As an alternative to the T-type injection on microchips, optically gated sample introduction previously has been demonstrated to provide fast, serial, and reproducible injections on a single-channel microchip. Here, the ability to perform high throughput, multichannel analysis with optically gated sample introduction is described using a voice coil actuator. The microchip is fixed on a stage, which moves back and forth via the voice coil actuator, scanning two laser beams across the channels on the microchip. For parallel analysis on a multichannel microchip, both the gating beam and the probe beam are scanned at 10 Hz to perform multiple injections and parallel detection. Simultaneous, fast separations of 4-choloro-7-nitrobenzofurazan (NBD)-labeled amino acids are demonstrated in multiple channels on a microchip. Serial separations of different samples in multiple channels are also reported. Optically gated sample introduction on multiple, parallel channels shows the potential for high-speed, high-throughput separations that are easily automated by using a single electronic shutter.
The reactions of methanethiol on cobalt overlayers
grown on Mo(110) were studied using a temperature-programmed reaction and X-ray photoelectron and high-resolution electron
energy loss spectroscopies.
Methyl thiolate was identified as the reaction intermediate on the
basis of X-ray photoelectron and high-resolution electron energy loss data. Methane, methyl radical, and
H2 were the only gaseous products.
The peak temperature for methane production from methyl thiolate
hydrogenolysis was relatively insensitive
to the Co coverage and geometric structure of the Co layer.
However, less methyl radical formation was
observed as the Co coverage increased from 1 to 2.5 monolayers.
The selectivity for hydrocarbon formation
was essentially the same, ∼48 ± 5%, for all Co coverages. The
total amount of methyl thiolate deposited
in the initial S−H bond breaking was independent of Co coverage.
At 400 K, sulfur-induced structural
rearrangement of the Co overlayer was insignificant and therefore did
not affect the reaction of methanethiol.
The mixed Co−S overlayer had a substantially lower activity for
the methanethiol reaction than any of
the clean surfaces; the total amount of reaction on both the sulfur and
Co−S overlayers was 30% that of
the clean Mo(110) and pure Co overlayers.
A great deal of progress has been made toward the development of the micro total analysis system (micro-TAS) since its inception in 1990. A wide variety of applications, including genomics, proteomics and drug discovery, have prompted the development of analytical methods capable of very high throughput while maintaining low cost. The micro-TAS concept addresses both of these requirements. Electrophoresis has been a key element in the development of the micro-TAS. Most chemical and biochemical assays utilize a separation component at some point during analysis. Genomics, in particular, depends almost exclusively on electrophoresis for size-based separations of DNA. This review examines sample introduction into microfabricated electrophoretic devices, or chips, primarily for DNA analysis. Sample introduction is an important component of these systems and is an essential process for making chip electrophoresis a widely applicable analytical technique. Specific issues, such as automation, the delivery of large numbers of samples to microfabricated devices and injection of picoliter-sized sample plugs into a separation lanes on chips, are presented.
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