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91.
It is well-known that matrix effects in high performance liquid chromatography coupled to electrospray ionization mass spectrometry (HPLC-ESI-MS) can seriously compromise quantitative analysis and affect method reproducibility. Paired ion electrospray ionization (PIESI) mass spectrometry is an approach for analyzing ultra-low levels of anions in the positive ion mode. This approach uses a structurally optimized ion pairing reagent to post-column associate with the anionic analyte, subsequently forming positively charged complexes. These newly formed complex ions are often more surface-active as compared to either the native anion or the ion pairing reagent. No studies have examined whether or not the PIESI approach mitigates matrix effects. Consequently, a controlled study was done using five analytes in highly controlled and reproducible synthetic groundwater and urine matrices. In addition, two different mass spectrometers (linear ion trap and triple quadrupole) were used. Compared to the negative ion mode, the PIESI-MS approach was less susceptible to matrix effects when performed on two different MS platforms. Using PIESI-MS, less dilution of the sample is needed to eliminate ionization suppression which, in turn, permits lower limits of detection and quantitation. 相似文献
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93.
陈协彬 《数学物理学报(A辑)》2003,23(1):65-76
设G是路或圈的笛卡尔乘积图,t(G)表示G的支撑树数.该文借助于第二类Chebyshev多项式给出t(G)的公式,并考虑了t(G)的线性递归关系及渐近性态. 相似文献
94.
95.
电子真空回旋器件是一种对磁场精度要求较高的微波源装置,一般采用超导磁体提供磁场环境.超导磁体的应用中,磁场分布的实现是超导磁体设计的核心问题.提供回旋器件磁场的高温超导磁体包含较复杂的磁体绕组,为了解决此类设计计算问题,本文提出了一种包含设计区域约束的线性优化方法进行回旋器件高温超导绕组的设计优化,通过分步的约束和线性优化计算,可得到同时满足设计要求和绕组可实现的设计磁场电流分布设计.计算实例的结果给出了一个提供磁场强度1.3 Tesla,长度285 mm的均匀磁场区域,同时满足多位置的磁场要求,设计结果与要求一致度较好,精度满足应用需求.该计算方法是一种可适用于较复杂磁场要求和超导绕组结构的设计优化方法. 相似文献
96.
在传统光学电流传感器技术的基础上,提出了一种四光路光学电流传感器,其通过四路输出信号可准确确定偏转角,使电流的测量范围不受正弦函数的单调性的限制,从而提高了电流的测量范围。配合四光路结构,提出了新的反正切函数数据处理方法,其不存在角度不灵敏区、可纠正原始数据的缺陷,从而提高了测量精度。实测了充电电压为4.5 kV、电容为50 μF和导线有效穿过磁光探头14次的快开快门的总短路电流,其峰值达85 kA,与理论值87 kA能较好地吻合,从而证明了四光路光学电流传感器可有效地测量脉冲大电流。 相似文献
97.
98.
C. Gonalves Joaquim C.G. Esteves da Silva M.F. Alpendurada 《Analytica chimica acta》2006,560(1-2):164-171
An extensive monitoring programme of pesticides was carried out in soil samples from an intensive horticulture area in north of Portugal, putting into practice the needs for increased control of soil quality as far as organic pollution is concerned. The area under investigation was additionally defined as vulnerable to nitrates due to local soil and aquifer characteristics, which might be extended to pesticides contamination. Five sampling sites were selected and soils analysed at three depths in eight sampling campaigns, for the period of 2 years. A stepwise multivariate statistical approach was selected to uncover most relevant patterns inside a complex environmental data matrix. Cluster analysis was applied both to group pesticides and samples, giving a primary and unsupervised overlook of privileged relationships. Clusters of persistent pesticides and selected herbicides were identified, whereas sample classes were also formed and disposed geographically. Thirty eight percent of analysed soils samples fell into one class characterized by low contamination (class 1 in cluster analysis), which is entirely representative of the sampling site no. 1. Afterwards, linear discriminant analysis was applied to identify those pesticides, which had a higher impact in the definition of classes. Finally, factor analysis using a five component model was implemented in order to bring to light the constitution and data variance explained by each of the five main principal components, as well as, their relation to pest management practices. A factor was identified (PC1 – 22% variance) composed of chlorinated pesticides, which was representative of one of the investigated sites indicating its high contamination status. Qualitative main findings and class average concentration values were obtained through this multivariate statistical approach. 相似文献
99.
Hua-Hong Zou Shu-Hua Zhang Ming-Hua Zeng Yan-Ling Zhou Hong Liang 《Journal of Molecular Structure》2008,885(1-3):50-55
A novel linear trimeric-based, Mn(II)–carboxylate chain well separated by long-linking flexible aliphatic tricarballylic acid ligands in a 3D coordination polymer [Mn3(C6H5O6)2(H2O)4]n (1, C6H5O6CH (COO−)(CH2COO−)2, TCA) exhibits low-dimensional antiferromagnetic order at 3.0 K. Such magnetic behavior is arises from the alternate Antiferro–Antiferro–Antiferro′ (J1 J1 J2) repeating interactions sequence, based on the nature of the binding modes of Mn(II)-carboxylate chain and the effect of interchains arrangement of 1. The reported carboxylate-bridged metal chain systems display a new structurally authenticated example of linear homometallic spin arranged antiferromagnet among metal carboxylates. 相似文献
100.
Lab-on-valve for the automatic determination of the total content and individual profiles of linear alkylbenzene sulfonates in water samples 总被引:1,自引:0,他引:1
Methods for the total content and individual determination of linear alkylbenzene sulfonates (LAS) in water samples based on the use of a lab-on-valve (LOV) module alone or coupled to CE equipment, respectively, have been developed. The total content of LAS has been determined by intrinsic absorption measurements (DA method) and after reaction with a methyl orange-cetylpyridine chloride mixture (MO method) with detection limits (LODs) of 21 ng/L and 15 microg/L, respectively, quantification limits (LOQs) of 70 ng/L, 50 microg/L, and development times of 100 and 124 s, respectively. The method for individual separation-quantification of LAS at very low concentration is based on automatic SPE preconcentration in the LOV module coupled on-line with the CE equipment. The LODs and LOQs thus obtained range between 1-21 and 4-70 ng/L, respectively, with linear dynamic ranges from the LOQ to 10 microg/L. Preconcentration factors of 10,000 and high efficiency to eliminate interferents by SPE enable application of the method to treated effluent, waste, surface and sea waters. 相似文献