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Salt removal is a prerequisite for electrospray ionization mass spectrometry (ESI-MS) analysis of biological samples. Rapid desalting and a low volume connection to an electrospray tip are required for time-resolved measurements. We have developed a microfabricated desalting device that meets both requirements, thus providing the foundational technology piece for transient ESI-MS measurements of complex biological liquid specimens. In the microfabricated device, the sample flows in a channel separated from a higher flow rate, salt-free counter solution by a monolithically integrated nanoporous alumina membrane, which can support pressure differences between the flow channels of over 600 kPa. Salt is removed by exploiting the large difference in diffusivities between salts and the typical ESI-MS target bioanalytes, e.g., peptides and proteins. We demonstrate the capability to remove 95% of salt from a sample solution in ∼1 s while retaining sufficiently high concentration of a relatively low molecular weight protein, cytochrome-c, for ESI-MS detection.

The scanning mass spectrometry (SMS) probe is new electrospray ion source. Motivated by the need for untargeted chemical imaging of dynamic events in solution, we have exploited an approach to electrospray ionization (ESI) that allows continuous sampling from a highly localized volume (~picoliters) in a liquid environment, softly ionizes molecules in the sample to render them amenable for mass spectrometric analysis, and sends the ions to the mass spectrometer. The key underlying concepts for our approach are This approach enables chemical monitoring or imaging of submerged interfaces, providing access to details of spatial heterogeneity and temporal changes within liquid samples. It also permits direct access to liquid/ liquid interfaces for ESI-MS analysis. In this Letter we report the first demonstrations of these capabilities of the SMS probe, and describe some of the probe's basic characteristics.Chemical imaging with micrometric resolution of dynamic biochemical interfaces, especially interfaces immersed in liquid, is an area of considerable interest. Cell biologists, for instance, are excited about the ability to use such techniques to elucidate details of complex cellular processes.1 Proteomics studies increasingly find that data including correlation in time and space of protein presence is essential to biological understanding. Currently, all nonspectroscopic chemical imaging techniques are inherently limited in their discovery potential by the requirement that target analytes be identified ahead of time. Spectroscopic methods of chemical imaging, on the other hand, can provide information about multiple and possibly unanticipated analytes. Among spectroscopic methods, mass spectrometry holds the greatest promise for biochemical imaging. Mass spectrometry (MS) is a powerful analysis method because it allows identification of multiple chemicals simultaneously, displaying considerable chemical specificity and sensitivity. 2 In particular, with the advent of soft ionization methods, MS has become unparalleled in its ability to identify large biomolecules. In this Letter we report the first demonstrations of an MS-based technology that provides a means for obtaining the spatial or temporal distribution of chemicals in solution, and hence dramatically expands that applicability of imaging mass spectrometry (IMS).The scanning mass spectrometry (SMS) probe is an electrospray ion source that helps fill a void in currently used imaging mass spectrometry technologies (e.g., MALDI, 3 MALDESI,4 LAESI, 5 SIMS, 6,7 DESI, 8, 9 and PESI10) in that it allows for continuous imaging of transient events at submerged interfaces in solution. 11 This is accomplished by direct sampling of the NIH Public Access

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We describe the DRILL (dry ion localization and locomotion) device, which is an interface for electrospray ionization (ESI)-mass spectrometry (MS) that exploits a swirling flow to enable the use of inertial separation to prescribe different fates for electrosprayed droplets based on their size. This source adds a new approach to charged droplet trajectory manipulation which, when combined with hydrodynamic drag forces and electric field forces, provides a rich range of possible DRILL operational modes. Here, we experimentally demonstrate sensitivity improvement obtained via vortex-induced inertial sorting of electrosprayed droplets/ions: one possible mode of DRILL operation. In this mode, DRILL removes larger droplets while accelerating the remainder of the ESI plume, producing a high velocity stream of gas-enriched spray with small, highly charged droplets and ions and directing it toward the MS inlet. The improved signal-to-noise ratio (10-fold enhancement) in the detection of angiotensin I is demonstrated using the DRILL interface coupled to ESI-MS along with an improved limit of detection (10-fold enhancement, 100 picomole) in the detection of angiotensin II. The utility of DRILL has also been demonstrated by liquid chromatography (LC)–MS: a stable isotope labeled peptide cocktail was spiked into a complex native tissue extract and quantified by unscheduled multiple reaction monitoring on a TSQ Vantage. DRILL demonstrated improved signal strength (up to a 700-fold) for 8 out of 9 peptides and had no effects on the peak shape of the transitions.

Large-scale manufacturing of therapeutic cells requires bioreactor technologies with online feedback control enabled by monitoring of secreted biomolecular critical quality attributes (CQAs). Electrospray ionization mass spectrometry (ESI-MS) is a highly sensitive label-free method to detect and identify biomolecules, but requires extensive sample preparation before analysis, making online application of ESI-MS challenging. We present a microfabricated, monolithically integrated device capable of continuous sample collection, treatment, and direct infusion for ESI-MS detection of biomolecules in high-salt solutions. The dynamic mass spectrometry probe (DMSP) uses a microfluidic mass exchanger to rapidly condition samples for online MS analysis by removing interfering salts, while concurrently introducing MS signal enhancers to the sample for sensitive biomolecular detection. Exploiting this active conditioning capability increases MS signal intensity and signal-to-noise ratio. As a result, sensitivity for low-concentration biomolecules is significantly improved, and multiple proteins can be detected from chemically complex samples. Thus, the DMSP has significant potential to serve as an enabling portion of a novel analytical tool for discovery and monitoring of CQAs relevant to therapeutic cell manufacturing.