Timothy J. Cornish

Tandem time-of-flight mass spectrometer

A compact, laser desorption tandem time-of-flight mass spectrometer is described. The instrument incorporates two dual-stage reflectron analyzers and a collision region for producing product ions by collision-induced dissociation. Selection of ions of a particular mass is accomplished by deflection of ions from stable trajectory angles entering the second reflectron, while the use of a pulsed valve for introduction of the collision gas obviates the need for differential pumping of the collision region. Initial results are presented, as well as a discussion for optimizing the performance of tandem time-of-flight instruments.

Compact two‐step laser time‐of‐flight mass spectrometer for in situ analyses of aromatic organics on planetary missions

RATIONALE A miniature time-of-flight mass spectrometer measuring 20 cm in length has been adapted to demonstrate two-step laser desorption/ionization (LDI) in a compact instrument package for enhanced organics detection. Two-step LDI decouples the desorption and ionization processes, relative to traditional LDI, in order to produce low-fragmentation mass spectra of organic analytes. Tuning the UV ionization laser energy would allow control of the degree of fragmentation, which might enable better identification of constituent species. METHODS A reflectron time-of-flight mass spectrometer prototype was modified to allow a two-laser configuration, with IR (1064 nm) desorption followed by UV (266 nm) postionization. A relatively low ion extraction voltage of 5 kV was applied at the sample inlet. RESULTS The instrument capabilities and performance were demonstrated with analysis of a model polycyclic aromatic hydrocarbon, representing a class of compounds important to the fields of Earth and planetary science. Two-step laser mass spectrometry (L2MS) analysis of a model PAH, pyrene, was demonstrated, including molecular ion identification and the onset of tunable fragmentation as a function of ionizing laser energy. Mass resolution m/Δm = 380 at full width at half-maximum was achieved for gas-phase postionization of desorbed neutrals in this highly compact mass analyzer. CONCLUSIONS Achieving L2MS in a highly miniaturized instrument enables a powerful approach to the detection and characterization of aromatic organics in remote terrestrial and planetary applications. Tunable detection of molecular and fragment ions with high mass resolution, diagnostic of molecular structure, is possible on such a compact L2MS instrument. The selectivity of L2MS against low-mass inorganic salt interferences is a key advantage when working with unprocessed, natural samples, and a mechanism for the observed selectivity is proposed.

Rapid assessment of high value samples: An AOTF-LDTOF spectrometer suite for planetary surfaces

We discuss the development of a miniature near-infrared point spectrometer, operating between 1.7-3.45 μm, based on acousto-optic tunable filter (AOTF) technology. This instrument may be used to screen and corroborate analyses of samples containing organic biomarkers or mineralogical signatures suggestive of extant or extinct organic material collected in situ from planetary surfaces. The AOTF point spectrometer will be paired with a laser desorption time-of-flight (LDTOF) mass spectrometer and will prescreen samples for evidence of volatile or refractory organics before the laser desorption step and subsequent mass spectrometer measurement. We describe the AOTF point spectrometer instrument and present laboratory analysis of geological samples of known astrobiological importance. We also present LDTOF spectra of the same samples analyzed with the AOTF, which highlights the value of a comparative data set with the two instruments. We discuss plans for the integration of the two instruments, which is scheduled to take place in the first half of 2012. The AOTF-LDTOF instrument pairing offers the powerful advantage of cross-checked chemical analyses of individual samples, which can reduce chemical and biological interpretation ambiguities.

A compact tandem two-step laser time-of-flight mass spectrometer for in situ analysis of non-volatile organics on planetary surfaces

Two-step laser desorption mass spectrometry is a well suited technique to the analysis of high priority classes of organics, such as polycyclic aromatic hydrocarbons, present in complex samples. The use of decoupled desorption and ionization laser pulses allows for sensitive and selective detection of structurally intact organic species. We have recently demonstrated the implementation of this advancement in laser mass spectrometry in a compact, flight-compatible instrument that could feasibly be the centerpiece of an analytical science payload as part of a future spaceflight mission to a small body or icy moon.

Tiny-TOF-MALDI mass spectrometry for particulate drug and explosives detection

The MALDI (matrix assisted laser desorption/ionization) technique, widely used to desorb and ionize large biomolecules, is applied here to small molecules having low vapor pressure, such as drugs and explosives. Furthermore, we report the coupling of the MALDI technique with a small, highly portable tiny-TOF (fime-of-flight) mass spectrometer developed in our laboratories. This mass spectrometer is a low voltage coaxial reflectron design with a short flight tube that is specifically designed for low molecular weight substances. The reflectron is designed to operate in two different modes that provide an expremely powerful pseudo-tandem mass spectrometry capability that is crucial for field applications. Using this system we have measured mass spectral signatures for cocaine, heroine, and the explosive RDX in the sub- nanogram range. Also reported here are continued developements on advanced MALDI sampling technologies, sensitivity, and mass resolution enhancements of the tiny-TOF, further decreases in system size and weight, and concepts for field operational systems.

Tandem mass spectrometry on a miniaturized laser desorption time-of-flight mass spectrometer

Tandem mass spectrometry (MS/MS) is a powerful and widely-used technique for identifying the molecular structure of organic constituents of a complex sample. Application of MS/MS to the study of unknown planetary samples on a remote space mission would contribute to our understanding of the origin, evolution, and distribution of extraterrestrial organics in our solar system. Here we report on the realization of MS/MS on a miniaturized laser desorption time-of-flight mass spectrometer (LD-TOF-MS), which is one of the most promising instrument types for future planetary missions. This achievement relies on two critical components: a curved-field reflectron and a pulsed-pin ion gate. These enable use of the complementary post-source decay (PSD) and laser-assisted collision induced dissociation (L-CID) MS/MS methods on diverse measurement targets with only modest investment in instrument resources such as volume and weight. MS/MS spectra of selected molecular targets in various organic standards exhibit excellent agreement when compared with results from a commercial, laboratory-scale TOF instrument, demonstrating the potential of this powerful technique in space and planetary environments.

Analysis of aqueous environments by laser desorption/ionization time-of-flight mass spectrometry

Laser desorption/ionization time-of-flight mass spectrometry (LD-TOF-MS) has been developed and used to characterize different groups of hydrous minerals. We have advanced the technique by including reversed polarity, precision ion gating, and a curved field reflectron mass analyzer. Reversed polarity provides capabilities in achieving complementary compositional information of the materials, and ion gating enhances the selectivity and sensitivity in specific mass ranges. Representative reference minerals including sulfates, clays, serpentine, and naturally collected complex samples have been analyzed by LD-TOF-MS as well as infrared (IR) spectroscopy, to provide supporting information. We demonstrate that mass spectrometry can identify water in mineral species, and reveal the presence of aqueous environments. Miniaturized LD-TOF-MS is a valuable instrument technique for the in situ characterization and analysis of samples as part of future landed planetary missions and astrobiology explorations.

A comparative study of in situ biosignature detection spectroscopy techniques on planetary surfaces

We demonstrate the biosignature detection capabilities of several classes of instruments, including a compact laser desorption/ionization time-of-flight mass spectrometer, an acousto-optic tunable filter IR point spectrometer, a laser-induced breakdown spectrometer, and a scanning electron microscope. We collected biotic and abiotic calcite, gypsum, and manganese oxide samples from Fort Stanton Cave to identify the presence of biomarkers with each instrument class. We find evidence of biologic activity in these samples including the presence of organic molecules, macroscopic and microscopic morphological features consistent with fossilized mircobes, and the presence of trace elements consistent with the biotic precipitation of minerals. The identification of extant or extinct microbial life is best supported by a suite of biosignatures, rather than a single observation. We demonstrate the unique biosignature detection results of each instrument class and discuss the importance of developing an instrument suite for future landed astrobiology missions on other planetary surfaces.

Investigation of the fragmentation of explosives by femtosecond laser mass spectrometry

We use femtosecond laser mass spectrometry (FLMS) to study the fragmentation patterns of solid phase explosive materials subjected to femtosecond laser pulse irradiation. In condensed phase FLMS a compound deposited on a solid substrate is desorbed into vacuum by femtosecond irradiation forming a plume of ionized and neutral species. Positive or negative ions are accelerated by an electric potential, allowed to drift in the field-free region of a time-of-flight (TOF) mass spectrometry instrument, and flight-times are recorded by a micro-channel plate detector and a digital oscilloscope. From the value of the accelerating field and the ion flight time, the mass-to-charge ratio of each ion is obtained. In this paper we report femtosecond laser mass spectra for the positive and negative ions formed by desorbing TNT and RDX with 150 fs pulses centered at 800 nm. The fragmentation pathways for the formation of the observed ions are described and are used to interpret femtosecond laser induced breakdown spectroscopy results.

Molecular analyzer for Complex Refractory Organic-rich Surfaces (MACROS)

The Molecular Analyzer for Complex Refractory Organic-rich Surfaces, MACROS, is a novel instrument package being developed at NASA Goddard Space Flight Center. MACROS enables the in situ characterization of a samples composition by coupling two powerful techniques into one compact instrument package: (1) laser desorption/ionization time-of-flight mass spectrometry (LDMS) for broad detection of inorganic mineral composition and non-volatile organics, and (2) liquid-phase extraction methods to gently isolate the soluble organic and inorganic fraction of a planetary powder for enrichment and detailed analysis by liquid chromatographic separation coupled to LDMS. The LDMS is capable of positive and negative ion detection, precision mass selection, and fragment analysis. Two modes are included for LDMS: single laser LDMS as the broad survey mode and two step laser mass spectrometry (L2MS). The liquid-phase extraction will be done in a newly designed extraction module (EM) prototype, providing selectivity in the analysis of a complex sample. For the sample collection, a diamond drill front end will be used to collect rock/icy powder. With all these components and capabilities together, MACROS offers a versatile analytical instrument for a mission targeting an icy moon, carbonaceous asteroid, or comet, to fully characterize the surface composition and advance our understanding of the chemical inventory present on that body.