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1.
Abstract: Techniques are described for measuring the isotope distribution in dissolved nitrate and N 2 using membrane inlet mass spectrometry, which allows several gases to be measured in a water sample without the need for any separation steps. The isotope distribution in dissolved nitrate was measured using denitrifying Pseudomonas nautica to reduce the nitrate to N 2 which was then measured by mass spectrometry. Pseudomonas nautica NCIMB 1967 was easily grown in nitrate-limited continuous culture minimising intra- or extracellular nitrate or nitrite pools, and the bioassay was tolerant of a range of salinities. The precision of the bioassay when measuring samples with high 15NO 3− contents (0.5 μmol) was 0.05 atom%; with 0.1 μmol 15NO 3−, the precision was around 0.2 atom%. Differences in labelling of N 2 in preserved samples obtained from 15NO 3− incubations of water-covered sediment cores were measured on parallel samples with membrane inlet MS and GC-MS. The membrane inlet technique was accurate but the precision on ratio measurements was lower than by GC-MS. 相似文献
2.
Abstract Newly developed low capacity columns were used in suppressed ion chromatography for rapid and highly reproducible determination of SO 42− in porewater samples from freshwater sediments without preconcentration of samples. With a 50 μl injection the detection limit for SO 42− was ca. 50 pmol (= 1 μ M) with a precision of 1–3% at the 10–200 μM level and <1% at concentrations above 200 μM. SO 42− could be measured in 4–5 min with the routinely used eluent (3.0 mM NaHCO 3/0.8 mM Na 2CO 3). When the strength of the eluent was increased to 3.0 mM NaHCO 3/2.0 mM Na 2CO 3, sulfate analysis was possible in less than 3 min, provided that samples were nitrate-free. Under these conditions S 2O 32− could also be sensitively determined in about 6 min. Examples of application of the method are given for measurements of sulfate reduction rates in freshwater sediment samples from Lake Constance. 相似文献
3.
We developed a reliable, simple and sensitive method to determine free and total morphine in human liver and kidney, using gas chromatography-mass spectrometry (GC-MS). Free morphine or total morphine obtained by acid hydrolysis from 0.2g tissue sample was extracted using an Extrelut NT column with an internal standard, dihydrocodeine, followed by trimethylsilylation. The derivatized extract was submitted to GC-MS analysis of EI-SIM mode. The calibration curves of morphine in both liver and kidney samples were linear in the concentration range from 0.005 to 5 microg/g. The lower limits of detection of morphine were 0.005 microg/g. This method proved successful when we determined free and total morphine in liver and kidney obtained from an autopsied man who was mis-ingested morphine compound in the hospital, which resulted in the cause of death being morphine intoxication. 相似文献
4.
A gas chromatographic-mass spectrometric (GC-MS) method is described for the measurement of amphetamine (AMP) using negative chemical ionization (NCI) mode. Without prior extraction AMP was derivatized with 2,3,4,5,6-pentafluorobenzoyl chloride (PFBC) and simultaneously extracted into toluene. The toluene extract was injected directly into GC-MS equipped with a HP-1 capillary column. The method is simple and more sensitive than most of the previously published methods. The limit of quantification of amphetamine is 25pg (1.4pg on column) with a very limited sample volume (25microl). The within-day precision was from 1.7 to 5.1% and between-day precision was from 2.2 to 7.3%. The method has been used for the measurement of several thousand microdialysate and ultrafiltrate samples and proven reliable. 相似文献
5.
The effect of vitamin B 6 on the levels of tissue selenium (Se) and glutathione peroxidase (GSH-Px) was studied. Male Wistar 4-week-old rats were fed a vitamin B 6-Se-deficient basal diet for 2 weeks, then divided into 10 groups of five or six rats and fed their respective diets for 4 weeks. The experimental design was a 2×2×2 factorial with two levels of vitamin B 6, two forms of Se, and two levels of Se, plus two extra groups (vitamin B 6-supplemented and deficient without Se). Vitamin B 6 was 0 and 250 μg pyridoxine-HCl/100 g of diet; Se forms were Na 2SeO 3 and DL-selenomethionine; Se levels were 0.5 and 5.0 mg Se/kg of diet. Regardless of form or level of Se, vitamin B 6-deficient rats had lower body weights and organ weights than vitamin B 6-supplemented rats. At 5.0 mg Se/kg of diet, Na 2SeO 3 caused a further depression. Vitamin B 6 deficiency resulted in a higher Se level and GSH-Px activity in plasma of rats fed selenomethionine. However, Se content an GSH-Px activity in erythrocytes were significantly elevated in vitamin B 6-supplemented rats compared with vitamin B 6-deficient rats. Se levels in muscle and heart were significantly lower in vitamin B 6-deficient groups fed Na 2SeO 3 than in vitamin B 6-supplemented groups. Vitamin B 6-deficient rats fed selenomethionine had higher Se levels in muscle, heart, spleen, liver, and kidneys than vitamin B 6-supplemented rats. Activity of GSH-Px in muscle, heart, and spleen was significantly lower in vitamin B 6-deficient groups than in vitamin B 6-supplemented groups, regardless of form of Se. A significant decrease of GSH-Px in liver was observed in vitamin B 6-deficient rats fed selenomethionine compared with vitamin B 6-supplemented rats, whereas no significant decrease was observed in those fed Na 2SeO 3. These results suggest that vitamin B 6 is involved in the distribution and transportation of Se in body and the metabolism of selenomethionine in liver. 相似文献
6.
The thermolysis of trans-IrL 2(CO)Cl(H)(C 6H 5) (1abd; L=P(i-Pr) 3; H trans to CO) produces benzene and the Vaska-type complex IrL 2(CO)Cl. A mechanistic study of the reaction has shown that 1a reversibly loses CO at 120 °C (as evidenced by the incorporation of 13CO) and isomerizes to the previously unreported 1b (H trans to Cl). It was found that 1b is the complex primarily responsible for the formation of benzene upon thermolysis under CO atmosphere; direct loss of benzene from 1a was determined to be, at most, a minor pathway. Benzaldehyde was also formed as a product of thermolysis of 1a under CO atmosphere. The first-order rate constant for benzene elimination in the absence of CO was found to be 8.5 × 10 −5 s −1. The presence of only 5 Torr CO results in a decrease to 2.0 × 10 −5 s −1, but little further inhibition is observed above 5 Torr CO. Added dihydrogen (100 Torr) was found to effect a novel catalysis of benzene elimination from 1a in the absence of CO atmosphere; it is suggested that trace amounts of dihydrogen, present in solutions of 1a, are responsible for the enhanced rate of elimination in the absence of CO. The thermolysis of 1-d 6 in toluene was found to proceed without any toluene incorporation, implying that arene loss is irreversible. 相似文献
7.
The reaction of Cu(II) ions with a sodium salt of new Schiff base ligand NaL 1, sodium N-2-methyl pyridine-2-imine benzoate, in alkaline medium produced an imine bond coupled ligand and a novel complex, Na 2[Cu(L 3) 2], L 3 = 2,5-di(2-benzoic acid)-4-(2-pyridine)-1-(2-methyl-2-pyridine)-imidazolidine. When the reduced form of the sodium salt of the Schiff base ligand, NaL 2, is employed, a simple hexacoordinated copper(II) complex, [Cu(L 2) 2], [L 2] − = bis( N-(2-methylpyridine)-2-aminomethylbenzoate), was isolated. The compounds were characterized by spectroscopic methods and the molecular structures of [Cu(L 2) 2] and Na 2[Cu(L 3) 2] were determined by single-crystal X-ray diffraction methods. Reaction mechanism for the synthesis of, Na 2[Cu(L 3) 2], copper(II) promoted imine bond coupling is proposed and discussed. The redox behavior of [Cu(L 2) 2] and Na 2[Cu(L 3) 2], studied using cyclic voltammetry and electron paramagnetic resonance spectroscopic methods, are also discussed. 相似文献
8.
The enthalpies of reaction of HMo(CO) 3C 5R 5 (R = H, CH 3) with diphenyldisulfide producing PhSMo(CO) 3C 5R 5 and PhSH have been measured in toluene and THF solution (R = H, Δ H= −8.5 ± 0.5 kcal mol −1 (tol), −10.8 ± 0.7 kcal mol −1 (THF); R = CH 3, Δ H = −11.3±0.3 kcal mol −1 (tol), −13.2±0.7 kcal mol −1 (THF)). These data are used to estimate the Mo---SPh bond strength to be on the order of 38–41 kcal mol −1 for these complexes. The increased exothermicity of oxidative addition of disulfide in THF versus toluene is attributed to hydrogen bonding between thiophenol produced in the reaction and THF. This was confirmed by measurement of the heat of solution of thiophenol in toluene and THF. Differential scanning calorimetry as well as high temperature calorimetry have been performed on the dimerization and subsequent decarbonylation reactions of PhSMo(CO) 3Cp yielding [PhSMo(CO) 2Cp] 2 and [PhSMo(CO)Cp] 2. The enthalpies of reaction of PhSMo(CO) 3Cp and [PhSMo(CO) 2Cp] 2 with PPh 3, PPh 2Me and P(OMe) 3 have also been measured. The disproportionation reaction: 2[PhSMo(CO) 2Cp] 2 → 2PhSMo(CO) 3Cp + [PhSMP(CO)Cp] 2 is reported and its enthalpy has also been measured. These data allow determination of the enthalpy of formation of the metal-sulfur clusters [PhSMo(CO) nC 5H 5] 2, N = 1,2. 相似文献
9.
The superoxide adduct of 5,5-dimethyl-l-pyrroline-N-oxide (DMPO) has been detected by EPR spectroscopy in aprotic solvents using KO 2 solubilized in 18-crown-6-ether as a source of superoxide. The EPR hyperfine splitting constants of the DMPO-superoxide adduct were as follows: benzene/toluene (a N = 12.65 G; a ββ = 10.4G; a γ = 1.3G); heptane (a N = 12.49G; a ββ = 10.29G; a γH = 1.2g); and acetone (a N = 12.6G; a ββ = 10.17 G; a γ = 1.3 G). The EPR parameters for benzene, toluene and heptane differ significantly from previously reported values. A plot of the hyperfine splitting constants for the DMPO superoxide adduct as a function of solvent polarity (Kosower Z value) indicates that while a N and a ββ both decrease by about 1 G on going from water to ethanol, further decreases in polarity do not greatly affect these EPR parameters. 相似文献
10.
The fluoro-hydrido-oxo complex [Re(F)(H)(O)Cyttp] + (3, Cyttp = PhP(CH 2CH 2CH 2PCy 2) 2) was prepared in high yield from [Re(H 2)H 4Cyttp]SbF 6 (1(SbF 6), NaSbF 6 and acetone in toluene at reflux. Reaction chemistry of 3 has been studied and, where appropriate, compared with that of the related dihydrido-oxo complex [ReH 2(O)Cyttp] + (2). Unlike 2, which readily reacts with both CO and SO 2, 3 was found to be inert to these reagents under comparable conditions. However, 3(SbF 6) reacts with NaSbF 6 at elevated temperature to afford the difluoro-oxo complex [ReF 2(O)Cyttp] + (4). 4 undergoes fluoride substitution by Cl − or Br − to yield [Re(X)(F)(O)Cyttp] + (X = Cl (5, Br (6)). 5 can also be obtained by treatment of 6(BPh 4) with LiCl. All of these complexes contain mer-Cyttp, and 3–6 contain trans fluoride and oxide ligands as inferred from spectroscopic data. 相似文献
11.
采用气相色谱法定量分析毛豆上腈菌唑的微量残留量。样品经乙腈提取,液液分配,中性氧化铝柱层析净化后,以气相色谱电子俘获检测器法(GC-ECD)测定,DB-1701毛细管柱、氮气为载气,柱温150℃20℃/min 260℃(10 min),气化室温度240℃,检测器温度300℃,外标法定量。该方法快速、准确,在0.05~2.00 mg/L范围内线性相关系数r 2=0.9998,平均回收率91.1%~99.0%,变异系数1.22%~2.94%,最小检测量1.0×10 -12 g,最低检出浓度5.0×10 -4 mg/kg。 相似文献
12.
The hydrolysis of inositol [ 32P]trisphosphate (IP 3) and inositol [ 32P]bisphosphate (IP 2) has been examined in subcellular fractions of rat liver. IP 3 was degraded by an enzyme located in the plasma membrane which did not degrade IP 2. Cytosolic fractions were found to degrade both IP 3 and IP 3. The IP 3 phosphatase activity of liver plasma membranes displayed a neutral pH optimum, was Mg 2+ dependent and was not inhibited by high concentrations of Li +. Half-maximal activity of the enzymes hydrolysing IP 3 and IP 2 was obtained with substrate concentrations in the range 1–2μM. The significance of these observations to the proposed Ca 2+ -mobilizing role of IP 3 is discussed. 相似文献
13.
Plasma selenium reference values from healthy donors in the metropolitan area of Barcelona are determined. A random sample from 156 healthy adults (control group) is analysed by using electrothermal atomic absorption spectrometry with Zeeman effect background correction. The relationship between several pathologies and Se content is also evaluated. Se content from 64 samples from subjects with chronic renal failure and 54 from subjects suffering from several malignancies are determined and the results are compared to the reference values. Moreover, Se contents are determined and compared in two groups of children, healthy (19 samples) and children of mothers infected with HIV-1 (16 samples). In the control group, Se plasma concentration ranges between 50 and 145 μg · L−1 (82.2 ± 17.5 μg · L−1). Significantly lower values are found in the two pathologies studied (malignancy and chronic renal failure), compared to the control group. However, no significant differences in Se content are found between the two groups studied regarding malignancy and chronic renal failure. In children of mothers infected with HIV-1, Se status is significantly lower than that of healthy children. 相似文献
14.
A rapid and simple method for enumerating total aerobic plate counts (APC) and coliforms in raw milk was developed and compared with conventional plating method. Following two-fold serial dilution of samples in a 96 well microtiter plate, double strength of two different modified media for APC or coliforms was added to each well. The final positive well (purple to yellow color) was determined and converted to dilution factors. The dilution factor of each sample was converted to Log 10 DF (Dilution factors) and compared to actual microbial numbers Log 10 CFU/mL. The results of 2-fold dilution method (Log 10 DF) were strongly correlated to conventional plating method (Log 10 CFU/mL) (P < 0.05). The correlation of the scatterplot of spread plating and 2-fold dilution method indicated a high level of agreement between two methods (R 2= 0.921 for total counts and R 2= 0.916 for forms from raw milk). This 2-fold dilution method is an easy, rapid, and economical method for enumeration of total microbial loads and coliforms in raw milk. 相似文献
15.
A method to determine Mn-superoxide dismutase activity by measuring directly the rate of decay of O 2- in a spectrophotometer, is described. Decay of O 2- generated by KO 2 at pH 9.5, was monitored as the fall in absorbance (A 250nm-A 360nm). Mn-superoxide dismutase was determined as the activity of cyanide-resistant superoxide dismutase, calculated from the rate of O 2- dismutation. Mn-superoxide dismutase could be determined in the presence of a 700 times higher Cu, Zn-superoxide dismutase activity. The alkaline pH did not cause analytical problems. The assay was used to measure both Mn- and Cu, Zn-superoxide dismutase activity in mitochondrial preparations. The assay had a detection limit of 2.8 ng/ml when Mn-superoxide dismutase from E. coli was used, and the between-day CV was 5.8%. The assay is an alternative to indirect methods for detecting superoxide dismutase activity. 相似文献
16.
Aqueous solutions of fractions of an extracellular linear mannan formed by Rhodotorula rubra yeast have been investigated by hydrodynamic methods (high-speed sedimentation, translation isothermic diffusion and viscometry). The molecular weight was determined according to Svedberg (
) and the polydispersity parameters of the initial sample were also determined ( Mw/ Mn = 1·20 and Mz/ Mw = 1·21). Relationships between the molecular weight ( M) and so, Do and [η] in the range
were: [η] = 2·33 × 10 −2 M0.75, Do = 1·65 × 10 −4 M0·58, so = 2·24 × 10 −15 M0·43. The equilibrium rigidity and hydrodynamic diameter of chains representing mannan molecules were evaluated. 相似文献
17.
A bienzyme (tyrosinase and horseradish peroxidase) electrochemical biosensor was developed for detection of Salmonella typhimurium, and evaluated for application in a flow injection system coupled with immunomagnetic separation for food samples. Parameters for immunomagnetic separation, enzymatic reaction, flow injection and electrochemical detection were determined using pure culture samples. The selectivity was tested in the presence of Listeria monocytogenes, Campylobacter jejuni and E. coli 0157:H7. The results showed a linear relationship for logarithmic values between peak current ratio and the cell number of S. typhimurium in the range of 10 3 10 5 cfu/mL, with R 2= 0.99. The detection limit of this method was 1.09 × 10 3 cfu/mL for S. typhimurium and the detection time was 2.5 h. Samples of chicken carcass wash water and ground beef were used to evaluate the biosensor. The results demonstrated that this biosensor has a potential for rapid detection of different pathogens in various food samples. 相似文献
18.
The roles of Ca 2+ and Cl − on the photosynthetic O 2 yield under flash illumination have been examined in EDTA-washed preparations of the cyanobacterium Anacystis nidulans. Especially the effect of Cl − deficiency on the O 2 yield and on the S-state distribution was analyzed. As the results show, omission of both Ca 2+ and Cl − (Mn 2+ present) almost totally inhibited O 2 evolution. When Ca 2+ was replaced by Na +, a substantial reduction of the O 2 yield was observed, but only a minor change in the S-state distribution occurred. However, when Cl − was displaced by NO −3, which is equivalent to Cl − deficiency of the water-splitting complex, a substantial reduction of the O 2 yield and in addition a significant change in the S-state distribution was observed. The comparison of deactivation kinetics in NO −3 containing samples with those in control samples indicated that Cl − deficiency allowed accumulation of oxidizing equivalents up to the S 3 state but modified the final step of O 2 evolution. Moreover, those centers which advanced to the S 3 state in the absence of Cl − deactivated in a special way which involved a faster deactivation of S 2 and an increased formation of S −1. 相似文献
19.
Binding characteristics of the selective V 2 antagonist radioligand [ 3H]desGly-NH 29-d(CH 2) 5[D-Ileu 2,Ileu 4]AVP to rat kidney were determined. Binding was specific, saturable and reversible. The peptide bound to a single class of high-affinity binding sites with B max 69.4±6.8 fmol/mg protein and K D 2.8±0.3 nM. AVP and other related peptides displaced [ 3H]desGly-NH 29-d(CH 2) 5[D-Ileu 2,Ileu 4]AVP binding. The order of potency of inhibition was desamino-D-AVP > AVP > d(CH 2) 5[D-Ileu 2,Ileu 4]AVP > oxytocin > d(CH 2) 3[Tyr(Me) 2]AVP > d(CH 2) 5[sarcosine 7]AVP, which is typical of a selective V 2 radioligand. Autoradiographic localization of [ 3H]desGly-NH 29-d(CH 2) 5[D-Ileu 2,Ileu 4]AVP binding sites in kidney showed dense binding in the inner and outer medulla with less binding in the cortex, which is consistent with known renal V 2 receptor distribution. 相似文献
20.
基于中国陆地生态系统通量观测研究网络(ChinaFLUX)4个站点(2个森林站和2个草地站)的涡度相关通量观测资料,分析了CO 2通量数据处理过程中异常值剔除参数设置、夜间摩擦风速(u *)临界值(u *c)确定及数据插补模型选择对CO 2通量组分估算的影响.结果表明: 3种数据处理方法均对净生态系统碳交换量(NEE)年总量估算有显著影响,其中u *c确定是影响NEE估算的重要因子;异常值剔除、u *c确定及数据插补模型选择导致NEE年总量估算偏差分别为0.62~21.31 g C·m -2·a -1(0.84%~65.31%)、4.06~30.28 g C·m -2·a -1(3.76%~21.58%)和0.69~27.73 g C·m -2·a -1(0.23%~55.62%),草地生态系统NEE估算对数据处理方法参数设置更敏感;数据处理方法不确定性引起的总生态系统碳交换量和生态系统呼吸年总量估算相对偏差分别为3.88%~11.41%和6.45%~24.91%. 相似文献
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