Improved limit of detection of a high-resolution fs-LIMS instrument through mass-selective beam blanking

Laser Ablation Ionisation Mass Spectrometry (LIMS) is an important quantitative method for chemical analysis of solids. Current limits of detections (LoDs) of LIMS instruments are in the ppm to sub-ppm range (atomic fractions), while other commonly used techniques for solid sample analysis reach LoDs at ppb levels or even below. This study presents the implementation of mass-selective beam blanking in the Laser Mass Spectrometer – Gran Turismo (LMS-GT) to improve the instruments’ detection limit. LMS-GT is a high-performance time-of-flight LIMS instrument coupled to a femtosecond laser ablation ion source reaching micrometre spatial resolutions and mass resolutions 12′000. A fast high voltage switch was developed in-house to induce potential changes at an Einzel lens at the intermediate time focus of the ion trajectory, leading to short deflections of the ion beam and hindering selected species from reaching the detector. The intensities of single mass lines are reduced with 100% efficiency to below the noise floor when blanked. The detector gain can safely be increased while blanking the most intense mass lines simultaneously, thus improving the detection limit. The LoD of LMS-GT prior to the installation of the mass-selective blanking device was at ppm level (at. frac.) with few sub-ppm detections, the installation pushed it to the lower ppb range, without compromising the initial performance. This emphasises that fs-LIMS can be a powerful quantitative technique for the chemical analysis of solids, with the potential to reach the levels of mass spectrometric analysis achievable with Secondary Ion Mass Spectrometry (SIMS) and Laser Ablation–Inductively Coupled Plasma–Mass Spectrometry (LA-ICP-MS)

Correlation Network Analysis for Amino Acid Identification in Soil Samples With the ORIGIN Space-Prototype Instrument

The detection of biomolecules on Solar System bodies can help us to understand how life emerged on Earth and how life may be distributed in our Solar System. However, the detection of chemical signatures of life on planets or their moons is challenging. A variety of parameters must be considered, such as a suited landing site location, geological and environmental processes favourable to life, life detection strategies, and the application of appropriate and sensitive instrumentation. In this contribution, recent results obtained using our novel laser desorption mass spectrometer ORganics INformation Gathering Instrument (ORIGIN), an instrument designed for in situ space exploration, are presented. We focus in this paper on the detection and identification of amino acid extracts from a natural permafrost sample, as well as in an analogue mixture of soils and amino acids. The resulting dataset was analysed using a correlation network analysis method. Based on mass spectrometric correlation, amino acid signatures were separated from soil signatures, identifying chemically different molecular components in complex samples. The presented analysis method represents an alternative to the typically applied spectra-by-spectra analysis for the evaluation of mass spectrometric data and, therefore, is of high interest for future application in space exploration missions

Characterization of bio-organic and inorganic chemistries using Laser-based Mass Spectrometry

This thesis contributes to the field of in-situ analytical chemistry by further expanding the measurement capabilities of a miniature laser ablation/ionization mass spectrometer (LIMS). The current version of LIMS used in this thesis was developed for in-situ space applications and represents the space-ready prototype of original size and figures of merit. The thesis expands on analytical problems related to the accurate measurement, classification, and identification of mass spectra registered from early (primitive) life and various minerals of inorganic origin. The investigated subjects cover specific aspects of ion generation in time-of-flight mass spectrometry, signal processing, and machine learning, applied to the large mass spectrometric data. The thesis outlines effective solutions for unsupervised characterization of compounds using graph theory and relational data analysis. The current state of space exploration places the identification of signatures of life on Mars among the biggest challenges of our time and represents the frontier of science. The challenge of unambiguous and deterministic identification of biogenicity of the given sample (of unknown origin) is an outstanding problem that requires identification of the range of biological signatures (biosignatures) on the micrometer scale and demands the presence of unique patterns and characteristics that as a whole indicate biological processing. This thesis explores the quality of chemical information that could be gathered from Precambrian microscopic fossils (microfossils) using three different wavelengths of the femtosecond laser radiation used as an ion source in the current LIMS system. The thesis discusses various aspects of mass spectrometric imaging and classification of spectra using the graph-theoretic approaches. Furthermore, the implementation of spectral similarity (proximity) networks will showcase the potential for the deterministic identification of bio-organic and inorganic chemistries. The current results provided in this thesis show high utility and perhaps, yet uncovered potential and importance of LIMS as an analytical method that can be used in future space exploration programs

Chemical identification of microfossils from the 1.88‐Ga Gunflint chert: Towards empirical biosignatures using laser ablation ionization mass spectrometer

In this contribution, we investigated the chemical composition of Precambrianmicrofossils from the Gunflint chert (1.88 Ga) using a miniature laser ablationionization mass spectrometer (LIMS) developed for in situ space applications.Spatially resolved mass spectrometric imaging (MSI) and depth profilingresulted in the acquisition of 68,500 mass spectra. Using single mass unit spec-tral decomposition and multivariate data analysis techniques, we identified thelocation of aggregations of microfossils and surrounding inorganic host min-eral. Our results show that microfossils have unique chemical compositionsthat can be distinguished from the inorganic chert with high fidelity. Chemicaldepth profiling results also show that with LIMS microprobe data, it is possibleto identify chemical differences between individual microfossils, thereby pro-viding new insights about nature of early life. Analysis of LIMS spectraacquired from the individual microfossils revea ls complex mineralization,which can reflect the metabolic diversity of the Gunflint microbiome. Anintensity-based machine learning model trained on LIMS Gunflint data mightbe applied for the future investigations of putative microfossils from silicifiedmatrices, where morphological integrity of investigated structures is lost, andpotentially in the investigation of rocks acquired from the Martian surfac

On Topological Analysis of fs-LIMS Data. Implications for in Situ Planetary Mass Spectrometry

In this contribution, we present results of non-linear dimensionality reduction and classification of the fs laser ablation ionization mass spectrometry (LIMS) imaging dataset acquired from the Precambrian Gunflint chert (1.88 Ga) using a miniature time-of-flight mass spectrometer developed for in situ space applications. We discuss the data generation, processing, and analysis pipeline for the classification of the recorded fs-LIMS mass spectra. Further, we define topological biosignatures identified for Precambrian Gunflint microfossils by projecting the recorded fs-LIMS intensity space into low dimensions. Two distinct subtypes of microfossil-related spectra, a layer of organic contamination and inorganic quartz matrix were identified using the fs-LIMS data. The topological analysis applied to the fs-LIMS data allows to gain additional knowledge from large datasets, formulate hypotheses and quickly generate insights from spectral data. Our contribution illustrates the utility of applying spatially resolved mass spectrometry in combination with topology-based analytics in detecting signatures of early (primitive) life. Our results indicate that fs-LIMS, in combination with topological methods, provides a powerful analytical framework and could be applied to the study of other complex mineralogical samples

Multiwavelength Ablation/Ionization and Mass Spectrometric Analysis of 1.88 Ga Gunflint Chert.

The investigation of chemical composition on planetary bodies without significant sample processing is of importance for nearly every mission aimed at robotic exploration. Moreover, it is a necessary tool to achieve the longstanding goal of finding evidence of life beyond Earth, for example, possibly preserved microbial remains within martian sediments. Our Laser Ablation Ionization Mass Spectrometer (LIMS) is a compact time-of-flight mass spectrometer intended to investigate the elemental, isotope, and molecular composition of a wide range of solid samples, including e.g., low bulk density organic remains in microfossils. Here, we present an overview of the instrument and collected chemical spectrometric data at the micrometer level from a Precambrian chert sample (1.88 Ga Gunflint Formation, Ontario, Canada), which is considered to be a martian analogue. Data were collected from two distinct zones-a silicified host area and a carbon-bearing microfossil assemblage zone. We performed these measurements using an ultrafast pulsed laser system (pulse width of ∼180 fs) with multiple wavelengths (infrared [IR]-775 nm, ultraviolet [UV]-387 nm, UV-258 nm) and using a pulsed high voltage on the mass spectrometer to reveal small organic signals. We investigated (1) the chemical composition of the sample and (2) the different laser wavelengths' performance to provide chemical depth profiles in silicified media. Our key findings are as follows: (1) microfossils from the Gunflint chert reveal a distinct chemical composition compared with the host mineralogy (we report the identification of 24 elements in the microfossils); (2) detection of the pristine composition of microfossils and co-occurring fine chemistry (rare earth elements) requires utilization of the depth profiling measurement protocol; and (3) our results show that, for analysis of heterogeneous material from siliciclastic deposits, siliceous sinters, and cherts, the most suitable wavelength for laser ablation/Ionization is UV-258 nm

High Mass Resolution fs-LIMS Imaging and Manifold Learning Reveal Insight Into Chemical Diversity of the 1.88 Ga Gunflint Chert

Extraction of useful information from unstructured, large and complex mass spectrometric signals is a challenge in many application fields of mass spectrometry. Therefore, new data analysis approaches are required to help uncover the complexity of such signals. In this contribution, we examined the chemical composition of the 1.88 Ga Gunflint chert using the newly developed high mass resolution laser ionization mass spectrometer (fs-LIMS-GT). We report results on the following: 1) mass-spectrometric multi-element imaging of the Gunflint chert sample; and 2) identification of multiple chemical entities from spatial mass spectrometric data utilizing nonlinear dimensionality reduction and spectral similarity networks. The analysis of 40′000 mass spectra reveals the presence of chemical heterogeneity (seven minor compounds) and two large clusters of spectra registered from the organic material and inorganic host mineral. Our results show the utility of fs-LIMS imaging in combination with manifold learning methods in studying chemically diverse samples