A glass microchip column was fabricated for free-solution electrophoresis. The channels were wet chemically etched on a substrate using standard photolithographic techniques and were sealed using a direct bonding technique. Two methods * Chemical and Analytical Sciences Division.

Fast, efficient separations are sought in liquid-phase analyses which incorporate a nondiscriminatory sample injection scheme and can implement a variety of detection modes. A glass microchip device for free solution electrophoresis was fabricated using standard photolithographic procedures and chemical wet etching. Separations were performed at several separation lengths from the injector to the detector with electric field strengths from 0.06 to 1.5 kV/cm. For a separation length of 0.9 mm, electrophoretic separations with baseline resolution are achieved in less than 150 ms with an electric field strength of 1.5 kV/cm and an efficiency of 1820 plates/s. For a separation length of 11.1 mm, a minimum plate height of 0.7 jtm and a maximum number of plates per second of 18 600 were achieved.Microfabricated chemical instruments show great promise for the laboratory and as advanced chemical sensors. Microfabrications of chemical separation techniques have received noticeable attention over the past several years and have included the techniques of gas chromatography,1 liquid chromatography,1 2 3456and capillary electrophoresis.3-7 Microelectronic devices have been able to achieve even faster response times in part due to miniaturization. Similar benefits may also accrue from miniaturization of some chemical measurement techniques. The response times of chemical measurements can often be an important issue, in particular in the case of chemical sensing.With microfabrication, the performance of many liquid separation techniques improves, especially capillary electrophoresis.8-10 For capillary electrophoresis, smaller column dimensions enable the power generated to be dissipated more efficiently, and as a direct result, separation devices can be operated at higher electric field strengths. The efficiency of the separations, therefore, improves in two areas. First, Joule heating, which leads to thermal gradients within the channel and ultimately contributes to the dispersion of the analyte

A glass microchip was constructed to perform chemical reactions and capillary electrophoresis sequentially. The channel manifold on the glass substrate was fabricated using standard photolithographic, etching, and deposition techniques. The microchip has a reaction chamber with a 1 nL reaction volume and a separation column with a 15.4 mm separation length. Electrical control of the buffer, analyte, and reagent streams made possible the precise manipulation of the fluids within the channel manifold. The microchip was operated under a continuous reaction mode with gated injections to introduce the reaction product onto the separation column with high reproducibility (< 1.8% rsd in peak area). The reaction and separation performances were evaluated by reacting amino acids with o-phthaldialdehyde to generate a fluorescent product which was detected by laser-induced fluorescence. Control of the reaction and separation conditions was sacient to measure reaction kinetics and variation of detection limits with reaction time. Ha-times of reaction of 5.1 and 6.2 s and detection limits of 0.55 and 0.83 fmol were measured for arginine and glycine, respectively.The microfabrication of analytical instrumentation will potentially enable the laboratory to be transported to the samples rather than vice versa. Miniature chemical instrumentation can be based on conventional laboratory approaches to chemical measurement problems. Many laboratory-based procedures require sample manipulation prior to the actual measurement, and many analyses are fully automated to circumvent operator bias. Similarly, a portable instrument should have these sample preparatory steps incorporated into the design and function of the instrument. In addition, micromachined chemical instruments as opposed to single-analyte chemical sensors should be able to identify and quantify all members of a desired class of compounds using a single device. The approach taken is to micromachine a channel manifold in a monolithic device that includes all desired fluid manipulation for complete chemical analysis. Chemical separation techniques including capillary electrophoresis,1-6 free-flow elec-(1) Harrison, D. J.; Manz, A.; Fan, Z.; Liidi, H.; Widmer, H. M. Anal. Chem. 1992, 64, 1926. (2) Manz, A; Harrison, J.; Verpoorte, E. M. J.; Fettinger, J. C.; Paulus, A; Liidi, H.; Widmer, H. M.trophore~is,~ open channel electrochromatography,s and capillary electrophoresis with postcolumn derivati~ation~ have been demonstrated using microfabricated devices.To demonstrate a reactor/analyzer microchip, we chose the relatively simple reaction of amino acids with o-phthaldialdehyde (OPA), which yields a fluorescent product.'O For capillary electrophoresis, both pre-and postseparation labeling using OPA have been studied.ll The reaction is moderately fast (a half-time of reaction for alanine at room temperature of x4 s l2 ), but the fluorescent product can be short lived (x10 min for glycineI3 1.This reaction is fast enough to perform postcolumn labeling when the analysis time is lo...

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A glass microchip having a channel with a cross section of 5.6

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Laser ablation mass spectrometry (LA-MS) has always been an interesting method for the elemental analysis of solid samples. Chemical analysis with a laser requires small amounts of material. Depending on the analytical detection system, subpicogram quantities may be sufficient. In addition, a focused laser beam permits the spatial characterization of heterogeneity in solid samples typically with micrometer resolution in terms of lateral and depth dimensions. With the advent of high-energy, ultra-short pulse lasers, new possibilities arise. The task of this review is to discuss the principle differences between the ablation process of short (>1 ps) and ultra-short (<1 ps) pulses. Based on the timescales and the energy balance of the process that underlies an ablation event, it will be shown that ultra-short pulses are less thermal and cause less collateral damages than longer pulses. The confinement of the pulse energy to the focal region guarantees a better spatial resolution in all dimensions and improves the analytical figures of merit (e.g., fractionation). Applications that demonstrate these features and that will be presented are in-depth profiling of multi-layer samples and the elemental analysis of biological materials.

The pH-dependent switching of a poly(acrylic acid) (PAA) polyelectrolyte brush was investigated in situ using infrared spectroscopic ellipsometry (IRSE). The brush was synthesized by a "grafting to" procedure on silicon substrate with a native oxide layer. The overall thickness of the PAA brush in the dry state was approximately 5 nm. Reversible switching of the polymer brush was studied at titration from pH 2 to 10 and back in steps of 1 pH unit. The switching process was observed by monitoring the characteristic vibrational bands of the carboxylic groups of the PAA molecules. Decreasing of the C=O vibrational band amplitude and arising of a COO(-) vibrational band proved the chemical changes in the molecular structure of the brushes due to changes of the pH value in the aqueous solution. Due to the strong absorption of these bands in the IR region, the switching process could be monitored clearly. Switching the brush in several cycles with increasing and decreasing pH value showed a hysteresis-like behavior. For the first time, such hysteresis is observed in titration experiments of polyelectrolyte brushes. This behavior is attributed to the complex mechanisms of the ion's mobility in the brush layer which is explained with a suggested simplifying model describing the influence of ions inside the brush layer. In addition to the IRSE measurements, X-ray standing waves (XSW), in situ visible ellipsometry, and contact angle measurements have been performed and were in good agreement with the results from IRSE. Repetition of the in situ measurement cycles proved the good reversibility of the switching process which is highly important for practical applications of polymer brushes.