LC/MS confirmation of ionophores in animal feeds.

A liquid chromatographic/mass spectrometric (LC/MS) electrospray confirmation method has been developed to confirm 4 ionophores (monensin, lasalocid, salinomycin, and narasin) in a variety of animal feeds using a single quadrupole mass spectrometer. The sodium ions of these compounds are dominant in the electrospray mass spectrum. Using optimized "in-source" collision induced dissociation, characteristic fragment ions seen previously using MS/MS can be observed. The drugs were extracted from the feed matrix using hexane-ethyl acetate and isolated using a silica solid-phase extraction cartridge. These ionophores were confirmed in both medicated feeds and nonmedicated feeds fortified with these drugs at the 1-50 ppm level. In addition, this method was used to confirm residues of monensin in a nonmedicated feed that was collected from a feed mill immediately after the production of a similar feed that was medicated with high levels of monensin.     

Proton-transfer reaction of 4-methyl 2,6-diformyl phenol in cyclodextrin nanocage

We report here on the steady-state and time-resolved fluorescence studies on proton-transfer (PT) reaction of 4-methyl 2,6-diformyl phenol (MFOH) in confined nanocavities in three solvents, dimethyl sulfoxide (DMSO), dimethyl formamide (DMF), and water. Though DMSO and DMF individually interact with MFOH in a similar fashion, their modes of interaction get significantly modified in the presence of cyclodextrin (CD) nanocages. In DMSO, in the ground state, the solvated molecular anion of MFOH forms 1:1 inclusion complex with beta- or gamma-CD and attains greater stability compared to the normal form. In DMF, the solvated molecular anion gets converted to the H-bonded complex within the CD cavity resulting in a 50-nm blue shift in the absorption spectra. In the excited state, the anionic species gets more stabilized in DMSO while in DMF it is significantly destabilized in the presence of CDs. However, in case of water, MFOH gets trapped inside the water cages so that the CDs fail to complex with it effectively. There are also no changes in the excited-state lifetimes in water in the presence of CDs, but in case of DMSO and DMF, because of restricted rotation of the formyl group within the CD cavity, the contribution of the shorter lifetime components reduce significantly increasing the larger components. Some theoretical calculations at the AM1 level of approximation have also been carried out to demonstrate how the dipolar nature of the solvent influences excited-state PT in confined media.     

Chromatographic behavior of pyrithiones

Pyrithione biocides are currently viewed as a major prospect for the replacement of tributyltin antifoulants in ship paints. The chromatographic behavior of 1-hydroxy-2-pyridinethione (pyrithione, PT), bis(2-pyridinyl)disulfide 1,1'-dioxide (PT2), and the metal complexes zinc [Zn(PT)2], iron [Fe(PT)3] and copper [Cu(PT)2] pyrithione, were investigated by means of UV-vis spectroscopy, ESI-MSn, HPLC-DAD and HPLC-ESI-MSnD. This revealed transformations of the analytes, which affect the development of adequate methods for species or environmental analysis of pyrithiones. PT transforms into copper- or iron- containing complexes and/or the oxidation product PT2, depending on the type of the stationary phase used in chromatographic analysis. Speciation complicates direct chromatography of [Zn(PT)2] and [Fe(PT)3].     

超高效液相色谱-电喷雾串联质谱法测定动物饲料中的大环内酯类和林可胺类抗生素

建立了动物饲料中竹桃霉素、红霉素、吉他霉素、交沙霉素、罗红霉素、泰乐菌素6种大环内酯和林可霉素、克林霉素2种林可胺抗生素的超高效液相色谱-电喷雾串联质谱(UPLC-ESI-MS/MS)检测方法。饲料样品采用甲醇提取,Oasis HLB固相萃取柱富集净化,Waters Acquity UPLC BEH C18色谱柱分离,以0.1%甲酸和乙腈为流动相进行梯度洗脱,流速为0.3 mL/min,正离子模式扫描,多反应监测模式检测,外标法定量。实验结果表明,8种药物在1～100 μg/L范围内具有良好的线性关系。在空白饲料样品中分别添加1、10和100 μg/kg 3个加标水平的8种药物,其平均回收率为68.6%～95.2%,相对标准偏差(RSD)为4.9%～11.8%,定量限均为1 μg/kg。结果表明,该方法简便快速、灵敏度高,适用于动物饲料中大环内酯类和林可胺类抗生素的同时检测。     

Direct crystallographic observation of catalytic reactions inside the pores of a flexible coordination polymer

A new flexible porous coordination polymer (PCP), {[Gd(2)(L)(3)(dmf)(4)]·4DMF·3H(2)O}(n) (1), was synthesized under solvothermal condition by reacting [Gd(NO(3))(3)]·6H(2)O with the ligand 2,6,2',6'-tetranitro-biphenyl-4,4'-dicarboxylic acid (H(2)L). Compound 1 had a 3D coordination polymeric structure with two types of 1D channels (A and B) that were occupied by DMF and water molecules. When crystals of 1 were separately exposed to vapors of various aromatic aldehydes, either the lattice or both the lattice and metal-bound solvent molecules were replaced by aldehyde molecules. The aldehyde molecules inside the pores spontaneously underwent cyanosilylation and Knoevenagel condensation reactions upon exposure to vapors of trimethylsilyl cyanide and malononitrile, respectively. These reactions took place at ambient temperature and pressure. Moreover, both the reactants and the products translocated from one cavity to another. The products that occupied the cavity were expunged upon exposure to the vapors of an aldehyde. Because crystallinity was maintained during these chemical transformations, direct crystallographic observation was possible. Herein, we showed that confinement of the reactants inside the void spaces of the PCP led to the products; we also assessed catalytic activities of this PCP in bulk quantities.     

Ultrasonic-Assisted Linker Exchange (USALE): A Novel Post-Synthesis Method for Controlling the Functionality,Porosity, and Morphology of MOFs

The introduction of organic ligands into metal–organic frameworks (MOFs) with a specific topology and that cannot be attained by direct synthesis is a big challenge. To meet this challenge, different ligand exchange/incorporation methods have been employed. Here, a new method, called ultrasonic-assisted linker exchange (USALE), has been developed to overcome the above-mentioned problems. USALE is a novel method for ligand exchange based on the use of ultrasonic waves. The temperature and pressure caused by the USALE method in microscopic zones are so intense that the linker exchange process is much faster than with other methods. In addition to saving time during synthesis, the use of the USALE method leads to a higher surface area and pore volume compared with other methods such as solvent-assisted linker exchange (SALE). In this way, improved gas adsorption capacity has been achieved for daughter frameworks synthesized by the USALE method. By using the USALE method, we have transformed a nonporous and easy-to-synthesize TMU framework ([Zn(OBA)(BPDB)0.5]n ⋅ 2DMF (TMU-4), in which H2OBA=4,4′-oxybis(benzoic acid) and BPDB=1,4-di(4-pyridyl)-2,3-diaza-1,3-butadiene) into another porous framework ([Zn(OBA)(H2DPT)0.5]n ⋅ DMF (TMU-34), in which H2DPT=3,6-di(4-pyridyl)-1,4-dihydro-1,2,4,5-tetrazine) that otherwise requires a relatively long time to synthesize. In addition to reducing the synthesis time for TMU-34 (in comparison with both direct sonochemical synthesis and the indirect SALE method), the data obtained revealed that the daughter TMU-34 framework synthesized by the USALE method has a higher surface area and accessible pore volume than TMU-34 frameworks synthesized by SALE and direct methods. The application of SALE-TMU-34 and USALE-TMU-34 in a catalytic Henry condensation reaction and Congo Red adsorption experiments showed that the higher porosity of USALE-TMU-34 leads to a higher turn-over frequency and saturation capacity compared with SALE-TMU-34.     

Electrocatalytical Application of Platinum Nanoparticles Supported on Reduced Graphene Oxide in PEM Fuel Cell: Effect of Reducing Agents of Dimethlyformamide or Hydrazine Hydrate on the Properties

Two kinds of reduced graphene oxide (rGO) were synthesized with the reducing agents of either dimethylformamide (DMF) or hydrazine hydrate (HYD). The decoration of platinum nanoparticles (Pt NPs) over these materials was provided by microwave irradiation (MWI) method. Detailed physical and electrochemical measurements were carried out. Based on the electrochemical results of both catalysts, it is not surprising the achievement of higher electrochemical active surface area (ECSA), higher oxygen reduction reaction (ORR) activity, higher electron transfer number, lower charge transfer resistance and higher fuel cell performance with the Pt/rGO (DMF) catalyst which surpasses Pt/rGO (HYD) in many ways.     

cis—Mo(DMF)_3Br_3异构体的晶体和分子结构

制得了cis—Mo(DMF)_3Br_3(DMF指N,N—二甲基甲酰胺)的一种异构体并用X射线三维衍射数据进行了晶体结构测定。晶体的空间群属Pca2_1。晶胞大小为a=20.157(4),b=13.950(4),c=13.142(4)。晶体的测量密度为2.02g/cm~3,与Z=8相符。结构用直接法-Fourier合成法解得,最终R因子为0.060。结构分析表明,晶体仍为cis-Mo(DMF)_3Br_3,分子中Mo周围的三个Br原子和三个DMF配位基的O原子仍按顺式排列成近八面体,但DMF的取向不规则。分子不再具有对称性。     

超高效液相色谱-电喷雾串联四极杆质谱法同时测定配合饲料中29种兽药

建立了同时测定配合饲料中喹诺酮类、磺胺类、大环内酯类和硝基呋喃类共计29种兽药的超高效液相色谱-电喷雾串联四极杆质谱(UPLC-ESI-MS/MS)检测方法。饲料样品用甲醇-乙腈(1:1, v/v)混合溶液提取,提取液经Oasis HLB固相萃取柱净化,采用UPLC-ESI-MS/MS检测。以甲醇和含0.1%(v/v)甲酸的水溶液作为流动相,进行梯度洗脱,用C18色谱柱分离,正离子模式扫描,多反应监测模式检测。29种兽药在0.01～5.0 mg/L范围内线性关系良好,相关系数(r)均大于0.99;在复合预混饲料、全价配合饲料、浓缩饲料中4个添加水平下29种兽药的平均回收率在61.2%～94.3%范围内,相对标准偏差(RSD)为2.2%～15.0%;方法的检出限(以信噪比大于10计)为0.01 mg/kg或0.05 mg/kg。该方法简便、快速、准确,重现性好,灵敏度高,适用于配合饲料中多种兽药的同时检测。     

高效液相色谱法测定饲料中的喹乙醇

报道饲料中喹乙醇的高效液相色谱分析方法。以乙酰苯胺为内标,样品用二甲替甲酰胺（ＤＭＦ）提取,在Ｃ８柱上进行色谱分析,紫外检测波长２６０ｎｍ,流动相为甲醇－水（２０８０,Ｖ／Ｖ）,喹乙醇的回收率为９８．５８％～１０１．６３％,相对标准偏差为２．６７％～４．２５％。     

High-throughput caco-2 cell permeability screening by cassette dosing and sample pooling approaches using direct injection/on-line guard cartridge extraction/tandem mass spectrometry

A method for high-throughput Caco-2 permeability screening of drug candidates has been developed using thirteen generic drugs as test compounds. The high throughput was achieved by either a sample pooling or a cassette dosing approach, along with the use of a rapid, simple and sensitive direct injection/on-line guard cartridge extraction/tandem mass spectrometric assay that was also developed in this study. It was of concern that possible drug-drug interactions (e.g., inhibition of P-glycoprotein-mediated transport of a drug by another, and/or competition of the drugs for transport pathways), when the cassette dosing regimen was implemented, may give rise to inconsistent results compared with those attained by a traditional single-drug dosing approach. However, the apparent permeability coefficients of the test drugs across Caco-2 monolayers measured by the sample pooling or cassette dosing (up to five drugs co-administered in this study) strategy were in good conformity with the data obtained by single-drug dosing followed by discrete sample analysis.     

Practical uses of proficiency testing as valuable tools for validation and performance assessment in environmental analysis

Besides their role as an external quality control tool, PT results or samples could be used as an alternative to fulfil some of the quality assurance requirements such as analytical precision, uncertainty assessment, and internal quality control. This additional use of proficiency testing could help laboratories to reduce the financial impact of their quality assurance process. The purpose of this paper is to highlight some practical uses of PT results or samples in the environmental analytical field, which have been implemented at ISSeP (Institut Scientifique de Service Public), either for method validation or for internal quality control.Presented at the Eurachem PT Workshop September 2005, Portorož, Slovenia     

Solid-solid phase transformation via internal stress-induced virtual melting, significantly below the melting temperature. Application to HMX energetic crystal

We theoretically predict a new phenomenon, namely, that a solid-solid phase transformation (PT) with a large transformation strain can occur via internal stress-induced virtual melting along the interface at temperatures significantly (more than 100 K) below the melting temperature. We show that the energy of elastic stresses, induced by transformation strain, increases the driving force for melting and reduces the melting temperature. Immediately after melting, stresses relax and the unstable melt solidifies. Fast solidification in a thin layer leads to nanoscale cracking which does not affect the thermodynamics or kinetics of the solid-solid transformation. Thus, virtual melting represents a new mechanism of solid-solid PT, stress relaxation, and loss of coherence at a moving solid-solid interface. It also removes the athermal interface friction and deletes the thermomechanical memory of preceding cycles of the direct-reverse transformation. It is also found that nonhydrostatic compressive internal stresses promote melting in contrast to hydrostatic pressure. Sixteen theoretical predictions are in qualitative and quantitative agreement with experiments conducted on the PTs in the energetic crystal HMX. In particular, (a) the energy of internal stresses is sufficient to reduce the melting temperature from 551 to 430 K for the delta phase during the beta --> delta PT and from 520 to 400 K for the beta phase during the delta --> beta PT; (b) predicted activation energies for direct and reverse PTs coincide with corresponding melting energies of the beta and delta phases and with the experimental values; (c) the temperature dependence of the rate constant is determined by the heat of fusion, for both direct and reverse PTs; results b and c are obtained both for overall kinetics and for interface propagation; (d) considerable nanocracking, homogeneously distributed in the transformed material, accompanies the PT, as predicted by theory; (e) the nanocracking does not change the PT thermodynamics or kinetics appreciably for the first and the second PT beta <--> delta cycles, as predicted by theory; (f) beta <--> delta PTs start at a very small driving force (in contrast to all known solid-solid transformations with large transformation strain), that is, elastic energy and athermal interface friction must be negligible; (g) beta --> alpha and alpha --> beta PTs, which are thermodynamically possible in the temperature range 382.4 < theta < 430 K and below 382.4 K, respectively, do not occur.     

A constrained variational approach to the designing of low transport band gap materials: A multiobjective random mutation hill climbing method

Neutral polythiophene (PT) and polyselenophene (PSe) are semiconductors with band gaps of about 2 eV. We have proposed and implemented a constrained variational method in which total energy of neutral PT or PSe oligomers is minimized under the constraint that the band gap measured by HOMO–LUMO energy difference is also a minimum in each case. The constrained (bimodal) minimization has been carried out by an adaptive random mutation hill climbing method within the basic framework of Su‐Schrieffer‐Heeger type of model. We show that the “band‐gap constrained minimization” automatically creates electron deficient quinoid regions (QR) in the PT or PSe chains, embedded in aromatic regions (ARs), on both sides. We have investigated how the number and distribution of such QRs can reduce the band gap. Band gap constrained electronic structure calculations thus provide designing clues for low transport band gap materials based on molecular chromophores. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

UPLC - ESI MS/MS法测定动物饲料中苯二氮卓类药物

建立了超高效液相色谱-电喷雾串联质谱(UPLC - ESI MS/MS)同时检测动物饲料中地西泮、奥沙西泮、硝西泮、三唑仑、艾司唑仑和咪达唑仑6种苯二氮卓类药物的方法.饲料样品采用碱性叔丁基甲醚提取,Oasis MCX固相萃取柱净化,反相色谱柱分离,以0.1％甲酸和乙腈为流动相进行梯度洗脱,正离子模式扫描,多反应监测模...     

固氮酶活性中心模拟物合成中的笼格效应及Fe(DMF)_6〔(FeCl_2)_2MoS_4〕的合成与晶体结构

以FeCl_2·4H_2O与(NH_4)_2MoS_4按3:1(克分子比)在DMF中反应,得到Fe(DMF)_5[(FeCl_2)_2MoS_4]。X-射线衍射单晶结构测定确定该化合物具层状结构。与笼状结构的G-系模型物相比较,指出Mg(DMF)_6~(2+)的较强成笼倾向使三核“元件”化合物Mg(DHF)_6[(FeCl_2)_2MoS_4)无法生成,据此提出Mg(DMF)_6~(2+)的笼格效应。     

双核锡配合物[Sn2Cl6(μ-OH)2(DMF)2]·4DMF的合成和晶体结构

A binuclear tin complex [Sn_2Cl_6(μ-OH)_2(DMF)_2]·4DMF has been synthesized through direct reaction of SnCl_4·5H_2O with DMF. Its molecular and crystal structure has been determined by single X-ray diffraction technique. The crystal is triclinic with space group P1. The unit cell parameters are a=0.9153(2), b=1.0722(3), c=1.2192(3) nm, α=63.07(2), β=93.26(2), γ=65.75 (2), V=0.92821(36) nm, D_c=1.649 g·cm~(-3), Z=1, The tin atom in the complex takes six-coordinated distorted octahedral configuration with sp~3 d~2 hybrid. The two tin atoms are connected through hydroxyl bridge to form a plane at the molecular center. The four noncoordinated DMF molecules distribute symmetrically around the dimer. The whole complex has an inversion center which coincides with the gravity center of the parallelogram.     

Determination of aflatoxins in animal feeds by liquid chromatography/tandem mass spectrometry with isotope dilution

The objective of the present study is to develop a simple, fast method for detection of aflatoxins in animal feeds. Simultaneous quantitation of four aflatoxins (AFB(1), AFB(2), AFG(1) and AFG(2)) in animal feeds was achieved in a single liquid chromatography/tandem mass spectrometry (LC/MS/MS) run. The solid-phase extraction cleanup step is eliminated with the stable isotope dilution method. Matrix effects were observed and overcome by isotope dilution. The method was tested in a variety of animal feed matrices and proved to be accurate and reliable. Method ruggedness tests resulted in recoveries of 78% to 122% with an intra-day assay precision of 2% to 15% and an inter-day assay precision of 3% to 17%. These results indicate that this method is suitable for quantitation of aflatoxins in animal feeds.     

Determination of inorganic elements in animal feeds by NIRS technology and a fibre-optic probe

In the present work we study the use of near infra-red spectroscopy (NIRS) technology together with a remote reflectance fibre-optic probe for the analysis of the mineral composition of animal feeds. The method allows immediate control of the feeds without prior sample treatment or destruction through direct application of the fibre-optic probe on the sample.The regression method employed was modified partial least squares (MPLS). The calibration results obtained using forty samples of animal feeds allowed the determination of Fe, Mn, Ca, Na, K, P, Zn and Cu, with a standard error of prediction (SEP(C)) and a correlation coefficient (RSQ) of 0.129 and 0.859 for Fe; 0.175 and 0.816 for Mn; 5.470 and 0.927 for Ca; 2.717 and 0.862 for Na; 4.397 and 0.891 for K; 2.226 and 0.881 for P; 0.153 and 0.764 for Zn, and 0.095 and 0.918 for Cu, respectively.The robustness of the method was checked by applying it to 10 animal feeds samples of unknown mineral composition in the external validation.