Liquid chromatography-mass interface devices

Tegeler, T.J., Mechref, Y., Boraas, K., Reilly, J.P and Novotny, M.V. (2004) Microdeposition device interfacing capillary electrochromatography and microcolumn liquid chromatography with matrix-assisted laser desorption/ionization mass spectrometry. Anal. Chem. 76, 6698—6706. 

Mass spectrometry (MS) is one of the most powerful detection techniques used in liquid-phase analyses,1 mainly due to the ease of interfacing with separation techniques such as capillary electrophoresis (CE)2,3 and high-performance liquid chromatography (HPLC).4 Due to its sensitivity and applicability to a wide variety of chemical and biochemical species, MS is also used for the analysis of (bio)chemical molecules processed in microfluidics devices.5,6 Electrospray ionization (ESI)7 10 is often used to transfer samples from microfluidics chips to a mass spectrometer, involving analyte ionization directly from solutions and operating at flow rates typically used in microfluidics devices.11 Due to its effectiveness, the use of chip-MS coupling has rapidly spread in many research areas with bioanalytical applications,12 such as the... 

The use of separation techniques, such as gel permeation and high pressure liquid chromatography interfaced with sensitive, silicon-specific aas or ICP detectors, has been particularly advantageous for the analysis of silicones in environmental extracts (469,483—486). Supercritical fluid chromatography coupled with various detection devices is effective for the separation of silicone oligomers that have molecular weights less than 3000 Da. Time-of-flight secondary ion mass spectrometry (TOF-sims) is applicable up to 10,000 Da (487). 

More recently, liquid chromatography (LC), supercritical fluid chromatography (SEC), and CZE devices connected to mass spectrometers have been used to separate components of complex mixtures prior to mass analysis. When vaporized, the solvent from an LC represents a volume of 100-1000 times greater than that of a carrier gas used in GC. Interfaces developed commercially have solved the problem of eliminating this gas load by using combinations of heating and pumping, sometimes with... 

Lab-on-a-chip analyzers are now available from several instrument companies. One commercial analyzer allows the analysis of DNA, RNA, proteins, and cells. Another commercial microfluidics device is used for nanoflow liquid chromatography and provides an interface to an elcctrospray mass spectromeu y detector. Lab-on-a-chip analyzers are envisioned for drug screening, for DNA sequencing, and for detecting life forms on I iarth, Mars, and other planets. These devices should become more important as the teehnol-ogy matures. 

The inlet system is used to introduce the sample into the mass spectrometer, to convert it into the gas phase, and to reduce its pressure before ionization. Forensic samples are often impure, so the analytes, have to be separated from the matrix before being inserted into the mass spectrometer. The inlet system is most often an interface between a chromatographic device and the mass spectrometer. By this approach, the analytes are separated from one another and from the contaminants by either gas chromatography (GC) or high-performance liquid chromatography (HPLC), and the isolated compounds in the effluents from the column flow directly into the mass spectrometer. 

There are numerous ionization methods that allow formation of ions to carry out mass spectrometry however, in this chapter we will only focus on those most common in LC-MS. The challenge in coupling HPLC to mass spectrometry is that the chromatography operates with liquids and under high pressure, while the detector operates under high vacuum. The device between the chromatograph and the mass spectrometer is called the interface. Here, ionization and transition from liquid to gas phase of the compounds occur. The development of the first commercial available interfaces started as early as in the 1970s. Since then numerous interfaces have been introduced. Table 3.6 shows a list of current interfaces and their acronyms. 

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