Analysis of tomato glycoalkaloids by liquid chromatography coupled with electrospray ionization tandem mass spectrometry

Steroidal glycoalkaloids (SGAs) extracted from tomato leaves and berries (Lycopersicon esculentum Mill.) were separated and identified using optimized reversed-phase liquid chromatography with electrospray ionization (ESI) and ion trap mass spectrometry (ITMS). The ESI source polarity and chromatographic conditions were evaluated. The ESI spectra contain valuable information, which includes the mass of SGAs, the mass of the aglycones, and several characteristic fragment ions. Cleavage at the interglycosidic bonds proximal to the aglycones is the most prominent process in the ESI process. A protonated molecule, [M+H]+, accompanied by a mixed adduct ion, [M+H+Na]2+, was observed for alpha-tomatine (i.e., m/z 1034.7 and 528.9) and dehydrotomatine (i.e., m/z 1032.6 and 527.9) in positive ion mode spectra. The structures of these tomato glycoalkaloids were confirmed using tandem mass spectrometry. The identification of a new alpha-tomatine isomer glycoalkaloid, named filotomatine (MW 1033), which shares a common tetrasaccharide structure (i.e., lycotretraose) with alpha-tomatine and dehydrotomatine, and soladulcidine as an aglycone, is described for the first time. It occurs in significant amounts in the extracts of wild tomato foliage. Multistage mass spectrometry both of the protonated molecules and of the doubly charged ions was used for detailed structural elucidation of SGAs. Key fragmentations and regularities in fragmentation pathways are described and the fragmentation mechanisms involved are proposed.     

Evaluation of the sampling procedure adopted by the EU pesticide residue control programme to assess consumer exposure to high acute toxicity pesticides – methamidophos in sweet peppers

Food chemical control, particularly control involving the analysis of pesticide residues in fruits and vegetables, is routinely performed on composite samples. This sample design is adequate for the control of the majority of pesticides which have only long-term effects. However, from the viewpoint of consumer risk assessment, this sample design is inadequate for pesticides with relevant acute toxicity, when their residues occur in large food items the consumption of which may represent an important fraction of a single meal or an important fraction of the consumption in 24 h. This work presents the results of the Portuguese official pesticide residue control authority concerning the variability of methamidophos concentration in sweet pepper units, collected from the market, in the framework of the EU 1999 co-ordinated programme for the official control of pesticides in products of vegetable origin. The results were expressed with uncertainty and the conclusion was that the observed dispersion cannot be allocated to the method precision. The studied samples presented a variability factor (ratio between the maximum and the mean concentration of the units) ranging from 1.8 to 3.5 supporting the need to consider a variability factor representing the potential unit-to-unit variation in residues concentration for the purpose of consumer risk assessment. Received: 8 December 2001 Accepted: 25 February 2001     

Composition,antibacterial, antioxidant and antiproliferative activities of essential oils from three Origanum species growing wild in Lebanon and Greece

The essential oils from Origanum dictamnus, Origanum libanoticum and Origanum microphyllum were analysed by GC-MS, finding carvacrol, p-cymene, linalool, γ-terpinene and terpinen-4-ol as major components. The antioxidant activity by the DPPH and FRAP tests and the antiproliferative activity against two human cancer cell lines, LoVo and HepG2, were investigated, showing that the essential oil of O. dictamnus was statistically the most inhibitory on both the cell lines, while all the oils exerted a weak antioxidant activity. Furthermore, the samples were tested against 10 Gram-negative and Gram-positive bacteria; all the oils were active on Gram-positive bacteria but O. dictamnus essential oil was the most effective (MIC = 25–50 μg/mL), showing also a good activity against the Gram-negative Escherichia coli (MIC = 50 μg/mL). Data suggest that these essential oils and particularly O. dictamnus oil could be used as valuable new flavours with functional properties for food or nutraceutical products.     

Evaluation of mobile phase, ion pairing, and temperature influence on an HILIC-MS/MS method for L-arginine and its dimethylated derivatives detection

Asymmetric N(G),-N(G)-dimethylarginine (ADMA) increases in diseases such as renal failure, diabetes mellitus, and hypercholesterolemia. The feasibility and utility of a hydrophilic interaction chromatography (HILIC) method for the separation of free L-arginine (Arg), ADMA, and symmetric N(G),-N(G')-dimethylarginine (SDMA) on a typical silica column were explored and the impact of some experimental parameters on the chromatographic behavior of these analytes was investigated. The effect of water and TFA content in mobile phase and of column temperature was investigated during the development of a fast and simple HILIC-MS/MS method that might be suitable for the quantification of free Arg, ADMA, and SDMA in plasma for routine analysis. Our results show that a good compromise between efficiency and peak shape with acceptable retention and total chromatographic run time is achieved using an ACN/water (90:10) mobile phase with TFA% as additive ranging from 0.015 to 0.025% and column temperature ranging from 25 to 30 degrees C.     

Assessment of the determination of water-soluble ionic composition of atmospheric aerosols from the analysis of crossed halves of filters

The water-soluble ionic composition of atmospheric aerosols is a key parameter for estimating its anthropogenic or natural origin. This evaluation depends on the reliability of the performed measurements. The differential approach for the evaluation of the measurement uncertainty was used for estimating, separately, the uncertainty associated with the extraction step, by difference from the observed intermediate precision and the combination of all the other uncertainty components affecting the estimated intermediate precision. The intermediate precision was estimated from the difference of results of the analysis, in different days, of several pairs of filters resulting from cross-changing of their halves. The precision associated with the symmetry of filters division, affecting the homogeneity of studied combined pairs of filters, was subtracted from the observed dispersion of results. The resulting detailed model of measurement performance allowed defining strategies for cost of analysis or magnitude of measurement uncertainty reduction. Measurements are fit for the analysis of urban aerosols since the expanded relative measurement uncertainty is smaller than a target value of 30 %.     

Weighted calibration with reduced number of signals by weighing factor modelling: Application to the identification of explosives by ion chromatography

The linear weighted regression model (LW) can be used to calibrate analytical instrumentation in a range of quantities (e.g. concentration or mass) wider than possible by the linear unweighted regression model, LuW (i.e. the least squares regression model), since this model can be applied when signals are not equally precise through the calibration range. If precision of signals varies within the calibration range, the regression line should be defined taking into account that more precise signals are more reliable and should count more to define regression parameters. Nevertheless, the LW requires the determination of the variation of signals precision through the calibration range. Typically, this information is collected experimentally for each calibration, requiring a large number of replicate collection of signals of calibrators. This work proposes reducing the number of signals needed to perform LW calibrations by developing models of weighing factors robust to daily variations of instrument sensibility. These models were applied to the determination of the ionic composition of the water soluble fraction of explosives. The adequacy of the developed models was tested through the analysis of control standards, certified reference materials and the ion balance of anions and cations in aqueous extracts of explosives, considering the measurement uncertainty estimated by detailed metrological models. The high success rate of the comparisons between estimated and known quantity values of reference solutions, considering results uncertainty, proves the validity of developed metrological models. The relative expanded measurement uncertainty of single determinations ranged from 1.93% to 35.7% for calibrations performed along 4 months.     

Critical assessment of three high performance liquid chromatography analytical methods for food carotenoid quantification

Three sets of extraction/saponification/HPLC conditions for food carotenoid quantification were technically and economically compared. Samples were analysed for carotenoids α-carotene, β-carotene, β-cryptoxanthin, lutein, lycopene, and zeaxanthin. All methods demonstrated good performance in the analysis of a composite food standard reference material for the analytes they are applicable to. Methods using two serial connected C₁₈ columns and a mobile phase based on acetonitrile, achieved a better carotenoid separation than the method using a mobile phase based on methanol and one C₁₈-column. Carotenoids from leafy green vegetable matrices appeared to be better extracted with a mixture of methanol and tetrahydrofuran than with tetrahydrofuran alone. Costs of carotenoid determination in foods were lower for the method with mobile phase based on methanol. However for some food matrices and in the case of E–Z isomer separations, this was not technically satisfactory. Food extraction with methanol and tetrahydrofuran with direct evaporation of these solvents, and saponification (when needed) using pyrogallol as antioxidant, combined with a HPLC system using a slight gradient mobile phase based on acetonitrile and a stationary phase composed by two serial connected C₁₈ columns was the most technically and economically favourable method.     

Multivariate analysis of nutritional information of foodstuff of plant origin for the selection of representative matrices for the analysis of pesticide residues

Testing safety of foodstuffs of plant origin involves the analysis of hundreds of pesticide residues. This control is only cost-effective through the use of methods validated for the analysis of many thousands of analyte/matrix combinations. Several documents propose representative matrices of groups of matrices from which the validity of the analytical method can be extrapolated to the represented matrices after summarised experimental check of within group method performance homogeneity. Those groups are based on an evolved expert consensus based on the empirical knowledge on the current analytical procedures; they are not exhaustive, they are not objectively defined and they propose a large list of representative matrices which makes their application difficult. This work proposes grouping 240 matrices, based on the nutritional composition pattern equivalence of the analytical portion right after hydration and before solvent extraction, aiming at defining groups that observe method performance homogeneity. This grouping was based on the combined outcome of three multivariate tools, namely: Principal Component Analysis, Hierarchical Cluster Analysis and K-Mean Cluster Analysis. These tools allowed the selection of eight groups for which representative matrices with average characteristics and objective criteria to test inclusion of new matrices were established. The proposed matrices groups are homogeneous to nutritional data not considered in their definition but correlated with the studied multivariate nutritional pattern. The developed grouping that must be checked with experimental test before use was tested against small deviations in food composition and for the integration of new matrices.     

Solvent effects on solution enthalpies of adamantyl derivatives

Solution enthalpies of 1-bromoadamantane, 1-adamantanol, and 2-adamantanone in a large set of protic and aprotic solvents are reported at 298.15 K. Solvent effects on the solution processes of these solutes are analyzed in terms of a modified TAKA equation, involving δ_cav h ^s as the cavity term. The nature and magnitude of the major interactions which influence these processes are assessed and discussed in terms of the solutes’ characteristics. New insights on the solution processes under scrutiny are presented.     

Indigenous silver jewellery of Northern Patagonia (19th century): a first analytical approach to composite objects

A set of Mapuche–Tehuelche composite silver jewellery items, produced in the 19th century and collected in a same indigenous camp in 1896, belonging to the La Vaulx's collection held at the Musée du Quai Branly (Paris), was observed by optical microscopy, scanning electron microscope and X‐radiography, and analysed by PIXE with a 3‐MeV external proton micro‐beam. We aimed to check if these jewels used daily by women evolved during their owners' lifetime, through the analysis of the alloys employed in their making and the silversmith's technologies. Results showed that the jewels were manufactured by different silversmiths, yet using the same workshop traditions. Silver‐based alloys of different compositions were identified. The presence of high Zn and Ni contents in many parts of certain items denotes the use of nickel silver alloys not by direct use of coins and native metals as expected but by remelting and reuse of coins and objects. Copyright © 2012 John Wiley & Sons, Ltd.