共查询到20条相似文献,搜索用时 46 毫秒
1.
D. Brynn Hibbert Nicholas Armstrong John H. Vine 《Accreditation and quality assurance》2011,16(7):339-345
Racehorses given a slurry of sodium bicarbonate (known colloquially as a ‘milkshake’) before a race have elevated concentrations of carbon dioxide in their blood. Racing administrators have reacted to this attempt to enhance the performance of the animal by setting limits to ‘total carbon dioxide’ (TCO2, the sum of carbon dioxide, carbonic acid, carbonate and bicarbonate) in prerace samples of plasma. The threshold limit for TCO2 in the rules of racing is an amount concentration of 36.0 mmol/L, with further action ensuing if the reported concentration is greater than an action limit that is calculated from the knowledge of the measurement uncertainty. At present in Australia, the action limit is 37.0 mmol/L, which is based on a combined standard measurement uncertainty of 0.22 mmol/L. From data obtained in a 1997 study in 515 normal racehorses, we have established the distribution (as a probability density function, PDF) of TCO2. This is combined with data from Australian laboratories of 126 horses that were tested following a positive screen, out of which 78 were confirmed positive. We employ the maximum entropy method to establish the PDFs and then apply Bayes Theorem to answer the question ‘given the measured TCO2 concentration what is the probability that a horse has been administered bicarbonate’? The distributions are not normal, which precludes simple approaches that calculate standard deviations from the data. For an action level of 37.0 mmol/L, there is a chance of only 1 in 2 020 000 that a nondoped horse will be judged to be doped, which implies this present threshold is unlikely to lead to conviction of an innocent trainer. 相似文献
2.
Xiangzhong Ren Yingkai Jiang Peixin Zhang Jianhong Liu Qianling Zhang 《Journal of Sol-Gel Science and Technology》2009,51(2):133-138
One-dimensional (1D) submicron-belts of V2O5 have been prepared by a sol–gel route using V2O5, H2O2 and aniline as starting materials. Thermogravimetric and differential thermal analysis, X-ray diffraction, Fourier transform
infrared spectroscopy and scanning electron microscopy were employed to characterize the samples. Electrochemical behaviors
as cathode material in rechargeable lithium-ion batteries were investigated by galvanostatic charge–discharge measurement
and cyclic voltammeter. The results showed that the synthesized V2O5 appeared to be submicron-belts and orthorhombic structure. The V2O5 submicron-belts exhibited a high initial discharge capacity of 346 mAh/g and stayed 240 mAh/g after 20 cycles at 0.1 C discharge
rate in the potential region 1.8–4.0 V. 相似文献
3.
García-Ruiz S Petrov I Vassileva E Quétel CR 《Analytical and bioanalytical chemistry》2011,401(9):2785-2792
The cadmium content in surface water is regulated by the last European Water Framework Directive to a maximum between 0.08
and 0.25 μg L−1 depending on the water type and hardness. Direct measurement of cadmium at this low level is not straightforward in real
samples, and we hereby propose a validated method capable of addressing cadmium content below μg L−1 level in natural water. It is based on solid-phase extraction using TiO2 nanoparticles as solid sorbent (0.05 g packed in mini-columns) to allow the separation and preconcentration of cadmium from
the sample, combined to direct isotope dilution and detection by inductively coupled plasma mass spectrometry (ID-ICP-MS).
The extraction setup is miniaturised and semi-automated to reduce risks of sample contamination and improve reproducibility.
Procedural blanks for the whole measurement process were 5.3 ± 2.8 ng kg−1 (1 s) for 50 g of ultrapure water preconcentrated ten times. Experimental conditions influencing the separation (including
loading pH, sample flow rates, and acid concentration in the eluent) were evaluated. With isotope dilution the Cd recovery
rate does not have to be evaluated carefully. Moreover, the mathematical model associated to IDMS is known, and provides transparency
for the uncertainty propagation. Our validation protocol was in agreement with guidelines of the ISO/IEC 17025 standard (chapter
5.4.5). Firstly, we assessed the experimental factors influencing the final result. Secondly, we compared the isotope ratios
measured after our separation procedure to the reference values obtained with a different protocol for the digested test material
IMEP-111 (mineral feed). Thirdly, we analysed the certified reference material BCR-609 (groundwater). Finally, combined uncertainties
associated to our results were estimated according to ISO-GUM guidelines (typically, 3–4% k = 2 for a cadmium content of around 100 ng kg−1). We applied the developed method to the groundwater and wastewater samples ERM-CA615 and BCR-713, respectively, and results
agreed with certificate values within uncertainty statements. 相似文献
4.
Chong Sun Xiao-Di Yang Liu-Yin Fan Wei Zhang Yu-Quan Xu Cheng-Xi Cao 《Analytical and bioanalytical chemistry》2011,399(10):3441-3450
As shown herein, a normal moving reaction boundary (MRB) formed by an alkaline buffer and a single acidic buffer had poor
stacking to the new important plant growth promoter of phenazine-1-carboxylic acid (PCA) in soil due to the leak induced by
its low pK
a. To stack the PCA with low pK
a efficiently, a novel stacking system of MRB was developed, which was formed by an alkaline buffer and double acidic buffers
(viz., acidic sample and blank buffers). With the novel system, the PCA leaking into the blank buffer from the sample buffer
could be well stacked by the prolonged MRB formed between the alkaline buffer and blank buffer. The relevant mechanism of
stacking was discussed briefly. The stacking system, coupled with sample pretreatment, could achieve a 214-fold increase of
PCA sensitivity under the optimal conditions (15 mM (pH 11.5) Gly-NaOH as the alkaline buffer, 15 mM (pH 3.0) Gly-HCl-acetonitrile
(20%, v/v) as the acidic sample buffer, 15 mM (pH 3.0) Gly-HCl as the blank buffer, 3 min 13 mbar injection of double acidic buffers,
benzoic acid as the internal standard, 75 μm i.d. × 53 cm (44 cm effective length) capillary, 25 kV and 248 nm). The limit
of detection of PCA in soil was decreased to 17 ng/g, the intra-day and inter-day precision values (expressed as relative
standard deviations) were 3.17–4.24% and 4.17–4.87%, respectively, and the recoveries of PCA at three concentration levels
changed from 52.20% to 102.61%. The developed method could be used for the detection of PCA in soil at trace level. 相似文献
5.
Charles Y. Cummings Susan J. Stott Michael J. Bonné Karen J. Edler Pauline M. King Roger J. Mortimer Frank Marken 《Journal of Solid State Electrochemistry》2008,12(12):1541-1548
The formation of variable-thickness CeO2 nanoparticle mesoporous films from a colloidal nanoparticle solution (approximately 1–3-nm-diameter CeO2) is demonstrated using a layer-by-layer deposition process with small organic binder molecules such as cyclohexanehexacarboxylate
and phytate. Film growth is characterised by scanning and transmission electron microscopies, X-ray scattering and quartz
crystal microbalance techniques. The surface electrochemistry of CeO2 films before and after calcination at 500 °C in air is investigated. A well-defined Ce(IV/III) redox process confined to
the oxide surface is observed. Beyond a threshold potential, a new phosphate phase, presumably CePO4, is formed during electrochemical reduction of CeO2 in aqueous phosphate buffer solution. The voltammetric signal is sensitive to (1) thermal pre-treatment, (2) film thickness,
(3) phosphate concentration and (4) pH. The reversible ‘underpotential reduction’ of CeO2 is demonstrated at potentials positive of the threshold. A transition occurs from the reversible ‘underpotential region’
in which no phosphate phase is formed to the irreversible ‘overpotential region’ in which the formation of the cerium(III)
phosphate phase is observed. The experimental results are rationalised based on surface reactivity and nucleation effects. 相似文献
6.
Lott S Henrion A Malz F Kessler A Güttler B Aderjan R 《Analytical and bioanalytical chemistry》2008,391(3):1003-1010
An isotope dilution gas chromatography/mass spectrometry (ID-GC/MS) reference measurement procedure for Δ9-tetrahydrocannabinol
(THC) in serum was developed and validated. The method complies with the concept of a ratio primary reference measurement
procedure. The uncertainty was determined for two concentrations of THC in serum (1 ng/mL and 2.4 ng/mL). The calculation
procedure is based on the Guide to the Expression of Uncertainty in Measurement (GUM). The relative expanded uncertainty was found to be less than 2% for both concentration levels, corresponding to a 95%
confidence interval. For the reference method, it was shown that the measurement of THC within the concentration range covered
by the current threshold values is very accurate. The method has the potential to provide traceability for the methods used
in practical forensics. 相似文献
7.
N. N. Gedam P. R. Padole S. K. Rithe G. N. Chaudhari 《Journal of Sol-Gel Science and Technology》2009,50(3):296-300
Thick film of nanocrystalline Co0.8Ni0.2Fe2O4 was obtained by sol–gel citrate method for gas sensing application. The synthesized powder was characterized by X-ray diffraction
(XRD) and transmission electron microscopy. The XRD pattern shows spinel type structure of Co0.8Ni0.2Fe2O4. XRD of Co0.8Ni0.2Fe2O4 revels formation of solid solution with average grain size of about 30 nm. From gas sensing properties it observed that nickel
doping improves the sensor response and selectivity towards ammonia gas and very low response to LPG, CO, and H2S at 280 °C. Furthermore, incorporation of Pd improves the sensor response and stability of ammonia gas and reduced the operating
temperature upto 210 °C. The sensor is a promising candidate for practical detector of ammonia. 相似文献
8.
Wanju Luo Dongliang Wang Xiande Peng Fangwei Wang 《Journal of Sol-Gel Science and Technology》2009,51(1):53-57
Nanosized multiferroic BiFeO3 powders were synthesized by a microwave combustion method. The average crystallite sizes of the samples stay at a same level
with the ratio of fuel glycine 0.5 ≤ G/N ≤ 1.5 and it increases significantly with G/N = 2.0. An inhomogeneity of amorphous
and microcrystallites is observed directly by HRTEM. A ferromagnetic hysteresis loop with a saturation magnetization (M
S) of ~0.09 μ
B
/Fe has been observed at room temperature in the sample with a crystallite size of 53 nm, whereas other powders with much
smaller crystallite size (~20 nm) will not saturate even at 20 kOe. These magnetic behaviors were ascribed to a combination
of the magnetic enhancement effect of a decreased crystallite size and superparamagnetic mechanism. 相似文献
9.
The photo-degradation of formaldehyde (HCHO) by nitrogen-doped nanocrystalline TiO2 (N-TiO2) powders under visible light irradiation has been systematically investigated. Experimental results show that the degradation
ratio reached up to 42.6% after 2 h visible light irradiation when the amounts of N-TiO2 powders were 0.5 g, the initial concentration of the HCHO was set at 0.98 mg/m3, the illumination intensity was fixed at 10,000 lux, the ambient temperature was set at 26 °C, and the relative humidity
was maintained at 33 ± 5%. Further research shows that the degradation ratios were all larger than 40% in ten repeated cycles
of photodegradation of HCHO by N-TiO2 powders. The degradation ratio was as high as 82.9% after 2 h visible light irradiation when the amount of N-TiO2 was 5 g. The degradation ratio was increased from 25.5 to 59.6% when the illumination intensity of the visible light was
increased from 0 to 30,000 lux. However, the degradation ratio could not be further increased by further increasing the illumination
intensity. 相似文献
10.
Yiping Guo Daisuke Akai Kazuaki Sawada Makoto Ishida Mingyuan Gu 《Journal of Sol-Gel Science and Technology》2009,49(1):66-70
Highly (110)-oriented Ba0.65Sr0.35TiO3 films were deposited on Pt/LaNiO3/SiO2/Si substrates by a sol–gel method. It was found that the (110)-preferred Pt film was very effective for growing (110)-oriented
ferroelectric films with perovskite structure. The as-grown Ba0.65Sr0.35TiO3 films showed good dielectric properties with dielectric constant and loss tangent tan δ = 0.026. Excellent dielectric tunability was also achieved in the (110)-oriented films. With applying
an electric field of 230 kV/cm at 100 kHz, the dielectric tunability and the figure of merit can reach up to 63.4% and 16,
respectively. These results indicate that the highly (110)-oriented Ba0.65Sr0.35TiO3 film is a promising candidate for the applications in microwave tunable devices. 相似文献
11.
A procedure is presented for estimation of uncertainty in measurement of the pK(a) of a weak acid by potentiometric titration. The procedure is based on the ISO GUM. The core of the procedure is a mathematical model that involves 40 input parameters. A novel approach is used for taking into account the purity of the acid, the impurities are not treated as inert compounds only, their possible acidic dissociation is also taken into account. Application to an example of practical pK(a) determination is presented. Altogether 67 different sources of uncertainty are identified and quantified within the example. The relative importance of different uncertainty sources is discussed. The most important source of uncertainty (with the experimental set-up of the example) is the uncertainty of pH measurement followed by the accuracy of the burette and the uncertainty of weighing. The procedure gives uncertainty separately for each point of the titration curve. The uncertainty depends on the amount of titrant added, being lowest in the central part of the titration curve. The possibilities of reducing the uncertainty and interpreting the drift of the pK(a) values obtained from the same curve are discussed. 相似文献
12.
In this study, a novel and enzyme-free electrochemical immunoassay was developed for the detection of alpha-fetoprotein (AFP;
as a model biomarker) by using a novel redox nanocatalyst, patterned gold-iridium oxide nanoparticle assemblies (Au-IrOx), on a Prussian blue (PB) functionalized glassy carbon electrode. The as-prepared Au-IrOx nanospheres were not only used for the labeling of secondary anti-AFP antibody but also executed for water oxidation. With
a sandwich immunoassay format, the electrochemical measurement was carried out in 0.1 M KNO3-HCl, pH 3.2, containing 1.0 mM p-aminophenol (AP). Initially, the added AP was oxidized to p-quinone imine (QI) with the help of the immobilized PB on the electrode, and then the generated QI was reduced back to AP
by hydrogenation reaction from water oxidation. The self-produced QI reactants were catalytically recycled and thus amplified
the signal of electrochemical response. Under optimal conditions, the electrochemical immunosensor displayed a wide working
range of 0.005 to 200 ng/mL with a low detection limit of 0.5 pg/mL AFP (at 3sB). Intra- and inter-assay coefficients of variation were below 10%. In addition, the methodology was validated with real serum
samples, receiving a good agreement with the results obtained from commercially available electrochemiluminescence automated
analyzer. 相似文献
13.
Uncertainty in aflatoxin B<Subscript>1</Subscript> analysis using information from proficiency tests
Maroto A Boqué R Riu J Ruisánchez I Odena M 《Analytical and bioanalytical chemistry》2005,382(7):1562-1566
We describe how to calculate uncertainty in the determination of aflatoxin B1 in nuts and maize using an HPLC method with prederivatisation with trifluoroacetic acid and fluorescence detection. The uncertainty is easily calculated using the information obtained from the participation in several proficiency tests. All the sources of uncertainty are grouped in two terms: (1) matrix variability, intermediate precision and sample heterogeneity, and (2) method concordance. This methodology has the advantage that no extra work needs to be done because all the information to calculate uncertainty comes from proficiency tests. The uncertainty values were calculated using samples whose concentration ranged between 2 and 20 g L–1. The relative standard uncertainty computed for aflatoxin B1 was 16.3%. 相似文献
14.
N. B. Babanly Yu. A. Yusibov R. J. Mirzoeva Yu. M. Shykhyev M. B. Babanly 《Russian Journal of Electrochemistry》2009,45(4):405-410
The Cu-B-Se (B = In, As, Sb, Bi) systems are studied by measurement of EMF for concentration circuits vs. a copper electrode in the temperature range of 300–430 K. A solid superionic Cu4RbCl3I2 conductor is used as an electrolyte. Diagrams of solid-phase equilibriums in the studied systems are constructed. Partial molar functions of alloyed copper are calculated on the basis of the equations of the temperature dependences of EMF. Potential-forming reactions corresponding to the measured EMF values are determined on the basis of the phase diagrams and standard thermodynamic formation functions and standard entropies of ternary compounds are calculated. 相似文献
15.
Stilbenes and zeranol are nonsteroidal estrogenic growth promoters which are banned in the European Union (EU) for use in
food-producing animals by Council Directive 96/22/EC. A liquid chromatography–tandem mass spectrometry (LC-MS/MS) method was
developed for the screening and confirmation of stilbenes (diethylstilbestrol, dienestrol, hexestrol) and resorcylic acid
lactones (zeranol and its metabolites taleranol and zearalanone as well as the mycotoxins α-zearalenol, β-zearalenol and zearalenone)
in bovine urine. The method permits the confirmation and quantification of stilbenes and resorcylic acid lactones at levels
below 1 μg L−1 and 1.5 μg L−1, respectively. The validation was carried out according to Commission Decision 2002/657/EC, Chap. 3.1.3 “alternative validation”
by a matrix-comprehensive in-house validation concept. Decision limit CCα, detection capability CCβ, recovery, repeatabiliy,
within-laboratory reproducibility and the uncertainty of measurement were calculated. Furthermore, a factorial effect analysis
was carried out to identify factors that have a significant influence on the method. Factors considered to be relevant for
the method in routine analysis (e.g. operator, matrix condition, storage duration of the extracts before measurement, different
cartridge lots, hydrolysis conditions) were systematically varied on two levels. The factorial analysis showed that different
cartridge lots, storage durations and matrix conditions can exert a relevant influence on the method. 相似文献
16.
Among the various positive electrode materials investigated for Li-ion batteries, spinel LiMn2O4 is one of the most important materials. Small particles of the active materials facilitate high-rate capability due to large
surface to mass ratio and small diffusion path length. The present work involves the synthesis of submicron size particles
of LiMn2O4 in a quaternary microemulsion medium. The precursor obtained from the reaction is heated at different temperatures in the
range from 400 to 900 °C. The samples heated at 800 and 900 °C are found to possess pure spinel phase with particle size <200 nm,
as evidenced from XRD, SEM, and TEM studies. The electrochemical characterization studies provide discharge capacity values
of about 100 mAh g−1 at C/5 rate, and there is a moderate decrease in capacity by increasing the rate of charge–discharge cycling. Studies also
include charge–discharge cycling and ac impedance studies in temperature range from −10 to 40 °C. Impedance data are analyzed
with the help of an equivalent circuit and a nonlinear least squares fitting program. From temperature dependence of charge-transfer
resistance, a value of 0.62 eV is obtained for the activation energy of Mn3+/Mn4+ redox process, which accompanies the intercalation/deintercalation of the Li+ ion in LiMn2O4. 相似文献
17.
The interaction of acetonitrile with superoxide radicals over a polycrystalline TiO2 (Degussa P25) surface was investigated using continuous-wave electron paramagnetic resonance (cw-EPR) spectroscopy. For the
first time, a thermally unstable radical intermediate has been observed following the low-temperature exposure of acetonitrile
to surface-adsorbed O2− radicals. The radical intermediate has been identified as an [O2−···CH3CN] type surface complex characterised by the g values of g
1 = 2.031, g
2 = 2.010 and g
3 = 2.003. This surface complex is thermally unstable and decomposes at temperatures of T > 240 K. A second oxygen-centred species was also observed following acetonitrile adsorption, characterised by the spin Hamiltonian
parameters of g
1 = 2.028, g
2 = 2.010, g
3 = 2.004, A
1 = 1.2 mT, A
2 = 1.0 mT and A
3 = 1.0 mT, and was assigned to a hydroperoxy radical (HO2•). 相似文献
18.
Daixin Ye Yanhong Xu Liqiang Luo Yaping Ding Yulong Wang Xiaojuan Liu 《Journal of Solid State Electrochemistry》2012,16(4):1635-1642
A novel electrochemical sensor based on LaNi0.5Ti0.5O3/CoFe2O4 nanoparticle-modified electrode (LNT–CFO/GCE) for sensitive determination of paracetamol (PAR) was presented. Experimental
conditions such as the concentration of LNT–CFO, pH value, and applied potential were investigated. Under the optimum conditions,
the electrochemical performances of LNT–CFO/GCE have been researched on the oxidation of PAR. The electrochemical behaviors
of PAR on LNT–CFO/GCE were investigated by cyclic voltammetry. The results showed that LNT–CFO/GCE exhibited excellent promotion
to the oxidation of PAR. The over-potential of PAR decreased significantly on the modified electrode compared with that on
bare GCE. Furthermore, the sensor exhibits good reproducibility, stability, and selectivity in PAR determination. Linear response
was obtained in the range of 0.5 to 901 μM with a detection limit of 0.19 μM for PAR. 相似文献
19.
Pinyang Fang Huiqing Fan Shaojun Qiu Liajun Liu Jin Chen 《Journal of Sol-Gel Science and Technology》2009,50(3):290-295
Lanthanum-modified bismuth titanate (Bi3.25La0.75Ti3O12, BLTO) powders were prepared by the complex polymerization method. The structure and morphology of BLTO powders were investigated
by X-ray diffraction and scanning electron microscopy. The complexation of citric acid with the metallic cations was detected
by Fourier transformed infrared (FT-IR). The thermal analyses of obtained gels were investigated by differential thermal gravimetric
(DTG). The pure and normally stoichiometric phase of BLTO powders could be obtained at relatively low temperature of 550–700 °C
even if the bismuth content is not excess in the starting precursors, while the secondary phase could be detected at lower
and higher calcination temperatures. The shape of the BLTO grains is similarly to platelet in Bi-layer structure and stoichiometry
BLTO was detected by the analysis of energy dispersive spectrometry. 相似文献
20.
This investigation examines the magnetorheological (MR) characteristics of Fe3O4 aqueous suspensions. Magnetite particles (Fe3O4) were synthesized using a colloidal process and their sizes were determined to be normally distributed with an average of
10 nm by TEM. Experimental results reveal that the MR effect increases with the magnetic field and suspension concentration.
The yield stress increases by up to two orders of magnitude when the sample is subjected to a magnetic field of 146 Oe/mm.
In comparison with other published results, concerning a concentration of approximately 10–15% v/v, this study demonstrates
that the same increase can be obtained with a concentration of nano-scale particles as low as 0.04% by volume. The viscosity
was increased by an order of magnitude while the shear rate remained low; however, the increase decayed rapidly as the shear
rate was raised. Finally, the MR effect caused by DC outperformed that caused by AC at the same current. 相似文献