Possibilities of dynamic headspace analysis coupled with capillary GC for the investigation of solid samples

The advantages of the dynamic headspace method for the analysis of solid samples, as compared with the static head space method, are discussed. Examples of dynamic headspace analyses are given to illustrate its possibilities.     

Reversed phase HPLC coupled on-line to GC by the vaporizer/precolumn solvent split/gas discharge interface; analysis of phthalates in water

Reversed phase liquid chromatography (RPLC) was coupled on-line to gas chromatography (GC) via the vaporizer chamber/preco-lumn solvent split/gas discharge interface outlined recently. Water-containing eluents were driven into a vaporizer chamber at 300°C by the LC pump. The Vapors were removed through an early vapor exist by the carrier gas. Solvent/solute separation occurred in hte retaining precolumn. Special attention was paid to the parame-ters determining the losses of the most volatile compounds. The oven temperature during transfer was lowered close to the dew point of the eluent (the temperature at which recondensation occurs) in order to maximise the retention power of the retaining precolumn. The dew point depends on the transfer rate, the gas flow rate, and the gas inlet pressure. Sometimes even better retention of the vola-tiles was observed at temperatures below the dew point, i.e. despite partial reconsideration. The method was applied to the analysis of phthalates in drinking and surface waters. The detection limits, using MS, were 5–10 ng/l.     

Evaluation of automated and manual hot-splitless,cold-splitless (PTV), and on-column injection technique using capillary gas chromatography for the analysis of organophosphorus pesticides

Three different injection modes were compared for the analysis of organophosphorus pesticides. Differing results were found for several compounds depending on their chemical structure and thermostability. The programmed temperature vaporizing injector used in this study seemed to be the most promising sampling device for pesticide residue analysis in biological samples.     

Wine analysis: Study and comparison of techniques developed for the study of volatile constituents

Summary A number of headspace techniques have been compared, using a standard solution containing 12 compounds and a wine sample, viz.: (1) purge and cold trap injection; (2) dynamic headspace combined with liquidliquid extraction; (3) static headspace with and without preconcentration; (4) direct liquid injection. The sensitivity, reproducibility and speed of analysis were determined. Considering the results obtained and dependent on the purpose of the experiments and the number of samples to be examined the appropriate technique can be selected.     

Reference standards for quantitative trace analysis of PCB's by GC. Technical PCB formulations for the calibration of ECD and MSD responses

Summary The composition of any technical PCB formulation can be determined directly by analyzing the PCB sample by gas chromatography with a flame ionization detector (GC-FID), provided the relative molecular masses of the components are known. The responses of electron capture and selected-ion monitoring, mass-spectra detectors can then be calibrated for individual PCB congeners by correlation of the chromatographic patterns with those of concentrated PCB samples obtained by GC-FID. This procedure, which uses a given technical PCB formulation as a secondary reference standard mixture, is to be preferred over existing calibration methods, when results with ±10% errors are acceptable because commercial PCB formulations cover the whole range of chlorination products.     

Thermo-gravimetric kinetics analysis for the synthesis of lithium aluminate and fabrication of pebbles by solid state reaction process

Lithium aluminate is considered as the solid breeder materials and it can be synthesized by different methods. In the present study, lithium aluminate was synthesized using lithium carbonate and alumina as raw materials, by using solid state reaction process (SSRP). The reaction temperature and time of reaction were optimized using TG-DTA and XRD analysis. The reaction kinetics for the synthesis of lithium aluminate was investigated using TG-DTA data, which is not reported till date. It was found that the reaction is controlled by third order chemical reaction at initial stage and further controlled by diffusion. The activation energy and pre-exponential factor are 292 kJ/mol and 2.29 × 10¹⁷ respectively. Lithium aluminate pebbles were fabricated using SSRP and found the process is highly suitable for the synthesis and fabrication of lithium aluminate pebbles. The density of the sintered pebbles was found to be about 90% of theoretical density. The details of the synthesis, pebble fabrication, sintering and kinetic study are discussed here.     

On the influence of the alumina precursor in Fe-K/Al2O3 structured catalysts for the simultaneous removal of soot and NOx: From surface properties to reaction mechanism

Cordierite-monolith supported Fe-K/Al₂O₃ catalysts were prepared using different alumina precursors. The catalysts were physico-chemically characterized, and their activity in the simultaneous removal of soot (carbon black) and NO_x was assayed with the aim of studying the influence of the particular features of each alumina precursor on the final properties of the different prepared catalyst. Structural and textural characteristics of the catalytic layer were found to be strongly dependent on the type of alumina used, which, in turn, determined the mobility of the alkali compound. This fact together with the weaker interaction of the catalytic phase with the alumina resulted in easier K diffusion and loss in some cases, whereas, on the other hand, a stronger interaction and favorable textural features of the layer resulted in notably enhanced catalytic activity.     

Study on the interaction of plasma protein binding rate between edaravone and taurine in human plasma based on HPLC analysis coupled with ultrafiltration technique

In this work, two high‐performance liquid chromatography (HPLC) assays were developed and validated for the independent determination of edaravone and taurine using 3‐methyl‐1‐p‐tolyl‐5‐pyrazolone and L ‐glutamine as internal standards. In in vitro experiments, human plasma was separately spiked with a mixture of edaravone and taurine, edaravone or taurine alone. Plasma was precipitated with acetonitrile containing 0.1% formic acid. Ultrafiltration was employed to obtain the unbound ingredients of the two drugs. The factors that might influence the ultrafiltration effiency were elaborately optimized. Plasma supernatant and ultrafiltrate containing taurine were derivated with o‐phthalaldehyde and ethanethiol in the presence of 40 mmol/L sodium borate buffer (pH 10.2) at room temperature within 1 min. Chromatographic separations were achieved on an InertSustain C₁₈ column (250 × 4.6 mm, 5 µm). Isocratic 50 mmol/L ammonium acetate–acetonitrile and gradient 50 mmol/L sodium acetate (pH 5.3)–methanol were respectively selected as the mobile phase for the determination of edaravone and taurine. All of the validation data including linearity, extraction recovery, precision, accuracy and stability conformed to the requirements. Results showed that there were no significant alterations in the plasma protein binding rate of taurine and edaravone, implying that the proposed combination therapy was pharmacologically feasible. Copyright © 2014 John Wiley & Sons, Ltd.     

Multiresidue method for the analysis of more than 140 pesticide residues in fruits and vegetables by gas chromatography coupled to triple quadrupole mass spectrometry

A new multiresidue method has been developed and validated for the determination of more than 140 pesticide residues in cucumber and orange by gas chromatography coupled to triple quadrupole mass spectrometry (GC-QqQ-MS/MS) in a single run of 25.50 min. The triple quadrupole (QqQ) analyzer simultaneously operated in the selected reaction monitoring (SRM) and selected ion monitoring (SIM) modes, acquiring two or three transitions per compound. Samples were extracted by the application of a single-phase extraction of 10 g of sample with acetonitrile containing 1% of acetic acid, followed by a liquid-liquid partition formed by the addition of 4 g of MgSO(4) and 1 g of NaOAc. A dispersive solid-phase extraction (D-SPE) with primary secondary amine (PSA) was applied to clean up the extracts. A final concentration step was included in order to increase sensitivity in the instrumental analysis. The method was properly validated in each matrix in a wide dynamic range (10-400 microg kg(-1)): this work relies on a new quantification strategy by the use of two calibration curves to increase the dynamic range, which permitted reduction of sample dilutions and increase in sample throughput. Recovery was studied at three concentration levels (11.5, 50.0, and 150.0 microg kg(-1)), yielding values in the range 70-110% with precision values, expressed as relative standard deviation (RSD), lower than 20 and 25% for the intraday and interday precision, respectively. Limits of quantification (LOQs) were established at 10 microg kg(-1), the lowest maximum residue level (MRL) value set by the European Union in vegetables. The method was successfully applied to the analysis of pesticide residues in real samples from the southeastern Spain. Copyright (c) 2008 John Wiley & Sons, Ltd.     

亚磷酸三乙酯硫化反应历程的GC/MS研究

用气相色谱-质谱联用技术研究了亚磷酸三乙酯和亚磷酸三苯酯与硫反应的机理.研究证明,硫与三价磷化合物的反应只发生在液相状态.