effects},
	journal = {Journal of Mass Spectrometry},
	volume = {35},
	number = {8},
	year = {2000},
	note = {ISI Document Delivery No.: 347MUTimes Cited: 7Cited Reference Count: 49},
	month = {Aug},
	pages = {981-989},
	type = {Article},
	abstract = {The utility of electrospray ionization mass spectrometry (ESI-MS) for characterizing dissolved metal species has generated considerable interest in the use of this technique for metal speciation, However, the development of accurate speciation methods based on ESI-R;IS requires a detailed understanding of the mechanisms by which dissolved metal species are ionized during electrospray. We report how the analysis of alkali and alkaline earth metal species pro,ides new information about some of the processes that affect electrospray ion yield. Selected metal ions and organic ligands were combined in 50:50 water-acetonitrile buffered with acetic acid or ammonium acetate and analyzed by flow injection ESI-MS using mild electrospray conditions. Species formed by alkali metal ions with thiol and oxygen-donating ligands were detected in acidic and neutral pH solutions. Electrochemical oxidation of N,N-diethyldithiocarbamate and glutathione during electrospray was indicated by detection of the corresponding disulfides as protonated or alkali metal species, The extent of ligand oxidation depended on solution pH and the dissociation constant of the thiol group, Tandem mass spectrometric experiments suggested that radical cations such as [NaL](+.) (where L = N,N -diethyldithiocarbamate) can be generated by in-source fragmentation of disulfide species. Greater complexation of alkali metals at neutral pH tvas indicated by a corresponding decrease in the relative abundance of the free metal ion, The number of alkali metal ions bound by glutathione and phthalic acid also increased with increasing pH, in accordance with thermodynamic equilibrium theory. Alkaline earth metal species were detected only in acidic solutions, the absence of 8-hydroxyquinoline complexes being attributed to their relative instability and subsequent dissociation during electrospray, Hence, accurate speciation by ESI-MS depends on experimental conditions and the intrinsic properties of each analyte, Copyright (C) 2000 John Wiley \&; Sons, Ltd.},
	keywords = {cell, COMPLEXES, electrochemical oxidation, ELECTROPHORESIS, electrospray ionization, ION-TRAP, MASS-SPECTROMETRY, metal speciation, OLIGONUCLEOTIDES, PEPTIDES, pH effects, PROTEINS, STOICHIOMETRY, thiol ligands, WATER},
	isbn = {1076-5174},
	url = {<Go to ISI>://000088934400006},
	author = {Ross, A. R. S. and Ikonomou, M. G. and Orians, K. J.}
}
@article {4394,
	title = {Determination of dissolved metal species by electrospray ionization mass spectrometry},
	journal = {Analytical Chemistry},
	volume = {70},
	number = {11},
	year = {1998},
	note = {ISI Document Delivery No.: ZR483Times Cited: 49Cited Reference Count: 50},
	month = {Jun},
	pages = {2225-2235},
	type = {Article},
	abstract = {The distribution of metal species in solution was determined using now injection electrospray ionization mass spectrometry. Complexes formed by selected metal ions with added organic ligands in 50:50 water/acetonitrile and 50:50 water/methanol under acidic, neutral, and basic conditions were detected using electrospray ionization conditions optimized to best represent solution-phase interactions. Metal species containing acetate, nitrate, and solvent molecules predominated in acidic solution but became less abundant at higher pH. Interactions between metal ions and added organic ligands became more selective with increasing pH, showing the expected preference of hard and soft ligands for metal ions:of the corresponding type. Species distributions also tended toward larger complexes as pH increased. Overall ion yield was greater for aqueous acetonitrile than for aqueous methanol solutions; however, reduction of copper(II) in aqueous acetonitrile resulted in the detection of copper(I) complexes for certain ligands. Experimental results for copper(II) and 8-hydroxyquinoline in 50:50 water/methanol showed good agreement with aqueous speciation predicted using the thermodynamic equilibrium model MINEQL. Detection of neutral complexes was achieved by protonation, deprotonation, or electrochemical oxidation during electrospray.},
	keywords = {COMPLEXES, copper, GAS-PHASE, LIGANDS, PHASE ION CHEMISTRY, PROTEINS, SOLVENT, SPECIATION, STOICHIOMETRY},
	isbn = {0003-2700},
	url = {<Go to ISI>://000073981600011},
	author = {Ross, A. R. S. and Ikonomou, M. G. and Thompson, J. A. J. and Orians, K. J.}
}
