Liquid Chromatography Coupled with Tandem Mass Spectrometry for Clinical Applications
November 1st 2008The use of mass spectrometry (MS) in clinical diagnosis goes back to the early 1970s with the application of gas chromatography (GC)–MS to the determination of a variety of biologically significant molecules. Because GC requires a certain level of analyte volatility, and since most biologically active molecules are polar, thermolabile, and involatile, elaborate extraction and derivatization protocols needed to be devised to make GC–MS useful for the analysis of clinically relevant samples. To make sample analysis less difficult by MS there had been a significant amount of R&D invested over several decades aimed at coupling high performance liquid chromatography (HPLC) with MS since HPLC is a much better separation technology than GC for polar thermolabile biologically relevant molecules. This coupling was not without significant challenges; most of the LC–MS coupling techniques that evolved during the 1970s and 1980s were not very successful, and many of those that enjoyed some widespread..
The Changing Face of LC–MS: From Experts to Users
November 1st 2008Two decades ago, MS was the preserve of experts and skilled technicians as the instrumentation required constant attention and adjustment. At that time, liquid chromatography (LC)–MS was in its infancy and atmospheric pressure ionization (API) source interfacing was just beginning. Samples requiring analysis were passed from the requesting scientist to these "experts for analysis." The samples would be analyzed, processed, and interpreted, and the results returned via a written report. Two decades later, the users and capabilities of LC–MS have changed significantly. Now mass spectrometers and LC–MS systems are ubiquitous in the analytical laboratory, especially in the pharmaceutical industry. These instruments are used by a wide variety of scientists for a diverse range of tasks, from purity screening in medicinal chemistry, to the quantification of drugs in blood and the identification of proteins for biomarker discovery. The usability of the current MS platforms has improved..
A New Perspective on the Challenges of Mass Spectrometry
November 1st 2008For drug discovery workflows, the issue of metabolite detection and identification in in vivo systems is a critical challenge. The wide range of complex matrices (such as bile, plasma, urine, and fecal extracts), and the ion suppression effects of these biological fluids, can cause a severe decrease in the ability to detect metabolites. Greater instrument sensitivity is necessary to detect these compounds and, at the same time, helps to minimize sample preparation, simply diluting the negative effects of these complex matrices and avoiding the time- and labor-consuming sample cleanup or concentration steps that otherwise might be required.
The Impact of Fast Chromatography and Its Effects on Mass Spectrometry
November 1st 2008For many years, and after several notable failures, many researchers were convinced that it was impossible to design a quadrupole time-of-flight (qTOF) mass spectrometer that was able to retain its ability to perform the high-resolution measurements necessary for definitive molecular formula determination of unknowns. Conventional wisdom indicated that there were many reasons (for example, temperature stability, ion diffusion, and ion loss on grids of reflectrons) that would make it impossible to improve resolution of these types of instruments. Figure 1 shows a schematic of an instrument designed for high-resolution measurements with fast chromatography (Maxis UHR-TOF mass spectrometer, Bruker Daltonics, Billerica, Massachusetts). The instrument includes an ion chiller, a series of ion refocusing operations, a single reflectron, and temperature control of the overall flight tube of the instrument.