September 30th I participated in the first Sciex Separations CESI-MS Users Meeting. The meeting was hosted by Ass. Prof. Yannis Francois at Strasbourg University. The meeting was organized by Drs. Stephen Lock and Jim Thorn of Sciex Separations.
CESI marks a novel combination of capillary electrophoresis (CE) and electrospray ionization (ESI) technologies to create an integrated workflow solution. The CE part consists of the former Beckman-Coulter PA800 CE System for Biologics Characterization and a choice of AB Sciex MS systems like the TripleTOF® 5600+ mass spectrometry system. The interface is based on the porous tip approach described by Moini (Anal. Chem. 2007, 79, 4241 - 4246) which has been extensively beta-tested by Beckman-Coulter (see e.g. Anal. Chem. 2010, 82, 9476–9483). With the formation of Sciex Separations, by combining the HPLC separation business of Eksigent with the CE separation business of Beckman Coulter, seamless complete offering for LC-MS and CE-MS is now commercially available by combining the best from Sciex MS portfolio e.g. AB Sciex TripleTOF® 5600+ mass spectrometry system.
More information can be found at the
Sciex Separations website.
Speakers at the meeting were users of the CESI-MS technology like e.g. Dr. Alain Beck of the Centre of Immunology Pierre Fabre and Yannis Francois of the Laboratory of Molecular Structure and Dynamics by Mass Spectrometry, University of Strasbourg and Prof. Herbert Lindner director of Innsbruck Medical University, Guinevere Kammeijer and Rawi Ramautar both from Leiden University, Netherlands Their presentations focused on the application of CESI-MS for glycan characterization in mAbs and proteins and not so much on aspects of the separation and the practice of working with the porous tip interface.
It was somewhat remarkable however that all, but for Herbert Lindner, claimed superior minimal detectable quantities (MDQ) but did not refer to the concentration in the sample. After doing a quick calculation on my notepad, it appeared that all are working at the comfortable sample concentration range of around 0.1 – 5 µM.
Lindner showed an example in which CESI-MS showed a slightly better Limit of Detection (LOD) than with nano HPLC-MS (see also H. Lindner and B. Sarg et al. Mol. Cell Proteomics, 2013, 2640-2656). He injected the same sample concentration sample in both cases but a 1000x larger volume in nano HPLC (7.7 nL vs 7.7 µL). These kinds of comparisons (talking about MDQ rather than LODs) will continue to be an issue since it may impress potential users but confuse practice.
Dr. Rawi Ramautar referred about their work comparing Agilent triple tube interface with the CESI-MS). Work that he recently published (Anal Chem., 84, 885-892 (2012). In essence Ramautar claimed that the gain in better detection limit by absence of dilution from the sheath solvent and the lower volumetric flow rate is significant but less that one would expect (10-50x). This is attributed to the beneficial effects of the sheath solvent on spray formation and ionization.
One further important detail in his talk came up. The CESI interface does not tolerate higher CE currents than 10 µA!! This is not much of a problem with low pH CE for cations since one can use acetic acid in the BGE (formic acid is already to mobile) which renders a very low current. But working in the negative mode with ammonium salts is impossible. An area about which Dr. Lock mentioned is a current research project in Beckman-Coulter.
During the lab tour I received a close view to the interface. There is a special CE cartridge for the CESI-MS (see also the website referred above). The capillary is 90 cm length and 30 µm i.d. (o.d. 150 I suppose). The CE capillary end is retained in a holder. Without MS operation, say for flushing etc. this holder connects to a large waste vial. When connected to the MS, it slips into an adapter which fixates the holder and moves the CE capillary out of spray needle. This adapter is connected to a standard nanoLC MS source which can move the adapter forward/backward and places the needle directly in front of the MS Inlet (on a 45° angle). The contact liquid is connected to the outlet vial of the CE instrument and grounded there. The ESI voltage is delivered from the MS. The MS inlet is at ground. In this way it was claimed that there are two separate circuits. MS and CE are connected by two ground cables.
The system that was demonstrated to my opinion still looked as a prototype, Dr. Lock has assured me that CESI-MS now is a product and shipping. There have been several sales in EMEA already. Sciex Separations sees a lot of interest from BioPharma and recently also from the omics community at HUPO. They are continually developing the product and expect new capillaries and solutions to be available over the next year.
Overall one may conclude from this meeting that Sciex Separations is very committed to CESI-MS and other micro separations methods coupled with MS.