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Sandia introduces lab-on-a-chip prototype For several years, Sandia National Laboratories has been developing a portable chemical analysis system, fabricated using microscale techniques, called µChemLab. Bits and pieces of the device have been presented previously. Now, a handheld research prototype has arrived. Christopher Bailey described this initial prototype, which is a modular dual-phase chromatography system intended for the detection and analysis of chemical warfare agents. The LC module, meant for detecting explosives, has two columns and can perform open-cell CE. Analysis takes only ~1 min, and detection of analytes at the part-per-billion level is possible using an indirect laser-induced fluorescence detection system with a ~0.5 cm 3 0.5 cm footprint. This system uses high-efficiency vertical cavity surface-emitting lasers, which are bonded onto the substrate, and the diffractive optics are etched into the substrate. The focusing optics, interference filters, and detector are mounted off the module. The GC module, meant for detection of chemical agents, such as sarin and mustard gas, uses sol–gel absorbents to preconcentrate the samples. Separations are carried out in a 2-mlong spiral channel that has been cut into a 1 cm2 area using deep ion etching. Analysis takes ~30 s, and detection is achieved with a surface acoustic wave detector (Anal. Chem. 1998, 70, 775 A). Future versions of µChemLab will incorporate additional modules and capabilities, including on-chip HPLC—made possible by the high-pressure electrokinetic pumping technique that can route liquids through the microscale channels without any moving parts (Anal. Chem. 1998, 70, 776 A). Future instruments are also expected to be more fully inteSandia National Laboratory’s prototype of the handheld chemical grated than the current prototype and able to detect both analysis system called µChemLab. biological and chemical warfare agents.
NEWS FROM ANALYTICA 2000 Veronika Meyer reports from Munich, Germany.
HPLC looks for orthogonal techniques In the pharmaceutical industry, the method of choice for determining impurities in a drug is most often reversed-phase HPLC. Yet, guidelines typically request the confirmation of such analytical methods by another technique or “orthogonal” procedure with totally different selectivity. Nebojsa Djordjevic of Novartis Pharma (Switzerland) has been using packed capillary electrochromatography as an orthogonal technique, although a suitable commercial instrument is not yet available. Usually, gradient separation is necessary, and this can be performed most easily by a fast temperature increase during the chro-
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matographic run (e.g., 25–60 °C at 3 °C/min). There are still numerous practical problems to overcome, says Djordjevic, such as designing frits that do not lower the separation performance, developing robust stationary phases that provide a broader pH and selectivity range, and improving column-to-column reproducibility. Meanwhile, Christoph Siffrin, also of Novartis, uses supercritical fluid chromatography (SFC) in packed columns as an orthogonal technique. Even highly polar compounds, such as the salts of drug substances, can be separated under normal-phase SFC conditions. The separations are much faster than with HPLC, he says. Roger Smith of Loughborough University (U.K.) advocates chro-
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matography with superheated water. This approach is orthogonal to HPLC with C18 and similar columns, because these silica-based stationary phases are not stable in water at temperatures as high as 200 °C. Smith uses instead styrene-divinylbenzene, polybutadiene-coated zirconia, or graphitic carbon phases. Water as a mobile phase is environmentally friendly and cheap. UV detection at wavelengths as low as 190 nm is easily possible, as well as the opportunity to couple MS and NMR (with D2O) or use of several GC-type detectors with the instrumentation. So far, a broad variety of analytes such as phenols, aromatic amines, various classes of drugs, and plant extracts have been successfully separated, says Smith.
