At-column injector for capillary GC — design and evaluation

The present paper describes constructional details and evaluations of an at-column injector for capillary GC. Injections were made via a sample loop on a 0.32 mm i.d. capillary column. Two rotary valves were employed to allow a wash of the sample loop and a backflush of the transfer line. Repeatability, calculated from absolute area counts for n-alkanes was between 0.3–1% RSD, for injected sample volumes between 5 and 100 μl. Promising results were also obtained with syringe-based injections on narrow bore (100 μ i.d.) columns. Repeatability on the basis of normalized area counts was in the order of 0.1–0.2% RSD, while solvent tailing was practically absent.     

乙烯系单体自由基聚合的阻聚效应──XIX．取代哌啶羟胺和二叔丁基羟胺及其稳定自由基对苯乙烯－丙烯腈共聚合的影响

研究了二叔丁基羟胺（ＤＴＢＨＡ），二叔丁基氮氧自由基（ＤＴＢＮＯ·），２，２，６，６－四甲基－４－羟基哌啶羟胺（ＴＭＨＰＨＡ）和２，２，６，６－四甲基－４－羟基哌啶－１－氧自由基（ＴＭＨＰＯ·）对过氧化苯甲酰（ＢＰＯ）６０℃引发的苯乙烯（Ｍ１）－丙烯腈（Ｍ２）共聚合的阻聚行为．结果表明，这些阻聚剂对Ｓｔ－ＡＮ共聚均表现良好的阻聚行为，其中氮氧自由基优于相应羟胺．同时观察到Ｓｔ—ＡＮ竞聚率的改变，羟胺使ｒ１有所降低，ｒ２略有增大．但相应的氮氧自由基是相反结果．阻聚剂为２００ｐｐｍ时，共聚物中的恒比共聚点由对照实验的０．６１９变化为０．５３３，０．６４５，０．５８９和０．６９８相对于ＤＴＢＨＡ，ＤＴＢＮＯ·，ＴＭＨＰＨＡ和ＴＭＨＰＯ·．     

Synthesis and performance of HPTLC plates modified with cyanopropyl- and octadecyl-trichlorosilane

Chemical modification of commercial high performance thin-layer chromatography plates with various mixtures of cyano-propyltrichlorosilane and octadecyltrichlorosilane is described. Surface coverage by different treatments is demonstrated as well as the variations in chromatographic performance. With regard to the development in aqueous media the utility of CN/ ODS plates compared to ODS plates is also shown.     

Gas-chromatographische Bestimmung von Glykokollbetain in Mischfuttermitteln

Zusammenfassung Es wird eine Methode zur gas-chromatographischen Bestimmung von Glykokollbetain in Mischfuttermitteln beschrieben. Die Extraktion erfolgt mit Alkohol, anschließend wird die Lösung über einen Kationenaustauscher gereinigt. Das Betain wird mit N-O-Bis-(trimethylsilyl)-trifluoracetamid und Acetonitril verestert und gas-chromatographisch bestimmt. Für die beschriebene Methode errechnete sich bei einem Mittelwert von 2309 ppm und 7 Parallelen ein Variationskoeffizient von 1,79%.

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Gas-chromatographic determination of glycocoll betaine in feeding-stuffs

The betaine is extracted with ethanol, purified by cation-exchange chromatography, esterified with N-O-bis-trimethylsilyl-trifluoracetamide and determined by gas chromatography. The coefficient of variation for the described method for 7 parallels and an average of 2309 ppm was 1.79%.

     

Characterization of OV-1/FFAP-mixture coated glass capillary columns used for the separation of free fatty acids

As an alternative to acid pretreated UCON and FFAP capillaries for the analysis of wide-boiling free fatty acid mixtures, OV-1 : FFAP phase mixtures were used on high-temperature silylated inert glass capillary columns. The HETP-carrier gas velocity curves, peak asymmetry factors, coating efficiency, gas phase and stationary phase contributions to the mass transfer resistance were determined for various OV-1 : FFAP ratios. Mixed-phase capillaries showed optimum performance at a 2 : 1 OV-1 : FFAP ratio. The thermal and long-term stability of OV-1-stabilized FFAP columns surpassed those of the UCON and pure FFAP reference column used.     

Continuous chromatographic separation of glucose-fructose mixtures using anion-exchange resins

Summary A semi-continuous, counter-current chromatographic refiner (SCCR) was packed with an anion resin in the bisulphite form and used to separate mixtures of sugars from different feedstocks. Products with purities of more than 99% were achieved and solid concentrations of the fructose products of 12% w/v were possible. The deterioration of the anion resin was controlled by simple precautions and thus its useful life was substantially prolonged.     

Evaluation of free hydroxyl radical scavenging activities of some Chinese herbs by capillary zone electrophoresis with amperometric detection

Due to the severe damage caused by free hydroxyl radicals (OH·) to cells and tissues, there is much interest in finding and studying effective and non-toxic OH· scavengers, including traditional Chinese herbs. In this paper, the simple and highly-sensitive technique of capillary zone electrophoresis with amperometric detection (CZE-AD) was used to study the OH· scavenging activities of aqueous extracts from some traditional Chinese herbs. Salicylic acid (SAL) was used as an OH· trap, and the content of OH· could be determined by assaying their products, 2,3-dihydroxybenzoic acid (2,3-DHBA) and 2,5-dihydroxybenzoic acid (2,5-DHBA). The optimum conditions for CZE-AD for the determination of 2,3-DHBA and 2,5-DHBA were explored. The linearity ranges of 2,3-DHBA and 2,5-DHBA were 1.0 ×10^–7~1.0 ×10^–4 mol L^–1, and their detection limits were as low as 2×10^–8 mol L^–1, which were much better than the CE-UV method often used. The traditional Chinese herbs studied included Radix angelicae sinensis, Rhizoma coptidis, Ligustrum lucidum, Ligusticum wallichii, Radices glycyrrhizae and Semen plantaginis. The experiments showed that the aqueous extracts from all of the above traditional Chinese herds had free OH· scavenging activities, although to different degrees.     

Fragmentation of carbohydrate anomeric alkoxyl radicals. Synthesis of highly functionalized chiral vinyl sulfones

The reaction of derivatives of 3-acetyl-d-glucal, 3-acetyl-l-rhamnal, 3-acetyl-d-galactal, and 3-acetyl-d-lactal with sodium benzenesulfinate in acid medium catalyzed by HgSO₄ afforded diastereoisomeric mixtures of the corresponding 2,3-dideoxy-3-(phenylsulfonyl)-hexopyranoses through a Ferrier rearrangement. The anomeric alkoxyl radical fragmentation of these γ-hydroxy sulfones using the system (diacetoxyiodo)benzene and iodine gave vinyl sulfones with structures of 1,2-dideoxy-4-O-formyl-2-(phenylsulfonyl)-pent-1-enitol and configurations d-erythro, l-erythro, and d-threo at the two stereogenic centers.     

Kinetics of Oxidation of 4-Oxoacids by <Emphasis Type="Italic">N</Emphasis>-Chlorosaccharin in Aqueous Acetic Acid Medium

The oxidation kinetics of substituted and unsubstituted 4-oxoacids (S) by N-chlorosaccharin (NCSA) have been studied in aqueous acetic acid media. The reaction follows first-order kinetics in each of the 4-oxoacids, NCSA and H⁺. The effect of changes in the electronic nature of the substrate reveals that positive charge develops in the transition state. Based on the kinetic results and product analysis, a suitable mechanism has been proposed for the reaction of NCSA with 4-oxoacids.