Leap technologies

Classical liquid-liquid and liquid-solid extractions are recently receiving additional examination, as new injection techniques for GC have made very simple, low-volume extractions feasible. Recently, several commercial systems for large-volume liquid injections (up to 150 pL all at once, or up to 1 to 2 mL over a short period of time) have become available. When combined with robotic sampling systems, these have become powerful tools in the trace analysis of a variety of sample types. Due to its simplicity, classical liquid-liquid extraction is often the method of choice for sample preparation. Some of the robotic samplers available for this type of analysis, such as the LEAP Technologies Combi-PAL robotic sampler, which has been licensed by several instrument vendors, are also capable of performing automated SPME and SHE. 

Figure 13-9. Configuration of a dual channel on-line sample extraction, the CTCTrio Valve system (LEAP Technologies, www.leaptec.com also see reference 100 for technical details), which is commercially available. AC and PC signify analytical and processing columns, respectively.

We are grateful to P. Tiller (Merck and Co.), Y.-Q. Xia (Bristol-Myers Squibb), A. Watt (Merck and Co.), T. Pereira (Merck and Co.), Waters, Finnigan, Sciex/Apphed Biosystems, Beckman-Coulter, Spark-Holland, Tomtec, and LEAP Technologies for providing some of the hgures and helpful discussions. 

Another approach to matrix application is to robotically deposit small (pL to nL) droplets of matrix on discrete areas of the sample surface. When the droplets are deposited as arrays over the entire tissue surface, mass spectra can be acquired at each matrix spot and reconstructed into an image. In this case, potential analyte delocalization is limited to the area under the matrix spot, typically -100-250 pm with commercially available spotters (e.g., Portrait 630 by Labcyte [23], ChIP by Shimadzu, TM iD by LEAP Technologies). This approach is fundamentally a trade-off between spatial integrity and resolution, because what limits resolution in most cases is the diameter of the laser beam, which is typically much smaller than the diameter of the matrix spot (on the order of 30-50 pm). Samples prepared by spray-coating, either manually or robotically, may be imaged at the diameter of the laser beam, but may not have maintained analyte localization throughout the spray process. 

LCVMS experiment was conducted with an Agilent llOOLC/MSD system. A CTC PAL autosampler from LEAP Technologies was used to introduce samples to the LC/MSD. Polaris 2000 C18 columns packed with 3 pm particles, 30 x 3 mm (i.d.) at 60°C were selected for the study. Flow rate was ImL/min, linear gradient starting form 100% water (0.05% formic acid) to 100% acetonitrile (0.05% formic acid) in 4 minutes. ESI source with positive selected ion monitoring mode (SIM) was employed to detect the corresponding ions of standard compounds. The positive ions (w/z) of 369, 371, 459, and 591 were selected to monitor Mono-Fmoc-Lysine, Bis-Cbz-Lysine, Fmoc-Cbz-Lysine, and Bis-Fmoc-Lysine separately. The mass spectra of standard compounds are shown in Figure 9.24. Four levels of calibration— 25 picomolar, 50 picomolar, 100 picomolar, and 200 picomolar of standard compounds— were used in the quantitation method. 

Detailed protocols for addressing carryover, once detected and evaluated as significant relative to the needs of the assay, have been described (Dolan 2001c), and an approach particularly relevant attention to such problems arising within an autosampler (LEAP Technologies 2005) is complemented by an instructive account of a case study in which the source of the problem within an autosampler was tracked down (Vallano 2005). The following abbreviated account is drawn from all these sources. 

Figure 11.36 Schematic diagram of the dual-column extraction system on-line via a Valeo 10-port switching valve with the chiral LC-MS/MS system. The components were as follows PI, a Leap Technologies autosampler with two HPLC pumps delivering mobile phases A and B to the extraction column EC-1 or EC-2 (Waters Oasis HLB 25 gm, 1 x 50 mm) P2, HPLC pump system delivering isocratic elution mobile phase through the extraction column to the chiral analytical column full bold arrows, pathway for mobile phase A (Table) used to load plasma sample onto extraction column dashed arrows, pathway for mobile phase (neither A nor B) used to elute analytes from extraction column to the chiral analytical column F, in-line filter G in-line guard column MS, a triple-quadrupole instrument in MRM mode. Reproduced from Xia, J. Chromatogr. B 788, 317, copyright (2003) with permission from Elsevier.

LEAP Technologies (2007), Steps to Assess and Remedy Carryover [available at http //www.leaptec.com/chromatogra phy/carry-over-prevention-and-abatement.php]. 

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