Development of a mild mercaptoethanol extraction method for determination of mercury species in biological samples by HPLC–ICP-MS

A mild, efficient and convenient extraction method of using 2-mercaptoethanol contained extractant solution combined with an incubator shaker for determination of mercury species in biological samples by HPLC–ICP-MS has been developed. The effects of the concentration of 2-mercaptoethanol, the composition of the extractant solution and the shaking time on the efficiency of mercury extraction were evaluated. The optimization experiments indicated that the quantitative extraction of mercury species from biological samples could be achieved by using 0.1% (v/v) HCl, 0.1% (v/v) 2-mercapoethanol and 0.15% (m/v) KCl extractant solution in an incubator shaker for shaking overnight (about 12 h) at room temperature. The established method was validated by analysis of various biological certified reference materials, including NRCC DOLT-3 (dogfish liver), IAEA 436 (tuna fish), IAEA MA-B-3/TM (garfish filet), IAEA MA-M-2/TM (mussel tissue), GBW 08193 (bovine liver) and GBW 08572 (prawn). The analytical results of the reference materials were in good agreement with the certified or reference values of both methyl and total mercury, indicating that no distinguishable transformation between mercury species had occurred during the extraction and determination procedures. The limit of detection (LOD) for methyl (CH₃Hg⁺) and inorganic mercury (Hg²⁺) by the method are both as 0.2 μg L⁻¹. The relative standard deviation (R.S.D.s) for CH₃Hg⁺ and Hg²⁺ are 3.0% and 5.8%, respectively. The advantages of the developed extraction method are that (1) it is easy to operate in HPLC–ICP-MS for mercury species determination since the extracted solution can be directly injected into the HPLC column without pH adjustment and (2) the memory effect of mercury in the ICP-MS measurement system can be reduced.     

An efficient method for constructing nonorthogonal localized molecular orbitals

A new method for constructing nonorthogonal localized molecular orbitals (NOLMOs) is presented. The set of highly localized NOLMOs is obtained by minimization of the spread functional starting from an initial set of canonical orthogonal molecular orbitals. To enhance the stability and efficiency, the centroids of the NOLMOs are constrained to be those of the corresponding orthogonal localized molecular orbitals (OLMOs), which are obtained with the Boys criterion in advance. In particular, these centroid constraints make the optimization for each NOLMO independent of the others, which is an attractive feature for application to large systems. The minimization with the constraints incorporated through the multiplier-penalty function method is stable and efficient in convergence. While exhibiting the classical bonding pattern in chemistry and sharing a spatial distribution similar to that of the corresponding OLMOs, the obtained NOLMOs are more compact than the corresponding OLMOs with about 10%-28% reduction in the value of the spread functional and devoid of the troublesome "orthogonalization tails."     

A novel class of amide-derived air-stable P,O-ligands for Suzuki cross-coupling at low catalyst loading

The benzamide-derived P,O-ligands efficiently promoted the Pd-catalyzed Suzuki cross-coupling reactions of aryl bromides with phenylboronic acid at 0.01 mol % of Pd loading at 60-80 °C to form biaryls in excellent yields. A sterically hindered arylboronic acid gave a quantitative yield of the coupling product at 110 °C with 1 mol % Pd.     

某些含二维液晶基元的热致液晶高分子的向列态纹影响构

发现某些含二维液晶基元的热致液晶高分子容易产生反向壁织构与含有高强度有错点（│Ｓ│大于１）的向列态纹影织构。这类液晶高分子的织构与形态学特点与含一维棒状液晶基元的其他液晶高分子不同。     

Structures, stabilities, and electronic and optical properties of c(58) fullerene isomers, ions, and metallofullerenes.

The 1205 classical isomers of fullerene C58, as well as one quasi-fullerene C58 isomer with a heptagonal ring (labeled as Cs:hept) have been investigated by the quantum chemical methods PM3, HCTH/3-21G, and B3LYP/6-31G(d). Isomer C3v:0001, which has the lowest number of adjacent pentagons, is predicted to be the most stable isomer, but the quasi-fullerene isomer Cs:hept is only 2.50 kcal mol-1 higher in energy. Systematic investigations of the electronic properties of C3v:0001 and Cs:hept find that the C3v:0001 isomer has high vertical electron affinity (3.19 eV). The nucleus-independent chemical shifts (NICS) value at the center of Cs:hept (-5.1 ppm) is more negative than that of C60 (-2.8 ppm). The NICS value at the center of the heptagonal ring in Cs:hept (-2.5 ppm) indicates weakly aromatic character. In contrast, the C58(6-) and C58(8-) ions of the C3v:0001 and Cs:hept geometries possess large aromatic character, with NICS values between -14.0 and -26.2 ppm. To clarify the thermodynamic stabilities of C58 isomers at different temperatures, the entropy contributions are taken into account on the basis of the Gibbs energy at the B3LYP/6-31G(d) level. The C3v:0001 isomer prevails in a wide range of temperatures, and the Cs:hept isomer is also an important component around 2800 K. The IR spectra of C58 isomers are simulated to facilitate experimental identification of different isomers. In addition, the electronic spectra and the second-order hyperpolarizabilities are predicted by ZINDO and the sum-over-states model. The static second-order hyperpolarizability of the C3v:0001 isomer is 96.5 % larger than that of C60, and its second-order hyperpolarizabilities at external field frequencies are at least nine times larger than those of C60.     

活性酚醛树脂中羟甲基含量的测定

本文提出一种酚醛树脂中羟甲基含量的化学分析法，分别以＾１３ＣＮＭＲ和化学分析法测定酚醛树脂的羟甲基含量。将两种测试结果与已知的投料量进行比较，证明所建立的化学分析法可行。     

Swelling kinetics and release characteristic of crosslinked chitosan: Polyether polymer network (semi-IPN) hydrogels

The aqueous swelling kinetics of a series of crosslinked chitosan (cr-CS) with glutaraldehyde (GA) interpenetrating polyether hydrogels have been studied as functions of pH, the N-deacetylation degree of chitosan, the amount of crosslinking agent, the electrolyte composition in solution, temperature, and gel composition. Based on these results, the swelling mechanism of the hydrogels was discussed. The release profiles of chlorhexidini acetas from the semi-IPN were also investigated. © 1994 John Wiley & Sons, Inc.     

RESEARCH ON CATALYSTS OF ANTI-CARBON DEPOSITION FOR CH_4 REFORMING WITH CO_2

IntroductionMethaneandcarbondioxidearetWomaincompositionsforthegreenhouseeffectandtheworldglobewanningll].ItisbeneficialtoourlivingenviroIUnenttocontrolthereleaseofthesetwogases.Theconversionofmethanetothecommonfeedstocksynthesisgas(carbonmonoxideandhydro…     

Construction and validation of an automated spray-and-trap gas chromatograph for the determination of volatile organic compounds in aqueous samples

An automated spray-and-trap (ST) chromatographic system was constructed for fast and efficient extraction of volatile organic compounds (VOCs) in aqueous samples with the capability to be deployed in the field for unattended continuous monitoring of surface or ground water. This system was built upon a commercial gas chromatograph with full automation capability using self-developed hardware and software. For sample analysis, fine droplets of the aqueous solution were generated in the extraction chamber by pressure expansion of a clean air stream through a spray nozzle. A portion of the VOCs distributed into the gas phase was retained by a multi-sorbent micro-trap kept at ambient temperature. Flash heating of the sorbent trap desorbed the enriched VOCs onto the gas chromatography (GC) with flame ionization detection (FID) for hydrocarbons or electron-capture detection (ECD) for halocarbons. In order to validate the performance of the ST method. it was compared with a more conventional method, i.e., a purge-and-trap (PT), by analyzing a serious of standard solutions containing benzene, toluene, ethylene. and o-, m-xylenes. Using a purge-and-trap method as a reference for complete extraction, the ST method showed less sensitivity. Extraction recoveries are in consistent with Henry's law constants. To test response time the ST-GC-ECD was periodically switched between tap and underground waters. Negligible carry-over of halogenated species and reproducibility better than 2% relative standard deviation (R.S.D.) can be achieved regardless of large concentration difference between the two sources, thus demonstrating applicability of the ST system for on-site monitoring.     

Simultaneous Determination of Oxytetra- cycline, Doxycycline, Tetracycline and Chlortetracycline in Tetracycline Antibiotics by High-Performance Liquid Chromatog- raphy with Fluorescence Detection

A simple, rapid and sensitive high-performance liquid chromatographic method with fluorescence detection for the simultaneous determination of oxytetracycline, doxycycline, tetracycline and chlortetracycline was developed, and successfully applied to the analysis of commercial tetracycline antibiotics. The separation was performed on a reverse-phase C₁₈ column with a gradient elution composed of methanol and sodium acetate buffer (containing disodium ethylenediaminetetraacetate and calcium chloride, pH 8.10) as the mobile phase, and fluorescence detection at 532 nm (excitation at 380 nm). The detection limits for oxytetracycline, doxycycline, tetracycline and chlortetracycline were 0.1, 0.5, 0.3 and 0.4 g L^–1, respectively. Data with respect to precision and accuracy were reported and discussed.