Analytical methods providing high throughput are required for the ever increasing number of samples in bioanalysis. Currently, the method of choice in bioanalysis is LC-MS-MS. This method is quite ...rapid and thereby the focus has been directed to sample preparation as being a bottleneck in total analysis systems. It has become necessary to develop sample preparation techniques to a new improved level. This development has been based on a systematic and scientific approach. The key factors in this development have been miniaturization, integration, and automation of the techniques. This review provides a short overview of recent developments. Special emphasis is on two techniques: microextraction in packed syringe (MEPS) and use of a monolithic acrylamide plug as sorbent in polypropylene tips primarily intended for use with 96-well plate systems.
The need for on-line sample preparation for high-throughput applications in bioanalysis has increased during the past decade. In this paper a robust and on-line sample preparation technique, micro ...extraction in packed syringe (MEPS) has been developed and validated. The method is a miniaturized, fully automated, solid-phase extraction (SPE) technique that can be connected on-line to GC or LC without any modification of the chromatographs. The performance of MEPS as sample preparation method is illustrated by the determination of local anaesthetics in human plasma samples on-line with high performance liquid chromatography (HPLC) and tandem mass spectrometry. The sampling sorbent was 1mg silica based benzenesulphonic acid cation exchanger that was inserted in a 250 microl syringe. Ropicavine and two of its metabolites (PPX and 3-OH-ropivacine), lidocaine and bupivacine were used as model substances. The accuracy values of quality control samples (QC) were between 95% and 109%, and precision (relative standard deviation, R.S.D.) had a maximum deviation of 9% for the analytes.
During the third MESSENGER flyby of Mercury on 29 September 2009, 15 crossings of the dusk‐side magnetopause were observed in the magnetic field data over a 2‐min period, during which the spacecraft ...traveled a distance of 0.2 RM (where RM is Mercury's radius). The quasi‐periodic nature of the magnetic field variations during the crossings, the characteristic time separations of ∼16 s between pairs of crossings, and the variations of the magnetopause normal directions indicate that the signals are likely the signature of surface waves highly steepened at their leading edge that arose from the Kelvin‐Helmholtz instability. At Earth, the Kelvin‐Helmholtz instability is believed to lead to the turbulent transport of solar wind plasma into Earth's plasma sheet. This solar wind entry mechanism could also be important at Mercury.
Chiral separation of amino acids and peptides by capillary electrophoresis (CE) is reviewed regarding the separation principles of different approaches, advantages and limitations, chiral recognition ...mechanisms and applications. The direct approach details various chiral selectors with an emphasis on cyclodextrins and their derivatives, antibiotics and chiral surfactants as the chiral selectors. The indirect approach deals with various chiral reagents applied for diastereomer formation and types of separation media such as micelles and polymeric pseudo-stationary phases. Many derivatization reagents used for high sensitivity detection of amino acids and peptides are also discussed and their characteristics are summarized in tables. A large number of relevant examples is presented illustrating the current status of enantiomeric and diastereomeric separation of amino acids and peptides. Strategies to enhance the selectivity and optimize separation parameters by the application of experimental designs are described. The reversal of enantiomeric elution order and the effects of organic modifiers on the selectivity are illustrated in both direct and indirect methods. Some applications of chiral amino acid and peptide analysis, in particular, regarding the determination of trace enantiomeric impurities, are given. This review selects more than 200 articles published between 1988 and 1999.
Microextraction by packed sorbent (MEPS) is a new format for solid-phase extraction (SPE) that has been miniaturized to work with sample volumes as small as 10
μL. The commercially available ...presentation of MEPS uses the same sorbents as conventional SPE columns and so is suitable for use with most existing methods by scaling the reagent and sample volumes. Unlike conventional SPE columns, the MEPS sorbent bed is integrated into a liquid handling syringe that allows for low void volume sample manipulations either manually or in combination with laboratory robotics. The key aspect of MEPS is that the solvent volume used for the elution of the analytes is of a suitable order of magnitude to be injected directly into GC or LC systems. This new technique is very promising because it is fast, simple and it requires very small volume of samples to produce comparable results to conventional SPE technique. Furthermore, this technique can be easily interfaced to LC/MS and GC/MS to provide a completely automated MEPS/LC/MS or MEPS/GC/MS system. This extraction technique (MEPS) could be of interest in clinical, forensic toxicology and environmental analysis areas. This review provides a short overview of recent applications of MEPS in clinical and pre-clinical studies for quantification of drugs and metabolites in blood, plasma and urine. The extraction of anti-cancer drugs, β-blockers drugs, local anaesthetics, neurotransmitters and antibiotics from biological samples using MEPS technique will be illustrated.
This study demonstrates the development and validation of a non-aqueous capillary electrophoresis (NACE) method for enantiomeric determination of omeprazole and its metabolite 5-hydroxyomeprazole. ...Heptakis-(2,3-di-
O-methyl-6-
O-sulfo)-β-cyclodextrin (HDMS-β-CD) was chosen as the chiral selector in an ammonium acetate buffer acidified with formic acid in methanol. Parameters such as CD concentration, concentration of buffer electrolyte, voltage and temperature were studied in order to optimize both the enantioresolution and migration times. An experimental design was utilized for method optimization, using software Modde 5.0. Validation of the developed method showed good linearity, which was tested over a concentration range of 2.5–500
μM. The regression coefficients for
S-omeprazole,
S-5-hydroxyomeprazole,
R-omeprazole and
R-5-hydroxyomeprazole were between 0.996 and 0.997. The limits of detection for the four enantiomers were in the range from 45 to 51
μM and the limits of quantification were between 149 and 170
μM with UV detection at 301
nm. Using a reduced temperature of 16
°C gave improved resolution values, reproducibility and also decreased the occurrence of current loss within the capillary. RSD values for peak migration time were calculated to be between 0.41 and 1.48% using an inter-day study.
A series of quasi-periodic magnetopause crossings were recorded by the MESSENGER spacecraft during its third flyby of Mercury on 29 September 2009, likely caused by a train of propagating ...Kelvin–Helmholtz (KH) vortices. We here revisit the observations to study the internal structure of the waves. Exploiting MESSENGER's rapid traversal of the magnetopause, we show that the observations permit a reconstruction of the structure of a rolled-up KH vortex directly from the spacecraft's magnetic field measurements. The derived geometry is consistent with all large-scale fluctuations in the magnetic field data, establishes the non-linear nature of the waves, and shows their vortex-like structure. In several of the wave passages, a reduction in magnetic field strength is observed in the middle of the wave, which is characteristic of rolled-up vortices and is related to the increase in magnetic pressure required to balance the centrifugal force on the plasma in the outer regions of a vortex, previously reported in computer simulations. As the KH wave starts to roll up, the reconstructed geometry suggests that the vortices develop two gradual transition regions in the magnetic field, possibly related to the mixing of magnetosheath and magnetospheric plasma, situated at the leading edges from the perspectives of both the magnetosphere and the magnetosheath.
► A series of Kelvin–Helmholtz waves were recorded at Mercury's magnetopause. ► MESSENGER's rapid boundary traversal permits a spatial reconstruction of the waves. ► The derived geometry shows the internal, vortex-like structure of the magnetic field. ► Each vortex develops two gradual transition regions.
UV‐initiated poly(butyl methacrylate‐ethylene glycol dimethacrylate) porous polymer monoliths were prepared in situ in polypropylene‐based pipette tips for high‐throughput sample preparation. Prior ...to the in situ polymerization, the surface of the PP tips was modified. In this work, two different surface modification approaches were tested for this purpose. First the photoinitiator benzophenone was used to generate radicals at the surface of PP by hydrogen ion. In the second modification approach, a thin layer of a polymer was directly grafted to the surface. The effect of surface modification was measured by contact angle measurements of a drop of water at the surface. As a result of the surface modification, scan electron microscopy images indicate a covalent attachment of the monolith to the wall of the pipette tip. Pipette tips modified with 5% BP in methanol and packed with a plug of monolith were further evaluated for high‐throughput sample preparation. Using a liquid handling system, the extraction performance of packed pipette tips was tested for the analysis of ropivacaine in plasma samples. The recovery and reproducibility results were in accordance with internationally accepted criteria for qualitative and quantitative analysis of the test substance, ropivacaine.
Sample adsorption to the inner surface of fused silica capillaries is a common problem in CE when analyzing macromolecules and is harmful to the analysis. We previously utilized the pH hysteresis ...effect of fused silica to facilitate electrophoresis of the strongly adsorbing protein β2gpI in plain‐fused silica capillaries at neutral pH. In the present paper, the effect of different pretreatments of the capillary on the adsorption of the β2‐glycoprotein I has been investigated using electroosmosis markers, SDS mobilization, and imaging based on indirect immunofluorescence microscopy for direct visualization. The amount of β2gpI adsorbed on the surface was probed using all these independent techniques after electrophoresis at neutral pH on capillaries pretreated with HCl, background electrolyte (BGE), and NaOH. BGE pretreatment was included as a positive control. We found that 80% or more of the starting material was adsorbed to the inner surface of the silica capillaries during electrophoresis after pretreatment with only BGE or with NaOH, but after acidic pretreatment the loss was consistently less than 20%. NaOH most efficiently removes adsorbed protein between runs. A theoretical calculation of the pH change of the BGE showed that electrolysis affects the pH more than the deprotonation of silanols during electrophoresis. We conclude that acidic pretreatment of fused silica capillaries diminishes adsorption of β2gpI by decreasing charge‐dependent wall adsorption.
PDF
