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Ultrathin-layer chromatography spotting and detection on the sub-millimeter scale Point-and-click chemistry is the dream of many a bench scientist. A recent AC article (DOI 10.1021/ac902945t) offers a glimpse into a future in which ultrathinlayer chromatography (UTLC) might be directed entirely with “instruments” available at an office supply store. Gertrud Morlock and co-workers at the University of Hohenheim (Germany), the University of Alberta, and NRC National Institute for Nanotechnology (both in Canada) report analyte spotting and reading techniques that incorporate common inkjet printers and scanners. Their techniques inexpensively address some of the difficulties inherent in miniaturized planar chromatography, which requires sub-millimeter spot sizes. High-performance thin-layer chromatography (HPTLC) is an indispensable tool in a variety of fields and is used to separate analytes qualitatively and quantitatively. With UTLC (a recently developed, related technology), the stationary phase is miniaturized even further, from the typical sorbent layer thickness of ⬃100 m in HPTLC to ⱕ10 m in UTLC. The makeup of the sorbent layers for UTLC is an active area of current research with a variety of manifestations, such as deposited SiO2 spiral nanostructures or commercially available monolithic silica. The result is a small, thin surface that requires less analyte and mobile phase than is required for HPTLC. Unfortunately, “the miniaturized plate formats are very difficult to manage with the current TLC and HPTLC equipment available,” says Morlock. “It’s not convenient at all.” As a result, UTLC has not been widely adopted by the analytical community, so the researchers sought to create an inexpensive solution. Their approach was to harness the mature technology of inkjet printing, refined over many years as a result of the demands of millions of users worldwide. In a thermal inkjet printer, microengineered chambers are filled with ink by capillary action; a heating element vaporizes the contents of the chamber to eject ink onto the facing paper surface. 3408
ANALYTICAL CHEMISTRY /
MAY 1, 2010
The plates were developed in small solvent chambers, and the researchers then harnessed another office stapleOthe flatbed scannerOas an analytical instrument. An inexpensive scanner outperformed two commercial systems commonly applied to Two commercial devices (A and B) did no better than an inexpenTLC-based analyses. sively adapted inkjet printer (C) in precisely applying volumes of just Although “the flatbed a few nanoliters to UTLC plates. scanner yielded better signal-to-noise ratios, a The array of ink chambers is aligned with fuller comparison would include a modern heating elements that actuate multiple scanning densitometer, which is likely to chambers at a time to create an individual be even more sensitive,” points out droplet (a single pixel). Nurok. Commercially available UTLC Morlock’s team used an inexpensive, plates, however, are very small and have commercially available printer with four semi-opaque backing, two qualities that separate ink cartridges and devised a simple vacuum apparatus in the lab to load make densitometry difficult with current cartridges with their test solutions contain- instruments. The inkjet apparatus doesn’t require a ing dye mixtures. By adjusting the printer physical barrier to create above-atmodriver software and loading UTLC plates spheric pressures to effect forced flow. into the printer’s interior tray (designed This open configuration can be an advanfor labeling compact discs), they precisely tage. The system can “synergistically benprinted bands and spots. efit from print and media technologies For direct comparison, they applied through its open, planar format,” says similar dye mixtures with both a commerMorlock. “We discovered that printing cially available TLC sampler (pressurized the mobile phase was possible, [as was] spray) and a piezoelectric nanojet. In a variety of analyses, such as the linearity and the generation of a minor forced flow. Thus, the potential for a fully online, autoprecision of application, the inket method mated system is clearly possible and has worked as well or better than the other immense potential to speed up routine devices, producing reliably placed volumes analysis.” in the low-nanoliter range. “The instrumentation described in the “In evaluating this approach, other article will likely allow UTLC to establish methods of depositing small spots need to itself,” says Susan Olesik of Ohio State be considered, such as Fenimore’s contact University. “New methods of making spotter and Liu’s electroosmosis-based highly efficient stationary phases now exnanopipettor, both of which are also caist, but they require the application of pable of depositing a sub-millimeter spot,” small sample sizes and the detection of says David Nurok of Indiana University⫺ small concentrations of analytes. This arPurdue University Indianapolis. Given ticle illustrates improvements in instruthe benefits derived from refinements mentation that will solve both of these in miniature spot deposition, he adds problems.” that “studies like this should be en—Steven C. Powell couraged.” 10.1021/AC100625S 2010 AMERICAN CHEMICAL SOCIETY
Published on Web 03/22/2010
