Stereoisomeric flavour compounds XXXVIII: Direct chirospecific analysis of γ-lactones using on-line coupled LC-GC with a chiral separation column

Summary Chiral -lactones from the raw flavour extract of strawberries and commercially available fruit-containing products are stereoanalyzed directly by on-line coupling of liquid chromatography (LC) to gas chromatography (GC) and enantiomer separation with 2,6-di-O-pentyl-3-O-acetyl--cyclodextrin as the chiral stationary phase.     

Cation distribution in Eu-Sc-Fe garnets

The cation distribution has been studied with ⁵⁷Fe Mössbauer spectroscopy in the garnet system Eu_3?ySc_2+yFe₃O₁₂ with y = 0.0, 0.2 and 0.5. It is shown that the previously proposed cation distribution is not correct. The problem of possible impurities in the investigated system is discussed in detail. Several possible cation distributions are considered compatible with Mössbauer data. Mössbauer results combined with the composition dependence of lattice constants show that the tetrahedral sites are accessible to Sc³⁺ ions. The system studied is a second example of a garnet structure in which Sc³⁺ ions are found at the tetrahedral sites. A small fraction of Sc³⁺ ions for the samples y = 0.2 and 0.5 is also found at the dodecahedral sites.     

基于正交信号回归法对中试在线近红外定量模型的模型传递研究

模型传递使在特定条件下建立的模型能够应用于新的样品状态、环境条件或仪器状态。本研究在中药金银花中试在线水提过程中,以水提液中的绿原酸含量为研究对象,建立绿原酸含量的近红外定量模型。针对由金银花来源不同带来的模型失效问题,从光谱背景校正的角度出发,提出以KS算法挑选待传递样本中的代表性样本,结合正交信号回归(OSR)光谱背景校正方法,对不同来源样本的近红外光谱进行光谱背景校正,并深入探讨OSR方法实现近红外定量模型在不同来源中试样本间传递的应用原理。经模型传递后,模型对新批次样本预测的RSEP由14.91%下降到7.11%,RPD由2.95上升到5.36,预测准确度明显提高。实验证明,选择代表性样本的KS算法结合OSR光谱背景校正的模型传递方法不仅能减小不同来源原料药之间的偶然误差,同时消除了中试制剂过程和算法本身的系统误差,因此能够有效地改善因样本来源差异而造成的模型失效现象。该研究充分阐释了OSR模型传递方法的应用原理,以光谱背景校正与挑选代表性样本回归的方法实现了近红外定量模型在不同来源原料药中试样本之间的模型传递,增强了模型应对原料药批次间变动的能力,提高了模型的稳健性,为多来源原料药中试在线制剂过程中有效成分含量的快速实时监测提供了有效方法。     

New pressure‐assisted sweeping on‐line preconcentration for highly polar environmentally relevant nitrosamines: Part 2. Cationic and anionic surfactants with zero‐flow capillaries

We recently introduced a pressure‐assisted sweeping‐reversed migration‐EKC (RM‐EKC) method for preconcentration of neutral polar N‐nitrosamines with low affinity for the micellar phase. The type of surfactant and phase ratio are dominant factors in dictating the magnitude of interactions between analyte and micellar phase, thus four surfactants (anionic and cationic) with a range of functionalities (SDS, ammonium perfluorooctanoate (APFO), bile salts, and cetyltrimethylammonium chloride (CTAC)) were evaluated for sweeping‐RM‐EKC of highly polar N‐nitrosamines. All gave acceptable results for sweeping‐RM‐EKC when used in high concentrations (≥200 mM) with low EOF. While no single surfactant was superior by all measures, all but the bile salts had useful performance characteristics. APFO showed the narrowest peak widths and highest number of theoretical plates, though two species co‐migrated at all concentrations (25–300 mM); SDS and the cationic surfactant CTAC also showed good separation characteristics and could resolve all peaks, but CTAC had wider separation window. Various types of capillaries coated for EOF control were compared for use with anionic and cationic surfactants. A commercial zero‐EOF capillary coated with a polymer bearing sulfonic acid functional groups showed superior EOF suppression and reproducibility of migration time with all surfactants.     

On‐site sampling and sample‐preparation approach with a portable sampler based on hollow‐fiber/graphene bars for the microextraction of nitrobenzene compounds in lake water

A novel on‐site sampling and sample‐preparation approach was developed and evaluated in the present work. In this procedure, hollow‐fiber/graphene bars (HF/GBs) were used for sampling and sample preparation. A handheld battery‐operated electric egg beater was utilized to support the HF/GBs and stir the sample solution to facilitate extraction at the sampling site. Four nitrobenzene compounds (nitrobenzene, o‐nitrophenol, m‐nitrophenol, and p‐nitrophenol) were used as model compounds. Several factors affecting performance, including types and amount of graphene used and extraction and desorption times, were investigated and optimized in the laboratory. Under optimized conditions, the enrichment factors of the four nitrobenzene compounds ranged from 46 to 69. Good linearities of 0.01–10 μg/mL with regression coefficients between 0.9917 and 0.9973 were obtained for all analytes. The LOD of the method was 0.3 ng/mL. Satisfactory recoveries (98–102%) and precision (1.0–5.8%) were also achieved. The ultrastructures and extraction mechanism of the HF/GBs were characterized and analyzed. The proposed approach coupled with high‐performance liquid chromatography was successfully applied in the extraction and determination of trace nitrobenzene compounds in lake water. Experimental results showed that the approach is simple, convenient, rapid, and practical for routine environmental monitoring.     

A novel technique for on-capillary preconcentration of anionic compounds applied to the trace analysis of rapamycin in human blood by capillary electrophoresis

A capillary electrophoretic (CE) method with UV detection at 278 nm has been developed for analysis of the immunosuppressant rapamycin (sirolimus) in human blood at low microg.L(-1) levels. Separation has been achieved in an acidic carrier electrolyte containing sodium dodecyl sulfate and 20% v/v methanol. For sample cleanup and preconcentration, both an off-line solid-phase extraction step using a silica-based reversed-phase material and a newly developed on-capillary focusing technique have been employed. The subsequent treatment of rapamycin under alkaline conditions leads to a cleavage of the lacton bond of the molecule, generating a negatively charged carboxylic group which allows electrokinetic injection into the CE instrument. During the injection process, the negatively charged analyte migrates into an acidic carrier electrolyte, so that it becomes neutral due to protonation and is focused at the capillary inlet. Injection times of 300 s at -7.5 kV could be applied without band-broadening. Results for real samples indicated that the method is fully suited for routine applications and may be an attractive alternative to established liquid chromatographic techniques.     

Tablet‐effervescence‐assisted dissolved carbon flotation for the extraction of four triazole fungicides in water by gas chromatography with mass spectrometry

A pretreatment method named tablet‐effervescence‐assisted dissolved carbon flotation was introduced for the determination of four triazole fungicides in environmental water. In this method, the use of effervescent tablet composed of nontoxic sodium carbonate and sodium dihydrogen phosphate could generate CO₂ in situ to assist the dispersion of extraction solvent and to accelerate mass transfer of target analytes. In addition, the simple phase separation simply based on the rising of low‐density organic solvent from the aqueous phase was applied rather than the application of apparatus, which demonstrated the potential for on‐site extraction in the field. The experimental variables, including the composition of effervescent tablets, amount of effervescent tablets, types and volume of extraction solvent, were investigated. Under the optimized conditions, the method showed good linearity for myclobutanil, tebuconazole, epoxiconazole, and difenoconazole in the range of 1–100 μg/L. The limits of detection and the limits of quantification were within the range of 0.15–0.26 and 0.49–0.86 μg/L, respectively. The obtained correlation coefficients varied from 0.997 to 0.999, and suitable enrichment factors were 422–589. The recoveries were 82.5–112.9% with relative standard deviations of 4.7–13.5%.     

石墨炉原子吸收光谱法测定水中镉铜铅的在线富集预处理

将流动注射在线预富集系统与石墨炉原子吸收光谱法联用 ,以C18 反相键合硅胶为柱材料,5 -磺基-8 -羟基喹啉为螯合剂 ,2mol/LHCl-0.1mol/LHNO3 为洗脱液 ,以固定体积方式测定了Cd、Cu和Pb ,富集倍数分别为22、28、26(与30μL进样量相比 ) ,检出限(3σ)分别为0.7ng/L、4.2ng/L、5.4ng/L。     

On-line concentration of peptides and proteins with the hyphenation of polymer monolithic immobilized metal affinity chromatography and capillary electrophoresis

An iminodiacetic acid (IDA)-type adsorbent is prepared at the one end of a capillary by covalently bonding IDA to the monolithic rods of macroporous poly(glycidyl methacrylate-co-ethylene dimethacrylate). Cu(II) is later introduced to the support via the interaction with IDA. By this means, polymer monolithic immobilized metal affinity chromatography (IMAC) materials are prepared. With such a column, IMAC for on-line concentration and capillary electrophoresis (CE) for the subsequent analysis are hyphenated for the analysis of peptides and proteins. The reproducibility of such a column has been proved good with relative standard deviations (RSDs) of dead time of less than 5% for injection-to-injection and 12% for column-to-column (n = 3). Through application on the analysis of standard peptides and real protein samples, such a technique has shown promising in proteome study.     

聚苯乙烯/顺丁橡胶共混过程中的相结构

利用激光背散射装置结合密炼机对聚合物共混过程进行了在线分析．以典型完全不相容体系聚苯乙烯／顺丁橡胶为共混体系，对不同共混速度下结构参数随共混时间及共混条件如剪切速率等的变化进行了详细讨论．利用扫描电镜与激光背散射在线分析对聚合物共混过程结构参数变化进行了比较，结果显示聚苯乙烯／顺丁橡胶共混物处于熔融态与处于固态时结构基本相同．