Development of a robotics platform for automated multi-ionization mass spectrometry.

Rationale: Successful coupling of a multi-ionization automated platform with commercially available mass spectrometers provides improved coverage of compounds in complex mixtures through implementation of new and traditional ionization methods. The versatility of the automated platform is demonstrated through coupling with mass spectrometers from two different vendors. Standards and complex biological samples were acquired using electrospray ionization (ESI), solvent-assisted ionization (SAI) and matrix-assisted ionization (MAI).

Methods: The MS™ prototype automated platform samples from 96- or 384-well plates as well as surfaces. The platform interfaces with Thermo Fisher Scientific mass spectrometers by replacement of the IonMax source, and on Waters mass spectrometers with additional minor source inlet modifications. The sample is transferred to the ionization region using a fused-silica or metal capillary which is cleaned between acquisitions using solvents. For ESI and SAI, typically 1 μL of sample solution is drawn into the capillary tube and for ESI slowly dispensed near the inlet of the mass spectrometer with voltage placed on the delivering syringe barrel to which the tubing is attached, while for SAI the sample delivery tubing inserts into the inlet without the need for high voltage. For MAI, typically, 0.2 μL of matrix solution is drawn into the syringe before drawing 0.1 μL of the sample solution and dispensing to dry before insertion into the inlet.

Results: A comparison study of a mixture of angiotensin I, verapamil, crystal violet, and atrazine representative of peptides, drugs, dyes, and herbicides using SAI, MAI, and ESI shows large differences in ionization efficiency of the various components. Solutions of a mixture of erythromycin and azithromycin in wells of a 384-microtiter well plate were mass analyzed at the rate of ca 1 min per sample using MAI and ESI. In addition, we report the analysis of bacterial extracts using automated MAI and ESI methods. Finally, the ability to perform surface analysis with the automated platform is also demonstrated by directly analyzing dyes separated on a thin-layer chromatography (TLC) plate and compounds extracted from the surface of a beef liver tissue section.

Conclusions: The prototype multi-ionization automated platform offers solid matrix introduction used with MAI, as well as solution introduction using either ESI or SAI. The combination of ionization methods extends the types of compounds which are efficiently ionized and is especially valuable with complex mixtures as demonstrated for bacterial extracts. While coupling of the automated multi-ionization platform to Thermo and Waters mass spectrometers is demonstrated, it should be possible to interface it with most commercial mass spectrometers.