Summary To match the need of high efficiency capillary column (plate number N2, Plate height H2 and carrier gas linear velocity U2), a new high efficiency packed column (N1, H1 and U1) at high carrier gas velocity with small capacity factor has been developed in the light of theoretical discussion of factors
effecting the column efficiency utilization ratio. 相似文献
A new approach has been developed and tested for the urgent analysis of dioxins in samples of air-dust filters originating from catastrophe emissions. The procedure consists of a fast extraction of the sample with microwave solvent extraction (MASE) and acetone as solvent followed by a fast cleanup of the extract with normal phase coupled column liquid chromatography (LC/LC).
The multi-dimensional LC/LC system employs a 50 mm×4.6 mm i.d. column packed with 3 μm silica and a 150 mm×4.6 mm i.d. column packed with 5 μm PYE as the first and second analytical column, respectively. Iso-hexane is used on both columns to perform cleanup and dichloromethane to perform efficient back-flush elution of the compounds from the second column. The obtained polarity-based separation in the first dimension and molecular-structure based separation in the second dimension provides a fast and powerful cleanup.
Validation was done by analysing samples of homemade RIVM air-dust with aged residues (n=8, spiking level about 15 pg mg−1 per compound) of dioxins/furans and samples of reference Urban Dust SRM 1649a (n=4) with both the new approach and the existing conventional procedure and were instrumentally analyzed with capillary gas chromatography and high resolution mass spectrometric detection (GC/HRMS).
In comparison to the existing conventional procedure, the new approach reduces sample processing from several days to several hours per sample.
As regards the aged-residue air-dust samples, the new method shows a good accuracy, precision and high selectivity providing a performance in good agreement with the existing procedure. In SRM air-dust, the concentration of a few compounds obtained by the new method was below (10–50%) the certified value. 相似文献
This report describes the determination of paraquat (PQ) in human blood plasma samples by a direct-injection reversed-phase ion-pair chromatographic method. Blood plasma filtrate was injected directly into the LiChrospher® RP-18 alkyl-diol silica (ADS) precolumn integrated in a column switching system using a mixture of 3% 2-propanol and 10 mM sodium octane sulfonate (SOS) in a 0.05 M phosphate buffer (pH 2.8). After washing with this phase, the ADS precolumn was back-flushed with the analytical mobile phase consisting of 40% of methanol and 10 mM SOS in a 0.05 M phosphate buffer (pH 2.8) at a flow rate of 1.0 ml min−1, in order to carry the analyte to a conventional reversed-phase analytical column, where the separation of PQ was achieved and finally detected by UV at 258 nm. The recoveries of PQ from human blood plasma samples ranged between 95.0 and 99.5% at nine different concentrations (from 0.05 to 3.00 μg of PQ ml−1) with coefficients of variation <2.5% (n=3). The precision expressed as relative standard deviation was below 3.5% for between-day and below 4.3% for within-day measurements (n=5). The detection limit (signal-to-noise ratio, S/N>3) was 0.005 μg ml−1 with an injection volume of 200 μl. The proposed method is promising for the identification and quantification of PQ at low concentration levels and is suitable for its analysis in human blood plasma samples from intentional or accidental poisonings cases with a sample throughput of 5 samples per hour. 相似文献
A chiral base route to a range of highly functionalised amino cyclopentenes has been developed. The key asymmetric step involved the chiral lithium amide base-mediated rearrangement of a protected trans-4-hydroxy cyclopentene oxide to give an allylic alcohol (88% ee). Subsequent Overman rearrangement gave a protected trans-1,2-aminocyclopentenol whereas Mitsunobu substitution with BocNHNs gave a protected cis-amino cyclopentenol. Both are proven intermediates for natural product synthesis. The protected cis-aminocyclopentenol was transformed in a few steps into a precursor of the cyclopentene core of nucleoside Q, a natural product whose deficiency in animals is related to tumour growth. 相似文献