Variation of S/G ratio and lignin content in a Populus family influences the release of xylose by dilute acid hydrolysis

Wood samples from second generation Populus cross were shown to have different lignin contents and S/G ratios (S: syringyl-like lignin structures; G: guaiacyl-like lignin structures). The lignin contents varied from 22.7% to 25.8% and the S/G ratio from 1.8 to 2.3. Selected samples spanning these ranges were hydrolyzed with dilute (1%) sulfuric acid to release fermentable sugars. The conditions were chosen for partial hydrolysis of the hemicellulosic fraction to maximize the expression of variation among samples. The results indicated that both lignin contents and S/G ratio significantly affected the yield of xylose. For example, the xylose yield of the 25.8% lignin and 2.3 S/G (hihg lignin, high S/G) sample produced 30% of the theoretical yield, whereas the xylose yield of the 22.7% lignin and 1.8 S/G (low lignin, low S/G) was 55% of the theoretical value. These results indicate that lignin content and composition among genetic variants within a single species can influence the hydrolyzability of the biomass.     

A simple gas chromatographic technique to determine trace impurities in gases

A new method is described which allows the determination of trace impurities in flowing gases without removing a sample. The technique is based upon gas fractionation by a sudden change of flow through a small orifice or capillary.     

超高效液相色谱-串联质谱法测定减肥类保健品中的西布曲明

采用超高效液相色谱-串联质谱法测定减肥类保健品中的西布曲明。样品经甲醇超声提取后,使用Phenomenex Kinetex C18色谱柱分离,以乙腈-10mmol·L-1乙酸铵溶液(含0.1%甲酸)为流动相进行梯度洗脱,质谱中选择多反应选择离子监测模式检测,以西布曲明-D6作为同位素内标进行定量。西布曲明的质量浓度在5.00~400μg·L-1范围内呈线性,测定下限(10S/N)为10ng·g-1。加标回收率在97.0%~104%之间,相对标准偏差(n=9)为1.1%~3.0%。     

A simple mathematical method to determine the efficiencies of log-conical detectors

A new type of photon detector, log-conical, is proposed. The average path length traveled by an incident photon of arbitrary energy as well as the geometrical solid angle are calculated in a mathematical expression to determine the efficiencies of this detector for an arbitrarily positioned isotropic radiating point source. The off-axis effect of the source position was analyzed to demonstrate the powerful capability of the proposed method. The results are compared with those obtained using a standard 3″×3″ cylindrical detector of the same volume in order to show the enhanced efficiency of the log-conical detector.     

A simple indirect automatic method to determine total iodine in milk products by flame atomic absorption spectrometry

A simple, precise and accurate automatic method for the determination of total iodine in milk products by indirect atomic absorption spectrometry is proposed. Iodide in solutions resulting from alkaline ashing of samples is precipitated with silver ion in a precipitation-dissolution flow manifold, which allows performing on-line the retention of the silver iodide precipitate formed on a filter, its wash with diluted ammonia and its dissolution with a diluted thiosulfate solution. Dissolved silver is also determined on-line by flame atomic absorption, and the achieved amount of this metal is proportional to that of iodine in the sample. The proposed method is very selective, avoids interferences from anions present in the samples, which can be also precipitated with silver, because these silver compounds are dissolved with ammonia at the washing step. This method allows the determination of iodine in the range 0.011-0.35 μg mL⁻¹ with a relative standard deviation between 1.3 and 6.8% at a rate of ca. 17 samples h⁻¹.     

A simple method to determine the mean cluster size in a molecular beam

A method based upon the tandem use of the Time-Of-Flight and Surface-Induced-Dissociation techniques is proposed for estimating the average cluster size in a neutral molecular beam. It consists of sending the beam through a buffer gas and measuring the variations of the average beam velocity as a function of the buffer gas pressure. The clusters are detected at the mass of the monomer by surface induced dissociation in the ionization source. This method has been applied to an argon cluster beam and the results are in good agreement with determinations using high energy electron diffraction. This technique appears to be a simple alternative for estimating mean cluster sizes in the range of 100 to a few 1000 monomers.     

超高效液相色谱-串联质谱法测定发泡聚苯乙烯材料中的六溴环十二烷

采用超高液相色谱-串联质谱法同时测定发泡聚苯乙烯材料中阻燃剂α,β,γ-六溴环十二烷(HBCD)。样品用乙腈进行萃取,选用Waters ACQUITY UPLC@BEH C18色谱柱分离,以乙腈-5 mmol·L-1乙酸铵溶液为流动相进行梯度洗脱,质谱中选用多反应监测模式分析。HBCD各异构体的质量浓度在一定范围内与峰面积呈线性关系,测定下限(10S/N)为0.2 mg·kg-1。加标回收率在81.7%~102%之间,测定值的相对标准偏差(n=7)小于15%。     

一种测定功能蛋白与其配体结合参数的简单方法

以羰基二咪唑法分别将牛血清白蛋白(BSA)和β2-肾上腺素受体(β2-AR)键合在大孔硅胶上,合成两种色谱固定相。采用直接进样法测定BSA与奥美拉唑、普萘洛尔和盐酸异丙嗪的结合常数及结合位点数,β2-AR与盐酸异丙肾上腺素、沙丁胺醇和去甲肾上腺素的结合常数及结合位点数。方法可用于功能蛋白与其配体分子相互作用的研究。     

A simple rapid method to precisely determine 13C/12C ratios of plant methoxyl groups

Stable isotope ratios of individual plant components have become a valuable tool for the determination of the geographical origin and authenticity of foodstuff. A recently published method with considerable potential in this context is the measurement of the deuterium/hydrogen (D/H) isotope ratios of plant matter methoxyl groups. The method entailed cleavage of methyl ethers or esters with hydriodic acid (HI) to form gaseous methyl iodide (CH₃I) and then measurement of the δ²H value of this gas. Here, as a follow up to a previous study, we describe a method for the rapid and precise δ¹³C analysis of plant matter methoxyl groups using gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). Conditions for sample preparation were investigated for isotope discrimination effects, the GC conditions optimized, the reproducibility of the measurement of standards undertaken, and the precision of the method defined. The reproducibility of the δ¹³C value determined for a CH₃I standard on 20 consecutive measurements was found to be 0.17‰. The method was also tested on four methoxyl‐rich plant components: vanillin, lignin, wood and pectin. The analytical precision obtained, expressed as the average standard deviation, for these compounds was found to be better than 0.13‰. The described procedure which is simple and rapid, allowing preparation and analysis of a sample within 1 h, produces accurate and reproducible isotopic measurements. We suggest that this validated δ¹³C method when employed together with the recently published δ²H method for two‐dimensional stable isotope studies of organic matter containing methoxyl groups will be of considerable value, e.g. for proving the authenticity of foodstuff. Copyright © 2009 John Wiley & Sons, Ltd.     

一种测定功能蛋白与其配体结合参数的简单方法

以羰基二咪唑法分别将牛血清白蛋白(BSA)和β2-肾上腺素受体(β2-AR)键合在大孔硅胶上,合成两种色谱固定相。采用直接进样法测定BSA与奥美拉唑、普萘洛尔和盐酸异丙嗪的结合常数及结合位点数,β2-AR与盐酸异丙肾上腺素、沙丁胺醇和去甲肾上腺素的结合常数及结合位点数。方法可用于功能蛋白与其配体分子相互作用的研究。     

Presence of 5-hydroxyguaiacyl units as native lignin constituents in plants as seen by Py-GC/MS

The presence of 5-hydroxyguaiacyl moieties in the lignin from several plants has been assessed by Py-GC/MS. Different woody (eucalypt) and nonwoody (flax, hemp, kenaf, jute, sisal and abaca) angiosperms were selected for this study. The pyrolysis of whole fibers released lignin-derived products with p-hydroxyphenyl, guaiacyl and syringyl structures. Indeed, a series of compounds having a 5-hydroxyguaiacyl nuclei, including 3-methoxycatechol, 5-vinyl-3-methoxycatechol and 5-propenyl-3-methoxycatechol, were detected and identified in all samples, although in lower amounts than the normal guaiacyl or syringyl compounds. The analysis of the lignins isolated from the same plants also showed the same 3-methoxycatechol derivatives found after whole fiber pyrolysis. These compounds are supposed to arise from the pyrolysis of 5-hydroxyguaiacyl moieties, which are supposed to be native constituents of lignin in plants forming benzodioxane substructures.     

A simple iodination protocol via in situ generated ICl using NaI/FeCl3

A novel iodination of silyl-enol ethers using hitherto unexplored NaI/FeCl₃ system is reported. The procedure has been extended to the iodination of aromatic and hetero aromatic compounds.     

A simple method to determine the anomeric configuration of sialic acid and its derivatives by 13C-NMR

The anomeric configuration of sialic acid and its derivatives could be determined on the basis of the coupling pattern of C-1 in the gated proton-decoupled or selective proton decoupled ¹³C-NMR spectra; the α anomer gave a doublet C-1 signal while the β gave a singlet.The α-anomers gave a doublet C-1 signal while the β gave a singlet in their selective proton-decoupled spectra.     

A simple and versatile method to determine the enantiomeric purity of Diels-Alder adducts

The determination of the enantiomeric purity of Diels-Alder adducts derived from cyclopentadiene and a series of electron-deficient dienophiles is conveniently achieved by HPLC analysis on their 2,4-dinitrophenylhydrazine derivatives formed in one pot directly from the cycloaddition reaction.     

Using gas chromatography/isotope ratio mass spectrometry to determine the fractionation factor for H2 production by hydrogenases

Hydrogenases catalyze the reversible formation of H(2), and they are key enzymes in the biological cycling of H(2). H isotopes have the potential to be a very useful tool in quantifying hydrogen ion trafficking in biological H(2) production processes, but there are several obstacles that have thus far limited the application of this tool. Here, we describe a new method that overcomes some of these barriers and is specifically designed to measure isotopic fractionation during enzyme-catalyzed H(2) evolution. A key feature of this technique is that purified hydrogenases are employed, allowing precise control over the reaction conditions and therefore a high level of precision. In addition, a custom-designed high-throughput gas chromatograph/isotope ratio mass spectrometer is employed to measure the isotope ratio of the H(2). Using our new approach, we determined that the fractionation factor for H(2) production by the [NiFe]-hydrogenase from Desulfovibrio fructosovorans is 0.273 ± 0.006. This result indicates that, as expected, protons are highly favored over deuterium ions during H(2) evolution. Potential applications of this newly developed method are discussed.     

超高效液相色谱-串联质谱法测定畜产品中6种青霉素类药物残留

采用超高效液相色谱-串联质谱法快速测定牛肉和牛奶中青霉素类药物残留。样品以磷酸盐缓冲溶液提取、乙酸锌沉淀蛋白、正己烷脱脂,然后经HLB固相萃取柱净化后,采用超高效液相色谱-串联质谱分离检测,外标法定量。6种青霉素的线性范围均在25.0μg·L-1以内,检出限(3S/N)为2μg·kg-1,测定下限(10S/N)为5μg·kg-1。加标回收率在77.0%~99.8%之间,测定值的相对标准偏差(n=6)在3.7%~13%之间。     

A simple approach to determine the equilibrium shape and position of sandwiched polymer droplets

The thermodynamic shape and position of a polymer drop sandwiched between two polymer melt plates were predicted by simulating the change of the interfacial energy according to various shapes and position of the drop. The calculation results were in a precise coincidence with the experimental results exhibiting lens, spreading, and encapsulation. The simple formula and easy concept of the calculation can be useful to predict the morphology of immiscible ternary blends with the information of the interfacial tensions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2729–2738, 2007     

A method to determine mixing enthalpies by DSC

A method has been developed that utilizes a special custom-made mixing device and HPLC micro liter syringe to perform mixing experiments of liquid systems directly in open measuring cells of differential scanning calorimeters. The present paper describes how to determine mixing enthalpies from time scans of the isothermal heat flux during an exothermal or endothermal process. Using ethylene glycol and the slightly volatile component water to calibrate the mixing calorimeter, the mixing enthalpy of the binary system poly(ethylene glycol) 400/water could be determined with sufficient precision compared to the results of measurements with a conventional flow calorimeter. This revised version was published online in July 2006 with corrections to the Cover Date.     

A new and simple method to determine trace levels of sulfonamides in honey by high performance liquid chromatography with fluorescence detection

A novel method for the simultaneous analysis at trace level of sulfonamides (sulfaguanidine, sulfanilamide, sulfacetamide, sulfathiazole, sulfapyridine, sulfachloropyridazine, sulfamerazine, sulfameter, sulfamethazine, sulfadoxine, sulfadiazine, sulfamonomethoxine, sulfadimethoxine) in honey is described. Methanol has been used in the sample treatment step to avoid the emulsion formation and to break the N-glycosidic bond between sugars and sulfonamides. The determination is carried out by liquid chromatography in gradient elution mode, with fluorescence detection after the on-line pre-column derivatization with fluorescamine. The influence of parameters such as the mobile phase composition, column temperature, pH or injection volume, on the separation has been taken into account and the derivatization step has also been optimized. Recoveries of the compounds on spiked honey samples ranged from 56% for sulfadoxine to 96% for sulfacetamide, with relative standard deviations below 10%. The quantitation limits are between 4 and 15 ng g⁻¹.