The Effect of Selenium Supplementation on the NMR Proton Relaxation Time T1 in Plasma

Selenium has been identified as an essential dietary trace e1ementQ)which is a component of glutathione peroxidase (GSH-Px)(₂)and a cytochrome C-like protein(₃), The enzyme,the four subunits of which each contain one atom of selenium in the form of selenocysteine, the selenium containing active centre being amenable to chemical modification, catalyses the reduction of H,O,and organic hydroperoxides to water.In this way GSH-Px plays an important role in the protection of the cell from oxidative stresses such as the superoxide anion,organic hydroperoxides and H₂O₂     

基于LIBS及时间分辨特征峰的激光除漆机理研究

激光除漆是一种高效、清洁的新型清洗技术，对激光除漆物理过程和机理的研究是该技术发展的关键。基于LIBS技术，测量得到油漆去除过程中等离子体的发光光谱，计算出油漆样品去除前后等离子体的电子密度和温度，研究了油漆中特征元素对应的光谱特征峰强度随时间的变化情况。结果表明，随着激光作用脉冲数量的增加，油漆去除深度逐渐增加，等离子体电子密度和温度在将漆去除干净的最后几个脉冲作用时呈下降趋势。油漆中Ti元素的所对应的特征峰信号持续时间为2个μs，油漆去除前后信号强度呈现跳跃减少，该现象可用于快速、准确、实时的判断油漆去除情况。     

Dynamics of plasma channel in a parallel-plate plasma gun

Lumped parameter models for describing dynamics of the plasma channel in a parallel-plate plasma gun are compared with the experimental results obtained from two plasma guns with different rail geometries. Comparison between the experiments and the numerical calculations reveals that the lumped parameter models can be utilized to describe the dynamic motion of the plasma channel quite well. Parametric study shows that minimizing the line inductance and increasing the charging voltage on a capacitor as well as minimizing the gas injection time for reducing the mass of the plasma channel are the key factors to increase the flow velocity of the plasma jet ejected from the plasma gun.     

Measurements of the optical absorption coefficient of Ar8+ ion implanted silicon layers using the photothermal radiometry and the modulated free carrier absorption methods

This paper presents a method of the measurement of the optical absorption coefficient of the Ar⁸⁺ ions implanted layers in the p-type silicon substrate. The absorption coefficient is calculated using a value of the attenuation of amplitudes of a photothermal radiometry (PTR) and/or a modulation free carrier absorption (MFCA) signals and the implanted layer thickness calculated by means of the TRIM program. The proposed method can be used to indicate the amorphization of the ions implanted layers.     

Iron Interference in the Measurement of Selenium in Whole Blood,Plasma and Serum by Graphite Furnace Atomic Absorption

Abstract

Selenium is considered to be a trace element and the determination of diagnostic levels are most conveniently measured in blood, plasma or serum in humans and animals. The approach that is taken varies according to laboratory preferences. One such method involves the use of Graphite furance Atomic Absorption Spectroscopy (GFAAS). The simplicity of diluting the sample followed by direct determination without further preparation is the most attractive characteristic of this method, coupled with good sensitivity. Proper precautions must be taken however, including that of choosing the proper instrumental parameters for the analysis. If deuterium background correctiopn is used then then analyses should be carried out at the 204.0 nm line of Selenium. By using a matrix modifier consisting of Cu/Mg, deuterium background correction and off the wall of the graphite tube atomization, the determination of the analyte was demonstrated to be possible at the mentioned wavelength, free from iron interference present in the samples.     

BGK states from the bump-on-tail instability

Numerical computations are presented of the BGK-like states that emerge beyond the saturation of the bump-on-tail instability in the Vlasov-Poisson system. The stability of these states towards subharmonic perturbations is explored in order to gauge whether the primary bump-on-tail instability always suffers a secondary instability that precipitates wave mergers and coarsening of the BGK pattern. Because the onset of the bump-on-tail instability occurs at finite wavenumber, and the spatially homogeneous state is not itself unstable to spatial subharmonics, it is demonstrated that mergers and coarsening do not always occur, and the dynamics displays a richer spatio-temporal complexity.     

SPE–HPLC–MS/MS method for the trace analysis of tobacco‐specific N‐nitrosamines and 4‐(methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanol in rabbit plasma using tetraazacalix[2]arene[2]triazine‐modified silica as a sorbent

Tobacco‐specific N‐nitrosamines (TSNAs), including N′‐nitrosonornicotine, 4‐(methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanone, N′‐nitrosoanatabine, and N′‐nitrosoanabasine, have been implicated as a source of carcinogenicity in tobacco and cigarette smoke. We present a rapid and effective method comprising SPE based on tetraazacalix[2]arene[2]triazine‐modified silica as sorbent and analysis with HPLC–MS/MS for the determination of TSNAs and 4‐(methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanol (NNAL), a metabolite of 4‐(methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanone, in rabbit plasma. The linear dynamic ranges were 10–2000 pg/mL for NNAL and 4–2000 pg/mL for the four TSNAs with good correlation coefficients (>0.9965). The LODs were in the range of 0.9–3.7 pg/mL, and the LOQs were between 2.9 and 12.3 pg/mL. The accuracies of the method were also evaluated and found to be in the range of 90.1–113.3%. This method is promising to be applied to the preconcentration and determination of TSNAs and NNAL in smoke and human body fluids.     

Graphene/polydopamine‐modified polytetrafluoroethylene microtube for the sensitive determination of three active components in Fructus Psoraleae by online solid‐phase microextraction with high‐performance liquid chromatography

Determination of bioactive compounds in traditional Chinese medicines and biological samples is usually interfered with by coexisting components in matrices. In this work, we prepared novel multilayer functional graphene/polydopamine‐modified polytetrafluoroethylene microtube for selective solid‐phase microextraction of three bioactive compounds in Fructus Psoraleae. Functional graphene/polydopamine‐modified polytetrafluoroethylene microtube showed good extraction efficiency toward bavachin, isobavachalcone, and bavachinin; enrichment from 357‐ to 737‐fold was obtained for these compounds. For qualitative analysis, an online solid‐phase microextraction with high‐performance liquid chromatography method was developed, which showed low limits of detection of 0.02 ng/mL by using UV detection, which is significantly more sensitive than previously reported methods. The proposed method has been used to determine bavachin, isobavachalcone, and bavachinin in Fructus Psoraleae, the contents of three compounds were quantified to be 64.0, 324.0, and 384.5 μg/g; recoveries were 93.4–101.1%. The proposed method has also been applied to determine bavachin, isobavachalcone, and bavachinin in rat plasma samples after oral administration of Fructus Psoraleae.     

Quantification of allantoin and other metabolites of the purine degradation pathway in human plasma samples using a newly developed HILIC-LC-MS/MS method

The development of a simple HILIC-LC-MS/MS method to quantify the plasma levels of allantoin, inosine, hypoxanthine, and adenosine, using stripped plasma for the bioanalytical method validation, was the purpose of this study. Chromatographic separation conducted using an XBridge BEH Amide column (2.1 × 150 mm, 3.5 μm) was achieved under gradient elution with two mobile phases: 0.1% formic acid–ACN (5:95) and 0.1% formic acid–ACN (50:50). Multiple reaction monitoring MS detection was performed using a triple quadrupole. The method validation experiments were performed according to the European Medicines Agency and the U.S. Food and Drug Administration guidelines. The lower LOQ was 50 nM, 5 nM, 20 nM, and 2 nM for allantoin, inosine, hypoxanthine, and adenosine, respectively. The recovery was repeatable and stable. The intraday precision ranged from 1.6% to 6.5%, while the interday precision ranged from 3.4% to 58.7%. Therefore, it is necessary to make a matrix-matched calibration curve each day to overcome this issue. Since the quality control samples’ stability did not always comply with the guidelines, the samples need to be analyzed soon after collection.