Rapid identification and quantitation of compounds with forensic interest using fast liquid chromatography-ion trap mass spectrometry and library searching

A fast liquid chromatography-electrospray tandem mass spectrometric (LC-ESI-MS-MS) method by using a monolithic column, gradient elution and ion trap mass spectrometer was developed for 14 forensically interesting and chemically different compounds. All compounds were eluted within 2.5 min and the total analysis time was 5 min including stabilisation time required for the next injection. All the compounds, basics, neutrals and acids were efficiently ionised by positive ion ESI. A laboratory library including MS-MS spectra and retention times was developed and tested. Results with 476 standard samples and 50 authentic samples showed that the compounds studied can be unambiguously identified with the library. A quantitative method was developed for the compounds using external calibration. The evaluation process showed good linearity of the method and reasonable repeatability. Limits of detection ranged from 10.0 to 50.0 ng/ml.     

Near infrared reflectance spectroscopy for the fast identification of PVC-based films

Near infrared (NIR) reflectance spectroscopy was used to develop a non-destructive and rapid qualitative method for the analysis of plastic films used by the pharmaceutical industry for blistering. Three types of films were investigated: 250 microm PVC [poly(vinyl chloride)] films, 250 microm PVC films coated with 40 g m(-2) of PVDC [poly(vinylidene dichloride)] and 250 microm PVC films coated with 5 g m(-2) of TE (Thermoelast) and 90 g m(-2) of PVDC. Three analyses were carried out using different pre-treatment options and a PLS (partial least squares) algorithm. Each analysis was aimed at identifying one type of film and rejecting all types of false sample (different thickness, colour or layer). True and false samples from four plastics manufacturers were included in the calibration sets in order to obtain robust methods that were suitable regardless of the supplier. Specificity was demonstrated by testing validation sets against the methods. The tests showed 0% of type I (false negative identification) and 1% of type II errors (false positive identification) for the PVC method, 13 and 3%, respectively, for the PVC-PVDC method and no error for the PVC-TE-PVDC method. Type II errors, mostly due to the slight sensitivity of the methods to film thickness, are easily corrected by simple thickness measurements. This study demonstrates that NIR spectroscopy is an excellent tool for the identification of PVC-based films. The three methods can be used by the pharmaceutical industry or plastics manufacturers for the quality control of films used in blister packaging.     

Diaryl ethers using Fischer chromium carbene mediated benzannulation

[formula: see text] The biological relevance and irresistible synthetic challenge of compounds containing the diaryl ether linkage encourages the development of new methodologies targeted toward this structural subunit. The syntheses of diaryl ethers 2 using a benzannulation strategy that formally involves a [3 + 2 + 1] cycloaddition between aryloxy-substituted Fischer carbenes 1 and alkynes are described. This methodology provides a neutral near ambient temperature formation of diaryl ethers.     

共混高聚物的混溶性研究(摘要)

在此介绍马萨诸塞州立大学在共混高聚物方面的研究工作。这些共混高聚物可分为三类:(1)非晶—非晶,如PCL(聚己内酯)(<50％)/PVC(聚氯乙烯);(2)结晶—非晶,如PCL(>50％)/PVC、i-PS(全同立构聚苯乙烯)/PPO(聚苯醚)、i-PS/α-PS(无规聚苯乙烯)、PVF_2(聚偏氟乙烯)/PMMA(聚甲基丙烯酸甲酯);(3)结晶—结晶,如PBT(聚对苯二甲酸丁二酯)/PET(聚对苯二甲酸乙二酯)。为研究第一类非晶共混物的混溶性,以 PCL/PVC     

Chemical modification of a viral cage for multivalent presentation

Here we present generalized methods for chemically modifying the surface of a viral protein cage; this exploits the chemistry of native and engineered surface exposed functional groups for multivalent presentation of ligands.     

Interaction Forces between Hydrophobic and Hydrophilic Self-Assembled Monolayers

An investigation is presented of the interaction of charged self-assembled monolayers (SAMs) with a monoprotic ionizable acid functional group (-COOH) and uncharged SAMs with a methyl terminated functional group (-CH(3)). The strength of the interactions are determined using an atomic force microscope. For all electrolyte conditions investigated the interactions are not well described by a summation of van der Waals attractions and electrostatic repulsions in a manner suggesting that van der Waals attractions are screened. The repulsions are accurately described as corresponding to two surfaces of different charge interacting with surface charges that are independent of separation (i.e., the constant charge model). A small adhesion force was observed under all conditions and its magnitude increased with NaCl concentration. Copyright 2000 Academic Press.     

Optimization by experimental design and artificial neural networks of the ion-interaction reversed-phase liquid chromatographic separation of twenty cosmetic preservatives

Particular attention are recently receiving antimicrobial agents added as preservatives in hygiene and cosmetics commercial products, since some of them are suspected to be harmful to the human health. The preservatives used belong to different classes of chemical species and are generally used in their mixtures. Multi-component methods able to simultaneously determinate species with different chemical structure are therefore highly required in quality control analysis. This paper presents an ion interaction RP-HPLC method for the simultaneous separation of the 20 typical antimicrobial agents most used in cosmetics and hygiene products, that are: benzoic acid, salicylic acid, 4-hydroxybenzoic acid, methyl-, ethyl-, propyl-, butyl-, benzyl-benzoate, methyl-, ethyl-, propyl-, butyl-, benzyl-paraben, o-phenyl-phenol, 4-chloro-m-cresol, triclocarban, dehydroacetic acid, bronopol, sodium pyrithione and chlorhexidine. For the development of the method and the optimization of the chromatographic conditions, an experimental design was planned and models were built by the use of artificial neural network to correlate the retention time of each analyte to the variables and their interactions. The neuronal models developed showed good predictive ability and were used, by a grid search algorithm, to optimize the chromatographic conditions for the separation of the mixture.     

Kinetics of formation and dissociation of lanthanide(III) complexes with the 13-membered macrocyclic ligand TRITA4-

The tetraazamacrocyclic ligand TRITA(4-) is intermediate in size between the widely studied and medically used 12-membered DOTA(4-) and the 14-membered TETA(4-). The kinetic inertness of GdTRITA(-) was characterized by the rates of exchange reactions with Zn(2+) and Eu(3+). In the Zn(2+) exchange, a second order [H(+)] dependence was found for the pseudo-first-order rate constant (k(0)=(4.2 +/- 0.5) x 10(-7) s(-1); k'=(3.5 +/- 0.3) x 10(-1) M(-1)s(-1), k" =(1.4 +/- 0.4) x 10(3) M(-2)s(-1)). In the Eu(3+) exchange, at pH <5 the rate decreases with increasing concentration of the exchanging ion, which can be accounted for by the transitional formation of dinuclear GdTRITAEu(2+) species. At physiological pH, the kinetic inertness of GdTRITA(-) is considerably lower than that of GdDOTA(-)(t(1/2)= 444 h (25 degrees C) vs. 3.8 x 10(5) h (37 degrees C), respectively). However, GdTRITA(-) is still kinetically more inert than GdDTPA(2-), the most commonly used MRI contrast agent (t(1/2)= 127 h). The formation reactions of LnTRITA(-) complexes (Ln = Ce, Gd and Yb) proceed via the rapid formation of a diprotonated intermediate and its subsequent deprotonation and rearrangement in a slow, OH(-) catalyzed process. The stability of the LnH(2)TRITA* intermediates (log K(LnH2L*)= 3.1-3.9) is lower than that of the DOTA-analogues. The rate constants of the OH(-) catalyzed step increase with decreasing lanthanide ion size, and are about twice as high as for DOTA-complexes.     

Spatial bistability and waves in a reaction with acid autocatalysis

The phenomenon of spatial bistability has recently been proposed for a comprehensive understanding of a number of chemical patterns observed in open spatial reactors consisting of thin films of gel diffusively fed from one side. We study experimentally and numerically this phenomenon in the tetrathionate-chlorite reaction characterized by an acid superautocatalysis. We focus on the similarities and differences with previous studies on the chlorine dioxide-iodide reaction. In addition, we show that this reaction, which is only bistable in a continuous stirred tank reactor, can exhibit oscillatory and traveling waves when diffusion comes into play. Our computations suggest that the nonstationary behaviour originates from differential diffusive transport.     

The utilization of classical spin Monte Carlo methods to simulate the magnetic behavior of extended three-dimensional cubic networks incorporating M(II) ions with an S = 5/2 ground state spin

The numerical simulations of the magnetic properties of extended three-dimensional networks containing M(II) ions with an S = 5/2 ground-state spin have been carried out within the framework of the isotropic Heisenberg model. Analytical expressions fitting the numerical simulations for the primitive cubic, diamond, together with (10-3) cubic networks have all been derived. With these empirical formulas in hands, we can now extract the interaction between the magnetic ions from the experimental data for these networks. In the case of the primitive cubic network, these expressions are directly compared with those from the high-temperature expansions of the partition function. A fit of the experimental data for three complexes, namely [(N(CH(3))(4)][Mn(N(3))] 1, [Mn(CN(4))](n)() 2, and [Fe(II)(bipy)(3)][Mn(II)(2)(ox)(3)] 3, has been carried out. The best fits were those obtained using the following parameters, J = -3.5 cm(-)(1), g = 2.01 (1); J = -8.3 cm(-)(1), g = 1.95 (2); and J = -2.0 cm(-)(1), g = 1.95 (3).