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PubMed1991

Large-area plan-view sample preparation for GaAs-based systems grown by molecular beam epitaxy.

We describe a method for plan-view transmission electron microscopy (TEM) sample preparation that takes advantage of extreme etch-rate selectivity in GaAs and AlAs in HF/H2O solutions. GaAs/InxGa1-xAs/GaAs strained-layer films (x = 0.05, 0.10, 0.19, 0.22) were chemically lifted off using this technique and were mounted on Cu TEM grids such that TEM transparent areas of up to 1 x 2 mm of constant thickness (196.4 nm) could be viewed. This simple, large-area plan-view technique uses only chemical methods and significantly extends the usefulness of TEM for the evaluation of crystal quality in GaAs-based epitaxial systems. The method requires the growth of a release layer of AlAs (10 nm thick) prior to the layered structure of interest.

Microscopy, Electron↗
PubMed2003

Polymer-coated fibrous extraction medium for sample preparation coupled to microcolumn liquid-phase separations.

Polymer-coated fibrous material has been introduced as the extraction medium for a miniaturized sample preparation method being coupled with microcolumn liquid chromatography. The preconcentration and the subsequent liquid chromatographic separation of tricyclic antidepressants (TCAs) drugs, amitriptyline, imipramine, nortriptyline and desipramine, was carried out with the hyphenated system. Several basic experimental parameters, such as extraction and separation conditions, were investigated along with the applicability of the method for the analysis of biological fluids. The results clearly showed that the on-line coupled system could be a powerful tool for the analysis of complex mixtures in biological matrix without a large solvent consumption and specially designed instruments. The lowest limit of quantification was quite acceptable for the analysis of TCAs in clinical and forensic situations.

Antidepressive Agents, Tricyclic↗
PubMed2005

Development and validation of a liquid chromatography and tandem mass spectrometry method for determination of roscovitine in plasma and urine samples utilizing on-line sample preparation.

Roscovitine, a purine analogue that selectively inhibits cyclin-dependent kinases, has been considered as a potential anti-tumor drug. The determination of roscovitine in plasma and urine was performed using microextraction in packed syringe as on-line sample preparation method with liquid chromatography and tandem mass spectrometry. The sampling sorbent utilized was polystyrene polymer. 2H3-lidocaine was used as internal standard. The limit of detection for roscovitine was as low as 0.5 ng/mL and the lower limit of quantification was 1.0 ng/mL. The accuracy and precision values of quality control samples were between +/-15% and < or =11%, respectively. The calibration curve was obtained within the concentration range 0.5-2000 ng/mL in both plasma and urine. The regression correlation coefficients for plasma and urine samples were > or =0.999 for all runs. The present method is miniaturized and fully automated and can be used for pharmacokinetic and pharmacodynamic studies.

Calibration↗
PubMed1981

Determination of flurbiprofen and ibuprofen in dog serum with automated sample preparation.

Methods for the determination of flurbiprofen and ibuprofen in dog serum were developed using high-performance liquid chromatography and automated serum extraction. Sample extraction was automated by use of cartridges packed with a styrene-divinylbenzene macroreticular resin in a microprocessor-controlled centrifugal system. The average recoveries were 98.9% for flurbiprofen and 94.5% for ibuprofen. The limits of detection were approximately 0.04 microgram/ml for flurbiprofen at 254 nm and 0.5 microgram/ml for ibuprofen at 230 nm. The relative standard deviations for the determination of a laboratory standard between days was 2.4% (20 microgram/ml) for flurbiprofen and 1.7% (13 microgram/ml) for ibuprofen. Peak height ratios were linear with concentrations of 0.04--100 microgram/ml for flurbiprofen and 1.0-50 microgram/ml for ibuprofen. These methods are simple, rapid, sensitive, and specific. The use of an automated sample preparation procedure improved the between-day precision by a factor of two when compared to a manual extraction procedure. These methods were applied to bioavailability studies in dogs.

Animals↗
PubMed1994

Use of supercritical fluid extraction for sample preparation of sustained-release felodipine tablets.

Supercritical fluid extraction (SFE) was shown to be an accurate and precise alternative to liquid extraction for sample preparation of sustained-release felodipine tablets (5 mg potency) while realizing an 80% reduction in solvent consumption. Extractions of felodipine spiked on an inert support were used to evaluate the solubility of felodipine in CO2 as well as analyte trapping after SFE. Even though the pure drug was found to be soluble in pure CO2, extractions of felodipine from the tablet matrix required moderate modifier concentrations [8.7% (v/v) methanol in CO2] in order to overcome strong matrix-drug interactions. Sequential static/dynamic extraction steps were also required to quantitatively recover the drug from the tablet matrix, indicating that the drug extraction was diffusion-limited. Average recoveries (n = 5) for the optimized SFE method were determined to be 4.93 mg felodipine tablet (98.6% claim) with an RSD of 1.2% versus those for the liquid extraction procedure (n = 5, 4.98 mg/tablet, 99.6% claim, 2.4% RSD). Similar levels of drug degradation (0.12% expressed as felodipine) were also obtained with both the traditional liquid extraction and with the SFE method.

Chromatography, High Pressure Liquid↗
PubMed2000

High-performance liquid chromatographic determination of p-aminohippuric acid and iothalamate in human serum and urine: comparison of two sample preparation methods.

A high-performance liquid chromatography method applied to determine p-aminohippuric acid (PAH) and iothalamate (IOT) in serum and urine samples of patients was evaluated according to recovery, reproducibility and linearity utilizing narrow-bore columns. The mobile phase consisted of 0.15 M sodium dihydrogenphosphate with 1.2 mM tetrabutylammonium sulphate, the pH was adjusted to pH 4.6, acetonitrile was added to a final ratio of 95:5 (v/v), the flow-rate was set at 0.3 ml/min. The separation was achieved on a ODS Hypersil column (200 x 2.1 mm I.D.). The UV detector was set at 254 nm. PAH and IOT are used for evaluation of kidney function [effective renal plasma flow (ERPF) and glomerular filtration rate (GFR)]). Under the described chromatographic conditions two sample preparation techniques, ultrafiltration and acetonitrile precipitation were compared. The results demonstrate the accuracy of both methods in evaluation of ERPF and GFR. Due to its cost-effectiveness we recommend the acetonitrile precipitation method in clinical routine.

Chromatography, High Pressure Liquid↗
PubMed1996

Sensitive high-performance liquid chromatographic determination of nifedipine in dog plasma using an automated sample preparation system with laboratory robot.

Nifedipine, a calcium-channel blocking drug was analysed in dog plasma after oral dosing with two different formulations. Sample preparation was automated with a laboratory robot. Quantitative determination of the drug was performed on a reversed-phase HPLC system with electrochemical detection (ED) using an internal standard. Validation of the analytical method showed that the system is well suited for pharmacokinetic studies on dogs. The assay was linear in the range 1-50 ng/ml. Inter-day and intra-day variability were between 6.43-18.15% C.V. and 1.57-5.53% C.V., respectively.

Animals↗
PubMed1996

An automated sample preparation and high performance liquid chromatographic method for the determination of MK-591, a novel leukotriene biosynthesis inhibitor, in human plasma.

A high performance liquid chromatography assay utilizing an automated sample preparation procedure for the determination of a novel leukotriene biosynthesis inhibitor, (MK-591), in human plasma has been developed. After aliquoting plasma samples and adding internal standard manually, the BenchMate Workstation executed protein precipitation and solid-phase extraction. Following evaporation to dryness, the residue was reconstituted and chromatographed isocratically on a cyano-phase analytical column. MK-591 and the internal standard were separated from each other and from endogenous plasma substances and detected with an absorbance detector. The assay has been validated in the concentration range 10-1000 ng ml-1 and has the sensitivity and specificity necessary to quantify plasma concentrations from several clinical studies.

Chromatography, High Pressure Liquid↗
PubMed2004

[The improvement of sample preparation for infrared spectroscopy analysis].

Routine preparation methods of liquid and solid samples for IR analysis are introduced, deficiencies of conventional KBr pellet and liquid film most often used are pointed out and a modified preparation method of sample is put forward, i.e. preparing a liquid film by using two blank KBr pellets or by dipping blank KBr pellet into solution which is the mixture of sample and low boiling point organic solvent. For low boiling point liquid sample, a liquid film is prepared by using two blank KBr pellets; for high boiling point liquid sample, dipping a blank KBr pellet is used; for solid sample, dipping a blank KBr pellet is used as well. From the comparison of routine and modified preparation methods, this new method can meet the need of qualitative analysis and overcome the deficiencies of conventional KBr pellet and liquid film.

Bromides↗
PubMed1986

Sample preparation procedure for determination of dopamine sulfate isomers in human urine by high-performance liquid chromatography with dual-electrode electrochemical detection.

We developed a procedure utilizing small columns of solid-phase extraction material for sample preparation for the determination of dopamine sulfate (DAS) isomers in human urine. Processed sample is then subjected to high-performance liquid chromatography (HPLC) with dual-series-electrode electrochemical detection. Dopamine 3-O-sulfate (DA-3-S) and dopamine 4-O-sulfate (DA-4-S) were determined using two different HPLC systems. The ratio of the urinary excretion rate of DA-3-S to DA-4-S was relatively constant, but the 24-h excretion rates of total DAS varied widely among individuals. This method should prove useful in future studies concerning the metabolic and physiologic roles of DAS isomers.

Adult↗
PubMed1985

Sample preparation and radioimmunoassay for circulating free and antibody-bound insulin concentrations in insulin-treated diabetics: a re-evaluation of methods.

Methods for blood sample preparation and radioimmunoassay of free and antibody-bound serum or plasma insulin concentrations, using polyethylene glycol (PEG) solution to precipitate bound insulin, have been evaluated and compared. Method A was rapid mixing of whole blood with PEG, followed by separation of bound insulin by centrifugation into Ficoll; method B was rapid PEG addition to whole blood, followed by centrifugation alone; method C was conventional PEG addition to thawed plasma or serum, followed by centrifugation to remove bound insulin. Method A was found to have acceptable performance and reproducibility; serum free insulin levels were not significantly different from those measured by the simpler method B. In samples from insulin-dependent diabetics, serum free insulin was significantly higher and bound insulin significantly lower in method A compared to the conventional method C. However, in samples from non-diabetics there was no significant difference between methods A and C. Spurious results were obtained by addition of PEG and assay of plasma and serum samples after either freezing and thawing or incubation at 37 degrees C for 2h, compared to PEG addition and assay of fresh plasma or serum samples. We conclude that conventional, delayed addition of PEG to plasma or serum may result in redistribution of free and bound insulin and that values more representative of in vivo blood insulin levels are obtained by rapid PEG addition methods.

Diabetes Mellitus↗
PubMed2003

Rapid determination of rat plasma uridine levels by HPLC-ESI-MS utilizing the Captiva plates for sample preparation.

A rapid, accurate and precise HPLC-ESI-MS method for the determination of rat plasma uridine concentrations was developed and is described here. Sample preparation involves methanol precipitation of plasma proteins in a 96-well Captiva protein precipitation filter plate. A clear extract is drawn through the filter plate with vacuum, followed by evaporation of the extract and subsequent reconstitution prior to chromatography on a reversed-phase column with an aqueous mobile phase [0.1% (v/v) glacial acetic acid]. Detection was accomplished by positive-ion electrospray ionization mass spectrometry. A calibration curve ranging in concentration from 0.78 to 25 microM was constructed by best-fit, 1/x weighting linear regression analysis of the calibration standard concentrations vs peak height ratios of analyte with internal standard. The correlation coefficient was >0.995. The overall assay accuracy as shown by the back-calculated concentrations of the calibration curve ranged from 96.6 to 103% with RSD ranging from 4.5 to 20%. While this assay method was developed for the determination of uridine in rat plasma, it could be readily adapted for determination of uridine in plasma from other species, such as human.

Animals↗
PubMed2002

Target specific sample preparation from aqueous extracts with molecular imprinted polymers.

In this paper we report a method for the synthesis of molecular imprinted polymers for use in sample preparation with aqueous biological materials. Highly cross-linked bulk polymers were synthesized in the presence of the template molecule, 2,6-pyridinedicarboxylic acid (DPA) using acrylamide (ACD) and 4-vinylpyridine (VP) as functional monomers. Conditions are described for the optimization of the template complex with temperature, copolymer mixture and crosslinker type. Selective binding of the template molecule is demonstrated in comparison to structural isomers and analogs for molecular imprinted polymers (MIPs) synthesized with three different crosslinkers, ethyleneglycol dimethacrylate (EGDMA), bisacrylamide and N,N'-1,3-phenylene bismethacrylamide (PBMA). The chromatographic capacity factors and selectivities for a series of structural analogs were compared. Molecular imprinted polymers prepared with equimolar ratios of ACD and VP and either PBMA or bisacrylamide resulted in highly selective binding for the template versus analogs with similar structure and chemistry. Multiple molecular dissociation constants were measured with the maximum binding capacities for EGDMA, PBMA and bisacrylamide measuring 17, 27 and 90 micromol/g, respectively.

Acrylamide↗
PubMed2004

Multidimensional on-line sample preparation of verapamil and its metabolites by a molecularly imprinted polymer coupled to liquid chromatography-mass spectrometry.

A new molecularly imprinted polymer (MIP) material was synthesized selective for verapamil and utilized for on-line metabolic screening of this common calcium antagonist in biological samples. Since some metabolites of verapamil have also shown pharmacological properties, a selective and sensitive sample preparation approach that provides a metabolic profile in biologically relevant samples is important. The MIP material was coupled on-line to a restricted access material (RAM) precolumn. The multidimensional nature of this set-up removed large matrix interferents such as proteins from the sample, while the selectivity of the MIP enabled further cleanup of the smaller analytes. The selectivity and extraction efficiency of the MIP for verapamil and its metabolites was evaluated in various biological matrices, such as cell cultures and urine. The experimental set-up with the developed method enabled the direct injection of biological samples for the selective isolation, preconcentration, identification and analysis of verapamil and its phase I metabolites by LC-MS(n). This multidimensional approach provided much qualitative information about the metabolic profile of verapamil in various biological matrices. An analytical method was developed for the quantification of verapamil and gallopamil in urine, plasma and cell culture. Acceptable linearity (R(2)=0.9996, 0.9982 and 0.9762) with an average injection repeatability (n=3) of 10, 25 and 15% R.S.D. was determined for urine, plasma and cell culture, respectively. This is the first application of the procedure for the selective metabolic screening of verapamil in biological samples.

Animals↗
PubMed2002

High-throughput bioanalytical method using automated sample preparation and liquid chromatography-atmospheric pressure ionspray mass spectrometry for quantitative determination of glybenclamide in human serum.

A liquid chromatographic-mass spectrometric (LC-MS) method with rapid automated sample preparation was developed and validated for determination of glybenclamide in human serum. Glybenclamide and its deuterated labelled internal standard were extracted from human serum samples by automated solid-phase extraction. The extract was injected into the LC-MS system for analysis. Glybenclamide and its internal standard were measured in multiple ion monitoring mode. The method was validated over a range of 10-1000 ng/ml with good accuracy and precision and was applicable for pharmacokinetic studies.

Atmospheric Pressure↗
PubMed2001

Lab-on-a-chip sample preparation using laminar fluid diffusion interfaces--computational fluid dynamics model results and fluidic verification experiments.

Microfluidic structures for the generation of laminar fluid diffusion interfaces (LFDIs) for sample preparation and analysis are discussed. Experimental data and the results of fluid modeling are shown. LFDIs are generated when two or more streams flow in parallel in a single microfluidic structure without any mixing of the fluids other than by diffusion of particles across the diffusion interface. It has been shown that such structures can be used for diffusion-based separation and detection applications. The method has been applied to DNA desalting, the extraction of small proteins from whole blood samples, and the detection of various constituents in whole blood, among other examples. In this paper the design and manufacture of self-contained microfluidic cartridges for the extraction of small molecules from a mixture of small and large molecules by diffusion is demonstrated. The cards are operated without any external instrumentation, and use hydrostatic pressure as the driving force. The performance of the cartridges is illustrated by separating fluorescein from a mixture of fluorescein and dextran of molecular weight 2 x 10(6). In a single pass, 98.6% of dextran was retained in the product whereas 43.1% of fluorescein was removed. The method is adjustable for different separation requirements, and computational fluid dynamics (CFD) models are shown that demonstrate the tuning of various microfluidic parameters to optimize separation performance. Other applications of LFDIs for establishment of stable concentration gradients, and the exposure of chemical constituents or biological particles to these concentration gradients are shown qualitatively. Microfluidic chips have been designed for high-throughput screening applications that enable the uniform and controlled exposure of cells to lysing agents, thus enabling the differentiation of cells by their sensitivity to specific agents in an on-chip cytometer coupled directly to the lysing structure.

Chemistry Techniques, Analytical↗
PubMed2001

Microchip module for blood sample preparation and nucleic acid amplification reactions.

A computer numerical control-machined plexiglas-based microchip module was designed and constructed for the integration of blood sample preparation and nucleic acid amplification reactions. The microchip module is comprised of a custom-made heater-cooler for thermal cycling, a series of 254 microm x 254 microm microchannels for transporting human whole blood and reagents in and out of an 8--9 microL dual-purpose (cell isolation and PCR) glass-silicon microchip. White blood cells were first isolated from a small volume of human whole blood (<3 microL) in an integrated cell isolation--PCR microchip containing a series of 3.5-microm feature-sized "weir-type" filters, formed by an etched silicon dam spanning the flow chamber. A genomic target, a region in the human coagulation Factor V gene (226-bp), was subsequently directly amplified by microchip-based PCR on DNA released from white blood cells isolated on the filter section of the microchip mounted onto the microchip module. The microchip module provides a convenient means to simplify nucleic acid analyses by integrating two key steps in genetic testing procedures, cell isolation and PCR and promises to be adaptable for additional types of integrated assays.

Cell Separation↗
PubMed1981

Interaction between sample preparation techniques and colorimetric reagents in nitrite analysis in meat.

The amount of nitrite measured in model and meat systems was a function of the interactions of the chloride and ascorbate concentrations with the method of sample preparation and the combination of Griess reagents used for colorimetric determination. Ascorbate caused loss of nitrite in the samples when heated and interfered in the Griess reaction, increasing the concentration of pigment formed from any given concentration of nitrite if sulfanilic acid and N-(1-naphthyl)-ethylenediamine were used, and decreasing the amount if sulfanilamide and 1-naphthylamine were used. The interference was eliminated by both the AOAC procedure and mercuric chloride addition, although the former were less effective at higher ascorbate concentrations. Chloride increased the amount of pigment formed from a given amount of nitrite with sulfanilic acid but had no effect on the amount of sulfanilamide pigment.

Ascorbic Acid↗