Mass Filter Research Articles

Hybrid Quadrupole Mass Filter-Radial Ejection Linear Ion Trap and Intelligent Data Acquisition Enable Highly Multiplex Targeted Proteomics.

Targeted mass spectrometry (MS) methods are powerful tools for the selective and sensitive analysis of peptides identified in global discovery experiments. Selected reaction monitoring (SRM) is the most widely accepted clinical MS method due to its reliability and performance. However, SRM and parallel reaction monitoring (PRM) are limited in throughput and are typically used for assays with around 100 targets or fewer. Here we introduce a new MS platform featuring a quadrupole mass filter, collision cell, and linear ion trap architecture, capable of targeting 5000-8000 peptides per hour. This high multiplexing capability is facilitated by acquisition rates of 70-100 Hz and real-time chromatogram alignment. We present a Skyline external software tool for building targeted methods based on data-independent acquisition chromatogram libraries or unscheduled analysis of heavy labeled standards. Our platform demonstrates ∼10× lower limits of quantitation (LOQs) than traditional SRM on a triple quadrupole instrument for highly multiplexed assays, due to parallel product ion accumulation. Finally, we explore how analytical figures of merit vary with method duration and the number of analytes, providing insights into optimizing assay performance.

Modulating Schottky barriers and active sites of Ag-Ni bi-metallic cluster on mesoporous carbon nitride for enhanced photocatalytic hydrogen evolution

The advancement of photocatalysis relies on the development of novel hetero-structured materials with unique architectures. In this study, we successfully synthesized a hetero-structured g-C3N4 (GCN) material with a distinctive surface-interface modification. To further enhance its photocatalytic performance, we optimized the Ag and Ni concentration to maximize the visible light absorption and catalytic active sites for hydrogen evolution reactions. By using systematic physicochemical characterizations and density functional theory (DFT) calculations, we elucidated the pivotal role of graphitic carbon nitride (g-C3N4) in facilitating the formation of an efficient charge transfer channel and promoting the effective generation and separation of photo-generated carriers. From the DFT calculations, we also demonstrated that the Ag and Ni nanoparticles provide more efficient visible light absorption and active sites than Ni nanoparticles for water splitting and hydrogen evolution and In-situ TEM exploration. Furthermore, the hetero microstructure consisting of thin g-C3N4 nano scrolls has a crucial role in shortening the migration distance of the carriers, effectively suppressing carrier recombination. Consequently, these extraordinary characteristics resulted in a superior solar light-driven photocatalytic H2 evolution rate of 2507 μmol.h-1.g−1, surpassing the rate achieved by g-C3N4 heterostructures by a remarkable 18.6-folds. Moreover, the apparent quantum efficiency of this hetero-structured material reached an exceptional value of 1.6 % under a 1.5 G air mass filter.

GGR Handbook of Rock and Mineral Analysis Chapter 7 Quadrupole Inductively Coupled Plasma‐Mass Spectrometry

This chapter (Quadrupole Inductively Coupled Plasma‐Mass Spectrometry) is a contribution to the Geostandards and Geoanalytical Research Handbook of Rock and Mineral Analysis – an online textbook that is a fully revised and updated edition of Handbook of the Silicate Rock Analysis (P. J. Potts, 1987, Blackie, Glasgow).Chapter 7 (from Section 2 of the handbook dealing with techniques for the determination of major and trace elements) describes both the history of ICP‐MS, including development of the plasma sampling interface and the operation of modern ICP‐MS instrumentation. Given their central importance to ICP‐MS operation, ion extraction through the sampling interface, ion transmission, ion separation (with a particular focus on the quadrupole mass filter) and counting are given particular attention. Discussion of the analytical characteristics of ICP‐MS particularly focusses on spectroscopic interferences (and their mitigation). Finally, an overview of geochemical analysis by ICP‐MS considers drift correction, calibration strategies, and laser ablation microsampling.

Design and characterization of a compact Einzel lens for portable quadrupole mass spectrometry (QMS)

Quadrupole mass spectrometry (QMS) offers better resolution, selectivity and sensitivity than the metal-oxide, field effect transistors and thermal-based gas sensors. However, existing QMS systems are unsuitable for field applications. The miniaturized QMS requires dimensionally scaled components with comparable performance to the conventional bulky systems. For a portable quadrupole mass spectrometry, a compact focusing ion system is required to transfer the maximum number of ions from the ion source to the filter. The present paper discusses the design of a miniature focusing Einzel lens and the effect of design parameters on its performance. The three-cylindrical axially symmetric compact Einzel lens assembly was designed using commercially available software. The relationship between the design parameters is explored for compact and low-powered ion optics. The beam focal length was tuned by varying the bias voltage. The dimensions, as well as voltages across the Einzel lens, were reduced significantly to open a new way for portable point-of-care applications. At an applied voltage of 70 V, the focal length of the ions is 11 mm without being scattered, which is favorable for a portable quadrupole mass filter. The designed Einzel lens was fabricated using micromachining techniques and characterized at a vacuum of 3.05 × 10−4 mbar. The developed lens system shows a current output of 0.114 µA at 72 V lens voltage. A current of 94.8 µA is observed with a background noise of 0.01 µA for the system with nitrogen (28 amu) as the sample.

Square Parametric Excitation: A Digital Resonant Method for the Quadrupole Ion Trap.

Digital ion trap technology is an alternate method for driving quadrupole ion traps and mass filters using variable frequency, fixed amplitude RF square waves in place of variable amplitude, fixed frequency RF sine waves. This technique offers some advantages such as an increase in the high mass analysis range by varying frequency and lower overall voltage requirements. Here, we present a complex square waveform developed for resonant parametric excitation in a quadrupole linear ion trap. Unlike traditional resonance methods, the driving RF square wave and auxiliary square wave are coupled using the same digital circuitry without the need for transformer coupling. In this work, we use this complex waveform to selectively excite the first order parametric resonances of ion motion. The square parametric excitation method presented here employs a simple and repetitive circuit design consisting of a low-voltage waveform generator followed by a series of high-voltage MOSFET switches. This design allows for resonance methods to be easily implemented in the all-digital quadrupole. The complex square waveform can perform the same useful functions as sine wave auxiliary signals, such as selective mass elimination and mass isolation. We also demonstrate that the mass resolution performance and S/N of our digital mass spectrometer is improved by applying the complex square waveform during ion ejection.

Experimental Investigation of a Digital Quadrupole Inductively Coupled Plasma Mass Spectrometer for Elemental Analysis.

We describe the development and initial characterization of a digital waveform scanning quadrupole mass filter (digital QMF) used for inductively coupled plasma mass spectrometry (ICP-MS). Unlike a conventional voltage scanning QMF, in the digital QMF, the frequency of the digital waveform is scanned to filter ions with different m/z through the quadrupole, and m/z is proportional to 1/f2. In digital QMF, the duty cycle of the digital waveform driving the quadrupole is modified such that stability regions of interest are accessible for mass analysis with no DC voltage applied. Here, we evaluate the performance of our digital ICP-QMS instrument at several duty cycles and corresponding stability zones: from zone 1 to zone 3,2. We demonstrate that, regardless of the stability zone used, frequency vs m/z calibration matches theory. For lower-order stability zones, the mass range of the analyzer is limited by the high-frequency waveform required; however, at zone 3,2, we demonstrate a mass range from at least 40 to 232 Th, which covers most of the elemental mass range. Similar to the conventional QMF, higher stability regions of the digital QMF can yield a higher resolution. We obtained the best resolution for our current instrument at zone 3,2 with a 62.50/37.50 duty cycle. The resolution at full-width at 10% peak height (R10%) was 1200 and 1100 for 115In+ and 232Th+, respectively. Lower pole bias yielded a R10% of 1400 for 40Ar+. Resolution and sensitivity comparisons indicate that higher q values and higher duty cycles lead to enhanced resolution, but lower sensitivity. Our results validate the operation of digital quadrupole ICP-MS and suggest that, with continuous improvement of electronics and instrumentation, a high resolution digital waveform scanning ICP-QMS for elemental analysis is possible.

Experimental Evaluation of Higher Order Stability Zones Using a Digitally Operated Quadrupole Mass Filter.

Recent improvements to the comparison-based method of digital waveform generation increased the reproducibility of the waveforms so that the higher-order Mathieu stability zones can be accessed reliably. Digitally driven quadrupole mass filters access these zones using a fixed AC voltage and rectangular waveforms that are defined by a duty cycle. In this context, the duty cycle is the fraction of the waveform period where the waveform remains in the high state. Because digitally driven quadrupoles navigate stability using a duty cycle, there is no need to apply a resolving DC offset between electrode pairs. Accessing the higher stability zones using a conventional resonantly tuned RF requires the use of thousands of AC and DC voltages making the mode of operation less accessible with these devices. Stability zones higher than (1,1) and (2,1) have theoretical resolving powers that are on the order 1,140 and 3,447 at fwhm which drives efforts to practically access these operational conditions. Accessing these zones digitally requires the use of extremely precise waveforms. In a previous effort, waveform generation produced waveforms to reliably access the (1,1) and (2,1) zones without impacting performance. However, recent work found more improvement was needed to reliably access neighboring higher stability zones. Derived from that work, it was determined that a waveform resolution of ∼10 ppm or less was needed to reliably access the (3,1) and (3,2) zones. The present work utilized digital waveforms that achieve this level of precision to experimentally access and characterize attributes of the (3,1) and (3,2) zones. This work dives into the investigation of different beam energies to overcome the destabilizing fringing fields, improve transmission, and their overall effect on the experimental resolving power and signal-to-noise. In addition, the AC voltage of the driving RF was varied to understand the effects on the initial ion beam energy that is needed to achieve balanced separation and how the overall signal-to-noise is affected. Lastly, an assessment was made on the effects of the temporal parameters of a digital mass scan on peak sensitivity, peak fidelity, and overall duration for a scan.

Hybrid Quadrupole Mass Filter - Radial Ejection Linear Ion Trap and Intelligent Data Acquisition Enable Highly Multiplex Targeted Proteomics.

Targeted mass spectrometry (MS) methods are powerful tools for selective and sensitive analysis of peptides identified by global discovery experiments. Selected reaction monitoring (SRM) is currently the most widely accepted MS method in the clinic, due to its reliability and analytical performance. However, due to limited throughput and the difficulty in setting up and analyzing large scale assays, SRM and parallel reaction monitoring (PRM) are typically used only for very refined assays of on the order of 100 targets or less. Here we introduce a new MS platform with a quadrupole mass filter, collision cell, linear ion trap architecture that has increased acquisition rates compared to the analogous hardware found in the Orbitrap™ Tribrid™ series instruments. The platform can target more analytes than existing SRM and PRM instruments - in the range of 5000 to 8000 peptides per hour. This capability for high multiplexing is enabled by acquisition rates of 70-100 Hz for peptide applications, and the incorporation of real-time chromatogram alignment that adjusts for retention time drift and enables narrow time scheduled acquisition windows. Finally, we describe a Skyline external software tool that implements the building of targeted methods based on data independent acquisition chromatogram libraries or unscheduled analysis of heavy labeled standards. We show that the platform delivers ~10x lower LOQs than traditional SRM analysis for a highly multiplex assay and also demonstrate how analytical figures of merit change while varying method duration with a constant number of analytes, or by keeping a constant time duration while varying the number of analytes.

Fabrication of pbs films for air mass filter of solar simulator

The production of solar panels is continuously increasing due to increasing demands at industrial and residential levels. This also leads to an increasing demand for solar simulator testing tools. A solar simulator is a tool to assess a solar panel's performance in lab and industry scales. One of the main components of the solar simulator is the Air Mass Filter (AMF). The primary function of AMF is to remove unwanted wave bands from the solar simulator light source (e.g., Xe arc lamp) so that the filtered spectrum is commensurate to that of solar irradiation. An AMF can be produced by fabricating a thin material layer on a transparent substrate like glass. The film would absorb certain wave bands in different ways. This paper reports the fabrication of the chalcogenide PbS thin films for applying AMF. The thermal evaporation technique is used for the film fabrication. PbS is known for its versatility for applications in different optical devices due to its tailorable optical properties. Different amounts (in grams) of PbS source powders are used to deposit the PbS thin films. The optical properties of the films are then examined using UV-Vis spectroscopy. The distributions of the transmittance intensity of the Xe-arc-lamp light with and without the use of the films as an optical filter are then examined using a solar simulator. From the experiments, the film deposited using a 0.012 g PbS powder source is regarded as the optimum one regarding the transmittance intensity distribution.

Optimizing Ion Optical Design for Laser Ablation Source in Mass Spectrometry

The study focuses on optimizing a Laser Ablation Source (LAS) for use in mass spectrometry, particularly aiming to enhance transmission of ions and and determination of isotopic compositions in diverse matrices at TRIUMF’s Ion Trap for Atomic and Nuclear Science (TITAN). Critical variables affecting mass spectrometer resolution, such as ion kinetic energy distribution and ion transport are optimized through LAS. The paper explores the importance of consistent initial conditions, ion transport efficiency, and ion capture for accurate and reproducible measurements. Using SIMION software, we optimized ion optical design to tackle challenges like collimating ions travelling off-axis and mass filtering. A significant part of the study is dedicated to ion optic design to enable low abundance measurement of ions of interest (e.g., 10 ions of interest out of 1014 total ions). Techniques like high voltage switching and beam shaping were explored, and the final design aims for high transport efficiency and a 4 mm effective target scan area with maximum transport efficiency. The integration of LAS with a Multiple-Reflection Time-Of-Flight Mass Spectrometer (MR-TOF-MS) is expected to yield an analytical tool with high spatial resolution and transport efficiency for isotope abundance measurement.

Increasing Isolation Efficiency Using a Segmented Quadrupole Mass Filter Operated with Rectangular Waveforms.

The performance of a segmented quadrupole mass filter operated with rectangular waveforms and capacitively coupled rectangular waveforms applied to the prefilters was examined on a home-built quadrupole-Orbitrap platform. For peak widths of 50 m/z, 100% isolation efficiency was achieved, which fell to approximately 20% for 5 m/z peak width for a rectangular waveform of 150 V0-p. Due to a small exit aperture following the mass filter, peak structure was observed in both experimental peak shapes and those simulated using SIMION. A larger radius quadrupole was examined and achieved similar performance. While the segmented quadrupole does remove the defocusing effects of the fringing fields, the ion beam is only slightly refocused due to the low RF voltage which limits achievable gains in isolation efficiency.

A laser ablation carbon cluster ion source for the FRS Ion Catcher

A Laser Ablation Carbon Cluster Ion source (LACCI) has been developed and commissioned at the FRS Ion Catcher at GSI. It is the first laser ablation ion source for long-term measurements with a multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS). This is enabled by two key developments: (i) a two-dimensional movable target platform that ensures the long-term stable production of ions and (ii) a mass filter for the isolation of the ions of interest. LACCI is capable of providing closely-spaced reference ions in the mass range up to ∼300 u for accurate mass measurements of exotic nuclei (relative mass uncertainty ∼10−8) and systematic studies of the mass uncertainties with the multiple-reflection time-of-flight mass spectrometer. Investigations of the laser energy and repetition rate and long-term measurements have been carried out with carbon targets (Sigradur®, Fullerene) and metallic targets (silver, gold, copper, tungsten, and erbium). In a test experiment, LACCI has delivered a stable ion current for more than 20 h at a laser repetition rate of 100 Hz, corresponding to an operation for one week at 10 Hz. It thus fully satisfies the requirements for long-term accurate mass measurements of exotic nuclei with an MR-TOF-MS. This enables the access of exotic ions, detected with rates as low as 0.1 per hour at the FRS Ion Catcher.

Simulation study of digital waveform-driven quadrupole mass filter operated in higher stability regions for high-resolution inductively coupled plasma mass spectrometry.

The use of a frequency-scanned digital quadrupole mass filter (QMF) with varying duty cycles shows promise for application as a high-resolution mass analyzer design for inductively coupled plasma mass spectrometry (ICP-MS). High resolution in ICP-MS is important to overcome isobaric polyatomic interferences. Here, we explore the possibility and the characteristics of using a digital quadrupole operating in higher stability regions for ICP-MS. We perform computational simulations in SIMION of a digital QMF that is operated by scanning the frequency of the digital waveform at a fixed driving voltage and various duty cycles. For ions in the atomic mass range (7-238 m/z), we investigate the expected resolution, transmission, fringe field effects, and ion trajectories. We compare different characteristics between sine and digital waveform QMF. Within the capability of current digital waveform generation technology, a digital QMF can produce variable mass resolution, from several hundred to more than 10 000. This mass resolution covers the low, medium, and high resolutions that are typical for sector-field ICP-MS. Additionally, simulations suggest that transmission of the QMF remains high at high resolution. For example, with 87.50/12.50 duty cycle (zone 4,1), resolution at 10% peak width is 10420 for m/z 80. The transmission through the quadrupole, which is constant for all isoenergetic ions, is ~2.5%, and most ion loss is due to the defocusing effects of the fringe field. Compared to sinusoidal QMFs, ions need many fewer cycles in the digital QMF to obtain high resolution. The results demonstrate that the use of a frequency-scanned, duty-cycle-modulated digital QMF as the mass analyzer for ICP-MS has the potential to produce high resolution while maintaining considerable transmission, thus overcoming most spectral interferences in elemental MS.

The One Hour Human Proteome

We describe deep analysis of the human proteome in less than 1 h. We achieve this expedited proteome characterization by leveraging state-of-the-art sample preparation, chromatographic separations, and data analysis tools, and by using the new Orbitrap Astral mass spectrometer equipped with a quadrupole mass filter, a high-field Orbitrap mass analyzer, and an asymmetric track lossless (Astral) mass analyzer. The system offers high tandem mass spectrometry acquisition speed of 200 Hz and detects hundreds of peptide sequences per second within data-independent acquisition or data-dependent acquisition modes of operation. The fast-switching capabilities of the new quadrupole complement the sensitivity and fast ion scanning of the Astral analyzer to enable narrow-bin data-independent analysis methods. Over a 30-min active chromatographic method consuming a total analysis time of 56 min, the Q-Orbitrap-Astral hybrid MS collects an average of 4319 MS1 scans and 438,062 tandem mass spectrometry scans per run, producing 235,916 peptide sequences (1% false discovery rate). On average, each 30-min analysis achieved detection of 10,411 protein groups (1% false discovery rate). We conclude, with these results and alongside other recent reports, that the 1-h human proteome is within reach.

Comparative Assessment of Lignan Profiling and Biological Activities of Schisandra henryi Leaf and In Vitro PlantForm Bioreactor-Grown Culture Extracts.

This research's scope encompassed biotechnological, phytochemical, and biological studies of Schisandra henryi, including investigations into its in vitro microshoot culture grown in PlantForm bioreactors (temporary immersion systems, TISs), as well as extracts from leaves of the parent plant, focusing on anti-inflammatory, antioxidant, anticancer, and antimicrobial activities. The phytochemical analysis included the isolation and quantification of 17 compounds from dibenzocyclooctadiene, aryltetralin lignans, and neolignans using centrifugal partition chromatography (CPC), HPLC-DAD, and UHPLC-MS/MS tandem mass spectrometry with triple quadrupole mass filter methods. Higher contents of compounds were found in microshoots extracts (max. 543.99 mg/100 g DW). The major compound was schisantherin B both in the extracts from microshoots and the leaves (390.16 and 361.24 mg/100 g DW, respectively). The results of the anti-inflammatory activity in terms of the inhibition of COX-1, COX-2, sPLA2, and LOX-15 enzymes indicated that PlantForm microshoot extracts showed strong activity against COX-1 and COX-2 (for 177 mg/mL the inhibition percentage was 76% and 66%, respectively). The antioxidant potential assessed using FRAP, CUPRAC, and DPPH assays showed that extracts from microshoot cultures had 5.6, 3.8, and 3.3 times higher power compared to extracts from the leaves of the parent plant, respectively. The total polyphenol content (TPC) was 4.1 times higher in extracts from the in vitro culture compared to the leaves. The antiproliferative activity against T-cell lymphoblast line Jurkat, breast adenocarcinoma cultures (MCF-7), colon adenocarcinoma (HT-29), and cervical adenocarcinoma (HeLa), showed that both extracts have considerable effects on the tested cell lines. The antimicrobial activity tested against strains of Gram-positive and Gram-negative bacteria and fungi showed the highest activity towards H. pylori (MIC and MBC 0.625 mg/mL).

Selected Ion Monitoring for Orbitrap-Based Metabolomics.

Orbitrap mass spectrometry in full scan mode enables the simultaneous detection of hundreds of metabolites and their isotope-labeled forms. Yet, sensitivity remains limiting for many metabolites, including low-concentration species, poor ionizers, and low-fractional-abundance isotope-labeled forms in isotope-tracing studies. Here, we explore selected ion monitoring (SIM) as a means of sensitivity enhancement. The analytes of interest are enriched in the orbitrap analyzer by using the quadrupole as a mass filter to select particular ions. In tissue extracts, SIM significantly enhances the detection of ions of low intensity, as indicated by improved signal-to-noise (S/N) ratios and measurement precision. In addition, SIM improves the accuracy of isotope-ratio measurements. SIM, however, must be deployed with care, as excessive accumulation in the orbitrap of similar m/z ions can lead, via space-charge effects, to decreased performance (signal loss, mass shift, and ion coalescence). Ion accumulation can be controlled by adjusting settings including injection time and target ion quantity. Overall, we suggest using a full scan to ensure broad metabolic coverage, in tandem with SIM, for the accurate quantitation of targeted low-intensity ions, and provide methods deploying this approach to enhance metabolome coverage.

A multi-reflection time-of-flight setup for the study of atomic clusters produced by magnetron sputtering

The Greifswald multi-reflection time-of-flight setup has been extended with a magnetron sputtering gas aggregation source for the production of atomic cluster ions with sizes ranging from a single to thousands of atoms. This source, combined with a newly added quadrupole mass filter and a linear Paul trap, opens up the possibility of many new atomic-cluster studies not feasible with the setup before. The new components and their interfacing with the previous setup are described, and benchmarking as well as the first experimental results are presented. The capability of the system to handle singly charged ions with masses of several ten thousand atomic mass units is demonstrated.

Simulation study of a planar quadrupole mass filter for MEMS mass spectrometer

Micro-electro-mechanical system (MEMS) based mass spectrometry, MEMS mass spectrometry, emerges a new technique branch of miniature mass spectrometry. One of the main challenges hindering the development of MEMS mass spectrometry is the poor compatibility between the complex electrode structure of traditional ion optics and MEMS processes. This paper proposed a planar quadrupole mass filter utilizing a highly simplified stacked-layer structure and film electrodes, which is easy to fabricate with high precision by MEMS surface micromachining. The ion trajectory simulation model of the MEMS mass spectrometry chip involving all necessary ion optics was elaborated for investigating the preliminary performance of the planar quadrupole mass filter. By optimizing the crucial parameters such as the frequency of radio frequency voltage, the ratio of direct current voltage and radio frequency voltage, pre-pole length, main-pole length, and injection kinetic energy, the preliminary simulation result of planar quadrupole mass filter achieved a 1–2 Da peak width (at 50% of peak height) and 20–80% ion transmission efficiency. Importantly, the planar quadrupole mass filter demonstrated a maximum working pressure of 0.1 Pa (using air as the buffer gas), 100 times higher than that of conventional quadrupole mass filters, while maintaining a 0.7–1.8 Da peak width and ∼5% ion transmission efficiency. Additionally, to modify the theoretical formulas for the non-ideal quadrupolar field of planar quadrupole mass filter, a novel approach based on stability diagrams obtained by simulation was also introduced. The pretty good linearity (R2=1) between ion masses in the range of 10 to 100 Da and the corresponding radio frequency voltages was verified through the simulated mass spectra. Notably, the proportional coefficient of ion mass and radio frequency voltage exhibited a minimal 4% deviation between the simulated value (4.7132 V0P/Da) and the calculated value (4.9036 V0P/Da) through the modified formula. In conclusion, the preliminary simulation results demonstrated that the planar quadrupole mass filter possessed moderate performance, high-pressure tolerance, and excellent theoretical consistency, which proved it a promising technology of MEMS mass spectrometry. It can find applications in the fields of gas detection, including the rapid response to hazardous gas emissions and in situ detection of dissolved gases in the deep sea.

Compact, Monolithically 3-D-Printed, Hyperbolic Quadrupole Mass Filters for CubeSat Mass Spectrometry

Compact, Monolithically 3-D-Printed, Hyperbolic Quadrupole Mass Filters for CubeSat Mass Spectrometry

Multiple ion isolation and accumulation events for selective chemical noise reduction and dynamic range enhancement in MALDI imaging mass spectrometry.

Abundant chemical noise in MALDI imaging mass spectrometry experiments can impede the detection of less abundant compounds of interest. This chemical noise commonly originates from the MALDI matrix as well as other endogenous compounds present in high concentrations and/or with high ionization efficiencies. MALDI imaging mass spectrometry of biological tissues measures numerous biomolecular compounds that exist in a wide range of concentrations in vivo. When ion trapping instruments are used, highly abundant ions can dominate the charge capacity and lead to space charge effects that hinder the dynamic range and detection of lowly abundant compounds of interest. Gas-phase fractionation has been previously utilized in mass spectrometry to isolate and enrich target analytes. Herein, we have characterized the use of multiple continuous accumulations of selected ions (Multi CASI) to reduce the abundance of chemical noise and diminish the effects of space charge in MALDI imaging mass spectrometry experiments. Multi CASI utilizes the mass-resolving capability of a quadrupole mass filter to perform multiple sequential ion isolation events prior to a single mass analysis of the combined ion population. Multi CASI was used to improve metabolite and lipid detection in the MALDI imaging mass spectrometry analysis of rat brain tissue.