Jill R. Scott

Effect of atmospheric conditions on LIBS spectra.

Laser-induced breakdown spectroscopy (LIBS) is typically performed at ambient Earth atmospheric conditions. However, interest in LIBS in other atmospheric conditions has increased in recent years, especially for use in space exploration (e.g., Mars and Lunar) or to improve resolution for isotopic signatures. This review focuses on what has been reported about the performance of LIBS in reduced pressure environments as well as in various gases other than air.

Glycine Identification in Natural Jarosites Using Laser Desorption Fourier Transform Mass Spectrometry: Implications for the Search for Life on Mars

The jarosite group minerals have received increasing attention since the discovery of jarosite on the martian surface by the Mars Exploration Rover Opportunity. Given that jarosite can incorporate foreign ions within its structure, we have investigated the use of jarosite as an indicator of aqueous and biological processes on Earth and Mars. The use of laser desorption Fourier transform mass spectrometry has revealed the presence of organic matter in several jarosite samples from various locations worldwide. One of the ions from the natural jarosites has been attributed to glycine because it was systematically observed in combinations of glycine with synthetic ammonium and potassium jarosites, Na(2)SO(4) and K(2)SO(4). The ability to observe these organic signatures in jarosite samples with an in situ instrumental technique, such as the one employed in this study, furthers the goals of planetary geologists to determine whether signs of life (e.g., the presence of biomolecules or biomolecule precursors) can be detected in the rock record of terrestrial and extraterrestrial samples.

Highly Reproducible Laser Beam Scanning Device for an Internal Source Laser Desorption Microprobe Fourier Transform Mass Spectrometer

Traditionally, mass spectrometry has relied on manipulating the sample target to provide scanning capabilities for laser desorption microprobes. This has been problematic for an internal source laser desorption Fourier transform mass spectrometer (LD-FTMS) because of the high magnetic field (7 Tesla) and geometric constraints of the superconducting magnet bore. To overcome these limitations, we have implemented a unique external laser scanning mechanism for an internal source LD-FTMS. This mechanism provides adjustable resolution enhancement so that the spatial resolution at the target is not limited to that of the stepper motors at the light source (∼5 μm/step). The spatial resolution is now limited by the practical optical diffraction limit of the final focusing lens. The scanning mechanism employs a virtual source that is wavelength independent up to the final focusing lens, which can be controlled remotely to account for focal length dependence on wavelength. A binary index provides an automatic align...

Recovery of phosphonate surface contaminants from glass using a simple vacuum extractor with a solid-phase microextraction fiber

Recovery of chemical contaminants from fixed surfaces for analysis can be challenging, particularly if it is not possible to acquire a solid sample to be taken to the laboratory. A simple device is described that collects semi-volatile organic compounds from fixed surfaces by creating an enclosed volume over the surface, then generating a modest vacuum. A solid-phase microextraction (SPME) fiber is then inserted into the evacuated volume where it functions to sorb volatilized organic contaminants. The device is based on a syringe modified with a seal that is used to create the vacuum, with a perforable plunger through which the SPME fiber is inserted. The reduced pressure speeds partitioning of the semi-volatile compounds into the gas phase and reduces the boundary layer around the SPME fiber, which enables a fraction of the volatilized organics to partition into the SPME fiber. After sample collection, the SPME fiber is analyzed using conventional gas chromatography/mass spectrometry. The methodology has been used to collect organophosphorus compounds from glass surfaces, to provide a simple test for the functionality of the devices. Thirty minute sampling times (ΔT(vac)) resulted in fractional recovery efficiencies that ranged from 10(-3) to >10(-2), and in absolute terms, collection of low nanograms was demonstrated. Fractional recovery values were positively correlated to the vapor pressure of the compounds being sampled. Fractional recovery also increased with increasing ΔT(vac) and displayed a roughly logarithmic profile, indicating that an operational equilibrium is being approached. Fractional recovery decreased with increasing time between exposure and sampling; however, recordable quantities of the phosphonates could be collected three weeks after exposure.

Practical high-resolution detection method for laser-induced breakdown spectroscopy

A Fabry-Perot etalon was coupled to a Czerny-Turner spectrometer to acquire high-resolution measurements in laser-induced breakdown spectroscopy (LIBS). The spectrometer was built using an inexpensive etalon coupled to a standard 0.5 m imaging spectrometer. The Hg emission doublet at 313.2 nm was used to evaluate instrument performance because it has a splitting of 29 pm. The 313.2 nm doublet was chosen due to the similar splitting seen in isotope splitting from uranium at 424.437 nm, which is 25 pm. The Hg doublet was easily resolved from a continuous-source Hg lamp with a 2 s acquisition. The doublet was also resolved in LIBS spectra of cinnabar (HgS) from the accumulation of 600 laser shots at rate of 10 Hz, or 1 min, under a helium atmosphere. In addition to the observed splitting of the 313.2 nm Hg doublet, the FWHM of the 313.1844 nm line from the doublet is reported at varying helium atmospheric pressures. The high performance, low cost, and compact footprint make this system highly competitive with 2 m double-pass Czerny-Turner spectrometers.

Direct LD-FTMS detection of mineral-associated PAHs and their influence on the detection of co-existing amino acids

Polycyclic aromatic hydrocarbon (PAH) compounds and amino acids (AAs) are both ubiquitous throughout the universe and can be co-located in mineral matrices (e.g., meteorites); therefore, co-detection of PAHs and AAs associated with terrestrial and extra-terrestrial minerals is of interest. Nine PAH compounds representing four chemical classes of PAH (unsubstituted, acetyl-, amino-, and nitro-substituted) were applied onto the surface of quartz, plagioclase, olivine, and ilmenite mineral standards and analyzed using laser desorption/ionization Fourier transform mass spectrometry (LD-FTMS). Mass-to-charge peaks derived from PAH compounds were detected from the surfaces of all minerals evaluated. All PAH compounds were detected in the positive ion mode, whereas only nitro-substituted PAH compounds were detected in negative ion mode. In this and earlier studies, the ability to directly detect mineral-associated AAs by LD-FTMS was dependent on the mineral geomatrix. On iron-bearing minerals AAs appeared as highly fragmented ions in the spectra or were not detectable; however, the addition of the PAH chrysene enabled the ionization and detection of AAs threonine and histidine by LD-FTMS. Thus, for mineral systems such as meteorites, interstellar dust particles, soils, and sediments, the co-detection of AAs associated with PAHs by LD-FTMS is feasible.

Detection of Biosignatures by Geomatrix-Assisted Laser Desorption/Ionization (GALDI) Mass Spectrometry

Identification of mineral-associated biosignatures is of significance for retrieving biochemical information from geological records here on Earth and for detecting signs of life on other planets, such as Mars. An investigation using laser desorption Fourier transform mass spectrometry was conducted to determine whether geomatrix-assisted laser desorption/ionization (GALDI) can be used to detect amino acids (e.g., histidine, threonine, and cysteine) and small proteins (e.g., gramicidin S) associated with mineral phases and whether the geomatrix impacts detection. Iron oxide (Fe2 O 3 ) and sodium chloride (NaCl) were investigated as clean chemical analogues of hematite and halite, respectively, which have both been detected on the surface of Mars. Samples were prepared by 2 methods: (1) application of analyte solution to the geomatrix surface with subsequent drying; and (2) physical mixing of analyte and geomatrix. Amino acids incorporated within NaCl by physical mixing yielded a better signal-to-noise ratio than those that were applied to the surface of a NaCl pellet. The composition of the geomatrix had an influence on the detection of biomolecules. Peaks corresponding to the cation-attached biomolecular ions were observed for the NaCl prepared samples. However, no biomolecular ion species were observed in samples using Fe 2 O 3 as geomatrix. Instead, only minor peaks that may correspond to ions derived from fragments of the biomolecules were obtained.

Automated Analysis of Mass Spectral Data Using Fuzzy Logic Classification

Automation of the instrument has also been described in the literature. It includes a Fuzzy-logic inference engine that color codes ‘pixels’ according to classification. A user friendly graphical interface (Figure 2) allows the user to check the cursor from one spot to the next; the user can see the line spectrum the inference engine used to generate that pixel. Data can then be displayed directly in the program or exported in formats compatible with commercial graphics programs.

Automation and Control of an Imaging Internal Laser Desorption Fourier Transform Mass Spectrometer (I2LD-FTMS)

This paper describes the automation of an imaging internal source laser desorption Fourier transform mass spectrometer (I2LD-FTMS). The I2LD-FTMS consists of a laser-scanning device [Scott and Tremblay, Rev. Sci. Instrum. 2002, 73, 1108–1116] that has been integrated with a laboratory-built FTMS using a commercial data acquisition system (ThermoFinnigan FT/MS, Bremen, Germany). A new user interface has been developed in National Instruments (Austin, Texas) graphical programming language LabVIEW to control the motors of the laser positioning system and the commercial FTMS data acquisition system. A feature of the FTMS software that allows the user to write macros in a scripting language is used creatively to our advantage in creating a mechanism to control the FTMS from outside its graphical user interface. The new user interface also allows the user to configure target locations. Automation of the data analysis along with data display using commercial graphing software is also described.

Exploring Biosignatures Associated with Thenardite by Geomatrix-Assisted Laser Desorption/Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (GALDI-FTICR-MS)

Geomatrix-assisted laser desorption/ionization (GALDI) in conjunction with a Fourier transform ion cyclotron resonance mass spectrometer (FTICR-MS) has been employed to determine how effectively bio/organic molecules associated with the mineral thenardite (Na 2 SO 4 ) can be detected. GALDI is based on the ability of the mineral host to assist desorption and ionization of bio/organic molecules without additional sample preparation. When glycine was mixed with thenardite, glycine was deprotonated to produce C 2 H 4 NO 2 − at m/z 74.025. The combination of stearic acid with thenardite produced a complex cluster ion at m/z 390.258 in the negative mode, which was assigned a composition of C 18 H 39 O 7 Na−. A natural sample of thenardite from Searles Lake in California also produced a peak at m/z 390.260. The bio/organic signatures in both the laboratory-based and natural samples were heterogeneously dispersed as revealed by chemical imaging. The detection limits for the stearic acid and thenardite combination were estimated to be 3 parts per trillion or ∼7 zeptomoles (10 − 21 ) per laser spot. Attempts to improve the signal-to-noise ratio by co-adding FTICR-MS data predetermined to contain the biosignatures of interest revealed problems due to a lack of phase coherence between data sets.