Laser-induced Fourier transform ion cyclotron resonance mass spectrometry of organic and inorganic compounds: methodologies and applications

Estimation of the time of zolpidem intake and differentiation between consumption and external contamination using MALDI-MSI for investigations on single hair samples

Estimation of drug ingestion time (event time) and distinguishing between drug ingestion and external contamination are important for interpreting hair analysis results in forensics practice. Here, we present a matrix-assisted laser desorption/ionization-mass spectrometry imaging (MALDI-MSI) method for in situ analysis of intact hair. We applied a longitudinal cutting method for a single hair to analysis authentic hair samples from a victim of a drug-facilitated sexual assault (DFSA) case and zolpidem-soaked hair. MALDI-MSI showed that zolpidem-positive segments distributed at 4-6 mm or 6-8 mm from the root in three single hairs of a DFSA victim collected 25 days after the event, at concentrations ranging from 0.1 to 5.7 pg mm-1, in agreement with the results from segmental analysis using liquid chromatography tandem mass spectrometry (LC-MS/MS). The estimation of drug intake time was about 20-30 days before sampling, which was consistent with the known time of drug intake. This MALDI-MS method allows imaging analysis of trace substances in a single hair and can realize the intuitive reflection of drug taking time. In addition, zolpidem applied by soaking was mainly distributed on both sides of the longitudinal hair shaft, whereas ingested zolpidem was found only in the middle of the hair shaft of the DFSA victim. The MALDI-MS images of unwashed and washed hair suggested that the amount of externally applied drug was decreased by washing, it was still present on surface layer (cuticle) sides although. Visualization using MALDI-MSI could therefore distinguish between drug ingestion and contamination by reflecting the distribution and deposition site of the drug in hair.

How to sample a seizure plant: the role of the visualization spatial distribution analysis of Lophophora williamsii as an example

Natural compounds in plants are often unevenly distributed, and determining the best sampling locations to obtain the most representative results is technically challenging. Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) can provide the basis for formulating sampling guideline. For a succulent plant sample, ensuring the authenticity and in situ nature of the spatial distribution analysis results during MSI analysis also needs to be thoroughly considered. In this study, we developed a well-established and reliable MALDI-MSI method based on preservation methods, slice conditions, auxiliary matrices, and MALDI parameters to detect and visualize the spatial distribution of mescaline in situ in Lophophora williamsii. The MALDI-MSI results were validated using liquid chromatography-tandem mass spectrometry. Low-temperature storage at -80°C and drying of "bookmarks" were the appropriate storage methods for succulent plant samples and their flower samples, and cutting into 40 μm thick sections at -20°C using gelatin as the embedding medium is the appropriate sectioning method. The use of DCTB (trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-propenylidene]malononitrile) as an auxiliary matrix and a laser intensity of 45 are favourable MALDI parameter conditions for mescaline analysis. The region of interest semi-quantitative analysis revealed that mescaline is concentrated in the epidermal tissues of L. williamsii as well as in the meristematic tissues of the crown. The study findings not only help to provide a basis for determining the best sampling locations for mescaline in L. williamsii, but they also provide a reference for the optimization of storage and preparation conditions for raw plant organs before MALDI detection.

Key Points

An accurate in situ MSI method for fresh water-rich succulent plants was obtained based on multi-parameter comparative experiments.Spatial imaging analysis of mescaline in Lophophora williamsii was performed using the above method.Based on the above results and previous results, a sampling proposal for forensic medicine practice is tentatively proposed.

LASER IONIZATION MASS SPECTROMETRY AT 55: QUO VADIS?

Laser ionization mass spectrometry (LIMS) was one of the first practical methods developed for in situ analysis of the surfaces of solid samples. This review will encompass several aspects related to this analytical method. First, we will discuss the process of laser ionization, the influence of the laser type on its performance, and imaging capabilities of this method. In the second chapter, we will follow the historic development of LIMS instrumentation. After a brief overview of the first-generation instruments developed in 1960-1990 years, we will discuss in detail more recent designs, which appeared during the last 2-3 decades. In the last part of our review, we will cover the recent applications of LIMS for surface analysis. These applications include various types of analyses of solid inorganic, organic, and heterogeneous samples, often in combination with depth profiling and imaging capability.

Study of the mainstream cigarette smoke aerosols by Fourier transform ion cyclotron resonance mass spectrometry coupled to laser/desorption and electrospray ionization - Additional insights on the heteroaromatic components

RATIONALE

The chemical composition of the particulate phase of cigarette smoke inhaled by the active smoker is still poorly known in spite of its importance from a health point of view. A non-targeted approach is applied to cigarette smoke particles collected on a quartz filter to obtain an as complete as possible description of this complex mixture.

METHODS

A home-made smoking machine including devices for volatile organic compounds (VOCs) and particle sampling was used. The validation of the cigarette smoking and cigarette smoke collection procedures was conducted by the quantification of some compounds by gas chromatography/mass spectrometry (GC/MS). The particles were investigated by Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) directly after their collection on quartz filters by laser/desorption ionization (LDI) or after extraction with CH2 Cl2 by electrospray ionization (ESI).

RESULTS

The determination of the benzene, toluene, ethylbenzene and xylenes (from 2 to 35 μg/cigarette) and nicotine (0.68 ± 0.05 mg/cigarette) validated the used sampling method. The complementarity of the LDI and ESI sources for the cigarette smoke analysis was established. The ESI analyses evidenced polar compounds and components with a pyridine group and LDI ensured the detection of poly-condensed heteroaromatic species. Finally, this methodology was employed to characterize particles from cigarettes with or without flavoring additives.

CONCLUSIONS

Some insights into the composition of cigarette smoke inhaled by active smokers have been obtained. The ~1750 observed features revealed the huge complexity of cigarette smoke particles and the diversity of the possible associated health issues. Both heteroaromatic and highly oxygenated compounds produced by combustion and pyrolysis have been highlighted.

Characterization of biomass and biochar by LDI-FTICRMS - Effect of the laser wavelength and biomass material

The pyrolysis of the lignocellulosic biomass is a promising process to produce biofuels or green chemicals. Specific analytical methods have to be developed in order to better understand the composition of biomass and of its pyrolysis products and therefore to optimize the design of pyrolysis processes. For this purpose, different biomasses (Douglas and Miscanthus) and one biochar were analyzed by laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry (LDI FT-ICR MS). This method allowed the biomass and biochar to be analyzed without any sample preparation and with a spatial resolution of about 100 μm. The influence of LDI conditions (laser wavelength and laser irradiance) and the nature of the biomass and biochar on the obtained mass spectrum were investigated. The nature and origin of the observed ions highly depended on LDI conditions. In the softest laser-biomass interaction conditions (low laser irradiance), the detected ions were related to the nature of the investigated biomass. Indeed, the main part of the detected species came from the different biomass subunits and was produced by photolysis of covalent bonds. When more severe laser irradiation conditions were used, the obtained mass spectra gathered the ions relative to (i) the chemical components of the investigated samples, (ii) the recombination products of these species in the gas phase after their ejection from the sample surface, and (iii) the compounds produced by laser pyrolysis of the sample. This was expected to be useful to mimic thermal pyrolysis. Graphical Abstract.

Detection and imaging of chrome yellow (lead chromate) in latent prints, solid residues, and minerals by laser-desorption/ionization mass spectrometry (LDI-MS)

In the past, chrome yellow (lead chromate, PbCrO₄ ), a bright orange-red substance, has been widely used as an inorganic pigment in the production of paints, coatings, and plastics. Herein, we demonstrate that laser desorption/ionization mass spectrometry (LDI-MS) is a powerful tool for the detection of lead chromate in solid residues. In fact, lead chromate in trace amounts is easily detectable by LDI-MS even from residues left as latent prints. For example, a latent print obtained by stamping the exposed laterally cut surface of a pencil over 50 years old on an acetonitrile-moistened paper, was successfully imaged for both lead and chromate using a Synapt G2 HDMS mass spectrometer. After rastering the print with a 355 nm laser beam and recording positive- and negative-ion mass spectra over the range m/z 50-1200, we generated false-color 'heat maps' (single-ion images) for ²⁰⁸ Pb^+• (m/z 207.98) and Cr₂ O₆^-• (m/z 199.85). The heat maps matched closely with the faint visual image of the pencil imprint. Moreover, our results confirmed that lead chromate was used in the pigment coatings of old pencils. Evidently, LDI-MS imaging is an efficient procedure to survey for the presence of lead and chromate in minerals and other materials. Copyright © 2017 John Wiley & Sons, Ltd.

The effect of laser power density on the observed products of combustion of gasoline using laser-induced thermal desorption with Fourier transform mass spectrometry

Layered soot analysis is explored as a potential indicator of gasoline in a fire. Current techniques lack the ability to analyze layered soot samples without the destruction of the layered information. Laser-induced thermal desorption (LITD) coupled with Fourier transform mass spectrometry (FTMS) is developed as a method for analyzing soot samples. Samples of soot on glass from the free combustion of gasoline are collected and analyzed using LITD-FTMS, and the effect of power density on the resulting chemical profile is reported. At higher power densities, a distribution of low m/z products is observed. At lower power densities, the products observed shift to higher molecular weights, with peaks attributable to the tropyllium ion, naphthalene, and pyrene. Results at low power densities suggest that LITD-FTMS is a viable method for the analysis of soot, with potential for use with layered soot samples. Peaks potentially useful for fuel differentiation of gasoline are identified.

Direct imaging of single cells and tissue at sub-cellular spatial resolution using transmission geometry MALDI MS

The need of cellular and sub-cellular spatial resolution in laser desorption ionization (LDI)/matrix-assisted LDI (MALDI) imaging mass spectrometry (IMS) necessitates micron and sub-micron laser spot sizes at biologically relevant sensitivities, introducing significant challenges for MS technology. To this end, we have developed a transmission geometry vacuum ion source that allows the laser beam to irradiate the back side of the sample. This arrangement obviates the mechanical/ion optic complications in the source by completely separating the optical lens and ion optic structures. We have experimentally demonstrated the viability of transmission geometry MALDI MS for imaging biological tissues and cells with sub-cellular spatial resolution. Furthermore, we demonstrate that in conjunction with new sample preparation protocols, the sensitivity of this instrument is sufficient to obtain molecular images at sub-micron spatial resolution.

Study by ESI-FTICRMS and ESI-FTICRMS(n) of zinc and cadmium thiophenolate complexes used as precursors for the synthesis of II-VI nanosemiconductors

[M(4)(SC(6)H(5))(10)][(CH(3))N](2), [M(10)L(4)(SC(6)H(5))(16)][(CH(3))N](4) and [Cd(17)S(4)(SC(6)H(5))(28)][(CH(3))N](2)(M = Cd or Zn, and L = S or Se) zinc and cadmium thiophenolates have been studied by electrospray ionization (ESI) Fourier transform ion cyclotron resonance (FTICR) mass spectrometry (ESI-FTICRMS) and tandem ESI-FTICRMS (ESI-FTICRMS(n)). ESI-FTICRMS demonstrated its ability to characterize and study such compounds, which may be used as precursors of II-VI nanomaterials. The obtained mass spectrum has been found to be highly relevant of the investigated thiophenolate and the fragmentation behavior of some of the detected ions is indicative of its stability. More specifically, it has been demonstrated that ESI in-source activation or fragmentation experiments conducted in the Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) cell induced the formation of a very stable entity, which corresponds to the general formula M(4)L(4) (M = Zn or Cd and L = S or Se). The elimination of SC(6)H(5)(-) and/or M(SC(6)H(5))(2) moieties by various activation processes from the studied thiophenolates led systematically to this structure.

Classification of organic and biological materials with deep ultraviolet excitation

We show that native fluorescence can be used to differentiate classes or groups of organic molecules and biological materials when excitation occurs at specific excitation wavelengths in the deep ultraviolet (UV) region. Native fluorescence excitation-emission maps (EEMs) of pure organic materials, microbiological samples, and environmental background materials were compared using excitation wavelengths between 200-400 nm with emission wavelengths from 270 to 500 nm. These samples included polycyclic aromatic hydrocarbons (PAHs), nitrogen- and sulfur-bearing organic heterocycles, bacterial spores, and bacterial vegetative whole cells (both Gram positive and Gram negative). Each sample was categorized into ten distinct groups based on fluorescence properties. Emission spectra at each of 40 excitation wavelengths were analyzed using principal component analysis (PCA). Optimum excitation wavelengths for differentiating groups were determined using two metrics. We show that deep UV excitation at 235 (+/-2) nm optimally separates all organic and biological groups within our dataset with >90% confidence. For the specific case of separation of bacterial spores from all other samples in the database, excitation at wavelengths less than 250 nm provides maximum separation with >6sigma confidence.