Time-of-flight Secondary Ion Mass Spectrometry Research Articles

Dissolved organic carbon spurs bacterial-algal competition and phosphorus-paucity adaptation: Boosting Microcystis' phosphorus uptake capacity

Dissolved organic carbon (DOC) can alter the availability of background nutrients by affecting the proliferation of heterotrophic bacteria, which exerts a notable influence on algal growth and metabolism. However, the mechanism of how allochthonous DOC (aDOC) precipitates shifts in bacterial-algal interactions and modulates the occurrence of cyanobacteria blooms remains inadequately elucidated. Therefore, this study investigated the relationship between bacteria and algae under aDOC stimulation. We found that excess aDOC triggered the breakdown and reestablishment of the equilibrium between Microcystis and heterotrophic bacteria. The rapid proliferation of heterotrophic bacteria led to a dramatic decrease in soluble phosphorus and thereby resulted in the inhibition of the Microcystis growth. When the available DOC was depleted, the rapid death of heterotrophic bacteria released large amounts of dissolved phosphorus, which provided sufficient nutrients for the recovery of Microcystis. Notably, Microcystis rejuvenated and showed higher cell density compared to the carbon-absent group. This phenomenon can be ascribed that Microcystis regulated the compositions of extracellular polymeric substances (EPS) and the expression of relevant proteins to adapt to a nutrient-limited environment. Using time of flight secondary ion mass spectrometry (TOF-SIM) and proteomic analysis, we observed an enhancement of the signal of organic matter and metal ions associated with P complexation in EPS. Moreover, Microcystis upregulated proteins related to organic phosphorus transformation to increase the availability of phosphorus in various forms. In summary, this study emphasized the role of DOC in algal blooms, revealing the underestimated enhancement of Microcystis nutrient utilization through DOC-induced heterotrophic competition and providing valuable insights into eutrophication management and control.

Effect of Al2O3 thickness and oxidant precursors on the interface composition and contamination in Al2O3/GaN structures

In this paper, we investigate the Al2O3/GaN critical buried interface of the next generation of gallium nitride (GaN)‐based transistors using time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) and hard X‐ray photoelectron spectroscopy (HAXPES). Results highlight that gallium oxidation at this interface is enhanced when increasing the Al2O3 thickness from 3 up to 20 nm. Gallium oxidation is reduced when using both O3 and H2O as oxidant precursors, compared with only H2O during the growth of Al2O3. In addition, the O3/H2O‐based Al2O3 favors a reduction of contaminants such as hydrogen and carbon but enhances the presence of halides (Cl− and F−) at this Al2O3/GaN interface.

The Molecular Profile of Soil Microbial Communities Inhabiting a Cambrian Host Rock.

The process of soil genesis unfolds as pioneering microbial communities colonize mineral substrates, enriching them with biomolecules released from bedrock. The resultant intricate surface units emerge from a complex interplay among microbiota and plant communities. Under these conditions, host rocks undergo initial weathering through microbial activity, rendering them far from pristine and challenging the quest for biomarkers in ancient sedimentary rocks. In addressing this challenge, a comprehensive analysis utilizing Gas Chromatography Mass Spectrometry (GC-MS) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) was conducted on a 520-Ma-old Cambrian rock. This investigation revealed a diverse molecular assemblage with comprising alkanols, sterols, fatty acids, glycerolipids, wax esters, and nitrogen-bearing compounds. Notably, elevated levels of bacterial C16, C18 and C14 fatty acids, iso and anteiso methyl-branched fatty acids, as well as fungal sterols, long-chained fatty acids, and alcohols, consistently align with a consortium of bacteria and fungi accessing complex organic matter within a soil-type ecosystem. The prominence of bacterial and fungal lipids alongside maturity indicators denotes derivation from heterotrophic activity rather than ancient preservation or marine sources. Moreover, the identification of long-chain (>C22) n-alkanols, even-carbon-numbered long chain (>C20) fatty acids, and campesterol, as well as stigmastanol, provides confirmation of plant residue inputs. Furthermore, findings highlight the ability of contemporary soil microbiota to inhabit rocky substrates actively, requiring strict contamination controls when evaluating ancient molecular biosignatures or extraterrestrial materials collected.

Performance of Phenolic-Epoxy Coatings after Exposure to High Temperatures

Phenolic-epoxy coatings, which are designed to protect substrates from thermal damage, are widely applied in many fields. There remains an inadequate understanding of how such coatings change during their service life after exposure to various temperature conditions. To further elucidate this issue, this case study investigated the effects of high temperatures on carbon steel panels coated with phenolic epoxy and exposed to different heating conditions. A general trend of decreasing barrier performance was observed after exposure to 150 °C for 3 d, as evidenced by the appearance of cracks on the panel surfaces. In contrast, the coating performance improved after exposure to isothermal conditions (120 °C) or thermal cycling from room temperature to 120 °C, as indicated by the increased low-frequency impedance modulus values of the coating. This unexpected improvement was further examined by characterising the coatings using transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), pull-off adhesion tests, and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The maximum pull-off adhesion force (24.9 ± 3.6 MPa) was measured after thermal cycling for 40 d.

Investigation of Iron Dissolution Mechanism in Acidic Solutions with and without Dissolved CO2—Part II: Time of Flight-Secondary Ion Mass Spectrometry 3D Mapping

Time-of-flight-secondary ion mass spectrometry (ToF-SIMS) 3D mapping and depth profiling were used to study the anodic iron dissolution mechanisms of mild steel in chloride-containing aqueous CO2 environments. The technique detected adsorbed hydroxide and chloride intermediates formed during the corrosion process, consistent with the proposed multipath reaction mechanism for anodic iron dissolution reaction. Despite the presence of aqueous carbonic species and their observed effect on the kinetics of iron dissolution, no additional adsorbed intermediates have been detected in aqueous CO2 environments, indicating that carbonic species do not directly participate in the iron dissolution reaction. ToF-SIMS 3D mapping results on characterization of the specimens immersed in a chloride-containing solution with and without CO2 suggest that one role of aqueous carbonic species CO2 could be to accelerate the adsorption of chloride ions and the formation of chloride intermediates.

Panoramic chemical imaging of opium alkaloids in Papaver somniferum by TOF-SIMS

Accurate mapping of opium alkaloids in Papaver somniferum (P. somniferum) is significant for comprehensively elucidating their biosynthetic pathways and metabolic regulations. Here we describe a panoramic chemical imaging strategy based on time-of-flight secondary ion mass spectrometry (TOF-SIMS) that enables a thorough and precise visualization of the spatial differentiation of five opium alkaloids (morphine, codeine, thebaine, papaverine and noscapine) in P. somniferum. Notably, the opium alkaloids exhibited enrichment in the capsule, pistil, receptacle and peduncle. Moreover, a series of cross sections of a capsule were imaged to reveal a three-dimensional horizon of internal distribution of opium alkaloids. Opium alkaloids were observed enriched within the pseudoseptum and the “tube-like” structure of the inner pod wall, witnessing a downward trend toward the stigmatic disk. Finally, in high spatial resolution mode of TOF-SIMS, direct single-cell level chemical mapping of opium alkaloids in the phloem of the vascular bundles of P. somniferum receptacle was achieved for the first time. The introduced imaging strategy can provide multi-dimensional insights into the spatial distribution of opium alkaloids in P. somniferum, and the findings are expected to facilitate shedding light on the biological activities of these pharmacologically valued alkaloids.

The Impact of AI on Contact Resistance and Its Suitability in Fine Pitch Interconnects

Integration issues for a three-dimensional (3D) interconnect in a Face-to-Face (F2F) configuration are discussed. In particular, the effect of AI and organic dielectrics under the bump and their effect in chip-package-interaction (CPI) stresses as well as AI contact resistance issues that arise as the interconnection pitch is decreased. This paper will present a finite-element model created to study the stresses in advanced 3D microelectronic package. To assess the reliability of the 3D packages a submodeling approach is used to capture the CPI stresses. The modeling study presented indicates that it is beneficial to continue using AI pads as it has significatly lower stresses compared to copper pads/vias. In the second portion of the paper, the effect of PBO developer on AI corrosion is presented. Reactive ion etching (RIE) chemistries and wet chemistries were optimized using contact resistance as the success metric. Process robustness was achieved by decoupling the hard dielectric opening from the PBO via opening. Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS), Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS) analysis were used to add clarity to the bump contact resistance values.

Characteristics of the Discoloration Switching Phenomenon of 4H-SiC Single Crystals Grown by PVT Method Using ToF-SIMS and Micro-Raman Analysis.

The discoloration switching appearing in the initial and final growth stages of 4H-silicon carbide (4H-SiC) single crystals grown using the physical vapor transport (PVT) technique was investigated. This phenomenon was studied, investigating the correlation with linear-type micro-pipe defects on the surface of 4H-SiC single crystals. Based on the experimental results obtained using time-of-flight secondary ion mass spectrometry (ToF-SIMS) and micro-Raman analysis, it was deduced that the orientation of the 4H-SiC c-axis causes an axial change that correlates with low levels of carbon. In addition, it was confirmed that the incorporation of additional elements and the concentrations of these doped impurity elements were the main causes of discoloration and changes in growth orientation. Overall, this work provides guidelines for evaluating the discoloration switching in 4H-SiC single crystals and contributes to a greater understanding of this phenomenon.

Enhanced adhesion strength between electroplated Cu and ABF substrate with isothermal annealing treatment

This study aimed to enhance the adhesion strength between electroplated Cu and a low-profile Ajinomoto build-up film (ABF) substrate through isothermal annealing treatment. We examined the electroplated Cu microstructure evolution (including grain size, orientation, and texture) and elemental distribution at the Cu/ABF interface after annealing at 180 °C and 210 °C by means of electron backscatter diffraction (EBSD), X-ray diffraction (XRD), and transmission electron microscopy (TEM) in conjunction with energy dispersive X-ray spectroscopy (EDS). Furthermore, the adhesion strength of the Cu/ABF structure after isothermal annealing for different times was investigated through a peeling test based on the IPC-TM-650 test methods. The chemical bond and atomic concentration depth profiles of the fracture surface (ABF side) after the peeling test were characterized by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). These investigations demonstrated that the adhesion strength of the Cu/ABF structure can be greatly enhanced by the electroplated Cu microstructure modification and Cu/ABF interdiffusion through appropriate isothermal annealing treatment.

Localized states in carbon dots: Structural and optical investigation of three systems with varying degrees of carbonization

Carbon dots (CDs) have been widely researched in recent years, mainly to investigate their potential in various applications such as drug delivery, photocatalysis, and sensing. However, understanding of their fundamental properties, including physical and electronic structure, has lagged behind their development in applied sciences. To address this, it is necessary to use novel methods which go beyond the current level of characterization in the literature. In this work, we utilize time of flight-secondary ion mass spectrometry (ToF-SIMS) to generate specific knowledge of the structural components of three CDs generated in our lab. This work revealed that black CDs (B-CDs) possess a highly carbonic structure with nitrogen and oxygen functionalization throughout the particle structure. Carbon nitride dots (CNDs) possess some of these same carbonic structures, but also show the presence of more organic structures which would be expected through a bottom-up approach. In terms of carbonization, CNDs lie between B-CDs and the third sample, yellow-CDs (Y-CDs). Y-CDs are believed to be almost completely polymeric/organic in structure and the groups detected through this mass analysis supports this idea. The structural information from ToF-SIMS is compared with other structural techniques. Additionally, the optical properties of CDs before and after oxidation and reduction are used to craft a proposed photoluminescence (PL) mechanism for each system. The analysis contained herein enables further understanding of the structure of these three samples, and the attained understanding of the surface structure is particularly important for future biomedical applications.

Microscopic and Spectroscopic Analysis of the Solid Electrolyte Interphase at Hard Carbon Composite Anodes in 1 M NaPF6/Diglyme

AbstractThe formation of the solid electrolyte interphase (SEI) on HC composite electrodes plays a crucial role in enhancing the performance and operational stability of sodium (Na+) ion batteries. It has been demonstrated that for HC anodes improved electrochemical performance, e. g., increase in coulombic efficiency (CE) and improved rate performance have been achieved in ether‐based electrolytes. Here, we investigate spray‐coated HC composite electrodes charged at low and high current rates in 1 M sodium hexafluorophosphate (NaPF6) in diglyme using half‐cell experiments. The pristine and cycled HC anodes were examined in terms of conductivity and their electrochemical properties after cycling. In 1 M NaPF6 ether‐based electrolyte, the spray‐coated HC composite electrodes (film thickness approx. 22.0 μm with an active mass loading of approx. 2.0 mg cm−2) reached a discharge capacity of 431 mA h g−1 at 0.1 C that stays constant for 40 cycles, which is substantially higher than that obtained in carbonate‐based electrolytes. We investigated the formed interphase using conductive atomic force microscopy (c‐AFM), scanning electrochemical microscopy (SECM), X‐ray photoelectron spectroscopy (XPS) and time‐of‐flight secondary‐ion mass spectrometry (ToF‐SIMS), revealing distinct differences for longer cycling and at varying current rates which indicates that the properties of the formed SEI layers are influenced by the formation conditions.

In-house synthesized poly(ether ether ketone) ionenes. II. ToF-SIMS spectra in the negative ion mode

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used to analyze poly(ether ether ketone) (PEEK) based membranes. PEEK membranes have been shown to be effective in the separation of CO2 from flue gases (post-combustion technique). The PEEK membranes were synthesized using novel aromatic ether-ketone linkages inspired by PEEK with polymeric backbone bistriflimide [Tf2N]− counterions. One of the keys to advancing this technology is developing membranes that are selective and permeable toward CO2, in which PEEK based membranes have been shown to be. Furthermore, the compatibility between various water lean solvents also needs to be investigated. Surface analytical techniques such as x-ray photoelectron spectroscopy and ToF-SIMS are useful for investigating chemical changes between membranes. Herein, we present ToF-SIMS data obtained in the negative ion mode for four different PEEK membranes designed for use in CO2 capture systems. Positive ion mode spectra are reported in Paper I.

In-house synthesized poly(ether ether ketone) ionenes. I. ToF-SIMS spectra in the positive ion mode

Static time-of-flight secondary ion mass spectrometry (ToF-SIMS) was performed for acquiring the high-resolution surface spectra of four types of synthesized imidazolium ionene membranes. These novel membranes have aromatic ether–ketone–ether linkages inspired by poly(ether ether ketone) (PEEK). The PEEK-ionenes synthesized for this study have imidazolium cations placed in the polymeric backbone with bistriflimide [Tf2N]− counterions. The attention given to synthetically modified PEEK derivatives, such as PEEK-ionenes, is considerable due to their ability to selectively capture CO2 molecules and other light gases. Therefore, it is important to characterize the surface of these synthesized novel PEEK-ionenes. In this work, characteristic and unique peaks were identified in the positive spectra of each sample. The differences in mass spectra among the samples provide insights for optimizing or fine-tuning the PEEK-ionenes synthesis to achieve a high-performance CO2 separation membrane with enhanced permeability, selectivity, and mechanical stability. The SIMS spectra and identified characteristic peaks of these synthesized ionenes will serve as a reference in the positive mode, complementing the corresponding spectra reported in the negative ion mode (Paper II).

High-Resolution Characterization of Enamel Remineralization Using Time-of-Flight Secondary Ion Mass Spectrometry and Electron Microscopy

Introduction: The aim of this in vitro study was to assess the suitability of high-resolution time-of-flight secondary ion mass spectrometry (ToF-SIMS) for visualizing cross-sectional changes in human enamel microstructure and chemical composition during treatment and remineralization cycling of artificially generated caries lesions underneath an artificial plaque. Methods: Treatments consisted of exposure to twice daily toothpaste/water slurries prepared from 0, 1,100, and 5,000 μg/g fluoride (F) NaF/silica toothpastes. In addition, treatments with slurries prepared from 1,100 μg/g F SnF2/silica toothpastes were done using 44Ca in the remineralization solution to allow for differentiation of newly formed mineral and exploration of incorporated metal dopants using ToF-SIMS. Complementary microhardness, scanning electron microscopy, and high-resolution transmission electron microscopy (HR-TEM) investigations were performed on enamel cross sections. Results: HR-TEM was used for the first time to determine the change in crystallinity during remineralization revealing distinct microstructural zones within one lesion. Chemical mapping using ToF-SIMS demonstrated that the distribution of F, while observed primarily in the new mineral phase, was widespread throughout the lesion with 44Ca substantially limited to the remineralizing mineral. Both penetrated the inter-rod spaces of the sound enamel illustrating how acid damage propagates into the native mineral as the caries lesion deepens. HR-TEM examination revealed different regions within the lesion characterized by distinct micro- and ultrastructures. Importantly, HR-TEM revealed a return of crystallinity following remineralization. F dose-response observations verified the ability of these high-resolution techniques to differentiate remineralization efficacy. Conclusion: The collective results provided new insights such as the visualization of F or calcium penetration pathways, as well as new tools to study the caries process.

Benchmarking of Coatings for Cathode Active Materials in Solid-State Batteries Using Surface Analysis and Reference Electrodes.

Fast and reliable evaluation of degradation and performance of cathode active materials (CAMs) for solid-state batteries (SSBs) is crucial to help better understand these systems and enable the synthesis of well-performing CAMs. However, there is a lack of well-thought-out procedures to reliably evaluate CAMs in SSBs. Current approaches often rely on X-ray photoelectron spectroscopy (XPS) for the evaluation of degradation. Unfortunately, XPS sensitivity is not very high, and minor but relevant degradation products may not be detected and distinguished. Furthermore, degradation caused by the current collector (CC) itself is usually not distinguished from CAM-induced degradation. This study uses a modified CC, which allows us to separate electrochemical degradation caused by the CC from degradation at the CAM itself. Using this CC, we present an approach using time-of-flight secondary ions mass spectrometry (ToF-SIMS) that offers high sensitivity and reliability. Principal component analysis (PCA) is applied to differentiate secondary ions as well as identify those mass fragments that correlate with degradation products. This approach also enables distinguishing between different pathways of degradation. To evaluate the kinetic performance of the samples, three-electrode rate tests are performed. Electrochemical characterization evaluates the kinetic performance of the samples under investigation. The samples are finally rated with a score that allows a reliable comparison between the different materials and offers a complete picture of the materials' characteristics in terms of electrochemical performance and degradation.

Novel principal component analysis tool based on python for analysis of complex spectra of time-of-flight secondary ion mass spectrometry

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is a powerful surface analysis tool, which can simultaneously provide elemental, isotopic, and molecular information with part per million (ppm) sensitivity. However, each spectrum may be composed of hundreds of ion signals, which makes the spectra data complex. Principal component analysis (PCA) is a multivariate analysis technique that has been widely used to figure out the variances among samples in ToF-SIMS spectra data analysis and is showing great success in the explanation of complex ToF-SIMS spectra. So far, several software tools have been developed for PCA of ToF-SIMS spectra; however, none of them are freely available. Such a situation leads to some difficulties in extending applications of PCA to various research fields. More importantly, it has long been challenging for common researchers to understand PCA plots and extract chemical differences among samples. In this work, we developed a new and flexible software tool (named “advanced spectra pca toolbox”) based on python for PCA of complex ToF-SIMS spectra along with an easy-to-read manual. It can generate data analysis reports automatically to explain chemical differences among samples, allowing less experienced researchers to easily understand tricky PCA results. Moreover, it is expandable and compatible with artificial intelligence/machine learning functions. Pure goethite and different lignin adsorbed goethite samples were used as a model system to demonstrate our new software tool, proving that our software tool can be readily used in complex spectra data processing. Our new software tool is open-source, convenient, flexible, and expandable. We expect this open-source tool will benefit the ToF-SIMS community.

Mechanistic interpretation of the sorption of terbuthylazine pesticide onto aged microplastics

Microplastics (MPs) pose a global concern due to their ubiquitous distribution. Once in the environment, they are subject to aging, which changes their chemical-physical properties and ability to interact with organic pollutants, such as pesticides. Therefore, this study investigated the interaction of the hydrophobic herbicide terbuthylazine (TBA), which is widely used in agriculture, with artificially aged polyethylene (PE) MP (PE-MP) to understand how aging affects its sorption. PE was aged by an accelerated weathering process including UV irradiation, hydrogen peroxide, and ultrasonic treatment, and aged particles were characterized in comparison to pristine particles. Sorption kinetics were performed for aged and pristine materials, while further sorption studies with aged PE-MP included determining environmental factors such as pH, temperature, and TBA concentration. Sorption of TBA was found to be significantly lower on aged PE-MP compared to pristine particles because aging led to the formation of oxygen-containing functional groups, resulting in a reduction in hydrophobicity and the formation of negatively charged sites on oxidized surfaces. For pristine PE-MP, sorption kinetics were best described by the pseudo-second-order model, while it was intra-particle diffusion for aged PE-MP as a result of crack and pore formation. Sorption followed a decreasing trend with increasing pH, while it became less favorable at higher temperatures. The isotherm data revealed a complex sorption process on altered, heterogeneous surfaces involving hydrophobic interactions, hydrogen bonding, and π-π interactions, and the process was best described by the Sips adsorption isotherm model. Desorption was found to be low, confirming a strong interaction. However, thermodynamic results imply that increased temperatures, such as those resulting from climate change, could promote the re-release of TBA from aged PE-MP into the environment. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) confirmed TBA sorption onto PE.

Self-Assembled Monolayers of a Fluorinated Phosphonic Acid as a Protective Coating on Aluminum

Aluminum (Al) placed in hot water (HW) at 90 °C is roughened due to its reaction with water, forming Al hydroxide and Al oxide, as well as releasing hydrogen gas. The roughened surface is thus hydrophilic and possesses a hugely increased surface area, which can be useful in applications requiring hydrophilicity and increased surface area, such as atmospheric moisture harvesting. On the other hand, when using HW to roughen specified areas of an Al substrate, ways to protect the other areas from HW attacks are necessary. We demonstrated that self-assembled monolayers (SAMs) of a fluorinated phosphonic acid (FPA, CF3(CF2)13(CH2)2P(=O)(OH)2) derivatized on the native oxide of an Al film protected the underneath metal substrate from HW attack. The intact wettability and surface morphology of FPA-derivatized Al subjected to HW treatment were examined using contact angle measurement, and scanning electron microscopy and atomic force microscopy, respectively. Moreover, the surface and interface chemistry of FPA-derivatized Al before and after HW treatment were investigated by time-of-flight secondary ion mass spectrometry (ToF-SIMS), verifying that the FPA SAMs were intact upon HW treatment. The ToF-SIMS results therefore explained, on the molecular level, why HW treatment did not affect the underneath Al at all. FPA derivatization is thus expected to be developed as a patterning method for the formation of hydrophilic and hydrophobic areas on Al when combined with HW treatment.

Hydroxyl transport mechanisms upon passivation of Cr-Fe-Co-Ni-Mo multi-principal element alloy surfaces investigated by isotopic labelling

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) combined with deuterium labelling (D2O), and X-ray photoelectron spectroscopy (XPS) were applied to investigate the interfacial transport mechanisms of hydroxyls between aqueous electrolyte and outer part of the protective oxide film during passivation of Cr15Fe10Co5Ni60Mo10 multi-principal element alloy surfaces. A ToF-SIMS signal treatment methodology was developed to retrieve the in-depth distribution of deuterated hydroxides in the nanometer-thick surface oxide film. After immersion at free potential or anodic passivation in acidified D2O, the initial bilayer structure is retained. The use of heavy water electrolyte has no effect on the composition alterations induced by passivation. Deuterated species were detected mostly in the outer layer of the surface oxide film. Pure inward hydroxyl diffusion from electrolyte/oxide to oxide/metal interface is excluded from being primarily responsible for oxide film growth induced by anodic passivation. The hydroxyls from the dissolving hydroxide species are retained in the oxide film and participate in forming Cr hydroxide, thus reducing the hydroxyl surface uptake from the electrolyte. This work provides deeper insight into the mechanisms of oxide growth and corrosion protection induced by anodic passivation.

High-Throughput Quantitative Analysis of Amino Acids in Freeze-Dried Drops Using Time-of-Flight Secondary Ion Mass Spectrometry.

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) has become a promising analytical tool for molecular profiling in biological applications. However, its ultrahigh vacuum environment and matrix effects hamper the absolute quantitation of solution samples. Herein, we present a rapid high-throughput platform for quantitative ToF-SIMS analysis of amino acids in matrix deposits formed from freeze-dried solution drops through ice sublimation on a parylene film microarray substrate. Droplets of the amino acid solutions, which were mixed with stable isotope-labeled phenylalanine (F*) of high concentration (10 mM), were loaded on wells of the microarray, then frozen and evaporated slowly below the freezing point, forming continuous solid-phase F* matrix deposits. The amino acids (≤500 μM), adequately well dispersed throughout the F* matrix deposits on each well, were quantitatively analyzed by ToF-SIMS in a rapid and high-throughput fashion. The lower limit of quantitation reached below 10 μM.