A sensitive confirmatory method for aflatoxins in maize based on liquid chromatography/electrospray ionization tandem mass spectrometry

A liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) method for measurement of aflatoxins B1, B2, G1, and G2 in maize is described. Aflatoxins (AFs) were extracted from 1 g samples by using tri-portions of acetonitrile/water (80:20, v/v) (10 + 7 + 7 mL), and 2/5 of the extract diluted to 500 mL by water was cleaned up with a 100 mg Carbograph-4 cartridge. After the addition of the internal standard AFM1, the final extract was analyzed by LC/ESI-MS/MS in positive ion mode using multiple reaction monitoring with a triple-quadrupole instrument. A C(18) column thermostatted at 45 degrees C with a mobile phase gradient of acetonitrile/water with 2 mmol/L ammonium formate was used. Although the matrix suppression effect was negligible, quantitation was achieved by an external calibration procedure using matrix-matched standard solutions to improve accuracy. Sample recoveries at four spiking levels ranged from 81 to 101% (relative standard deviation (RSD) 相似文献   

A rapid method based on hot water extraction and liquid chromatography-tandem mass spectrometry for analyzing tetracycline antibiotic residues in cheese

A rapid, specific, and sensitive procedure for determining residues of 4 widely used tetracycline antibiotics and 3 of their 4-epimers in cheese is presented. The method is based on the matrix solid-phase dispersion (MSPD) technique followed by liquid chromatography/tandem mass spectrometry (LC/MS/MS). After dispersing samples of mozzarella, asiago, parmigiano, gruyere, emmenthal, and camembert on sand, target compounds were eluted from the MSPD column by passing through it 6 mL water heated at 70 degrees C. After acidification and filtration, 200 microL of the aqueous extract was directly injected into the LC column. For analyte identification and quantification, MS data acquisition was performed in the multireaction monitoring mode, selecting 2 precursor ion-to-product ion transitions for each target compound. Hot water appeared to be an efficient extractant, because absolute recoveries were no lower than 78%. Using demeclocycline as a surrogate analyte, recoveries of analyte added to the 6 types of cheeses at the 30 ng/g level were 96-117%, with relative standard deviation (RSD) not higher than 9%. Statistical analysis of the mean recovery data showed that the extraction efficiency was not dependent on the type of cheese analyzed. This result indicates that this method could be applied to other cheese types not considered here. At the lowest concentration considered, i.e., 10 ng/g, the accuracy of the method ranged between 90 and 107%, with RSDs not larger than 12%. Based on a signal-to-noise ratio of 10, limits of quantitation were estimated to be 1-2 ng/g.     

Effects of the exciting wavelength and viscosity on the photobehavior of 9- and 9,10-bromoanthracenes

The widely investigated photobehaviors of 9-bromo and 9,10-di-bromoanthracenes have been revisited here to clarify the competition among different relaxation paths of their lowest two electronic excited states. The results obtained show that these two molecules exhibit a parallel photobehavior, which depends on the excited electronic and vibronic transition, the medium viscosity, and the temperature. The first electronic state of either of these does not exhibit photochemistry in fluid solution or rigid matrices (80 K). The fluorescence emission occurs with a very low quantum yield (approximately 10(-2)) at room temperature but with a very high quantum yield (0.9 to approximately 1) at 80 K. When exciting in the second electronic transition, the fluorescence intensity is lower than when exciting in S1 at both room temperature and low temperature due to competition with the observed photocleavage of the C-Br bond. The reaction yield decreases as the temperature decreases and depends on the viscosity of the solvent; the higher the viscosity, the lower the observed yield of photochemistry. Temperature and viscosity effects are a consequence of the fact that the radicals produced by C-Br bond breakage cannot escape from the solvent cage and, moreover, quickly recombine within the cage giving the appearance that no photochemistry occurred. The presence of photochemistry in S(2) and its absence in S(1) is principally due to the fact that S(2) has a pi,sigma* character in the C-Br bond, whereas the S(1) state has its origin from a pi,pi* delocalized configuration.     

First principles studies on boron sites in zeolites

A systematic computational investigation on protonated and nonprotonated boron-containing zeolites (boralites), performed by using different periodic density functional theory approximations, is presented. Both minimum energy structures and finite temperature behavior of model boron sodalites were analyzed. All of the adopted computational schemes agree in predicting an acid site composed of a silanol Si-OH group loosely linked to a planar BO(3) structure in the protonated system and a BO(4) tetrahedral site in the sodium-containing zeolite. Calculated structural and vibrational properties are in line with experimental data. Comparisons of the protonated boralite site with Al and Ga zeolitic acid sites are discussed as well. Results indicate that this class of mild acid catalysts is characterized by significant framework flexibility and pronounced thermal effects due to the loosely bound acid site.     

Liquid chromatography/tandem mass spectrometry determination of organophosphorus flame retardants and plasticizers in drinking and surface waters

A liquid chromatography/electrospray ionization tandem mass spectrometric method for analyzing organophophorus flame retardants and plasticizers in drinking and environmental waters was developed. Five alkyl phosphates, three chlorinated alkyl phosphates, two aryl phosphate and triphenylphosphine oxide were selected for this study. These compounds were extracted from water samples by a hydrophilic polymeric solid-phase extraction cartridge. Accuracy and precision were evaluated analyzing 0.5 L of water samples spiked at concentrations of 10 and 100 ng/L for drinking water and at 300 and 1000 ng/L for river water. Except for trimethyl phosphate, analyte recoveries were better than 80%, and were not dependent on the type of aqueous matrix in which they were dissolved. At the spike levels considered, within-day precision was between 3 and 12% for tap water and between 4 and 14% for river water, and estimated method quantification limits ranged from 0.2 to 3.9 ng/L. A short survey conducted by analyzing some river water samples (River Tiber) ascertained the presence of ten organophosphorus compounds at concentration levels ranging from a few nanograms per liter to 323 ng/L for tris(2-butoxyethyl) phosphate.     

Serum protein profiling in patients with inflammatory bowel diseases using selective solid-phase bulk extraction, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and chemometric data analysis

The identification of new biomarkers or a disease-related protein fingerprint for inflammatory bowel diseases (IBDs) represents a major task in the diagnosis, prognosis and pharmacological therapy. To address these issues, a simple and rapid analytical proteomic method for serum protein profiling based on selective beads-based solid-phase bulk extraction, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and chemometric data analysis was developed. Serum proteins from healthy subjects (22) and patients with Crohn's disease (15) and ulcerative colitis (26) were selectively extracted according to reversed-phase (C18), strong anion-exchange (SAX) and metal ion affinity (IDA-Cu(II)) principles. This approach allowed enrichment of serum proteins/peptides due to the high interaction surface between analytes and the solid phase and high recovery due to the elution step performed directly on the MALDI-target plate. The MALDI-TOF MS serum protein profiles were acquired and, after a data pre-processing step, analyzed by linear discriminant analysis (LDA), a chemometric classification technique, in order to classify serum samples among healthy subjects and patients with inflammatory bowel diseases (IBDs). Since the high number of variables in the MALDI spectra (more than 16000 m/z values) prevents the use of LDA, the variables were reduced to 10-20 by features selection, thus allowing the evaluation of a pattern of m/z values with high discriminant power. Serum protein profiles obtained by reversed-phase extraction and the selection of 20 m/z values gave the best overall prediction ability (96.9%). The recognition of these m/z values may allow the identification of protein biomarkers involved in IBDs.     

Determination of aflatoxins in olive oil by liquid chromatography-tandem mass spectrometry

A liquid chromatography-tandem mass spectrometric with electrospray ionization (LC/ESI-MS/MS) method for determining the four naturally occurring aflatoxins (AFs) B1, B2, G1, and G2 in olive oil is proposed. AFs were extracted from oil sample by means of matrix solid phase dispersion (MSPDE), utilizing C18 as dispersing material. No further purification step, such as lipid removal, was performed. Aflatoxin M1, the hepatic metabolite of AFB1, was employed as internal standard. Olive oil extract was analyzed by LC/ESI-MS/MS in positive ionization mode, with multireaction monitoring acquisition. Due to a signal suppression ranging between 4 and 23%, quantitation was performed by matrix-matched calibration curves. The regression line coefficients of determination were above 0.9991. Sample recoveries ranged from 92 to 107%, with relative standard deviations below 13% for spiking levels between 0.5 and 5 ng g⁻¹; method quantification limits ranged between 0.04 and 0.12 ng g⁻¹. The developed LC/ESI-MS/MS method, although not as sensitive as LC coupled to fluorescence detection, is rapid, selective, accurate and precise, thus it can be used as confirmatory assay. The MSPDE appears suitable for application to other oleaginous matrices and for multiresidue investigation.     

Field effect transistors with organic semiconductor layers assembled from aqueous colloidal nanocomposites

We demonstrate field effect transistors based on organic semiconductor molecules dispersed in a self-organized polystyrene (PS) latex bead matrix. An aqueous colloidal composite made of PS and tetrahexylsexithiophene (H4T6) is deposited with a micropipet into the channel of a bottom-contact field effect transistor. The beads self-organize into a network whose characteristic distances are governed by their packing. The semiconductor molecules crystallize in the interstitial voids, leading to the growth of large interconnected domains. Depending on the bead size and the ratio between H4T6 and PS, the fraction of the different phases in the polymorph can be controlled. In the transistors where the H4T6 metastable "red phase" is the largest, the device response and the charge mobility are comparable to those of sexithienyl thin films grown by high-vacuum sublimation.     

Identification of a time-dependent UV-photon source in an interstellar cloud

Abstract Consider an interstellar cloud that occupies the region , bounded by the known surface , and assume that the scattering cross section σ_s and the total cross section σ are also known. Then, we prove that it is possible to identify the source q=q(x,t) that produces UV-photons inside the cloud, provided that the UV-photon distribution function arriving at a location , far from the cloud, is measured at times , , ..., . Keywords: Photon transport, Semigroups and linear evolution equations, Inverse problems Mathematics Subject Classification (2000): 82A25, 82C70, 34K29, 65M32     

Structures of Solvent-Free,Monomeric LiCCH,NaCCH, and KCCH

The simplest alkali metal acetylides MCCH were made in the gas phase for the first time (see drawing), and their bond lengths were determined by millimeter/submillimeter spectroscopy of their isotopomers. The M−C bond lengths r_CM are the shortest known for organoalkali metal compounds. In the case of LiCCH, the experimentally determined Li−C distance of 1.888 Å has an estimated accuracy of ±0.0005 Å, which should allow a rigorous test of theoretical methods.