Selective determination of oxygenates in complex samples with the O-FID analyzer

A gas-chromatographic analyzer allowing the selective detection of individual oxygenates in complex organic mixtures, such as gasolines, is described. The analyzer is based on the oxygen-specific response flame ionization detection (O-FID) method. The system operates with capillary columns and includes a cracking reactor to convert any oxygenate to carbon monoxide and a special FID equipped with a microreactor for the catalytic hydro-genation of CO and detection as methane. Hydrocarbons give no signal. The selectivity of the method is better than 1:10⁷ and the linear range approaches 10⁵. The analysis of modern fuels containing oxygenated additives, to improve octane ratings, may greatly benefit from the proposed analytical method.     

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.     

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.     

Quantitation of cortico-steroids as common adulterants in local drugs by HPLC

Summary A sensitive and specific method for quantitation of the steroids betamethasone, prednisolone and cortisone acetate commonly used as adulterants in locally produced herb extracts and in certain homeopathic drugs is described. Reverse-phase liquid chromatography with UV detection has been 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.     

高效液相色谱法测定忍冬藤和叶中8种活性成分

建立了多波长分析忍冬藤和叶中化学成分含量的高效液相色谱分析方法,色谱柱为Aglient Zorbax80A,Extend-C18(4.6mm×250mm,5μm);流动相为0.3%甲酸-乙腈,梯度洗脱;流速为1.5mL/min;检测波长为240、330、360nm;柱温38℃。各指标成分的检出限均低于0.29mg/L;精密度RSD均低于2.29%;标准加入的回收率为91.2%～103.6%。应用新建立的方法测定了7个不同产地忍冬藤和叶中8种活性成分的含量。该方法简单、快速、准确,可用于忍冬藤和叶的质量控制。     

Crosslinking of vinyl‐terminated biphenyl and naphthalene side‐chain liquid‐crystalline poly(epichlorohydrin) derivatives

We performed the crosslinking of vinyl‐terminated biphenyl and naphthalene side‐chain liquid‐crystalline polyethers using peroxide‐type initiators with and without the addition of tertiary amine promoters. The crosslinking temperatures were chosen in the range of mesophase stability to allow the mesophase order to be frozen. The biphenyl derivatives, with a high isotropization temperature, were crosslinked to a large extent. This led to anisotropic thermosets. To crosslink naphthalene derivatives, amine promoters were needed, but degrees of crosslinking were lower, and anisotropic elastomers were obtained. Crosslinking processes were studied by differential scanning calorimetry, polarized optical microscopy, and Fourier transform infrared spectroscopy. The nature of the frozen mesophase was confirmed by X‐ray diffraction studies on mechanically oriented samples. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2237–2244, 2002     

An integrated coupled column liquid chromatography system for the determination of leukotriene metabolites in biological samples

Summary A fully integrated chromatographic system was developed for the determination of leukotrienes in biological samples using photodiode-array detection (PDAD), which eliminates time consuming manual sample handling steps. A special solid phase extraction, (SPE) methodology for leucotriene metabolite stability was developed which increased the recoveries and eliminates the contamination risk of biological samples. The inherent instability (autooxidation) of many of the leukotriene mediators, and the adsorption effects onto exposed surfaces in vials and in the chromatographic system were found to be very important parameters to control in order to circumvent high loss of sample analytes. By binding the cell supernatants to the functionalities of the SPE support stabilised these mediators. Cell culture samples were eluted through a disposable C₁₈ SPE column. The SPE columns were allowed to thaw and deposited in an automated sample handling unit (ASPEC XL). Desorption of the analytes was followed by a second on-line SPE step, to eliminate remaining interfering matrix compounds. Typical recoveries when stored at −70°C were in-between 55–97% except for (LTE₄) which was found to be around 40% after 72 days of storage. Seven reversed-phase packings were studied. Selectivity factors, as well as the separation efficiencies, were found to differ for the various C₁₈ bonded silica stationary phases. This integrated on-line column liquid chromatographic system was applied to the determination of leukotriene B₄, leukotriene C₄, leukotriene D₄, leukotriene and E₄ in human cell extracts using prostaglandin B₂ as the internal standard. More than 1500 biological samples were analysed. Some validation data are presented for unattended operations.     

Influence of some inorganic salts on the polarity of apolar polymer phases in capillary gas chromatography

Different stationary phases were prepared by mixing a series of inorganic salts with dimethylsiloxane polymer (SE-30) and then tested by capillary gas chromatography. It was demonstrated that the polarity (as evaluated by measurement of Rohrschneider constants) of the mixed stationary phases, which is inferior or equal to that of a medium-polar OV-25 phases, reached even lower values than SE-30 alone. The influence of NaF, NaCl, NaBr, AgNO₃, and other inorganic salts on the polarity of capillaries is reflected by a better resolution and shorter retention time of cis/trans isomers of fatty acid methyl esters (FAMES) as well as positional isomers of triglycerides.     

Glass capillary gas chromatography of amino acid enantiomers

Glass capillaries coated with Chirasil-Val, a chirally functionalised polysiloxane, are capable in principle of resolving all protein amino-acid enantiomers in a single run and within a short analysis time, thus allowing for example the quantitative amino acid determination by enantiomer labelling. The elution characteristics of the individual amino acids however are also dependent upon the chemical nature of the capillary wall surface, and a surface pretreatment is found to be necessary if all protein amino acids are to be analysed. Of the various methods of pretreatment tested, etching of borosilicate glass with gaseous HCl followed by deposition of colloidal silicic acid is considered to be the most suitable.