Juan Yao

Improving the Molecular Ion Signal Intensity for In Situ Liquid SIMS Analysis

AbstractIn situ liquid secondary ion mass spectrometry (SIMS) enabled by system for analysis at the liquid vacuum interface (SALVI) has proven to be a promising new tool to provide molecular information at solid–liquid and liquid–vacuum interfaces. However, the initial data showed that useful signals in positive ion spectra are too weak to be meaningful in most cases. In addition, it is difficult to obtain strong negative molecular ion signals when m/z>200. These two drawbacks have been the biggest obstacle towards practical use of this new analytical approach. In this study, we report that strong and reliable positive and negative molecular signals are achievable after optimizing the SIMS experimental conditions. Four model systems, including a 1,8-diazabicycloundec-7-ene (DBU)-base switchable ionic liquid, a live Shewanella oneidensis biofilm, a hydrated mammalian epithelia cell, and an electrolyte popularly used in Li ion batteries were studied. A signal enhancement of about two orders of magnitude was obtained in comparison with non-optimized conditions. Therefore, molecular ion signal intensity has become very acceptable for use of in situ liquid SIMS to study solid–liquid and liquid–vacuum interfaces. Graphical Abstractᅟ

Enhancing the chemical mixture methodology in emergency preparedness and consequence assessment analysis

Emergency preparedness personnel at U.S. Department of Energy (DOE) facilities use the chemical mixture methodology (CMM) to estimate the potential health impacts to workers and the public from the unintended airborne release of chemical mixtures. The CMM uses a Hazard Index (HI) for each chemical in a mixture to compare a chemicals concentration at a receptor location to an appropriate concentration limit for that chemical. This limit is typically based on Protection Action Criteria (PAC) values developed and published by the DOE. As a first cut, the CMM sums the HIs for all the chemicals in a mixture to conservatively estimate their combined health impact. A cumulative HI>1.0 represents a concentration exceeding the concentration limit and indicates the potential for adverse health effects. Next, Health Code Numbers (HCNs) are used to identify the target organ systems that may be impacted by exposure to each chemical in a mixture. The sum of the HIs for the maximally impacted target organ system is used to provide a refined, though still conservative, estimate of the potential for adverse health effects from exposure to the chemical mixture. This paper explores approaches to enhance the effectiveness of the CMM by using HCN weighting factors. A series of 24 case studies have been defined to evaluate both the existing CMM and three new approaches for improving the CMM. The first approach uses a set of HCN weighting factors that are applied based on the priority ranking of the HCNs for each chemical. The second approach uses weighting factors based on the priority rankings of the HCNs established for a given type of concentration limit. The third approach uses weighting factors that are based on the exposure route used to derive PAC values and a priority ranking of the HCNs (the same ranking as used in the second approach). Initial testing indicates that applying weighting factors increases the effectiveness of the CMM in general, though care must be taken to avoid introducing non-conservative results. In the near future, additional testing and analysis will be conducted that may lead to the adoption of one of the tested approaches into the CMM.

In Situ Correlative Imaging and Spectroscopy of Boehmite Particles in Liquid

This work presents an example of in situ imaging of boehmite (AlOOH) particles, suspended in liquid, in a vacuum compatible microfluidic sample holder using a suite of tools including scanning electron microscopy (SEM) and time-of-flight secondary ion mass spectrometry (ToF-SIMS), highlighting the advantage of multiscale analysis in material sciences. Nanometer-sized boehmite particles exist in highlevel radioactive wastes at the Hanford site. [1] It is known that they are difficult to dissolve and cause rheological problems for processing in the nuclear waste treatment plant. Therefore, it is important to understand how boehmite particles form aggregates in waste tanks. Of particular interest is the pH effect on the boehmite aggregation and morphological change simulating tank waste relevant conditions.

Mesoscopic Structure Facilitates Rapid CO2 Transport and Reactivity in CO2-Capture Solvents

Mass transfer coefficients of CO2 are anomalously high in water-lean solvents as compared to aqueous amines. Such phenomena are intrinsic to the molecular and nanoscale structure of concentrated organic CO2 capture solvents. To decipher the connections, we performed in situ liquid time-of-flight secondary ionization mass spectroscopy on a representative water-lean solvent, 1-((1,3-Dimethylimidazolidin-2-ylidene)amino)propan-2-ol (IPADM-2-BOL). Two-dimensional (2D) and three-dimensional (3D) chemical mapping of the solvent revealed that IPADM-2-BOL exhibited a heterogeneous molecular structure with regions of CO2-free solvent coexisting with clusters of zwitterionic carbonate ions. Chemical mapping were consistent with molecular dynamic simulation results, indicating CO2 diffusing through pockets and channels of unreacted solvent. The observed mesoscopic structure promotes and enhances the diffusion and reactivity of CO2, likely prevalent in other water-lean solvents. This finding suggests that if the size, shape and orientation of the domains can be controlled, more efficient CO2 capture solvents could be developed to enhance mass-transfer and uptake kinetics.

In Situ Imaging and Spectroscopy of Particles in Liquid

This work presents an example of in situ imaging of particles, suspended in liquid, in a vacuum compatible microfluidic sample holder using a suite of tools including scanning electron microscopy (SEM) and time-of-flight secondary ion mass spectrometry (ToF-SIMS), highlighting the advantage of multiscale analysis in material sciences. Nanometer-sized boehmite (AlOOH) particles synthesized at our laboratory are used as a model system in this work [1]. Such particles exist in high-level radioactive wastes at the Hanford site. It is known that they are difficult to dissolve and cause rheological problems for processing in the nuclear waste treatment plant. Therefore, it is important to build the capability to characterize boehmite particles suspended in liquid.

In Situ Characterization of Boehmite Particles in Water Using Liquid SEM

In situ imaging and elemental analysis of boehmite (AlOOH) particles in water is realized using the System for Analysis at the Liquid Vacuum Interface (SALVI) and Scanning Electron Microscopy (SEM). This paper describes the method and key steps in integrating the vacuum compatible SAVLI to SEM and obtaining secondary electron (SE) images of particles in liquid in high vacuum. Energy dispersive x-ray spectroscopy (EDX) is used to obtain elemental analysis of particles in liquid and control samples including deionized (DI) water only and an empty channel as well. Synthesized boehmite (AlOOH) particles suspended in liquid are used as a model in the liquid SEM illustration. The results demonstrate that the particles can be imaged in the SE mode with good resolution (i.e., 400 nm). The AlOOH EDX spectrum shows significant signal from the aluminum (Al) when compared with the DI water and the empty channel control. In situ liquid SEM is a powerful technique to study particles in liquid with many exciting applications. This procedure aims to provide technical know-how in order to conduct liquid SEM imaging and EDX analysis using SALVI and to reduce potential pitfalls when using this approach.

In Situ Characterization of Shewanella oneidensis MR1 Biofilms by SALVI and ToF-SIMS

Bacterial biofilms are surface-associated communities that are vastly studied to understand their self-produced extracellular polymeric substances (EPS) and their roles in environmental microbiology. This study outlines a method to cultivate biofilm attachment to the System for Analysis at the Liquid Vacuum Interface (SALVI) and achieve in situ chemical mapping of a living biofilm by time-of-flight secondary ion mass spectrometry (ToF-SIMS). This is done through the culturing of bacteria both outside and within the SALVI channel with our specialized setup, as well as through optical imaging techniques to detect the biofilm presence and thickness before ToF-SIMS analysis. Our results show the characteristic peaks of the Shewanella biofilm in its natural hydrated state, highlighting upon its localized water cluster environment, as well as EPS fragments, which are drastically different from the same biofilms dehydrated state. These results demonstrate the breakthrough capability of SALVI that allows for in situ biofilm imaging with a vacuum-based chemical imaging instrument.

Correlative Imaging and Spectroscopy of Particles in Liquid

Correlative imaging and spectroscopy has been widely used in biological and medical sciences. Its power of providing a holistic view of the system of interest makes it an intense research topic that often utilizes correlative optical microscopy, cryo electron microscopy, and a variety of spectroscopy techniques. With the advent of liquid handling in vacuum, in situ electron microscopy has become increasingly popular in studying complex systems, adding another palette in correlative imaging and spectroscopy. This work presents an example of characterization of particles suspended in liquid in a vacuum compatible microfluidic sample holder using a suite of tools including scanning electron microscopy (SEM), transmission electron microscopy (TEM), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and synchrotron vacuum UV (VUV) single photon ionization mass spectrometry (SPI-MS), highlighting the advantage of multiscale analysis in material sciences.

Summer 2012 Testing and Analysis of the Chemical Mixture Methodology -- Part I

This report presents the key findings made by the Chemical Mixture Methodology (CMM) project team during the first stage of their summer 2012 testing and analysis of the CMM. The study focused on answering the following questions: o What is the percentage of the chemicals in the CMM Rev 27 database associated with each Health Code Number (HCN)? How does this result influence the relative importance of acute HCNs and chronic HCNs in the CMM data set? o What is the benefit of using the HCN-based approach? Which Modes of Action and Target Organ Effects tend to be important in determining the HCN-based Hazard Index (HI) for a chemical mixture? o What are some of the potential issues associated with the current HCN-based approach? What are the opportunities for improving the performance and/or technical defensibility of the HCN-based approach? How would those improvements increase the benefit of using the HCN-based approach? o What is the Target Organ System Effect approach and how can it be used to improve upon the current HCN-based approach? How does the benefits users would derive from using the Target Organ System Approach compare to the benefits available from the current HCN-based approach?

Enhancing the Benefit of the Chemical Mixture Methodology: A Report on Methodology Testing and Potential Approaches for Improving Performance

Extensive testing shows that the current version of the Chemical Mixture Methodology (CMM) is meeting its intended mission to provide conservative estimates of the health effects from exposure to airborne chemical mixtures. However, the current version of the CMM could benefit from several enhancements that are designed to improve its application of Health Code Numbers (HCNs) and employ weighting factors to reduce over conservatism.