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This study aimed to assess the microbiological profile of conventional and organic vegetables grown in Brazilian farms through the detection of Salmonellaand other Enterobacteriaceae. A total of 200 samples (100 conventional and 100 organic), including leafy greens, spices/herbs, and other unusual vegetables, were submitted to the enumeration of Enterobacteriaceae by plating on VRBG agar. Moreover, colonies of Enterobacteriaceae were randomly selected and submitted to identification by MALDI-TOF MS. Samples were also tested for Salmonella, using culture-based and PCR-based enrichment methods. The mean counts of Enterobacteriaceae in conventional and organic vegetables were 5.1 ± 1.5 and 5.4 ± 1.4 log CFU/g, respectively (P> 0.05). A total of 18 genera (including 38 species) of Enterobacteriaceae were identified, and the most frequent ones found in samples from both farming systems were Enterobacter(76%) and Pantoea(68%). Salmonellawas identified in 17 samples (8.5%): nine (4.5%) in conventional and eight (4.0%) in organic vegetables. These results indicate that the farming system had no impact on the Enterobacteriaceae populations and rates of Salmonellaand revealed unsatisfactory microbiological safety of some samples, mainly due to the presence of Salmonella. These findings highlight the need for control measures during vegetable production, regardless of the farming system, to reduce microbial contamination and the risks of foodborne illnesses.

Electron ionization (70 eV) mass spectra, double-stage (MS2) 10 eV collision-induced dissociation (CID) product-ion mass spectra of molecular ions and triple-stage (MS3) sequential product-ion mass spectra of major fragment ions are reported for the parent N-phenyl and the isomeric ortho-, meta- and para-N-chlorophenyl- and N-bromophenyl-2-aminobenzamidines. Dissociation is greatly influenced by an orthoeffect that favors the loss of orthoH atoms and particularly the loss of the orthohalogen substituents. Dissociation occurs via a two-step intramolecular aromatic substitution reaction and a distonic-ion intermediate inhibits scrambling of ring hydrogens thus favoring the loss of the orthosubstituents. The orthoisomers form an abundant and diagnostic [M – X]+fragment ion (X = Cl, Br) and are easily distinguished. Protonated 2-(1H-benzimidazol-2-yl)-phenylammonium ions are likely formed; they dissociate mainly by NH3loss upon CID and react readily with pyridine by proton transfer.

Trap and release membrane introduction mass spectrometry (T&R-MIMS) using a removable direct insertion membrane probe (DIMP) is employed to determine the total homocysteine concentration (tHcy) directly from human plasma after derivatization with ethyl chloroformate. The method uses no chromatographic separation, is linear, reproducible, and displays limit of quantitation (2 µM) sufficiently below the threshold concentration of tHcy in plasma. It also combines chemical, membrane, and mass spectrometric discrimination, and can be used to determine selected amino acids in human plasma simultaneously. After derivatization with ethyl chloroformate, many amino acids in aqueous solution are observed to be efficiently detected; hence T&R-MIMS is promising as a simple and sensitive technique for simultaneous quantitation of selected amino acids in plasma and urine, and in other aqueous matrices.

Primary carboxonium (H2C=O+-R) and carbosulfonium (H2C=S+-R) ions (R = CH3, C2H5, Ph) and the prototype five-membered cyclic carboxonium ion are found to react in the gas phase with cyclic acetals and ketals by transacetalization to form the respective O-alkyl-1,3-dioxolanium and S-alkyl-1,3-oxathiolanium ions. The reaction, which competes mainly with proton transfer and hydride abstraction, initiates by O-alkylation and proceeds by ring opening and recyclization via intramolecular displacement of the carbonyl compound previously protected in its ketal form. As indicated by product ion mass spectra, and confirmed by competitive reactions, carbosulfonium ions are, by transacetalization, much more reactive than carboxonium ions. For acyclic secondary and tertiary carboxonium ions bearing acidic a-hydrogens, little or no transacetalization occurs and proton transfer dominates. This structurally related reactivity distinguishes primary from both secondary and tertiary ions, as exemplified for the two structural isomers H2C=O+-C2H5and CH3C(H)=O+-CH3. The prototype five- and six-membered cyclic carboxonium ions react mainly by proton transfer and adduct formation, but the five-membered ring ion also reacts by transacetalization to a medium extent. Upon CID, the transacetalization products of the primary ions often dissociate by loss of formaldehyde, and a +44 u neutral gain/-30 u neutral loss MS3scan is shown to efficiently detect reactive carboxonium and carbosulfonium ions. Transacetalization with either carboxonium or carbosulfonium ions provides a route to 1,3-oxathiolanes and analogs alkylated selectively either at the sulfur or oxygen atom.

A novel gas-phase reaction of diacylium ions of the O&dbond;C&dbond;X⁺&dbond;C&dbond;O type (X = N, CH) is reported: double transacetalization with cyclic acetals or ketals. The reaction is exothermic and highly efficient, and forms members of a new class of highly charged-delocalized ions: cyclic ionic diketals. Pentaquadrupole double- and triple-stage mass spectrometric (MS² and MS³) experiments reveal the high double transacetalization reactivity of O&dbond;C&dbond;N⁺&dbond;C&dbond;O and O&dbond;C&dbond;CH⁺&dbond;C&dbond;O, whereas the synthesis of differently substituted cyclic ionic diketals is performed in MS³ experiments via sequential mono- and double transacetalization of O&dbond;C&dbond;N⁺&dbond;C&dbond;O and O&dbond;C&dbond;CH⁺&dbond;C&dbond;O with different acetals. With cyclic acetals, the acylium-thioacylium ion O&dbond;C&dbond;N⁺&dbond;C&dbond;S reacts promptly and selectively by mono-transacetalization at its acylium site, but the free thiacylium site of its cyclic ionic ketal is nearly unreactive by double transacetalization. Therefore, only the acylium site of O&dbond;C&dbond;N⁺&dbond;C&dbond;S can be efficiently protected by transacetalization. Low-energy MS³ collision-induced dissociation of the cyclic ionic diketals of O&dbond;C&dbond;N⁺&dbond;C&dbond;O and O&dbond;C&dbond;CH⁺&dbond;C&dbond;O sequentially frees each of the protected acylium site to form the mono-derivatized ion, and then the fully deprotected diacylium ion. Copyright © 2000 John Wiley & Sons, Ltd.

Gaseous 2‐pyridyl and 2‐pyrimidyl cationsreact promptly with 1,3‐dienes by annulation to produce a new pyrrole ring. ortho‐Hetarynium ions and 1,3‐dienes thus provide the two building blocks for the efficient gas‐phase synthesis of ionized indolizines and their derivatives (see scheme).

This paper presents the first membrane inlet mass spectrometry system capable of detecting large biomolecules, such as testosterone (M_r 288), testosterone acetate (M_r 330) and α-tocopherol (M_r 430, vitamin E). The result was obtained using a home-made chemical ionization ion source with a thermostated tubular silicone membrane mounted right in the centre of a methane CI plasma. The liquid sample was flushed through the inside of the membrane for a period of 20–25 min, where the analyte diffused into the membrane. Following this trapping period the analyte was released from the membrane into the mass spectrometer by the combined action of heat radiation from the filament and charge transfer from the chemical ionization plasma. As a result of this stimulated desorption a good desorption peak was obtained as the analyte vaporized out of the membrane. Retinol (M_r 286, vitamin A), cholecalciferol (M_r 384, vitamin D₃) and cholesterol (M_r 386) were also detected. However, these compounds (all containing a long hydrocarbon chain and being aliphatic alcohols) did not give a protonated molecule. They gave a series of cluster ions with the dominant located 20 mass units below the molecular ion. The detection limits of the new desorption chemical ionization MIMS technique were at low or sub-micromolar concentrations (high ppb levels) and the reproducibility was within 20%, when the area of the desorption peak was used for quantitation.

A new design for a trap and release membrane introduction mass spectrometry (T&R-MIMS) system using a removable direct insertion membrane probe (DIMP) for combined trace level analysis (low or sub ppb range) of volatile (VOC) and semi-volatile organic compounds (SVOCs) is reported. The system differs from the original T&R-MIMS system (M. Leth and F. R. Lauritsen, Rapid Commun. Mass Spectrom., 1995, 9, 591) as it uses a removable DIMP probe to place a capillary membrane loop inside the ion source block exactly between two parallel filaments. The more versatile DIMP-T&R-MIMS system can be operated, during the trapping step of T&R-MIMS analysis, in the standard MIMS mode for VOC detection; during the T&R-MIMS thermal desorption step needed for SVOC analysis, the system permits faster and more uniform heating of the membrane, thus SVOC sensitivity is improved and memory effects are minimized.

On-line Mass Spectrometry and MS2are applied to monitor and identify the by-products and total mineralization products of TiO2/UV photocatalytic degradation of four chlorinated volatile organic compounds (VOCs): trichloroethylene (TCE), tetrachloroethylene (TeCE), chloroform, and dichloromethane. Selected multiple ion mass spectrometry monitoring using characteristic 70 eV electron ionization ionic fragments monitors in real time the destruction of the starting VOC and the formation of by-products, i. e., the degrees of VOC mineralization, as a function of the flow and relative humidity of the carrier gas (synthetic air). Several by-products were detected: phosgene for TCE, TeCE, and chloroform; dichloroacetyl chloride for TCE; and trichloroacetyl chloride for TeCE. Cl2and CO2were also detected as final mineralization products of the four chlorinated VOCs. Structural characterization of by-products was accomplished via MS2collision-induced dissociation of molecular ions or characteristic ionic fragments.

Transacetalization‐like reactions with 2‐methyl‐1,3‐dioxolaneallow the 2‐pyridyl cation (1 a) to be distiguished from its 3‐ (1 b) and 4‐pyridyl (1 c) isomers. In addition, all three isomeric 2‐, 4‐, and 5‐pyrimidyl cations (2 a–c) display characteristic dissociation behavior. Thus the transacetalization‐like reactivity and/or the unique collision‐induced dissociation behavior can be applied generally to reveal the position of the charge site in the 2‐pyridyl and the three pyrimidyl heteroaromatic cations.

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