Anders Engström

New interface for coupling flow-injection and capillary electrophoresis

Abstract A new interface for coupling flow injection analysis (FIA) and capillary electrophoresis (CE) has been developed. An FIA system is connected to a flow-through channel of the interface. One end of a capillary is positioned in a flow-through channel inside the interface together with a platinum electrode. The other end and a second platinum electrode are immersed in a liquid reservoir situated outside the interface. A constant high voltage is applied across the capillary. A sample plug injected in the FIA part of the system is carried by an electrolyte stream towards the interface and when it passes by the first capillary end, a minor fraction of the sample is introduced into the capillary and gets separated. A UV spectrophotometric detector is placed close to the second capillary end. The FIA-CE interface enables multiple injections so that a high sampling throughput can be achieved (up to 150 samples per hour). The interface was tested by running a standard mixture of nine common anions. The repeatability was approximately 2% (r.s.d.). Rapid, qualitative screening of samples can be performed. Real samples such as tap and rain water were also analyzed. The new interface allows mechanized sample handling prior to the CE separation step.

Direct and indirect chiral separation of amino acids by capillary electrophoresis

Abstract Two approaches to the chiral separation of racemic mixtures of amino acids by means of capillary electrophoresis have been evaluated. These were indirect separation of diastereomers formed by derivatization with (+)- or (−)-1-(9-fluorenyl)ethyl chloroformate and direct chiral separation after derivatization with 9-fluorenylmethyl chloroformate. Separation conditions were optimized by the application of a full factorial design. For indirect separation, concentration of sodium dodecyl sulphate (SDS) and pH were the most important separation variables, and for direct separation, concentration of isopropanol (IPA), β-cyclodextrin and SDS were the most prominent factors affecting separation. The presence of IPA was a prerequisite for chiral recognition. With regard to selectivity, efficiency, analysis time and ease of method development the best results were provided by the indirect method. It should be noted, however, that the success of this approach is based on the availability of a derivatization reagent in high optical purity.

Do organics contribute to small particle formation in the Amazonian upper troposphere

3-D cloud-resolving model simulations including explicit aerosol physics and chemistry are compared with observations of upper tropospheric (12 km) aerosol size distributions over the Amazon Basin. ...

Direct chiral separation of amino acids derivatized with 2-(9-anthryl)ethyl chloroformate by capillary electrophoresis using cyclodextrins as chiral selectors Effect of organic modifiers on resolution and enantiomeric elution order

Abstract Direct chiral separation of amino acids derivatized by 2-(9-anthryl)ethyl chloroformate (AEOC) has been performed by capillary electrophoresis in capillary zone electrophoretic (CZE) mode and micellar electrokinetic (MEKC) mode using cyclodextrins (CDs) as chiral selectors. The concentrations of chiral selector, surfactant and organic modifier were optimized. Application of β - and γ -CD as chiral selectors in MEKC, resulted in d/l separation of 12 and 13 amino acids, respectively. In CZE, chiral separation was obtained only with γ -CD, 8 amino acids were chirally separated in this mode. Separation in the MEKC mode resulted in higher resolutions of the enantiomers than in the CZE mode. Addition of 2-propanol to the buffer caused reversal of the enantiomeric elution order for some amino acids in MEKC mode.

Impact of meteorological factors on the correlation between aerosol optical depth and cloud fraction

The aerosol optical depth has in several recent studies been found to correlate with cloud fraction. This study examines the global distribution of the total correlation between aerosol optical dep ...

Enantiomeric determination of amino compounds with high sensitivity using the chiral reagents (+)- and (−)-1-(9-anthryl)-2-propyl chloroformate

New chiral precolumn reagents, (+)- and (-)-1-(9-anthryl)-2-propyl chloroformate (APOC), are introduced for the chiral separation of amino acids and small peptides in capillary electrophoresis. Chiral separation of 17 amino acids and four small peptides as their diastereomeric 1-(9-anthryl)-2-propyl carbamate derivatives have been achieved by micellar electrokinetic chromatography. The detection limit for the derivatives is in the femtomole range with UV detection and in the attomole range with laser-induced fluorescence (LIF) detection. LIF detection was used to determine the enantiomeric excess of four APOC-derivatised peptides. The use of the new, anthracene-based reagents in conjunction with argon ion LIF makes enantiomeric determinations at ppm levels feasible. In this paper determinations below promille levels are performed without overloading the separation system.

Determination of chiral reagent purity by capillary electrophoresis

Abstract A method for the determination of the enantiomeric purity of the chiral reagent 1-(9-fluorenyl)ethyl chloroformate (FLEC) has been developed. The reagent is reacted with glycine, an achiral compound, and separated by capillary electrophoresis using β- or γ-cyclodextrin as chiral selectors. A general equation for the recalculation of the measured values with respect to the chiral reagent purity is presented. The suitability of this approach is practised on the peptide d -Arginine-Glycine to determine trace amounts of the enantiomeric contaminant, the l -form.

Impact of Two-Way Aerosol–Cloud Interaction and Changes in Aerosol Size Distribution on Simulated Aerosol-Induced Deep Convective Cloud Sensitivity

Recent cloud-resolving model studies of single (isolated) deep convective clouds have shown contradicting results regarding the response of the deep convection to changes in the aerosol concentrati ...

Observational and modelling evidence of tropical deep convective clouds as a source of mid-tropospheric accumulation mode aerosols

High concentrations (up to 550 cm−3 STP) of aerosols in the accumulation mode (>0.12 μm) were observed by aircraft above 7.5 km altitude in the dynamically active regions of several deep convect ...

The Importance of Representing Mixed-Phase Clouds for Simulating Distinctive Atmospheric States in the Arctic*

AbstractObservations from the Surface Heat Budget of the Arctic Ocean experiment (SHEBA) suggest that the Arctic Basin is characterized by two distinctly different preferred atmospheric states during wintertime. These states appear as two peaks in the frequency distribution of surface downwelling longwave radiation (LWD), representing radiatively clear and opaque conditions. Here, the authors have investigated the occurrence and representation of these states in the widely used ECMWF Interim Re-Analysis (ERA-Interim) dataset. An interannually recurring bimodal distribution of LWD values is not a clearly observable feature in the reanalysis data. However, large differences in the simulated liquid water content of clouds in ERA-Interim compared to observations are identified and these are linked to the lack of a radiatively opaque peak in the reanalysis. Using a single-column model, dynamically controlled by data from ERA-Interim, the authors show that, by tuning the glaciation speed of supercooled liquid c...