Coupling of Laser Ablation and the Liquid Sampling-Atmospheric Pressure Glow Discharge Plasma for Simultaneous, Comprehensive Mapping: Elemental, Molecular, and Spatial Analysis

Abstract

The spatial distributions of elemental and molecular species are vital pieces of information for a broad number of applications such as material development and bio/environmental analysis. There is currently no single analytical method that can simultaneously acquire elemental, molecular, and spatial information from a single sample. This paper presents the coupling of an NWR213 laser ablation (LA) system to the liquid sampling-atmospheric pressure glow discharge (LS-APGD) microplasma for combined atomic and molecular (CAM) analysis. The work demonstrates a fundamental balance that must be considered between the extent of fragmentation of molecules and ionization of atoms for CAM analysis. Detailed studies showed that the interelectrode gap to be a critical parameter for controlling the ionization efficiency of atomic and molecular species. Utilizing Design-of-Experiment (DoE) procedures, the discharge current was also found to be a significant parameter to control. Elemental lead, caffeine, and simultaneous lead and caffeine analysis via LA-LS-APGD-MS was made possible through improved understanding of the influence of plasma parameters on the product mass spectra of laser-ablated particles. Finally, a chemical map of elemental lead and molecular caffeine, from lead nitrate and caffeine residues, was generated, demonstrating the comprehensive mapping capabilities of LA-LS-APGD-MS. The practical relevance of the capabilities is demonstrated by mapping glutamic acid from a cryosectioned chicken breast with a thallium spike deposited within the tissue. It is believed that the LA-LS-APGD-MS could be a valuable methodology for the simultaneous mapping of elemental and molecular species from a variety of samples.

Laser-induced excitation mechanisms and phase transitions in spectrochemical analysis – Review of the fundamentals

“…Next to LA-ICP-MS, LA-ICP-AES and LIBS, many other laser-based spectrochemical analysis methods have namely been developed (see Figure 1). One class of alternatives employ a different ionization process between the laser ablation stage and the spectrometer, such as atmospheric pressure chemical ionization (LA-APCI-MS) [10,11], ambient desorption/ionization (LA-ADI-MS) [12], electrospray ionization (LA-ESI-MS) [13][14][15][16] or liquid sampling-atmospheric pressure glow discharge (LA-LS-APGD-MS) [17,18]. The laser ablated particles can also be caught first into a liquid phase before further analysis, by extraction techniques as liquid vortex capture (LA-LVC-ESI-MS) [19] or a liquid microjunction surface sampling probe coupled to high-precision liquid chromatography (LA-LMJSSP-HPLC-ESI-MS) [20].…”

Improved Uranium Isotope Ratio Analysis in Liquid Sampling–Atmospheric Pressure Glow Discharge/Orbitrap FTMS Coupling through the Use of an External Data Acquisition System

“…15 In addition to its use in atomic (elemental) mass spectrometry, the LS-APGD has been demonstrated to serve as a combined atomic and molecular (CAM) ionization source, effectively ionizing small polar molecules, polyaromatic hydrocarbons, and proteins using the same hardware; 18−21 indeed doing so simultaneously. 22 Of direct relevance to the effort here, prior implementations have demonstrated the capabilities of the LS-APGD coupled to Orbitrap Fourier transform mass spectrometers (FTMS) for uranium isotope ratio (IR) analysis, with UO 2 being the measured species (illustrated in Figure S1, Supporting Information). 23−28 In each of these works, the system was found to meet the International Atomic Energy Agency's (IAEA) International Target Values (ITV) for measurement uncertainty for various enrichment levels of uranium.…”

“…In recent years, the application of microplasma sources for spectrochemical analysis has garnered general attention in hopes of reducing operational overhead, sample and waste volumes, and the potential for instrument transportability. − The liquid sampling–atmospheric pressure glow discharge (LS-APGD) microplasma source has been developed by Marcus and co-workers at Clemson University, , with mass spectrometric advances begun in collaboration with Koppenaal et al at the Pacific Northwest National Laboratory. , The LS-APGD is a low cost, low power (<50 W), and low consumption ionization source with gas flow rates of <1 L min –1 and solution flow rates of <50 μL min –1 , while operating with total consumption of analyte-containing solutions . In addition to its use in atomic (elemental) mass spectrometry, the LS-APGD has been demonstrated to serve as a combined atomic and molecular (CAM) ionization source, effectively ionizing small polar molecules, polyaromatic hydrocarbons, and proteins using the same hardware; − indeed doing so simultaneously …”

Resolving Severe Elemental Isobaric Interferences with a Combined Atomic and Molecular Ionization Source–Orbitrap Mass Spectrometry Approach: The 87Sr and 87Rb Geochronology Pair

“…32 Recently, simultaneous CAM ionization has been demonstrated in the LA mapping of synthetic and natural materials. 33 Unlike dispersive-type mass spectrometers that increase resolution by reducing slit widths, and thus reduce ion transmission, Fourier transform instruments achieve higher resolution by trapping the ions and measuring the same ion packet for extended periods of time. As described by Hoegg et al, 16 Eiler et al, 18 and Marshall, 34 there should also be a corresponding increase in measurement precision at longer transient lengths, so long as sufficient signal integrity is maintained.…”

“…Importantly, the microplasma accepts a variety of sample forms via introduction by laser ablation (LA), ambient desorption (AD), and the use of “plate reader” technology . Recently, simultaneous CAM ionization has been demonstrated in the LA mapping of synthetic and natural materials …”