Electrospray ionization—mass spectroscopy ESI-MS

The majority of reports have used electrospray ionization mass spectroscopy (ESI-MS) as an analytical detection method because of its sensitivity and the soft namre of its ionization procedure, which generally only leads to the detection of the molecular ions of the positive library members. Many separation techniques have been coupled to ESI-MS, including affinity chromatography (49), size exclusion chromatography (50, 51), gel filtration (52), affinity capillary electrophoresis (53-58), capillary isoelectric focusing (59), immunoaffinity ultrafiltration (60), and immunoaffinity extraction (61). ESI-MS has also been used alone (62) to screen a small carbohydrate library. Other examples reported alternative analytical techniques such as MALDI MS, either alone (63, 64) or in conjunction with size exclusion methods (65), or HPLC coupled with immunoaffinity deletion (66). 

Many catalyst complexes that are suitable for operation and immobilization in ionic liquids are ionic themselves with the charge either located at the metal center or in the ligand sphere. Thus, these complexes are accessible to electrospray ionization mass spectroscopy (ESI-MS). However, it is not a trivial task to investigate an ionic catalyst complex next to the vast excess of ionic liquid ions. Dyson s group reported a combination of ESI-MS with quadropole ion trap methods that enabled the detection of, e.g. several cationic Rh-complexes in the ionic liquid [BMIM][PF6] [62]. They could demonstrate that the detection limit of their methodology (catalyst concentrations down to 1 x 10 mol 1 were analyzed) is so low that even complexes in the typically very low concentration of a catalytic experiment could be easily characterized, even in the presence of a large excess of ionic liquid ions. 

Matsuda et al. studied the solvation state of lithium ions in various EC-based solutions by electrospray ionization-mass spectroscopy (ESI-MS). They reported that two species, [Li(EC)J and [Li(EC)3], in which lithium ions... 

Over the past decades several techniques have been used to obtain direct experimental information on the speciation of peroxo metal complexes heteronuclear NMR, IR and Raman spectroscopy, potentiometry and electrospray ionization mass spectrometry (ESI-MS). Often, more than one technique was used at the same time for acquiring complementary evidence. A significant, although nonexhaustive, list of examples related to several metals is given in Table 2. They include cases with hydrogen peroxide or alkyl... 

Infrared spectroscopy has been rarely used for PolyP characterization (Datema et al, 1977). Electrospray ionization mass spectrometry (ESI-MS) has been applied to the characterization of phosphates (P , PP , PolyP3, PolyPs and tricyclophosphate). The high selectivity of ESI-MS allowed the detection of these compounds without any pre-separation by ion chromatography or capillary electrophoresis. The limits of detection for ESI-MS were estimated to be in the range from approximately 1 to 10 ng ml-1 (Choi et al, 2000). 

Luminescence measurements can also be carried out by using a conventional stopped-flow apparatus. In additional, stopped-flow techniques are used in conjunction with NMR see Nuclear Magnetic Resonance (NMR) Spectroscopy of Inorganic/Organometallic Molecules), MS, and electrospray ionization mass spectrometry (ESI-MS). 

It is noteworthy here that electrospray ionization mass spectrometry (ESI MS) is suitable for this case. To study reaction product structure, the preparative-scale photolysis is ordinary used. However, in this case the azide concentration in the solution is several orders of magnitude higher than that in the kinetic studies, and the composition of the products of the aromatic azide photolysis can change significantly with the change of the concentration [78]. ESI MS can analyze reaction mixtures at the reagents concentration of ca 10 M that enables direct comparison with the data of kinetic absorption spectroscopy. 

Similar manganese porphyrin dimers linked by different spacer molecules had catalase activity [196]. The activity was highest when the Mn-Mn separation was ca 4 A, in agreement with the Mn-Mn separation in the hypothetical Mn -O-O-Mn complex [196]. The high-valent Mn porphyrin dimer has been prepared by the oxidation of the Mn dimer with wCPBA. The Mn dimer thus formed was stable for hours at temperatures ranging from —78 to -20 °C and it was detected by ESI MS (electrospray ionization mass spectroscopy) [197]. Cyclooctene was oxidized by mCPBA (1.1 equivalent for each Mn ion) with the Mn dimer to... 

---