Optimally Dense Packings of Hyperbolic Space

In previous work, a probabilistic approach to controlling difficulties of density in hyperbolic space led to a workable notion of optimal density for packings of bodies. In this paper we extend an ergodic theorem of Nevo to provide an appropriate definition of those packings to be considered optimally dense. Examples are given to illustrate various aspects of the density problem, in particular the shift in emphasis from the analysis of individual packings to spaces of packings.     

Fe3O4/葡聚糖/抗体磁性纳米生物探针的制备和层析检测

在免疫检测中 ,经常利用一些具有特殊物理化学性质的标记物对抗体 (或抗原 )进行偶联标记 ,在抗体与抗原识别后 ,通过对标记物的定性和定量检测而达到对抗原 (或抗体 )检测的目的 .传统的免疫标记物包括放射性同位素 [1] 、酶 [2 ] 、胶体金 [3] 和有机荧光染料分子 [4 ] 等 .近年来 ,随着纳米技术的发展 ,半导体荧光纳米晶 [5,6 ] 和磁性纳米晶 [7] 在免疫检测方面受到了广泛关注 .磁性纳米晶性能稳定 ,较易制备 ,可与多种分子复合使粒子表面功能化 ,并且由于磁纳米晶具有超顺磁性 ,为样品的分离、富集和提纯提供了很大方便 .这些优点使它…     

单分散亲水两性离子交换树脂的制备及其在生物大分子分离中的应用

采用分散聚合与溶胀聚合相结合的方法及高分子溶液致孔技术, 成功地制备了粒径为5.0 μm大孔和超大孔结构的单分散亲水性交联聚甲基丙烯酸环氧丙酯树脂, 并进行了结构表征. 将该树脂经胺化后再与1,3-丙磺酸内酯反应, 得到一种新型的两性离子交换(强阳-强阴型)高效液相色谱填料. 研究了该填料对标准蛋白分离性能及流动相中有机溶剂、 流速和pH值对蛋白保留的影响. 实验结果表明, 在流速为3 mL/min时, 采用线性梯度洗脱, 在4.0 min内可同时快速基线分离3种酸性和2种碱性蛋白.     

Dicyanobiphenyl polysioloxane stationary phases for capillary column gas chromatography

Summary The chromatographic performance of newly developed dicyanobiphenyl polysiloxane stationary phases were evaluated and compared with the performance of other polar stationary phases, including the previously reported monocyanobiphenyl polysiloxanes. Due to the unique combination of polarizable biphenyl and polar cyano functionalities in the side chains of the flexible polysiloxane backbone, and by virtue of their mild liquid crystalline properties, the new stationary phases provide excellent resolution of a wide variety of analytes, both polar and nonpolar, in both GC and SFC. They can be easily coated and cross-linked in open tubular columns, and the resultant columns demonstrate excellent efficiency and performance at temperatures up to 280–300°C. The new stationary phases exhibit enhanced selectivities for various types of isomeric compounds.     

Quality evaluation of fingerprints of herbal medicine with chromatographic data

In this study, local least squares (LLS) and principal component analysis (PCA) were applied to deal with the disturbances in a data set of chromatographic fingerprints after necessary data transformations. It has been demonstrated that PCA with standard normal variate (SNV) transformation of data led to meaningful classification of 33 different Erigeron breviscapus herbal samples. The result was also corroborated by variance squares discriminant method. The quality of herbal objects was further evaluated, and the causes of this fact have been explained from a chemical point of view. At the same time, it implied an idea for qualitative evaluation of the herbal objects with a common class pattern of chromatographic fingerprints.     

Surface modification of soft-glass capillaries for gas chromatography by treatment with water vapour

“Leaching” or “etching” by strong mineral acids seems to be a necessary pretreatment step for the most commonly used deactivation procedures of glass capillaries by reaction with either polyethylene glycol or silylation reagents. The acidic sites which are formed on the surface during this acid treatment cannot be completely removed by the subsequent deactivation process. This drawback can be overcome by performing the leaching with water vapour, resulting in an accumulation of cations at the surface and a decrease in the number of silanol groups. Capillaries of this type show excellent properties for the chromatography of strongly basic compounds. After the wash-out of the alkaline surface layer, the acidity of the support is suited for the chromatography of strongly basic as well as strongly acidic compounds. Due to a lack of reactive acidic sites, special deactivation procedures have to be applied to capillaries produced in this way.     

Quantitative aspects of gradient HPLC of copolymers from styrene and ethyl methacrylate

Summary Prerequisite of quantitative evaluation in chromatography is equivalence of sample composition and detector signal. This includes complete retention and proper elution of all sample constituents. In polymer HPLC, complete retention requires a poor starting eluent, a sufficiently active column, and a low ratio of injection volume to column volume. On small pore columns, insufficient retention caused the polymer to elute either in the interstitial volume (sample exclusion), together with the sample solvent, or immediately after the solvent plug.Stat-copoly(styrene/ethyl methacrylate) samples are more difficultly retained thanstat-copoly(styrene/acrylonitrile) specimes. With the former copolymer it could be shown that incomplete retention did not cause sample demixing. In order to gain complete retention, non-exclusion HPLC of polymers should be performed with columns whose solvent volume is at least 50 times as large as the injection volume. This consequence is of practical importance in chromatographic cross-fractionation where rather large volumes of SEC eluate are injected into the apparatus for gradient HPLC.     

Determination of methylated dibenzothiophenes in environmental sarnples by on-line HPLC-CGC

Concurrent solvent evaporation with a loop-type interface was used for on-line HPLC-CGC in the analysis of methylated dibenzothiophene (DBT) isomers in oil samples. The chromatographic behavior of 20 methyl DBT's was studied by HPLC on an aminopropylsilane DBTA phase and by GC on a selective methyl-phenylsilicone phase. That provided a method for analyzing by GC-flame photometric detection, the individual components of the DBT family, previously picked out of the crude oil matrix by HPLC. The GC oven temperature was shown to be critical during HPLC eluent introduction into the GC pre-column. Too high a temperature induced a severe broadening of early eluted peaks whereas a temperature too close to the boiling point of the liquid at the inlet pressure induced double peaks. Optimized conditions were retained on this basis and may be used for the analysis of other families of polyaromatic hydrocarbons.     

Detectability enhancement of spectrophotometric detectors by the use of multidimensional gas chromatography

Multidimensional gas chromatography (2D GC) is demonstrated as a way to improve limits of detectability of spectrophotometric detectors. UV and IR detectors are generally less sensitive than mass spectrometers or other GC detectors. This has placed some limitations on the useful capabilities provided by spectrophotometric detectors, such as the ability to provide structure‐related information for a particular analyte. In this paper, we report results from interfacing a 2D GC instrument to a UV detector. Symmetry factor and the ratio of retention time divided by peak width did not show deterioration of the quality of chromatography when a megabore column was used with this detector. Furthermore, an increase in the limits of detectability over that attainable in a single‐column system was realized by using the 2D GC system. However, the low flow (1 mL/min) imposed by the use of a microbore column (250 μm ID) caused significant tailing when the UV detector was used.