Martin Pumera

Towards disposable lab‐on‐a‐chip: Poly(methylmethacrylate) microchip electrophoresis device with electrochemical detection

A fully disposable microanalytical device based on combination of poly(methylmethacrylate) (PMMA) capillary electrophoresis microchips and thick‐film electrochemical detector strips is described. Variables influencing the separation efficiency and amperometric response, including separation voltage or detection potential are assessed and optimized. The versatility, simplicity and low‐cost advantages of the new design are coupled to an attractive analytical performance, with good precision (relative standard deviation RSD = 1.68% for n = 10). Applicability for assays of mixtures of hydrazine, phenolic compounds, and catecholamines is demonstrated. Such coupling of low‐cost PMMA‐based microchips with thick‐film electrochemical detectors holds great promise for mass production of single‐use micrototal analytical systems.

A chip-based capillary electrophoresis-contactless conductivity microsystem for fast measurements of low-explosive ionic components.

A miniaturized analytical system for separating and detecting inorganic explosive residues, based on the coupling of a micromachined capillary electrophoresis (CE) chip with a contactless conductivity detector is described. The low electroosmotic flow (EOF) of the poly(methylmethacrylate) (PMMA) chip material facilitates the rapid switching between analyses of cations and anions using the same microchannel and run buffer (and without an EOF modifier), and hence offers rapid (< 1 min) measurement of seven explosive-related cations and anions. Experimental parameters relevant to the separation and detection processes have been optimized. Addition of a 18-crown-6 ether modifier has been used for separating the peaks of co-migrating potassium and ammonium ions. The ionic-explosive microchip system combines the distinct advantages of contactless conductivity detection with the attractive features of plastic CE microchips. The new microsystem offers great promise for monitoring explosive-related ions at the sample source, with significant advantages of speed/warning, efficiency, cost, or sample size.

Capillary electrophoresis-electrochemistry microfluidic system for the determination of organic peroxides

A microfluidic analytical system for the separation and detection of organic peroxides, based on a microchip capillary electrophoresis device with an integrated amperometric detector, was developed. The new microsystem relies on the reductive detection of both organic acid peroxides and hydroperoxides at -700 mV (vs. Ag wire/AgCl). Factors influencing the separation and detection processes were examined and optimized. The integrated microsystem offers rapid measurements (within 130 s) of these organic-peroxide compounds, down to micromolar levels. A highly stable response for repetitive injections (RSD 0.35-3.12%; n = 12) reflects the negligible electrode passivation. Such a lab-on-a-chip device should be attractive for on-site analysis of organic peroxides, as desired for environmental screening and industrial monitoring.

Thick-Film Electrochemical Detectors for Poly(dimethylsiloxane)-based Microchip Capillary Electrophoresis

A new poly(dimethylsiloxane) (PDMS)-based microchip capillary electrophoresis (CE) device, with a thick-film electrochemical detector, is described. The end-column design relies on screen-printing the amperometric carbon working electrode on the base plate of a PDMS microchip (opposite to the exit of the microchannel). Since the channel depth and electrode height are quite similar, this is a flow-onto/flow-by hybrid arrangement. The influence of relevant experimental variables, such as the separation and detection potentials, is reported along with the attractive analytical performance. Flat baselines and extremely low noise levels are observed even at high separation fields (approaching 700u2005V/cm), reflecting the effective electrical isolation of the detector. The resulting detection limits (150u2005nM for epinephrine and 280u2005nM for catechol) compare favorably with those obtained by other PDMS-based electrochemical detectors. Such coupling of low-cost and versatile PDMS chips and thick-film electrochemical detectors holds great promise for high-volume production of disposable microfluidic analytical devices.

β-Cyclodextrin-modified monolithic stationary phases for capillary electrochromatography and nano-HPLC chiral analysis of ephedrine and ibuprofen

ABSTRACT Chiral monolithic capillary columns for reversed-phase capillary electrochromatography (CEC) and for nano-HPLC were prepared by linking β-cyclodextrin modifier into the acrylic monolithic phase. Columns with the physically and chemically bonded β-cyclodextrin derivatives were tested under CEC and nano-HPLC conditions; enatioselective separation of (−)-ephedrine/(+)-pseudoephedrine and (+/−)-ibuprofen was successfully performed. The separation efficiency of CEC and HPLC was examined and compared; resolution of (+/−) ibuprophen was 2.45 and 2.97 for CEC and HPLC respectively, number theoretical plates of thiourea were 41,600u2005N/m in CEC.

Chiral analysis of biogenic DL‐amino acids derivatized by urethane – protected α‐amino acid N‐carboxyanhydride using capillary zone electrophoresis and micellar electrokinetic chromatography

A new analytical method for enantioselective separation of DL‐amino acids derivatized by N‐fluorenylmethoxycarbonyl‐L‐alanyl N‐carboxyanhydride (FMOC‐L‐Ala‐NCA) using capillary electrophoresis was developed. Separation parameters, such as composition and pH of the background electrolyte, and concentration of γ‐cyclodextrin (in capillary zone electrophoresis) and sodium dodecyl sulfate (in micellar electrokinetic chromatography) were optimized. The separation method was validated and it suits well for purity analysis. Detection limit of the method was 0.2% of the minor enantiomer in the major one. The level of racemization in coupling during solid‐phase peptide synthesis was studied using capillary electrophoresis with γ‐cyclodextrin as a chiral selector. The anchorage of the first (C‐terminal) amino acid derivative to the solid supports bearing the hydroxylic groups is the key step of the synthesis affecting the extent of its racemization. FMOC‐L‐phenylalanine was chosen as the suitable model amino acid derivative making it possible to study the degree of racemization of N‐fluorenylmethoxycarbonyl‐L‐alanine‐L‐phenylalanine synthesized on different polymer resins, using the different condensation agents.

Contactless Conductivity Detector for Microchip Capillary Electrophoresis: Fast Measurements of Explosives and Explosive Residues

INTRODUCTION Improvised explosives have been used in recent terrorist bombing activities. These home-made explosives generates significant amount of inorganic ions, such as ammonium, methylammonium, potassium, sodium, perchlorate, chloride or nitrate. Such explosives and explosive residues are frequently analyzed using ion-chromatography (IC) or capillary electrophoresis (CE) systems. However, these laboratory-based methods are not field portable, nor can they analyze relevant samples within extremely short (<30 sec) time scales. Therefore, fast-responding field-deployable analytical systems are desired for monitoring ionic (“low-energy”) explosives at the sample source. Lab-on-a-chip technology offers great possibility for obtaining the desired forensic information in a faster, simpler, and cheaper manner compared to traditional laboratory-based instruments. This paper describes a microchip capillary electrophoresis with an integrated contactless conductivity detection system in connection to a low-energy explosives detection. The new contactless conductivity microchip detector is based on placing two planar sensing aluminum-film electrodes on the outer side of a microchip (without contacting the solution) and measuring the impedance of the solution in the separation channel. The contactless route obviates problems (i.e., fouling, unwanted reactions) associated with the electrode-solution contact, offers isolation of the detection system from high separation fields, and greatly simplifies the detector fabrication. Relevant experimental variables, such as the frequency and amplitude of the applied ac voltage were examined and optimized. The detector performance was illustrated by the separation of low-explosive ionic components, such as the potassium, sodium, ammonium and methylammonium cations and the nitrate, perchlorate and chloride anions.