Radial sample preconcentration

In this paper we present a radial sample preconcentration strategy enabled by axisymmetric concentration polarization in a microfluidic chamber on a uniform nanoporous film. Sample analytes are focused into the centre, creating a concentrated plug that is injected vertically into the microfluidic analysis layer. No balancing pressure driven flows or tangential fields are required, and the process has essentially zero footprint on the analysis layer. An electrokinetic loading scheme enables repeat loading/concentration cycles, and a finned radial chamber geometry dampens instabilities and accommodates larger volumes. Modelling results indicate over 1800-fold concentration increases are possible in 10 s, for high mobility buffers and high applied field strength. At moderate field strength and buffer mobility, experiments demonstrate a 168-fold increase in concentration of FITC-BSA protein in 36 s.     

On-line sample preconcentration in micellar electrokinetic chromatography using ion-pair reagents

To improve the detection sensitivity of some aromatic carboxylic acids and naphthalenesulfonic acids, the use of ion-pair reagents was examined in sweeping micellar electrokinetic chromatography (MEKC) with an anionic sodium dodecyl sulfate (SDS) micelle. Tetraalkylammonium (TAA) salts were used as ion-pair reagents to improve the sweeping efficiency. The effects of the alkyl chain length of the TAA groups and the TAA salt concentration on sweeping were examined. Under optimized conditions, about 400-fold enhancement in detection sensitivity was obtained in terms of peak heights by addition of ion-pair reagents in sweeping MEKC. This value was about 10 times greater than that obtainable by the SDS micelle used alone.     

Solvent polymeric membrane ion-selective electrodes

The significant role of poly(vinyl chloride) as a support polymer in solvent polymeric ion-selective electrodes is briefly reviewed. This lays emphasis on the way PVC has contributed to the relatively high state of development of conventional ion-selective electrodes, microelectrodes, coated-wire electrodes and ion-sensitive field effect transistors based on liquid ion-exchanger and neutral carrier ionophore sensors. Also discussed are possibilities of using alternative polymer matrices for overcoming some of the shortfalls of the PVC electrodes.     

Determination of tetracycline and related compounds using plastic membrane ion-selective electrodes

PVC membrane electrodes selective for hydrochlorides of tetracycline (TC), doxycycline (DC) and oxytetracycline (OTC) are prepared. The electrodes show a linear response with Nernstian slope over the range of 1.6 × 10⁻⁵–10⁻²M, 7.9 × 10⁻⁵–1.9 × 10⁻³M, and 6.3 × 10⁻⁵–6.3 × 10⁻³M for TC, DC, and OTC, respectively. The effects of pH of the test solution and time of soaking on the electrodes' performance are studied. The electrodes exhibit good selectivity for the investigated antibiotics with respect to a large number of inorganic cations and organic substances of biological importance. TC, DC, and OTC are determined successfully in pure solutions and in some pharmaceutical preparations using the standard additions method.     

Ultrafiltration for proteomic sample preparation

Proteome analysis represents significant challenges to the existing sample preparation techniques. Traditional methods, such as two-dimensional electrophoresis, typically separate high-molecular-weight proteins while discarding low-molecular-weight species. This approach is well justified considering the complexity of any proteome. However, it is desirable to extract the maximum amount of information from each sample to investigate the entire range of biomolecules. We have demonstrated that ultrafiltration not only improves two-dimensional electrophoresis (2-DE) resolution of the protein fraction but also yields the low-molecular-weight fraction amenable for further analysis by high-resolution mass spectrometry. This approach was successfully adapted to the variety of biological samples including cell and tissue lysates and serum. Therefore, ultrafiltration offers an alternative sample preparation technique that enables more thorough analysis of a proteome.     

Chemically modified polymeric sorbents for sample preconcentration

Solid-phase extraction is an attractive alternative in sample preparation because it overcomes many drawbacks of liquid-liquid extraction and makes on-line determination possible by hyphenation with chromatographic techniques. Driven by the need for more effective and more selective sorbents, advances in solid-phase extraction include the development of new materials. This paper describes different types of chemically modified sorbents for the solid-phase extraction of compounds from aqueous samples. Chemical introduction of different functional groups into a polymeric resin improves the efficiency of solid-phase extraction by providing better surface contact with the aqueous samples; also, these sorbents have a greater capacity than the typical solid-phase materials for polar compounds have. The most important new sorbents are the chemically modified resins based on styrene-divinylbenzene copolymers. Preparation of these new sorbents is described, and advantages and drawbacks of off-line procedures and on-line procedures are also discussed. Applications for off-line and on-line chromatographic determinations of polar compounds are presented.     

Urine sample preparation for proteomic analysis

Sample preparation for both environmental and more importantly biological matrices is a bottleneck of all kinds of analytical processes. In the case of proteomic analysis this element is even more important due to the amount of cross‐reactions that should be taken into consideration. The incorporation of new post‐translational modifications, protein hydrolysis, or even its degradation is possible as side effects of proteins sample processing. If protocols are evaluated appropriately, then identification of such proteins does not bring difficulties. However, if structural changes are provided without sufficient attention then protein sequence coverage will be reduced or even identification of such proteins could be impossible. This review summarizes obstacles and achievements in protein sample preparation of urine for proteome analysis using different tools for mass spectrometry analysis. The main aim is to present comprehensively the idea of urine application as a valuable matrix. This article is dedicated to sample preparation and application of urine mainly in novel cancer biomarkers discovery.     

Supported liquid membrane extraction for sample work-up and preconcentration of methoxy-s-triazine herbicides in a flow system

A method for sample preparation of methoxy-s-triazine herbicides using supported liquid membrane extraction has been developed. The analytes were selectively extracted from the donor solution of pH 7.0 into a porous polytetrafluoroethylene (PTFE) membrane impregnated with di-n-hexyl ether. After diffusion through the hydrophobic membrane the analytes were irreversibly trapped in the acidic acceptor phase of pH 1.0. The donor waste was monitored for estimating the amount of sample trapped at certain time intervals. Comparison of the selectivity with solid-phase extraction has been performed. A low detection limit, ca. 15 ng/l, has been obtained with liquid membrane extraction.     

Electrochemical studies on ion-selective polymer membrane electrodes

The selectivity and response of neutral carrier based polymer membrane electrodes are investigated via exchange current measurements for systems containing valinomycin, dibenzo-18-crown-6, and plasticizer alone in a polyvinyl chloride matrix. Using a transient galvanostatic step method, apparent exchange current densities of 1.3 X 10^?3 A/cm², 5.4 X 10^?6 A/cm², and 2.2 X 10^?9 A/cm² were obtained with K⁺ as the primary ion for the three types of membranes, respectively. Preliminary results indicate that the exchange current data obtained with this technique are complementary to the potentiometric response observed for the membranes studied.     

Determination of sulpha-drugs with ion-selective membrane electrodes--II

Two liquid-membrane electrodes, one sensitive to Cu(2+) and the other to Ag(+), were used for the determination of various sulpha-drugs with pK(a) > or = 6 (as the sodium salts) by potentiometric titration with CuSO(4) and AgNO(3). The construction and basic characteristics of these two electrodes are discussed.     

Mechanized techniques for sample decomposition and element preconcentration

High performance decomposition techniques for organic and inorganic samples are discussed. Wet decomposition in closed vessels with conventional and microwave heating enables the decomposition of a wide variety of sample materials. A complete mineralization of organic samples with nitric acid is just possible by means of the High Pressure Asher®. After microwave digestion 2–20% of the carbon of the introduced sample remains in the digestion solution. Trace elements in aqueous samples or in digestion solutions can be determined with high sensitivity and free of systematic errors by means of a combined analytical method consisting of a computer controlled preconcentration device (TraceCon®) and a simultaneous ICP emission spectrometer.     

Determination of sulpha-drugs with ion-selective membrane electrodes

A liquid-membrane mercury(II)-sensitive electrode is used for determination of various sulpha drugs by addition of excess of mercuric nitrate and potentiometric back-titration of the surplus mercury(II) with EDTA. The performance of the electrode is compared with that of an Ag(2)S crystal-membrane electrode. Attempts to prepare a sulphamethoxazole-sensitive electrode failed.     

Inexpensive device for measurements with ion-selective and pH electrodes

The design and construction of a simple device for measuring ionic concentrations (or pH) with ion-selective electrodes are described. The automated system includes a special electronic circuit with an operational amplifier, a signal conditioner and a personalcomputer. A digital multimeter can be used if automation is not required. The results obtained in tests with iodide-, chloride- and nitrate-selective electrodes and glass electrodes show very good agreement with those obtained with sophisticated commercial apparatus.     

Simultaneous derivatization/preconcentration of volatile aldehydes with a miniaturized fiber-packed sample preparation device designed for gas chromatographic analysis

A novel in-needle sample preparation device has been developed for the determination of volatile aldehydes in gaseous samples. The needle device is designed for the gas chromatographic (GC) analysis of aldehydes and ketones commonly found in typical in-house environments. In order to prepare the extraction device, a bundle of polymer-coated filaments was longitudinally packed into a specially designed needle. Derivatization reactions were prompted by 2,4-dinitrophenylhydrazine (NDPH) included in the needle, and so the aldehydes and ketones were derivatized to the corresponding hydrazones and extracted with the extraction needle. A reproducible extraction needle preparation process was established, along with a repeatable derivatization/extraction process that ensures the successful determination of aldehydes. The storage performance of the extraction needle was also evaluated at room temperature for three days. The results demonstrate the successful application of the fiber-packed extraction device to the preparation of a gaseous sample of aldehydes, and the future possibility of applying the extraction device to the analysis of in-house environments.     

Sol-gel microextraction phases for sample preconcentration in chromatographic analysis

Sol-gel technology provides a simple and reliable method for solid-phase microextraction (SPME) fiber preparation through in situ creation of surface-bonded organic-inorganic hybrid coatings characterized by enhanced thermal stability and solvent-resistance properties that are important for the coupling of SPME with GC and HPLC, respectively. The sol-gel coating technology has led to the development of an extensive array of sol-gel sorbent coatings for SPME. In this article, sol-gel microextraction coatings are reviewed, with particular attention on their synthesis, characterization, and applications in conjunction with GC and HPLC analyses. In addition, the development of sol-gel-coated stir bars, their inherent advantages, and applications are discussed. Next, the development and applications of sol-gel capillary microextraction (CME) in hyphenation with GC and HPLC is extensively reviewed. The newly emerging germania- and titania-based sol-gel microextraction phases look promising, especially in terms of pH and hot solvent stability. Finally, sol-gel monolithic beds for CME are reviewed. Such monolithic beds are in a position to greatly improve the extracting capabilities and enhanced sensitivity in CME.     

Photopolymerized microtips for sample preparation in proteomic analysis

We demonstrate a novel method for the fabrication of disposable plastic microtips, which we name "EasyTip", by a photopolymerization technique. C18 reversed-phase (C18) and ion metal affinity chromatography (IMAC) beads were immobilized on a plastic pipette tip, made of polypropylene materials, by photo-initiated polymerization. The fabricated EasyTips can be manipulated using commercial pipettes for wash/elution of minute amount of biological samples (< 10 microL) and can be applied for mass spectrometry (MS)-based proteomic analysis, in which the detection sensitivity depends critically on the optimal sample preparation. The recovery of a sample of 25 fmol of tryptic hemoglobin digest loaded in a C18 EasyTip was near 100% and we estimated the loading capacity to be around 0.4-2.0 microg of total proteins or peptides, which is well above a sufficient quantity for MS analysis. The effectiveness of the C18 EasyTips in enhancing the detection sensitivity of matrix-assisted laser desorption/ionization (MALDI)-MS signal, and thus providing a greater sequence coverage, was also demonstrated by the analysis of hemoglobin digest and the in-gel digested epidermal growth factor receptor (EGFR) protein from A431 cell lysate. We also demonstrated the usefulness of the immobilized IMAC EasyTips in extracting the signal of tryptic phosphopeptides of beta-casein (10 pmol) having one and four phosphorylation sites by using an IMAC EasyTip prior to off-line analysis by MS. The combination of IMAC EasyTips and MALDI-MS allowed the unambiguous identification of phosphopeptides based on the phosphatase assay as well as the post-source decay. Compared to other miniaturized devices, this fabrication method is simple, cheap, and requires less human intervention. Moreover, the method of manipulating the EasyTips is straightforward and can be automated readily by a robotic system for high-throughput analysis.     

Transport of ions through an elliptic ion-selective membrane

The rate of transport of ions through an annular ion-selective membrane having an elliptic cross section is analyzed. This is a generalization to a hollow-fiber type of device, and represents a wide class of membranes which are capable of providing a large (surface area/volume) ratio for ion transport. The Nernst–Plank equation governing the transport of ions is solved numerically. The results obtained reveal that, if the concentration of fixed charge is high, its current efficiency is insensitive to fixed charge distribution, and the local electroneutrality can be assumed. On the other hand, if the concentration of fixed charge is low, the distribution of fixed charge becomes significant, and assuming local electroneutrality can be inappropriate. In general, the higher the average concentration (or the greater the total amount) of fixed charge of a membrane, the higher its current efficiency. We show that the results for planar and cylindrical membranes can be recovered from the present model.     

Emulsion membrane systems for preconcentration of uranium

Various double emulsion systems with liquid membranes containing tri-n-octylphosphine oxide /TOPO/, tri-n-butylphosphate /TBP/, KELEX 100^® and di-2-ethylhexylphosphoric acid /DEHPA/, as carriers for uranium/VI/ pertraction, were studied. The conditions were found at which the systems are most efficient, comparing with solvent extraction. The use of DEHPA as a membrane carrier with solutions of H₂SO₄ and H₃PO₄ encapsulated in the membrane was substanfiated.