New NIST sediment SRM for inorganic analysis

NIST maintains a portfolio of more than 1300 standard reference materials (SRM), more than a third of these relating to measurements in the biological and environmental fields. As part of the continuous renewal and replacement efforts, a set of new marine sediments has been recently developed covering organic and inorganic determinations. This paper describes the steps taken in sample preparation, homogeneity assay, and analytical characterization and certification with specific emphasis on SRM 2702 inorganics in marine sediment. Neutron activation analysis showed the SRM to be highly homogeneous, opening the possibility for use with solid sampling techniques. The certificate provides certified mass fraction values for 25 elements, reference values for eight elements, and information values for 11 elements, covering most of the priority pollutants with small uncertainties of only several percent relative. The values were obtained by combining results from different laboratories and techniques using a Bayesian statistical model. An intercomparison carried out in field laboratories with the material before certification illustrates a high commutability of this SRM.Electronic Supplementary Material Supplementary material is available in the online version of this article at     

Microdialysis sampling and monitoring of uric acid in vivo by a chemiluminescence reaction and an enzyme on immobilized chitosan support membrane

A new detection system based on microdialysis sampling and chemiluminescence (CL) reaction was developed for in vivo monitoring of uric acid (UA) with high sensitivity, selectivity and accuracy. The uric acid is indirectly monitored by CL detection of enzymatic reaction product formation (H₂O₂), catalyzed by Uricase. A microprobe was modified and coated with immobilized enzyme through a Streptavidin-biotin mediated linker by using a chitosan support membrane, polyurethane trapped ferrocene film is employed to protect the probe surface and diminish the interference from reductant molecules, which often are present in the blood (e.g. ascorbic acid). The earlier mentioned probe and the constructed sensor can detect uric acid in the range of 0.01-1 mM with detection limit (3σ) of 5 μM. Finally, the system is used to monitor uric acid (UA) variation through an acute myocardial infarction (AMI) model. Following AMI-induced oxidative stress, the UA level decreases continuously, thus suggesting that UA plays a protective role as a substitute antioxidant. Furthermore, the in vivo monitoring results show good agreement with those obtained by a standard method, and the procedure is recommended for in vivo and real time monitoring of UA. In addition, the proposed method can be more accurate since the UA may be potentially oxidized by in vitro exposure to oxygen in the presence of a catalyst.     

新的脉冲进样AAS法测定“麻杏石甘汤”中的微量金属元素

本文研制了一种新的脉冲进样装置，用于火娄原子吸收分光光度法测定中药煎剂中的Ｃａ，Ｍｇ，Ｆｅ，Ｍｎ，Ｚｎ五种金属元素含量，实验表明，利用此种装置可以同时获得两种进样方式的分析结果，线性范围比常规法宽两倍，耗样量，精密度及分析速度均优于常规法。     

Comparison of slurry sampling and microwave-assisted digestion for calcium, magnesium, iron, copper and zinc determination in fish tissue samples by flame atomic absorption spectrometry

The development of a slurry sampling method for the determination of calcium, copper, iron, magnesium and zinc in fish tissue samples by flame atomic absorption spectrometry is described. In comparison with microwave-assisted digestion, the proposed method is simple, requires short time and eliminates total sample dissolution before analysis. Suspension medium was optimized for each analyte to obtain quantitative recoveries from fish tissue samples without matrix interferences. Nevertheless, iron recoveries higher than 46% were not found. Treatment of samples slurried in nitric acid by microwave irradiation for 15-30 s at 75-285 W permitted to achieve efficient recoveries for calcium, iron, magnesium and zinc. Further improvement in the matrix effects for iron determination was accomplished by the use of an additional step of short microwave-assisted suspension treatment. However, standard addition method was required for calcium and copper determination, being necessary hydrochloric acid as suspension medium for the last one. Although copper could not be determined in the certified reference material using microwave-assisted digestion, the accuracy of the slurry sampling method was verified for all the investigated analytes. Detection limits were 22.8 ± 8.0, 0.884 ± 0.092, 5.07 ± 0.76, 35.5 ± 0.7 and 1.17 ± 0.04 μg g⁻¹ for calcium, copper, iron, magnesium and zinc, respectively. The standard deviations obtained using slurry sampling method and microwave-assisted digestion were not significantly different, and the mean relative standard deviation of the over-all method (n = 3) of the slurry sampling method for different concentration levels was below 12%.     

ICP-AES detection of silicon carbide impurities volatilized in a graphite furnace with the use of carbon tetrachloride vapour

The analytical capability of high-temperature halogenation with carbon tetrachloride vapour in a graphite furnace was investigated for silicon carbide powder with known chemical composition and particle size. Intensity vs heating time curves were determined for analytical lines of Al, B, Ba, Ca, Cr, Cu, Fe, Mg, Mn, Ti, V and Si constituents, volatilized with and without the presence of CCl₄ vapour in the furnace atmosphere. Igniting 10 mg SiC at 2100 °C for 60 s in chlorinating atmosphere, the evaporated fraction of most of the constituents was higher than 90% (for Al about 50%). The line intensity vs sample mass (4–26 mg) relationships were linear for all impurities studied, while the intensity of silicon line showed a relatively small change with the sample mass. BEC (background equivalent concentration) values for this solid sampling technique (10 mg loaded sample) were 2–20 fold lower than those calculated for the conventional solution sample introduction method.     

Determination of mercury in soils and sediments by graphite furnace atomic absorption spectrometry with slurry sampling

A graphite furnace atomic absorption spectrometric procedure for the determination of mercury is presented, in which the samples are suspended in a solution containing hydrofluoric and nitric acids. Silver nitrate (4% m/v) and potassium permanganate (3%) are incorporated, in the order specified, and aliquots are directly introduced into the graphite furnace. A fast heating programme with no conventional pyrolysis step is used. The detection limit for mercury in a 125 mg ml⁻¹ suspension is 0.1 μg g⁻¹. Calibration is performed by using aqueous standards. The reliability of the procedure is proved by analysing certified reference materials.     

Direct determination of manganese in vitamin-mineral tablets using solid sampling electrothermal atomic absorption spectrometry

Manganese in vitamin-minerals tablets was determined by solid sampling electrothermal atomic absorption spectrometry (SS-ETAAS) using three different calibration methods, namely calibration against aqueous standards, standard addition with aqueous standards on solid samples and calibration against solid certified standards. Samples were only finely ground and introduced directly into the furnace by means of solid autosampler system without any dissolving process. Effects of different calibration techniques, temperatures and heating rates of atomization and pyrolysis steps on the accuracy and precision of the analyte elements were investigated. After optimization of the experimental parameters, there is good agreement (at 95% confidence level) between the results obtained by solid sampling and those obtained by acid digestion of samples.     

排序集抽样下Inverse Rayleigh分布的Fisher信息量及其在参数估计中的应用

文章分别在简单随机抽样和排序集抽样下研究了Inverse Rayleigh分布中对应样本所含刻度参数θ的Fisher信息量.数值结果表示,同等样本容量的排序集样本比简单随机样本提供更多关于θ的信息.接着分别基于简单随机样本和排序集样本构造了θ的一些优良估计,并对估计结果进行了数值比较.     

Simultaneous distillation-extraction and dynamic headspace methods in the gas chromatographic analysis of Parmesan cheese volatiles

Summary Dynamic headspace and simultaneous steam distillation-extraction techniques were used to isolate volatile components of Parmesan cheese. Identification of the substances was carried out by GC and GC-MS; 110 compounds were identified in the samples obtained using the headspace technique, 105 in the extracts; among them, about 50 compounds were isolated with both procedures. Mass spectral data showed evidence for a number of newly reported compounds such as 3-(methylthio)propanal, -tetradecalactone, 9-tetra-decenoic and 9-hexadecenoic acids. Mass spectra of some compounds are discussed and a comparison between the results obtained with the two sampling methods is given.     

Electron microprobe analysis of micro amount powder samples: A case study on high purity coal

For the major, minor and trace element analysis of the inorganic compounds of a Ruhr-Saar coal different preparation techniques are investigated with X-ray fluorescence analysis, electron microprobe and classical wet chemical methods minimizing sample weight at standard preparation times and analytical accuracies. Considering accuracy as well as preparation efforts, determinations by electron microprobe on small sample amounts (<50 mg) proved to be superior to the other methods.Abbreviations AAS atomic absorbtion spectrometry - EMA electron microprobe analysis - IC ion chromatography - ISE ion sensitive electrode - PHOT photometry - WCA wet chemical analysis - XRF X-ray fluorescence analysis - LTA low temperature plasma ashing - HTA high temperature ashing - l.o.i. loss on ignition