Benzene and toluene have been proposed previously as dopants in atmospheric pressure photoionization (APPI) experiments on compounds exhibiting ionization energies higher than the energy of photons used for irradiation. Their low ionization energies lead to their easy photoionization and the ions so formed lead to the ionization of analytes through charge exchange. However, some measurements have shown that some protonation reactions also take place, and a series of experiments was undertaken to investigate this unexpected behavior. It was shown that, when benzene is irradiated in the APPI source, the odd-electron molecular ions of phenol, diphenyl ether and phenoxyphenol are produced in high yield, together with protonated diphenyl ether and protonated phenoxyphenol. These results have been confirmed by deuterium labelling and MS(n) experiments. A possible mechanism is proposed, based on a radical attack by benzene molecular ions on oxygen molecules present inside the APPI source, analogous to that proposed in the literature for phenyl radicals. Similar results have been obtained with toluene, proving that APPI is able to activate a series of reactions leading to highly reactive species which are highly effective in promoting ionization of molecules with ionization energies higher than the photon energy.

A new ionization method named surface-activated chemical ionization (SACI) has been realized. In this invention a commercially available atmospheric pressure chemical ionization (APCI) chamber, employed without any corona discharge (no-discharge APCI), has been modified with the insertion of a gold surface, leading to a significant improvement in the ionization efficiency. The ionization of the sample takes place by both gas-phase and surface-activated processes. This new ionization source is able to generate ions with high molecular mass and low charge states, leading to improved sensitivity and reduced noise. The new device has been tested in the analysis of some peptides. A comparison between the performance with and without the presence of the surface, and the optimization of the operating conditions (nebulizing gas flow, sample solution flow, pH of solution, and surface area), are reported and discussed.

In previous studies, the production of ions in an APCI source without any corona discharge was observed, and the intensity of the ion signals showed significant increases on placing a metallic surface at 45 degrees inside an orthogonal ion source. This method was named surface-activated chemical ionization (SACI). The present study was performed to investigate the mechanisms of ion production with or without the presence of the metallic surface, by varying instrumental parameters and the geometrical configuration. Approximate calculations show that, in the absence of corona discharge and of any additional surfaces, ions cannot be produced by collisional phenomena, because of their low kinetic energy, in the 10(-2) to 10(-3) eV range. Two alternative possibilities have been considered: the first takes into account that ions may originate by collision of neutral clusters of polar solvent molecules with the APCI source surfaces through clusterelectric effect. The second takes into account that the water dissociation constant k(w) is temperature dependent, passing from 10(-14.1669) at 20 degrees C to 10(-12.4318) at 90 degrees C. It means that the [H(+)] varies from 8.3 x 10(-8) to 6.1 x 10(-7) M going from 20 to 90 degrees C. Hence, at the high temperatures experimented in the APCI vaporizer, H(+) becomes available in solution in molar quantities analogous to those of analyte, and the protonation of the analyte itself can consequently occur. The activation of further ionization processes in the presence of the metallic surface can be reasonably attributed to interactions between gas-phase analyte molecules and solvent molecules adsorbed on the surface. Experiments performed with a thin layer of deuterated glycerol on the surface led to unequivocal results, i.e. the production of [M + D](+) ions of the analyte.

The standardization and quality control of plant extracts is an important topic, in particular, when such extracts are used for medicinal purposes. Consequently, the development of fast and effective analytical methods for metabolomic fingerprinting of plant extracts is of high interest. In this investigation, electrospray mass spectrometry (ESI-MS) and (1)H NMR techniques were employed with further statistical analyses of the acquired data. The results showed that negative ion mode ESI-MS is particularly effective for characterization of plant extracts. Different samples of the same species appear well-clustered and separated from the other species. To verify the effectiveness of the method, two other batches of extracts from a species, in which the principal components were already identified (Cynara scolymus), were analyzed, and the components that were verified by the principal component analysis (PCA) were found to be within the region identified as characteristic of Cynara Scolymus extracts. The data from extracts of the other species were well separated from those pertaining to the species previously characterized. Only the case of a species that was strictly correlated from a botanical point of view, with extracts that were previously analyzed, showed overlapping.

Advanced glycation end products (AGEs) accumulate in serum and tissues of patients with chronic renal failure, even in the absence of diabetes, and a different clearance of these species has been observed by hemodialysis and peritoneal dialysis (CAPD). Furthermore, it has been shown that not only AGE but also 1,2-dicarbonyl compounds are formed during heat sterilization of glucose-based peritoneal dialysis fluids. Therefore, we investigated the level of some AGEs (pentosidine and free pentosidine) and dicarbonyl compounds (glyoxal and methylglyoxal) in end-stage renal disease patients subjected to peritoneal dialysis. Samples (20 from healthy subjects, 16 from uremic patients before and after 12 h of peritoneal dialysis) were analyzed, and the plasma and dialysate levels of glyoxal, methylglyoxal, pentosidine, and free pentosidine were determined. In plasma of uremic patients, mean values of pentosidine showed a small decrease after dialysis and were always higher than those of healthy control subjects. An analogous trend was observed for free pentosidine. In the case of peritoneal dialysate, no pentosidine and free pentosidine were found at time zero, whereas both compounds were detected after 12 h of dialysis. Glyoxal and methylglyoxal mean levels showed a decrease in plasma after dialysis even if their values were always higher than those of healthy control subjects. Surprisingly, an analogous trend was observed also in dialysate. These results might indicate that glyoxal and methylglyoxal already present in the dialysis fluid react with the peritoneal matrix proteins, accounting for the gradual loss of peritoneal membrane function that is often observed in patients subjected to CAPD for a long time.

Atmospheric pressure photoionization (APPI) 1 is a new technique, highly interesting for its features, mainly selectivity and sensitivity, somehow overlapping the performances of the well-established electrospray (ESI) 2 and atmospheric pressure chemical ionization (APCI) 3 techniques. The basic principle of this method is, at first sight, very simple: a molecule M can be ionized by interaction with a photon beam only if its ionization energy (IE) is lower, or equal to, the photon energy h :Hence the irradiation by a Kr discharge lamp (exhibiting a dish-topped emission band between 8 and 10 eV 4 ) of a sample solution vaporized at atmospheric pressure by a heated insertion line would lead to the formation of odd-electron molecular ions (M Cž ) of substances exhibiting IE values lower than 10 eV, without practically any interference from the solvents usually employed in liquid chromatography (LC) conditions. In fact, for example, H 2 O, CH 3 CN, CH 3 OH all exhibit IE values higher than 10 eV. 5 However, this view is not always correct. It has been shown 6,8 that photon irradiation can activate processes different from simple ionization: in some cases, the electronically excited molecule can isomerize, leading to species with ionization energies lower than that of the original molecule. This is the case of acetonitrile (IE D 12.2 eV), 4 which, under 10 eV photon irradiation, isomerizes to ketene imine (IE D 9.5 eV), which can be photoionized, becoming an active intermediate in ionization processes of analyte molecules in CH 3 CN solutions: 6,7 CH 3 CN C h ! [CH 3 CN]

Keywords: Technetium / Rhenium / Radiopharmaceuticals / NMR spectroscopy / P ligands (1) displays a distorted, square-pyramidal geometry with the dithiocarbamate sulfur and the diphosphane phosphorus atoms spanning the four coordination positions on the equatorial plane. If the additional interactions between the nitrido nitrogen and the weakly bonded trans N-diphosphane heteroatom, the molecular geometry can be viewed as pseudooctahedral. The structure in solution, as established by multinuclear NMR spectroscopy and ESI spectrometry, is mono-

Electrospray ionization mass spectrometry (ESI-MS) has been applied to the study of solution equilibria between Al(III) and the two ligands 4-hydroxy-3-pyridinecarboxylic acid (4H3P) and 3-hydroxy-4-pyridinecarboxylic acid (3H4P). The results compare well with the speciation data obtained from potentiometric, UV-visible spectroscopy, and NMR measurements. This agreement suggests the applicability of ES-MS to the study of more complicated aluminium-ligand systems.