羰基铁粉掺杂整体柱萃取-在线热解吸进样气相色谱-串联质谱法分析茶叶样品中拟除虫菊酯类农药残留

制备了羰基铁粉掺杂硅胶整体柱，用于拟除虫菊酯类农药残留萃取，并与气相色谱-串联质谱（GC-MS/MS）法联用，建立了在线富集、热解吸GC-MS/MS测定茶叶样品中拟除虫菊酯类农药残留方法。研究将端羟基聚二甲基硅氧烷共价键合到SiO₂网络表面，并同时键合羰基铁粉。将目标分析物吸附并浓缩在聚二甲基硅氧烷位点上后，利用羰基铁粉的高频感应加热特性成功实现了GC-MS/MS直接气体进样并可达到快速、均匀解吸的目的。实验结果表明，在最佳条件下，本方法的富集倍数可达到约1000倍。拟除虫菊酯类农药残留的检出限为3.8~7.5 μg/kg，相对标准偏差为3.2%~6.8%（n=6）。该方法的提取回收率为97.7%~110.5%，相关系数≥0.9960。该法的吸附容量大，在电磁感应的条件下进行热脱附继而直接与GC-MS结合实现在线分析以及无溶剂洗脱。与常规固相微萃取（SPME）方法相比，该方法具有富集因子高、整体柱吸附容量大、可重复使用、自动化程度高、普适性好等优点。在样品前处理及复杂基质中农药残留的提取方面具有重要的研究意义。     

Die Wärmeaggregation von Proteinen in Lösung

Zusammenfassung Die W?rmeaggregation verschiedener Proteine (Rinderserumalbumin, β-Lactoglobulin, Insulin, Ribonuclease) wurde mit Hilfe von Messungen der Lichtstreuung ihrer L?sungen bei Temperaturen zwischen 50° und 80° untersucht, um zu kl?ren, inwieweit Reaktionen zwischen Sulfhydryl- und Disulfidgruppen der Proteine daran beteiligt sind. Proteine mit SH- und SS-Gruppen wie Rinderserumalbumin und β-Lactoglobulin werden bei ihrer W?rmeaggregation durch SH-blockierende und SS-spaltende Reagentien, Proteine ohne SH-Gruppen nur durch letztere beeinflu?t. Rinderserumalbumin reagiert nach zwei verschiedenen Mechanismen; im isoelektrischen Bereich tritt Koagulation vermutlich durch Ausbildung intermolekularer Wasserstoffbrücken ein. Au?erhalb dieses Bereichs aggregiert es nicht mehr, wenn die SH-Gruppen durch Chinon blockiert sind, bei freien SH-Gruppen führt dann jedoch eine SH-SS-Redoxreaktion zwischen 2 Proteinmolekülen zu Aggregationen. Die Koagulation ist stark, die Redoxreaktion wenig vom p_H abh?ngig. β-Lactoglobulin koaguliert in der W?rme bei allen p_H-Werten, doch nur, wenn nach einer anf?nglichen Spaltung vorher eine SH-SS-Redoxreaktion — die wahrscheinlich zu Dimeren führt — ablaufen kann. Durch die Koppelung der Redoxreaktion und Koagulation wird letztere von ersterer abh?ngig und durch die SH-Reagentien beeinflu?bar. Insulin(und Ribonuclease) aggregieren nicht über einen SH-SS-Mechanismus, dieser kann aber künstlich durch SS-Gruppen reduzierende Substanzen ausgel?st werden. Aus Messungen der λ_c-Konstante der Drudeschen Gleichung der Rotationsdispersion wurde geschlossen, da? das Rinderserumalbuminmolekül beim Erw?rmen und bei der Aggregation zumindest keine irreversible ?nderung seiner Anteile an Helixstrukturen erleidet, w?hrend beim β-Lactoglobulin eine ?nderung zu beobachten ist, die der Einwirkung von etwa 3,8 mol Harnstoff entspricht.     

Iodine determination in milk by isotope dilution analysis

Iodine is an essential trace element in the human diet. It is utilized in the synthesis of L-monoiodothyrosine, which is a precursor of the thyroid hormones, thyroxin and triiodothyronin. In this study, a method that can determine iodine concentrations in milk has been developed. The method is based on substoichiometric isotope dilution analysis (IDA). Iodine concentrations were measured in milk, which has been collected from three big cities and environment municipalities of Aegean Region. The iodine concentration ranges were within 436.8 and 896.7 μg/kg in milk samples. Mean iodine concentration was not greatly changed from season to season, between 1998 and 2002. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis and spectral characterization of new benzimidazolium compounds containing sulfur

Abstract

N-heterocyclic carbene (compound b) was synthesized from reaction of 1-(3-phenylpropyl)-3-methylbenzimidazolium iodide (a) and a strong base in an argon atmosphere. Then, 1-(3-phenylpropyl)-3-methylbenzimidazolium-2-carbodithioate (c) was prepared with carbene and CS₂. Finally, a group of alkyl 1-(3-phenylpropyl)-3-methylbenzimidazolium-2-carbodithioate halides was synthesized with alkyl halides and compound c, occurring products 1-6. Structural characterization of compounds was performed ¹H, and ¹³C NMR, IR, and MS spectroscopy and elemental analysis.     

Characterization of Hollow Chemical Garden Fibers from Metal Salts and Water Glass

Hollow fibers formed from water glass and metal salts of IIA(Ca), VIIB(Fe, Co, Ni) and IB(Cu) groups were characterised in this study. Fragile fibres obtained herein broke down into small pieces during isolation and drying. Quantitative information about morphology, chemical composition and surface structure of the fibres were obtained. The diameter and wall thickness of the fibers were around 50 and 3 . respectively. They had particulate inner and smooth outer surfaces. Fibers had variable composition with metal (II) oxide/SiO₂ ratio in the range 0.31 to 1.02. While group VIIB metal (II) fibres were amorphous, group IIA and IB metal (II) fibres were partially crystalline All the fibres had pores both in micro pore and meso pore region. The B.E.T surface area from N₂ adsorption data was in the range of 10–249 m³ g^–1 and 8–176 m² g^–1 from Langmuir and B.E.T models respectively.     

Preparation of L-asparagine complex of technetium-99m

Attempts have been made to employ magnesium oxide as the preconcentration agent for determination of trace metal sin seawater by neutron activation analysis. Hydrous magnesium oxide can efficienthy adsorb most cationic transition metals and rare earths in a simple water system. The adsorption behavior is believed to depend mainly from the association of the cationic species of the metals with MgO ₂ ^2– adsorbent. In seawater matrix some of the metal ions such as Hg²⁺, Ni²⁺, etc. may become inefficiently adsorbed owing to the formation of highly stable metal-chloro complexes with chloride ion. Usually the adsorption efficiencies of the metals can be recovered to be as high as the case in the simple water system if an acidified seawater (to pH1) is subjected to the adsorption experiment. In practice, a large volume of seawater (5 1) is stirred with a small amount of hydrous MgO (1 g). Thereafter, the trace metals adsorbed MgO is separated and taken to be neutron activated. The abundant sodium ion and ubiquitous bromide ion can be obviated by the adsorption process, thereby beneficial to the -spectrometry of the metals enriched on MgO.     

On The Potential of Dynamic Nuclear Polarization Enhanced Diamonds in Solid‐State and Dissolution 13C NMR Spectroscopy

Dynamic nuclear polarization (DNP) is a versatile option to improve the sensitivity of NMR and MRI. This versatility has elicited interest for overcoming potential limitations of these techniques, including the achievement of solid‐state polarization enhancement at ambient conditions, and the maximization of ¹³C signal lifetimes for performing in vivo MRI scans. This study explores whether diamond's ¹³C behavior in nano‐ and micro‐particles could be used to achieve these ends. The characteristics of diamond's DNP enhancement were analyzed for different magnetic fields, grain sizes, and sample environments ranging from cryogenic to ambient temperatures, in both solution and solid‐state experiments. It was found that ¹³C NMR signals could be boosted by orders of magnitude in either low‐ or room‐temperature solid‐state DNP experiments by utilizing naturally occurring paramagnetic P₁ substitutional nitrogen defects. We attribute this behavior to the unusually long electronic/nuclear spin‐lattice relaxation times characteristic of diamond, coupled with a time‐independent cross‐effect‐like polarization transfer mechanism facilitated by a matching of the nitrogen‐related hyperfine coupling and the ¹³C Zeeman splitting. The efficiency of this solid‐state polarization process, however, is harder to exploit in dissolution DNP‐enhanced MRI contexts. The prospects for utilizing polarized diamond approaching nanoscale dimensions for both solid and solution applications are briefly discussed.     

1,2-Bis-[(5-methyl/chloro/nitro)-2-1H-benzimidazolyl]-1,2-ethanediols and their PdCl2 complexes

1,2-Bis-[(5-methyl)-2-1H-benzimidazolyl]- (L ¹), 1,2-bis-[(5-chloro)-2-1H-benzimidazolyl]- (L ²), 1,2-bis-[(5-nitro)-2-1H-benzimidazolyl]-1,2-ethanediol (L ³) and their PdCl₂ complexes were synthesized and characterized by elemental analysis, molar conductivity, i.r. and ¹H-n.m.r. spectra. The benzene ring substituents lead to a decrease in melting point. The methyl group reduces the solubility and the acidity of L ¹ and Pd(L ¹)Cl₂, whereas the Cl and NO₂ groups increase the solubility and the acidity of L ², L ³, Pd(L ²)Cl₂ and Pd(L ³)Cl₂. In Pd(L ¹)Cl₂ and Pd(L ²)Cl₂ complexes, the ligands act as a bidentate through two nitrogen atoms. In Pd(L ³)Cl₂, ligand coordination occurs through one OH group oxygen atom and one of the benzimidazole nitrogen atoms.     

Mass flow-rate control unit to calibrate hot-wire sensors

Hot-wire anemometry is a measuring technique that is widely employed in fluid mechanics research to study the velocity fields of gas flows. It is general practice to calibrate hot-wire sensors against velocity. Calibrations are usually carried out under atmospheric pressure conditions and these suggest that the wire is sensitive to the instantaneous local volume flow rate. It is pointed out, however, that hot wires are sensitive to the instantaneous local mass flow rate and, of course, also to the gas heat conductivity. To calibrate hot wires with respect to mass flow rates per unit area, i.e., with respect to (ρU), requires special calibration test rigs. Such a device is described and its application is summarized within the (ρU) range 0.1–25 kg/m² s. Calibrations are shown to yield the same hot-wire response curves for density variations in the range 1–7 kg/m³. The application of the calibrated wires to measure pulsating mass flows is demonstrated, and suggestions are made for carrying out extensive calibrations to yield the (ρU) wire response as a basis for advanced fluid mechanics research on (ρU) data in density-varying flows.     

离子交换固相萃取-气相色谱-质谱联用法测定方便面皮复合包装袋中2,4-二氨基甲苯的迁移量

建立了方便面皮复合包装袋中2,4-二氨基甲苯迁移量的离子交换固相萃取-气相色谱-质谱联用检测方法。样品用4%（v/v）乙酸溶液浸泡,然后采用MCX混合型阳离子交换柱富集净化,以5.0 mL水淋洗小柱,用3.0 mL 5%（v/v）氨化甲醇洗脱样品,洗脱液经过溶剂交换,七氟丁酸酐衍生后,用气相色谱-质谱联用仪对目标物进行检测,外标法定量。2,4-二氨基甲苯在1~50 μg/L范围内,线性相关系数（r）为0.9991,检出限（S/N=3）为0.2 μg/L,定量限（S/N=10）为0.6 μg/L,回收率在89.0%~94.2%之间,相对标准偏差为1.9%~3.6%。该方法的前处理过程无需调节提取液的pH值,也不需要液液萃取,大幅简化了前处理过程,降低了有机溶剂的消耗,具有操作便捷、结果准确的优点,适用于方便面皮复合包装袋中2,4-二氨基甲苯迁移量的检测。