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Nano-LC/ESI on a chip close together without the typical connections, both the delay time for the gradient to arrive at the head of the column and the dead volume between the separation column and the ESI tip are minimized. The end result is that the LC run time can be much shorter and band broadening is reduced compared with traditional nanoLC/MS. Agilent plans to start selling the chip early this year. Initially, the chip interface will only be compatible with Agilent mass spectrometers. But van de Goor says that Agilent is evaluating this situation. He cautions that adapting the chip for use with multiple systems could be tricky because each vendor has different MS inlet systems. Agilent researchers are not content to stop with this initial nano-LC/ESI chip. In fact, they are already adding more components to the device. At meetings, the researchers have reported their development of a chip with three LC columns and an ESI tip. A sample first flows through a strongcation-exchange column, then it flows through two reversed-phase columns. Until the three-column chip is available commercially, researchers can connect Agilent’s initial chip to traditional LC columns for additional separation capabilities. Van de Goor says that they also may add an affinity capture step to help reduce sample complexity and isolate particular types of proteins. “What the chip format allows us to do, [because] many of these affinity media are available on beads, is to customize chips,” he says. As an example, he explains that a chip could include a phosphopeptide affinity step to enrich for phosphorylated peptides in a sample. “I think [the chip] will help people to really focus on particular applications, and [it] is an easy format.” a —Katie Cottingham COPYRIGHT 2004 AGILENT TECHNOLOGIES
Sometimes, proteomics researchers feel like plumbers. They have to make sure the LC columns are connected properly to the mass spectrometer. They have to troubleshoot leaks and blockages in a maze of tubing and fittings, which is a difficult prospect when the system is running at very low flow rates. But according to Hongfeng Yin, Tom van de Goor, and their colleagues at Agilent Laboratories, proteomics researchers can finally doff their toolbelts! In the January 15 issue of Analytical Chemistry (pp 527–533), the researchers describe an integrated nano-LC/ESI microfluidic chip in which an enrichment column, a reversed-phase LC column, and an ESI tip have been laser-ablated into a polyimide film. The chip provides reproAgilent’s nano-LC/ESI chip. ducible results that are comparainkjet cartridges, it is no coincidence—it’s ble to those obtained from a traditional the same material. When inkjet nozzles nano-LC/MS setup, without the usual were first developed, they were formed connections and tubing. on a polyimide surface with the same The LC/ESI chip fits inside a valve and is aligned by fitting the valve pins into laser ablation process now used to fabricate the nano-LC/ESI chip. Van de Goor holes in the chip. Fluids pass through a says that development of the chip began rotor, which directs the flow to different while Agilent was still a part of Hewlett channels on the chip. In the sample loadPackard, the computer company, so reing configuration, fluid goes through the sample enrichment column to a waste cap- searchers had many opportunities to share innovations from different areas. illary. When the rotor is switched to the A big advantage of the new microfluLC run configuration, the sample is eluted idic chip is that it is easy to use. The refrom the enrichment column and moves to the separation column. Finally, the sam- searchers say that small columns are often run at low flow rates when sensiple is sprayed from the ESI tip into the tivity is important or when there is a mass spectrometer. limited amount of sample. Nano-LC is Although other researchers have dethe ultimate platform for this situation, veloped ESI chips, no one has placed HPLC capabilities on the same chip until they say. But because nano-LC is difficult to set up and troubleshoot, only a now, says van de Goor. Finding a way to few scientists actually use it. “We hope apply and control the high pressures rethe chip will make nano-LC/MS much quired for nano-LC was a difficult task. “I think the innovation step here was the easier to use and, therefore, more accessible to a larger group of people,” says idea to integrate the chip with the valve van de Goor. for flow switching,” he says. Yin points out other advantages. BeIf the shiny orange polyimide chip recause the chip components are placed minds you of the orange film on your
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