Determination of rare earth elements in tomato plants by inductively coupled plasma mass spectrometry techniques

In recent years identification of the geographical origin of food has grown more important as consumers have become interested in knowing the provenance of the food that they purchase and eat. Certification schemes and labels have thus been developed to protect consumers and genuine producers from the improper use of popular brand names or renowned geographical origins. As the tomato is one of the major components of what is considered to be the healthy Mediterranean diet, it is important to be able to determine the geographical origin of tomatoes and tomato‐based products such as tomato sauce. The aim of this work is to develop an analytical method to determine rare earth elements (RRE) for the control of the geographic origin of tomatoes. The content of REE in tomato plant samples collected from an agricultural area in Piacenza, Italy, was determined, using four different digestion procedures with and without HF. Microwave dissolution with HNO₃ + H₂O₂ proved to be the most suitable digestion procedure. Inductively coupled plasma quadrupole mass spectrometry (ICPQMS) and inductively coupled plasma sector field plasma mass spectrometry (ICPSFMS) instruments, both coupled with a desolvation system, were used to determine the REE in tomato plants in two different laboratories. A matched calibration curve method was used for the quantification of the analytes. The detection limits (MDLs) of the method ranged from 0.03 ng g^?1 for Ho, Tm, and Lu to 2 ng g^?1 for La and Ce. The precision, in terms of relative standard deviation on six replicates, was good, with values ranging, on average, from 6.0% for LREE (light rare earth elements) to 16.5% for HREE (heavy rare earth elements). These detection limits allowed the determination of the very low concentrations of REE present in tomato berries. For the concentrations of REE in tomato plants, the following trend was observed: roots > leaves > stems > berries. Copyright © 2009 John Wiley & Sons, Ltd.     

Organocatalytic Stereoselective α‐Alkylation of Aldehydes with Stable Carbocations

The organocatalytic stereoselective alkylation of aldehydes is carried out with the four stable carbocations 1 , 2 , 3 , 4 in the presence of a catalytic amount (20 mol%) of MacMillan imidazolidinones 5 , 6 . In all reactions, lutidine was used as a base. The alkylation reactions are investigated at different temperatures with linear and branched aldehydes. In the case of carbocation tropylium fluoroborate, an interesting reversal of alkylation product configuration was observed, which is driven by entropic effects in the reaction. The absolute configuration of the products obtained is determined by chemical correlation and found to be in general agreement with the model proposed by MacMillan to justify the stereoselectivity obtained in the reactions promoted by catalysts of type 5 , 6 .     

A hyphenated microLC-Q-TOF-MS platform for exosomal lipidomics investigations: application to RCC urinary exosomes

Urinary exosomes are released from every renal epithelial cell type facing the urinary space and therefore, they may carry molecular markers of renal dysfunction and structural injury. Here, we present a hyphenated microLC-Q-TOF-MS platform for lipidomics studies applied to investigate the urinary exosome lipid repertoire. Lipids were separated by reversed-phase chromatography using a linear gradient of formic acid 0.2% and tetrahydrofuran, in 40 min of analysis. Features (m/z with associated own retention time) were extracted by MarkerLynx(TM) (Waters) and processed, demonstrating good analytical performance in terms of repeatability and mass accuracy of the microLC Q-TOF MS platform. In particular, a stable retention time (RSD less than 4%) and relative intensity (RSD from 2.9% to 11%) were observed. Moreover, the method takes advantages by the use of a lock spray interface (Waters) that allows readjusting the m/z data after acquisition, obtaining inaccuracy below 6 ppm in measuring the m/z value of the reference compound during chromatographic run. The method was employed in a preliminary application to perform comparative analysis from healthy control subjects and renal cell carcinoma (RCC) patients, in order to possibly highlight differences in lipid composition to be exploited as potential tumor biomarker. Differential lipid composition in RCC urinary exosomes was achieved and tentatively identified by accurate mass, providing a preliminary indication of a relationship between lipid composition of urinary exosomes and RCC disease. Among the total features significantly different in RCC exosomes, the ion at m/z 502.3 was taken as an example for molecular confirmation by MS/MS fragmentation analysis.     

An experimental study on the effect of substituents on aromatic-aromatic interactions in dithia[3,3]-metaparacyclophanes

Simple model systems based on the 2,11-dithia[3,3]-metaparacyclophane skeleton were synthesized to study the effects of substituents on the intramolecular aromatic-aromatic interactions between benzene rings. X-ray crystallography established that, in their more stable conformations, these metaparacyclophanes featured partially overlapping aromatic rings (interplanar distances of about 3.5??), with the planes of the aromatic systems arranged in a slightly tilted disposition (interplanar angles in the range 5-19°). Calculations showed that these derivatives underwent topomerization by flipping of the meta-substituted ring over the para-substituted one, a process in which the two rings adopted a continuum of edge-to-face dispositions, including an orthogonal one, which were less stable than the starting face-to-face arrangement. The energy barriers to the isomerization process were experimentally determined by variable-temperature NMR spectroscopy, by using an internal temperature standard to assess even minor differences in energy (relative experimental error: (±0.1?kJ?mol(-1)). The variation in the barriers as a function of the different substituents on the interacting ring was small and apparently unrelated to the effect of the substituents on the polarity of the π-systems. An explanation based on the charge-penetration effect seemed more-suitable to rationalize the observed trends in the barriers.     

Speciation analysis of selenoproteins in human serum by microbore affinity-HPLC hyphenated to ICP-Sector field-MS using a high efficiency sample introduction system

Silica gel and nanometer SiO₂ modified with 4-(2-aminoethylamino)-N-(2-(2-aminoethyl amino)ethyl)butanamide (SG-AAEB and nanometer SiO₂-AAEB), which were prepared based on chemical immobilization, were used as sorbents for the solid phase extraction of Cu(II), Fe(III), and Pb(II) prior to their determination by inductively coupled plasma optical emission spectrometry. Adsorption efficiencies of the two sorbents towards metal ions were investigated by batch and column procedures. For both sorbents the preconcentration conditions of analytes including effects of pH, shaking time, sample flow rate and adsorption capacity, were investigated and compared. The differences of silica gel and nanometer SiO₂ in sizes and surface structures resulted in distinct chemical activity and selectivity toward metals. At pH 4, the adsorption capacity of SG-AAEB was found to be 12.2, 14.5 and 9.8 mg g^?1 for Cu(II), Fe(III), and Pb(II), respectively. In comparison, nanometer SiO₂-AAEB showed a high selectivity toward Pb(II) and has a much larger adsorption capacity (22.3 mg g^?1). Furthermore, the application of SG-AAEB and nanometer SiO₂-AAEB for simultaneous preconcentration of trace Cu(II), Fe(III), and Pb(II) from natural samples was performed with satisfactory results.     

The barrier to carbon-phosphorus bond rotation in tribenzoylphosphine. An experimental reinvestigation

An examination of the ¹³C NMR spectrum of tribenzoylphosphine over the temperature range ?75 to +70°C fails to disclose any evidence for hindered rotation about the PC bonds, contrary to a previous claim.