Microspray and microflow LC-MS/MS: the perfect fit for bioanalysis.

The advantages of microflow LC (MFLC) and nanoflow liquid chromatography coupled with a mass spectrometer are well known and include improved signal, low solvent consumption, reduced matrix effects and reduced source contamination [1]. In the past, microflow and nanoflow MS/MS have mainly been used in academic and fundamental research labs requiring high sensitivity analysis with limited sample volumes for qualitative or comparative analysis. The analytical advantages of low flow methods have led the technological development of specialized LC pumps that accurately deliver ≤100 μl/min of solvent, for use with columns with an inside diameter of ≤1 mm. With the use of these specialized LC pumps and rugged API–MS ionization sources, the realm of using MFLC–MS/MS for quantitative bioanalysis is a possibility. Researchers have used nanoflow or MFLC–MS/MS for analysis of proteomic samples, food samples, the petroleum products and other applications [2,3]. Nanoflow LC–MS/MS publications as early as 1994 include applications in discovery bioanalysis [4]. However, application of nano or MFLC-MS/MS methods in regulated bioanalysis including application in pharmaceutical and clinical space has not been extensively studied. The adoption of MFLC–MS/ MS in regulated bioanalytical laboratories has been limited by the perception that the technique lacks sufficient robustness, and the technical hurdles of implementation. The high volume requirement of bioanalytical quantitation typically demands operation on a continuous 24-7 basis. Downtime is not acceptable. Fortunately, development on the instrumentation side from vendors, and the application side of leading bioanalytical labs, have fostered many developments in the design and coupling of sources for nanospray ESI-MS to improve the ruggedness and ease of use of MFLC-MS/MS. More recently a design successful in coupling the HPLC column within the conventional ESI has been shown to provide better signal and better chromatography compared with traditional segregated techniques [5].