A review of recent trends in electrospray ionisation–mass spectrometry for the analysis of metal–organic ligand complexes (original) (raw)
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Rapid …, 2001
The recently developed technique of energy-dependent electrospray ionisation mass spectrometry (EDESI-MS) has been implemented on a triple quadrupole mass spectrometer such that fragmentation occurs in the collision cell rather than at the skimmer cone. This modification enables a superior two-dimensional map of the collision voltage versus mass-to-charge ratio to be generated, providing unambiguous peak assignments. This latest enhancement to the technique is referred to as energy-dependent electrospray ionisation tandem mass spectrometry (EDESI-MS/MS). In the present work the technique has been applied to investigate the sequential removal of ligands from the inorganic mixed-metal anionic cluster compound [Ru 5 CoC(CO) 16 ] À , which serves to illustrate the advantages of this approach.
Rapid Communications in Mass Spectrometry, 2012
Metals play a very important role in many scientific and environmental fields, and thus their detection and analysis is of great necessity. A simple and very sensitive method has been developed herein for the detection of metals in positive ion mode ESI-MS. Metal ions are positively charged, and as such they can potentially be detected in positive ion mode ESI-MS; however, their small mass-to-charge (m/z) ratio makes them fall in the low-mass region of the mass spectrum, which has the largest background noise. Therefore, their detection can become extremely difficult. A better and well-known way to detect metals by ESI-MS is by chelating them with complexation agents. In this study eleven different metals, Fe(II), Fe(III), Mg(II), Cu(II), Ru(III), Co(II), Ca(II), Ni(II), Mn(II), Sn(II), and Ag(I), were paired with two commercially available chelating agents: ethylenediaminetetraacetic acid (EDTA) and ethylenediaminedisuccinic acid (EDDS). Since negative ion mode ESI-MS has many disadvantages compared to positive ion mode ESI-MS, it would be very beneficial if these negatively charged complex ions could be detected in the positive mode. Such a method is described in this paper and it is shown to achieve much lower sensitivities. Each of the negatively charged metal complexes is paired with six cationic ion-pairing reagents. The new positively charged ternary complexes are then analyzed by ESI-MS in the positive single ion monitoring (SIM) and single reaction monitoring (SRM) modes. The results clearly revealed that the presence of the cationic reagents significantly improved the sensitivity for these analytes, often by several orders of magnitude. This novel method developed herein for the detection of metals improved the limits of detection (LODs) significantly when compared to negative ion mode ESI-MS and shows great potential in future trace studies of these and many other species.
Journal of The American Society for Mass Spectrometry, 2012
The interaction between two Lewis "superacid" catalysts Zn(OTf) 2 and In(OTf) 3 and series of amide and phosphate ligands is quantitatively characterized by electrospray ionization mass spectrometry (ESI-MS). A specific feature of the ESI-MS spectra of the mixture of metal triflates and Lewis bases is the formation of ionic adducts resulting from the displacement of one triflate anion by two neutral ligands. A ligand competition model is developed, which describes the relative intensities of the ionic adducts as a function of relative ligand concentrations. The relative affinities deduced from the ligand competition method are combined in an affinity scale for the metal triflate.
Journal of Chromatography A, 1998
Metal speciation was carried out by on-line hyphenation of capillary electrophoresis (CE) with mass spectrometry (MS) via an electrospray ionization (ESI) interface. The commercially available interface was hardly able to produce stable electrospray conditions over an extended period of time, mainly caused by an insufficient positioning of the CE capillary inside the ESI stainless steel tip. A device was developed, which allowed an infinitely variable adjustment of the capillary. The optimum position for stable electrospray conditions was set to 0.4-0.7 mm outside the ESI tip. Off-line ESI-MS investigations of free metal ions [Cu(II)], metal ion-containing complexes [CuEDTA, (CH) SbCl ] and covalent 3 3 2 organometallic compounds (selenocystamine, selenomethionine) were carried out in order to assess the suitability of the technique for metal speciation. The usefulness of ESI-MS as a detection method largely depends on the stability of the analysed species. Inorganic species (i.e. metal ions) alter their composition when being electrosprayed. Parts of the weakly complexing ligands will be exchanged by solvent molecules, mainly originating from the sheath liquid. The destruction of ion-solvent clusters by heating, collision-induced decomposition or use of a sheath gas may lead to charge reduction of transition metal ions. Organometallic complexes with strongly complexing ligands remain intact, while those with weakly complexing ligands suffer from the same disadvantages as inorganic species. ESI-MS is best suited for the speciation of covalent organometallic compounds. The ionisation process does not alter their structure and they will mostly be detected as singly charged molecular ions. The application of CE-ESI-MS for selenium speciation to an existing method using an alkaline buffer system (Na CO-NaOH) gave unsatisfactory results. The non-volatile electrolyte affects the ESI process 2 3 dramatically. The final CE method used an acidic background electrolyte (2% acetic acid) for the separation of three organometallic selenium species [selenomethionine (SeM), selenocystamine (SeCM) and selenocystine (SeC)]. The Se species were sufficiently separated from each other and appeared at 6.49 min (SeCM), 19.47 min (SeM) and 20.60 min (SeC). Detection limits were calculated as 1-6 mg / l for the organic Se species.
Rapid Communications in Mass Spectrometry, 2011
Increases in the study of protein-metal complexes, as well as in metal displacement in protein-metal complexes under native conditions for optimum catalytic properties in drug research and catalyst design, demands a separation/detection technology that can accurately measure metal displacement and stoichiometry in protein-metal complexes. Both nuclear magnetic resonance (NMR) and X-ray diffraction techniques have been used for this purpose; however, these techniques lack sensitivity. Electrospray ionization mass spectrometry (ESI-MS) using direct infusion offers higher sensitivity than the former techniques and provides molecular distribution of various protein-metal complexes. However, since protein-metal complexes under native conditions usually are dissolved in salt solutions, their direct ESI-MS analysis requires off-line sample clean-up prior to MS analysis to avoid sample suppression during ESI. Moreover, direct infusion of the salty solution promotes nonspecific salt adduct formation by the protein-metal complexes under ESI-MS, which complicates the identification and stoichiometry measurements of the protein-metal complexes. Because of the high mass of protein-metal complexes and lack of sufficient resolution by most mass spectrometers to separate non-specific from specific metal-protein complexes, accurate protein-metal stoichiometry measurements require some form of sample clean up prior to ESI-MS analysis. In this study, we demonstrate that capillary electrophoresis/electrospray ionization in conjunction with a mediumresolution (10 000) mass spectrometer is an efficient and fast method for the measurement of the stoichiometry of the protein-metal complexes under physiological conditions (pH 7). The metal displacement of Co 2R to Cd 2R , two metal ions necessary for activation in the monomeric AHL lactonase produced by B. thuringiensis, has been used as a proof of concept.
Mass spectrometry in bioinorganic analytical chemistry
Mass Spectrometry Reviews, 2006
A considerable momentum has recently been gained by in vitro and in vivo studies of interactions of trace elements in biomolecules due to advances in inductively coupled plasma mass spectrometry (ICP MS) used as a detector in chromatography and capillary and planar electrophoresis. The multiisotopic (including non-metals such as S, P, or Se) detection capability, high sensitivity, tolerance to matrix, and large linearity range regardless of the chemical environment of an analyte make ICP MS a valuable complementary technique to electrospray MS and MALDI MS. This review covers different facets of the recent progress in metal speciation in biochemistry, including probing in vitro interactions between metals and biomolecules, detection, determination, and structural characterization of heteroatom-containing molecules in biological tissues, and protein monitoring and quantification via a heteroelement (S, Se, or P) signal. The application areas include environmental chemistry, plant and animal biochemistry, nutrition, and medicine. #
Journal of Mass Spectrometry, 2008
We describe an approach for the determination of binding constants for protein-ligand complexes with electrospray ionization mass spectrometry, based on the observation of unbound ligands competing for binding to a protein target. For the first time, dissociation constants lower than picomolar could be determined with good accuracy by electrospray ionization mass spectrometry. The presented methodology relies only on the determination of signal intensity ratios for free ligands in the low mass region. Therefore, all the advantages of measuring low masses with mass spectrometry, such as high resolution are preserved. By using a reference ligand with known binding affinity, the affinity of a second ligand can be determined. Since no noncovalently bound species are observed, assumptions about response factors are not necessary. The method is validated with ligands binding to avidin and applied to ligands binding to p38 mitogen-activated protein kinase.