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1.
An on-line and fully automated method was developed for the continuous and dynamic in vivo monitoring of four arsenic species [arsenite (AsIII), arsenate (AsV), monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA)] in urine of living organisms. In this method a microdialysis sampling technique was employed to couple on-line with high performance liquid chromatography (HPLC) and hydride generation atomic absorption spectrometry (HGAAS). Dialysates perfused through implanted microdialysis probes were collected with a sample loop of an on-line injector for direct and automated injection into HPLC system hyphenated with HGAAS. The saline (0.9% NaCl) solution was perfused at the rate of 1 microl min(-1) through the microdialysis probe and the dialysate was loaded into 50 microl of sample loop. The separation conditions were optimally selected to be in phosphate buffer solution at a pH 5.2 with a flow rate of 1.2 ml min(-1). The effluent from the HPLC was first mixed on-line at the exit of the column with HCl (1 M) solution and then mixed with a NaBH4 (0.2% m/v) solution. Based on the optimal conditions obtained, linear ranges of 2.5-50 ng ml(-1) for AsIII and 6.75-100 ng ml(-1) for the other three arsenic species were obtained. Detection limits of 1.00, 2.18, 1.03 and 2.17 ng ml(-1) were obtained for AsIII, DMA, MMA and AsV, respectively. Typical precision values of 3.4% (AsIII), 5.4% (DMA), 3.6% (MMA) and 7.5% (AsV) were obtained, respectively, at a 25 ng ml(-1) level. Recoveries close to 100%, relative to an aqueous standard, were observed for each species. The average in vivo recoveries of AsIII, DMA, MMA and AsV in rat bladder urine were 56+/-5%, 60+/-9%, 49+/-3% and 55+/-7%, respectively. The use of an on-line microdialysis-HPLC-HGAAS system permitted the determination of four urinary arsenic species in the bladder of an anesthetized rat with a temporal resolution of 50 min sampling. 相似文献
2.
In this paper a gauge theory is proposed for the two-band model of Chern insulators.Based on the so-calle't Hooft monopole model,a U(1)Maxwell electromagnetic sub-field is constructed from an SU(2)gauge field,from which arise two types of topological defects,monopoles and e2 merons.We focus on the topological number in the Hall conductance σxy=e2/hC,where C is the Chern number.It is discovered that in the monopole case C is indeterminate,while in the meron case C takes different values,due to a varying on-site energy m.As a typical example,we apply this method to the square lattice and compute the winding numbers(topological charges)of the defects;the C-evaluations we obtain reproduce the results of the usual literature.Furthermore,based on the gauge theory we propose a new model to obtain the high Chern numbers|C|=2,4. 相似文献
3.
Mounicou S Vonderheide AP Shann JR Caruso JA 《Analytical and bioanalytical chemistry》2006,386(5):1367-1378
Selenoproteins have been identified in a diverse range of organisms, including bacteria and animals. Their occurrence and
role in the plant kingdom are, however, less well-understood. This work investigated the water-soluble selenium-containing
proteins extracted from a selenium-accumulating plant species (Brassica juncea) and a nonaccumulator species (Helianthus annuus) exposed to varying forms and concentrations of selenium. Firstly, protein extracts were analyzed by size exclusion chromatography
coupled to inductively coupled plasma mass spectrometry; specific detection was achieved by monitoring characteristic isotopes.
Then, proteolytic digests of the plant extracts were analyzed by reversed phase chromatography coupled to ICP–MS in order
to investigate selenoamino acid and selenopeptide content. Selenomethionine was observed to be the primary constituent of
the proteins of the nonaccumulator plant, while selenocystine and selenomethionine were found in the same proportion in the
accumulator extract. One main selenium-containing species was present at higher levels in the root digests than in the leaf
digests; levels were greater in the nonaccumulator than in the accumulator plant. 相似文献
4.
Wei-Chang Tseng Keng-Chang Hsu Christopher Stephen Shiea Yeou-Lih Huang 《Analytica chimica acta》2015
Trace element speciation in biomedical and environmental science has gained increasing attention over the past decade as researchers have begun to realize its importance in toxicological studies. Several nanomaterials, including titanium dioxide nanoparticles (nano-TiO2), carbon nanotubes (CNTs), and magnetic nanoparticles (MNPs), have been used as sorbents to separate and preconcentrate trace element species prior to detection through mass spectrometry or optical spectroscopy. Recently, these nanomaterial-based speciation techniques have been integrated with microfluidics to minimize sample and reagent consumption and simplify analyses. This review provides a critical look into the present state and recent applications of nanomaterial-based microanalytical systems in the speciation of trace elements. The adsorption and preconcentration efficiencies, sample volume requirements, and detection limits of these nanomaterial-based speciation techniques are detailed, and their applications in environmental and biological analyses are discussed. Current perspectives and future trends into the increasing use of nanomaterial-based microfluidic techniques for trace element speciation are highlighted. 相似文献
5.
Linear programming (LP) is the core model of constrained optimization. The Simplex method (Simplex in short) has been proven in practice to perform very well in small- or medium-sized LP problems. A new algorithm called the direct cosine Simplex algorithm (DCA) is presented here to improve upon Simplex and to solve LP problems. The proposed DCA implements a specific cosine criterion to choose the entering variable instead of the traditional most negative rule used in Simplex. Three examples are given to illustrate the implementation of the proposed DCA to improve Simplex and to serve as the optimization tool. The utility of the proposed approach is evident from the extensive computational results on test problems adapted from NETLIB. DCA reduced the number of iterations of Simplex in most cases in our computational experiment. Preliminary results for medium-sized problems are encouraging. 相似文献
6.
Mueller-Spitz SR Vonderheide AP Shann JR Caruso JA Kinkle BK 《Analytical and bioanalytical chemistry》2006,386(1):142-151
The potential of chromium to bind to DNA isolated directly from soil microbial communities was investigated in this study.
An analytical scheme was developed to distinguish between chromium bound to DNA and its fragments or chromium contained elsewhere
in an environmental DNA extract. DNA was extracted from chromium-contaminated soils and purified using DNA clean-up resins.
Size-exclusion chromatography was employed due to its advantages in the separation and molecular weight approximation of large
biomolecules. It was coupled with two on-line detection systems (spectrophotometric and inductively coupled plasma mass spectrometric)
to study the binding of chromium to DNA or other components in a DNA extract. A collision cell was pressurized with helium
to remove diatomic and polyatomic interferents resulting from the chosen mobile phase. Chromium peaks were observed in both
the large and small molecular weight regions of the chromatogram; to further confirm that the environmentally extracted DNA
contained Cr, the subsequently purified DNA was examined for total Cr using flow injection ICP–MS to accommodate small sample
volumes. DNA samples isolated from the two soils examined contained 0.5–0.7 ppb Cr, indicating that DNA isolated directly
from a chromium-contaminated soil has chromium bound to the nucleic acids. 相似文献
7.
金属卟啉能够在温和条件下催化烃类的部分氧化,且有较好的选择性因此,金属卟啉的仿生催化研究不仅具有重大的理论意义,亦有广阔的应用前景,现已成为仿生催化领域中人们极感兴趣的工作,但是,金属卟啉化合物催化领域中人们极感举的工作,但是,金属卟啉化合物催化烃类氧化时,一般须使用诸如PhIO、NaClO、H2O2这样的单氧原子供体作氧化剂,或使用诸如锌粉、Vc等还原剂加分子氧体系,从实际应用来看,单独使用分子氧为氧化剂用于金属卟啉催化烃类氧化是最具诱惑力的。然而,在这方面的研究报导仅见于多卤代卟啉,我们在探索单独用空气作用氧化剂进行金属卟啉仿生催化时发现,象乙苯这样含有相对较为活泼的C-H键的分子,在μ-氧化双锰卟啉([TPPMn]2O)的催化下,亦能够直接被分子氧氧化,本工作考察了各种因素对该反应的影响。 相似文献
8.
Jenn-Yuan Sheu Po-Hua Chen Wei-Chang Tseng Chang-Yu Chen Li-Yu Tsai Yeou-Lih Huang 《Analytical sciences》2003,19(6):957-960
A simple and sensitive spectrophotometric method for the determination of a thiobarbituric acid-reactive substance (TBARS) in human hair has been developed. The proposed method is based on the formation of a red-colored product by the reaction of products of lipid peroxidation with thiobarbituric acid in an acidic medium. The absorbance of the resulting red product was measured at 534 nm. The linear dynamic range was between 1.0 and 20 micromol/L. The recoveries were 98.3-105.0%, and the relative standard deviations (RSD) were 0.32-1.24, respectively. TBARS in digested hair sample was stable for 3 days at room temperature. It was found that, using this method, the hair TBARS concentration in smokers (0.116 +/- 0.030 micromol/g, n = 30) was significantly higher than that in non-smokers (0.096 +/- 0.015 micromol/g, n = 30) (p < 0.05). 相似文献
9.
本文得到氧氯化催化剂的转化率-空速关系曲线.由高空速到低空速和由低空速到高空速所测得的曲线差异较大,在高空速下催化剂活性衰减比低空速下快得多;其根源是催化剂的成份、结构和活性随反应气氛而变化.文中建议用络合-还原氧化机理来解释有关现象.此催化剂在一定温度和原料配比下有一“最宜空速”,在此空速下HCl转化率最高,低于此空速HCl转化率不但不增高反而降低,原因是生成的二氯乙烷再裂解生成HCl.副反应由乙烯氧化生成的CO和CO2是并联反应,它是CuCl2催化氧化的结果. 相似文献
10.
核壳结构镍的制备及催化性能 总被引:2,自引:0,他引:2
利用软化学方法制备出了聚苯乙烯(PS)/镍核壳结构和纳米镍催化剂, 并利用SEM和XRD对材料的形貌和结构进行了表征. 将上述催化剂应用于亚甲基蓝染料加氢反应, 一步实现染料褪色和硼氢化钠水解制氢. 研究表明, 核壳结构极大地提高了镍的催化能力. 在相同条件下, 核壳结构镍的加氢催化效率是纳米镍的1.42倍, 产氢效率是纳米镍的4.76倍, 这说明核壳结构在催化领域具有一定的优势. 相似文献