APCI microchip brings GC and MS closer together

Despite their relatively high cost, GC/MS systems are readily used for forensic analysis, tracking organic pollutants and detecting illegal drugs and explosives. This popularity is due to the impressive ability of GC/MS to detect volatile and thermally stable analytes. Much of the high cost of GC/MS systems is caused by the difficulty of coupling GC and MS. Currently, electron ionization is the most commonly used ionization source in GC/MS systems, but it requires a vacuum. To generate this, the GC carrier gas has to be pumped away before ionization and this can be a tricky process. Ionization techniques that work at atmospheric pressure and don't require a vacuum, such as APCI, should theoretically offer an easier way to link GC and MS. They are already the most popular ionization techniques for use with liquid chromatography/MS systems and are able to ionize a wide variety of molecules, with APCI especially good at generating ions from non-polar and neutral biomolecules. So far, however, a simple commercial method for linking GC and APCI-MS has not been developed. The APCI microchip developed by the chemists from the University of Helsinki, led by Risto Kostiainen, is based on a 380?m-thick silicon wafer, into which is etched a 520?m-wide capillary insertion channel and a 300?m-wide vaporizer channel. The effluent from the GC is transported to the APCI microchip through a capillary tube, which is inserted into the capillary insertion channel until it hits a stopper. The GC effluent flows out of the capillary tube into the vaporizer channel, where it is mixed with a nebuliser gas (which in this case is nitrogen) and then heated. This heated gaseous mixture is then forced out of the nozzle at the end of the microchip, where it comes into contact with the electrical discharge produced by a corona discharge needle. This causes the effluent and nebuliser gas to react together, generating analyte ions that are then analysed by the MS. Kostiainen and his team found that their GC/APCI-MS system could detect a range of small organic compounds, including anisole, benzaldehyde and 2-acetylnapthalene, with limits of detection at the nanomole per litre range. The chemists propose that this sensitivity could be further improved by simply using a more sensitive mass spectrometer. In addition, Kostiainen and his team discovered that their system could identify compounds that are normally difficult to detect using GC. It generated a clear peak for testosterone in a urine sample, whereas testosterone usually needs to be modified by reacting it with another compound to make it detectable by GC. Another advantage of this APCI microchip is that it can be used with LC/MS as well as GC/MS. Indeed, this microchip is based on a version that Kostiainen and his colleagues developed in 2004 specifically for LC/MS systems. "This means that the usability of MS systems designed for LC/MS can be enlarged and separate systems for GC/MS and LC/MS are not necessarily needed," claim the researchers. "Source":[ http://www.separationsnow.com/coi/cda/detail.cda?id=13787&type=Feature&chId=7&page=1]

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