Electrochromatography on acrylate-based monolith in cyclic olefin copolymer microchip: a cost-effective and easy-to-use technology.

This article shows that there is great interest in using an electrochromatographic microchip made of hexyl acrylate (HA) based porous monolith cast within the channel of a cyclic olefin copolymer (COC) device. The monolith is simultaneously in situ synthesized and anchored to the inner walls of the channel in less than 10 min. By appropriate choice of light intensity used during the synthesis, the separation efficiency obtained for nonpolar solutes such as polycyclic aromatic hydrocarbons (PAH) is increased up to 250 000 plates/m. The performance of this HA-filled COC microchip was investigated for a wide range of analytes of varying nature. The reversed-phase separation of four aflatoxins is obtained in less than 2 min. The baseline separation of a mixture of neurotransmitters including six amino acids and two catecholamines is possible thanks to the superimposition of the differences in electrophoretic mobility on the chromatographic process. The durability of the system at pH 13 allows the separation of five biogenic amines and the quantitative determination of two of them in numerous wine samples. The feasibility of on-line preconcentration is also demonstrated. Hydrophilic surface modification of COC channel via UV-photografting with poly(ethylene glycol) methacrylate (PEGMA) before in situ synthesis of HA, is necessary to reduce the adsorption of very hydrophobic solutes such as PAH during enrichment. The detection limit of fluoranthene is decreased down to less than 1 ppb with a preconcentration of 4.5 h on the HA-filled PEGMA functionalized COC microchip.

Fabrication of acrylate monolith using photopolymerization: effect of light intensity on electrochromatographic performance.

A hexyl acrylate monolith was prepared via photopolymerization into a cyclic olefin copolymer micro-device for reversed-phase electrochromatography purposes. This work deals with the influence of the irradiation conditions (irradiation time and light intensity) used during synthesis on the electrochromatographic performances of the monolithic column obtained. Up to day, the monolith structure was often controlled by means of irradiation time at constant light intensity, but the effect of light intensity (irradiance) on the monolith structure was scarcely considered. This study shows a strong effect of light intensity on electrochromatographic efficiency. Using an optimal light intensity of 4.7 mW/cm(2) and an irradiation time of a few minutes allows obtaining heights equivalent to a theoretical plate reaching down to 5 µm for the reversed-phase separation of six polycyclic aromatic hydrocarbons.

Development of an acrylate monolith in a cyclo-olefin copolymer microfluidic device for chip electrochromatography separation.

An acrylate monolith has been synthesized into a cyclic olefin copolymer microdevice for reversed-phase electrochromatography purposes. Microchannels, designed by hot embossing, were filled up with an acrylate monolith to serve as a hydrophobic stationary phase. A lauryl acrylate monolith was formulated to suit the hydrophobic material, by implementing 100% organic porogenic solvent. This new composition was tested in capillary prior to its transfer into the microfluidic device. Surface functionalization of the cyclic olefin copolymer surface was applied using UV-grafting technique to improve the covalent attachment of this monolith to the plastic walls of the microfluidic chip. The on-chip performances of this monolith were evaluated in detail for the reversed-phase electrochromatographic separation of polycyclic aromatic hydrocarbons, with plate heights reaching down to 10 microm when working at optimal velocity.

Heart-cutting two-dimensional liquid chromatography methods for quantification of 2-acetyl-4-(1,2,3,4-tetrahydroxybutyl)imidazole in Class III caramel colours.

Heart-cutting two-dimensional liquid chromatography/UV detection methods were developed to determine 2-acetyl-4-(1,2,3,4-tetrahydroxybutyl)imidazole (noted as THI) in Class III caramel colours. In the first dimension, the caramel sample diluted in water was fractionated either by reversed-phase chromatography on C18 silica packing or by ion-exchange chromatography using strong cationic exchanger (SCX) stationary phase. In each case, THI elution domain was recovered in a loop and transferred to a second column packed with porous graphitic carbon (PGC) for the selective separation of THI. From the accuracy profiles with acceptance limit fixed at 20% and beta-expectation tolerance interval fixed at 90%, the two methods, C18-PGC and SCX-PGC, were validated for THI/caramel ratios included between 5-50 and 10-50 ppm, respectively. Finally, the two methods were compared for the analysis of numerous caramel samples.

Potential and limitations of on-line comprehensive reversed phase liquid chromatography×supercritical fluid chromatography for the separation of neutral compounds: An approach to separate an aqueous extract of bio-oil.

On-line comprehensive Reversed Phase Liquid Chromatography×Supercritical Fluid Chromatography (RPLCxSFC) was investigated for the separation of complex samples of neutral compounds. The presented approach aimed at overcoming the constraints involved by such a coupling. The search for suitable conditions (stationary phases, injection solvent, injection volume, design of interface) are discussed with a view of ensuring a good transfer of the compounds between both dimensions, thereby allowing high effective peak capacity in the second dimension. Instrumental aspects that are of prime importance in on-line 2D separations, were also tackled (dwell volume, extra column volume and detection). After extensive preliminary studies, an on-line RPLCxSFC separation of a bio-oil aqueous extract was carried out and compared to an on-line RPLCxRPLC separation of the same sample in terms of orthogonality, peak capacity and sensitivity. Both separations were achieved in 100min. For this sample and in these optimized conditions, it is shown that RPLCxSFC (with Hypercarb and Acquity BEH-2EP as stationary phases in first and second dimension respectively) can generate a slightly higher peak capacity than RPLCxRPLC (with Hypercarb and Acquity CSH phenyl-hexyl as stationary phases in first and second dimension respectively) (620 vs 560). Such a result is essentially due to the high degree of orthogonality between RPLC and SFC which may balance for lesser peak efficiency obtained with SFC as second dimension. Finally, even though current limitations in SFC instrumentation (i.e. large extra-column volume, large dwell volume, no ultra-high pressure) can be critical at the moment for on-line 2D-separations, RPLCxSFC appears to be a promising alternative to RPLCxRPLC for the separation of complex samples of neutral compounds.

New "one-step" method for the simultaneous synthesis and anchoring of organic monolith inside COC microchip channels.

A new method for monolith synthesis and anchoring inside cyclic olefin copolymer (COC) microchannels in a single step is proposed. It is shown that type I photoinitiators, typically used in a polymerization mixture to generate free radicals during monolith synthesis, can simultaneously act as type II photoinitiators and react with the plastic surface through hydrogen abstraction. This mechanism is used to "photograft" poly(ethylene glycol) methacrylate (PEGMA) on COC surfaces. Contact angle measurements were used to observe the changes in surface hydrophilicity when increasing initiator concentration and irradiation duration. The ability of type I photoinitiators to synthesize and anchor a monolith inside COC microchannels in a single step was proved through SEM observations. Different concentrations of photoinitiators were tried. Finally, electrochromatographic separations of polycyclic aromatic hydrocarbons were realized to illustrate the beneficial effect of anchoring on chromatographic performances. The versatility of the method was demonstrated with two widely used photoinitiators: benzoin methyl ether (BME) and azobisisobutyronitrile (AIBN).

Separation and analysis of lanthanides by isotachophoresis coupled with inductively coupled plasma mass spectrometry.

This study is a large project initiated by the French Nuclear Agency, and concerns the development of a new electrolyte system for the separation of lanthanides by isotachophoresis. This new system is based on a leading electrolyte that incorporates 2-hydroxy-2-methylbutyric acid as complexing agent. The optimization of separation conditions (complexing agent concentration, pH, capillary dimensions, injection conditions, and current intensity) performed by experiments on a commercial capillary instrument with contactless conductivity detection, which allows to improve the separation of 13 lanthanides (La to Lu, except Pm and Ho). We have also directly coupled the isotachophoresis to an inductively coupled plasma mass spectrometer to visualize the mono-elementary elution bands and demonstrate the potentiality of the method for isotope ratio measurements. The application to a simulated solution representative of a fraction of fission products present in a MOX spent fuel is presented in this paper to demonstrate the possible application in future on nuclear fuel samples.

Quantification of 4-methylimidazole in class III and IV caramel colors: validation of a new method based on heart-cutting two-dimensional liquid chromatography (LC-LC).

4-Methylimidazole (4MeI) is a nitrogen compound formed during the manufacture of class III and IV caramel colors. The European Commission has limited its content to 250 ppm. Two methods were compared to perform 4MeI quantification in caramels. The first one, currently used and considered to be the reference method, consists of a hot extraction of caramel color with dichloromethane and an analysis of the acetyl derivative of the extract by gas chromatography coupled to mass spectrometry (GC-MS). The second method is based on the heart-cutting two-dimensional liquid chromatography technique (LC-LC) to directly separate 4MeI from the other components present in caramel color sample (diluted in water) in <30 min. The accuracy profile validation method and the comparison between the results obtained with the two methods show that the new and completely automated LC-LC method is usable to quantify 4MeI in caramels.

Electrochromatography in poly(dimethyl)siloxane microchips using organic monolithic stationary phases.

This paper shows the in situ synthesis of an hexyl acrylate monolith in PDMS microfluidic devices and its subsequent use as stationary phase for electrochromatography on chip. To overcome the ability of PDMS material to absorb organic monomers, surface modification of the enclosed channels was realized by UV-mediated graft polymerization. This grafting procedure is based on the preliminary adsorption of a photoinitiator onto the PDMS surface and polymerization of charged monomers. Next, hexyl acrylate monoliths were cast in situ using photopolymerization process. The chromatographic behavior of the monolithic column was confirmed by the successful separation of derivatized catecholamines in the PDMS device using a 30 mm effective separation length (100 microm x 100 microm section). Efficiencies reached up to 200,000 plates per meter.

Some advantages of high temperature for the separation of pharmaceutical compounds with mass spectrometry detection.

The beneficial effects of high temperature on separation and detection of basic compounds, the detection being performed by MS via ESI, are investigated. The influence of various parameters on both separation and detection performances is studied. These parameters include the mobile phase pH, the temperature, and the type of stationary phase. Experiments are performed under gradient elution conditions. The results obtained with four different supports, silica-, zirconia-, carbon-, and polymer-based columns, are compared by means of different criteria including the elution composition, the peak asymmetry, and the S/N. High temperature liquid chromatography at high pH with volatile buffers suitable for MS detection was shown to be an interesting choice for solutes with basic sites.