Elemental imaging of heterogeneous inorganic archaeological samples by means of simultaneous laser induced breakdown spectroscopy and laser ablation inductively coupled plasma mass spectrometry measurements

Metal leakage from orthodontic appliances chemically alters enamel surface during experimental in vitro simulated treatment

Human enamel is composed mainly of apatite. This mineral of sorption properties is susceptible to chemical changes, which in turn affect its resistance to dissolution. This study aimed to investigate whether metal leakage from orthodontic appliances chemically alters the enamel surface during an in vitro simulated orthodontic treatment. Totally 107 human enamel samples were subjected to the simulation involving metal appliances and cyclic pH fluctuations over a period of 12 months in four complimentary experiments. The average concentrations and distribution of Fe, Cr, Ni, Ti and Cu within the enamel before and after the experiments were examined using ICP‒MS and LA‒ICP‒MS techniques. The samples exposed to the interaction with metal appliances exhibited a significant increase in average Fe, Cr and Ni (Kruskal-Wallis, p < 0.002) content in comparison to the control group. The outer layer, narrow fissures and points of contact with the metal components showed increased concentrations of Fe, Ti, Ni and Cr after simulated treatment, conversely to the enamel sealed with an adhesive system. It has been concluded that metal leakage from orthodontic appliances chemically alters enamel surface and microlesions during experimental in vitro simulated treatment.

Analysis of Laser-Induced Breakdown Spectroscopy Data Acquired from Boundary of Two Matrices

Laser-induced breakdown spectroscopy (LIBS) data obtained from the elemental imaging of heterogenous samples were processed with various chemometric algorithms. The intention was to cluster obtained characteristic spectra and to provide additional information about the sample surface composition and distribution of individual matrices. However, there is a gray zone on the boundary of two matrices and the consequent clustering of the spectra obtained on this boundary is ambiguous. This paper focuses on the transition between two well-defined matrices in a simplified case for a better transparency in data visualization. Steel and aluminum samples that are represented by characteristic spectra with significantly distinct structures (e.g., different number of spectral lines). Using a carefully designed experiment, several Fe:Al ratios were ablated and analyzed by principal component analysis (PCA), self-organizing maps (SOM), and standard data metrics. This paper shows the strategy for the discrimination of unrecognized spectra and possibilities in their clustering.

MODERN PLASMA-BASED DESORPTION/IONIZATION: FROM ATOMS AND MOLECULES TO CHEMICAL SYNTHESIS

Since the first mass spectrometry (MS) experiments were conducted by Thomson and Aston, plasmas have been used as ionization sources. Historically, plasma ion sources were used for these experiments because they were one of the few known sources of gas-phase ions at the time and they were relatively simple to setup and operate. Since then, developments in plasma ionization have continued to inform and motivate advances in other areas of MS. For example, plasma-desorption MS demonstrated ionization of large peptides and polymers more than 10 years before the first descriptions of electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI). As a result, significant effort was placed on development of ionization approaches, mass analysis, and detection approaches for very large molecules: even before the advent of ESI and MALDI. Since then, new analytical challenges and opportunities in plasma ionization have arisen. In this review, the emerging trends in plasma-based ionization for several areas of MS will be discussed, including molecular ionization, elemental ionization, hybrid elemental and molecular ion sources, and unique chemical transformations. © 2020 John Wiley & Sons Ltd. Mass Spec Rev.

Improved plasma stoichiometry recorded by laser ablation ionization mass spectrometry using a double-pulse femtosecond laser ablation ion source

RATIONALE

Femtosecond (fs) laser ablation ion sources have allowed for improved measurement capabilities and figures of merit of laser ablation based spectroscopic and mass spectrometric measurement techniques. However, in comparison to longer pulse laser systems, the ablation plume from fs lasers is observed to be colder, which favors the formation of polyatomic species. Such species can limit the analytical capabilities of a system due to isobaric interferences. In this contribution, a double-pulse femtosecond (DP-fs) laser ablation ion source is coupled to our miniature Laser Ablation Ionization Mass Spectrometry (LIMS) system and its impact on the recorded stoichiometry of the generated plasma is analyzed in detail.

METHODS

A DP-fs laser ablation ion source (temporal delays of +300 to - 300 ps between pulses) is connected to our miniature LIMS system. The first pulse is used for material removal from the sample surface and the second for post-ionization of the ablation plume. To characterize the performance, parametric double- and single-pulse studies (temporal delays, variation of the pulse energy, voltage applied on detector system) were conducted on three different NIST SRM alloy samples (SRM 661, 664 and 665).

RESULTS

At optimal instrument settings for both the double-pulse laser ablation ion source and the detector voltage, relative sensitivity coefficients were observed to be closer (factor of ~2) to 1 compared with single-pulse measurements. Furthermore, the optimized settings worked for all three samples, meaning no further optimization was necessary when changing to another alloy sample material during this study.

CONCLUSIONS

The application of a double-pulse femtosecond laser ablation ion source resulted in the recording of improved stoichiometry of the generated plasma using our LIMS measurement technique. This is of great importance for the quantitative chemical analysis of more complex solid materials, e.g., geological samples or metal alloys, especially when aiming for standard-free quantification procedures for the determination of the chemical composition.

Identifying Ancient Ceramics Using Laser-Induced Breakdown Spectroscopy Combined with a Back Propagation Neural Network

This study investigated the rapid identification of ceramics via laser-induced breakdown spectroscopy (LIBS) to realize the identification of ancient ceramics from different regions. Ceramics from different regions may have large differences in their elemental composition. Thus, using LIBS technology for ceramic identification is feasible. The spectral intensities of 11 common elements, namely, Si, Al, Fe, Ca, Mg, Ti, Mn, Na, K, Sr, and Ba, in ceramics were selected as classification indices. Principal component analysis (PCA) and kernel principal component analysis (KPCA) combined with the back propagation (BP) neural network were used to identify ceramics. Furthermore, the effects of the PCA and KPCA data processing methods were compared. Finally, this work aimed to select a suitable method for obtaining spectral data on ceramics identified by LIBS through experiments. Results revealed that LIBS technology could aid the routine, rapid, and on-site analysis of archeological objects to rapidly identify or screen various types of objects.