Inorganic mass spectrometric techniques and methods for direct solid analysis are widely required to obtain valuable information about the multi-elemental spatial distribution of the major and trace constituents and/or isotope ratio information of a sample in a wide variety of solid specimens, including environmental wastes, biological samples, geochemical materials, coatings and semiconductors. The increasing need to characterize complex materials in industry (e.g. production control and quality assurance processes), and in different fields of science is forcing the development of various inorganic mass spectrometric methods for direct solid chemical analysis. These methods allow the characterization of solid materials both in bulk and in spatially resolved analysis (with lateral and/or in-depth resolution). This review critically discusses the analytical performance, capabilities, pros and cons, and trends of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), secondary ion (neutral) mass spectrometry (SIMS/SNMS), and glow discharge mass spectrometry (GD-MS) because they represent the most widespread and powerful inorganic mass spectrometric methods currently further improved and applied for the direct characterization of solids.

A substantial proportion of cancer patients do not benefit from platinum-based chemotherapy (CT) due to the emergence of drug resistance. Here, we apply elemental imaging to the mapping of CT biodistribution after therapy in residual colorectal cancer and achieve a comprehensive analysis of the genetic program induced by oxaliplatin-based CT in the tumor microenvironment. We show that oxaliplatin is largely retained by cancer-associated fibroblasts (CAFs) long time after the treatment ceased. We determine that CT accumulation in CAFs intensifies TGF-beta activity, leading to the production of multiple factors enhancing cancer aggressiveness. We establish periostin as a stromal marker of chemotherapeutic activity intrinsically upregulated in consensus molecular subtype 4 (CMS4) tumors and highly expressed before and/or after treatment in patients unresponsive to therapy. Collectively, our study underscores the ability of CT-retaining CAFs to support cancer progression and resistance to treatment.

The analytical figures of merit of ultra-violet femtosecond laser ablation inductively coupled plasma mass spectrometry (UV-fs-LA-ICP-MS) using the 3rd and 4th harmonics of Ti:Sapphire (∼265 and ∼200 nm, respectively) were explored. For this purpose, elemental ratios of aerosols produced by LA of silicate glass (SRM NIST 610) were studied under varying fluence conditions ranging from moderate values of 2 J cm⁻² up to 30 J cm⁻², taking into account e.g. laser-induced (⁶⁶Zn/⁶⁵Cu) and particle size-related (²³⁸U/²³²Th) phenomena. It could, for instance, be shown that signal ratios were less dependent on the wavelength or laser repetition rate chosen. Furthermore, fractionation indices defined using the temporal drift of elemental ratios over two equal parts of the acquired signal were subject to systematic changes for threshold-close fluences. As a consequence, corresponding ⁴²Ca-normalized values were found to deviate by more than 20% from unity. In contrast, LA at higher fluences resulted in less pronounced discrepancies, falling below 5% even for the most critical elements such as ⁶⁶Zn, ¹¹¹Cd, and ²⁰⁸Pb. The complete suppression of particle size-related fractionation quantified on the basis of the ²³⁸U/²³²Th-system turned out to be highly consistent with the absence of μ-sized particles which were measured by optical particle counting (OPC). The relative fraction of particles >0.5 μm was determined to be less than 5%, independent on the wavelength, fluence, or laser repetition rate chosen. Moreover, our results indicate the occurrence of ICP-induced elemental fractionation during analysis due to an increased mass loading of the plasma source if medium or high fluences are applied. Using the ⁶⁶Zn/⁶⁵Cu-ratio as a thermometric probe, the change in plasma ionization temperature among low and high mass loading conditions was estimated to be −900 K. Nevertheless, UV-fs-LA-ICP-MS analysis of different matrices (silicate glass SRM NIST 610 and brass (Zn ∼20%)) performed within the high fluence range was found to enhance the accuracy for non-matrix-matched calibration. Evidence is given that the enhancement observed mainly depends upon the suppression of laser- and/or transport-induced fractionation.

The quantification capabilities of iron-based samples were investigated using three commercially available ultraviolet (UV) nanosecond (ns) and femtosecond (fs) laser ablation systems coupled to inductively coupled plasma mass spectrometry (LA-ICP-MS). A comparison of three pulsed laser ablation systems (ArF* excimer, Nd:YAG and Ti-sapphire) with different wavelengths and pulse time durations (15 ns, 4 ns and 150 fs, respectively) was performed. Minor and trace elements were determined using ⁵⁷Fe as internal standard element. Using similar spatial resolution for all laser systems and commonly applied operating conditions for each system, higher ion-signals (25–30%) and more stable elemental ratios (10% TRSD) were obtained for UV-fs-LA-ICP-MS. Scanning electron microscope images and particle size distributions measured for UV-ns-LA systems showed a bimodal distribution formed by nano-sized agglomerates and micro-sized molten spherical particles. In contrast, due to reduced thermal effects achieved using ultra-short pulses, the particle size distribution measured using UV-fs-LA showed a broad monomodal distribution (nano-sized agglomerates in the range of 50–250 nm). Matrix-matched (within metallic samples) and non-matrix matched calibrations were applied for the analysis of Fe-based samples, using a silicate glass (SRM NIST 610) as non-matrix matched calibration sample (glass-metals). Improved analytical results in terms of precision and accuracy were obtained using femtosecond laser ablation when using similar matrices for calibration. Moreover, non-matrix matched calibration used for quantification provides more accurate results (5–15%) in comparison with both UV-ns-LA-ICP-MS (5–30% using Nd:YAG laser and 15–60% using ArF* laser).