Predicting image quality degradation as a result of two-phase sample transport in LA-ICP-TOFMS mapping of carbon-based materials

Recent findings reported by Van Helden et al. (Anal. Chim. Acta, 2024, 1287, 342089) have revealed that a whole suite of elements (S, Zn, As, Se, Cd, I, Te and Hg) undergoes two-phase sample transport during mapping of carbon-based materials using nanosecond laser ablation (LA) combined with an ICP-mass spectrometer equipped with a quadrupole or time-of-flight analyzer (ICP-QMS or ICP-TOFMS). Examining single pulse response (SPR) profiles, it became evident that these elements are transported in both gaseous and particulate forms. This phenomenon leads to notable widening of the SPR profiles, exhibiting two peaks in which the distribution of the ablated sample material across the peaks depends on the laser fluence. Consequently, the image quality may degrade, especially at higher pixel acquisition rates typically used with low-dispersion ablation cells. This is experimentally demonstrated by mapping of kidney tissue at low and high pixel acquisition rates and including elements which show one-phase (Mg, Ca, Fe and Cu) and two-phase (S, Zn, I and Hg) sample transport. To predict the impact of sample transport phenomena on the image quality through modeling, well-established computational models were utilized for virtual LA-ICP-MS mapping of a phantom and incorporate the experimentally obtained element-specific SPR profiles referenced in the aforementioned work. Downloadable interactive Python-based software for MS Windows was developed to study the effect of mapping parameters on the image quality, which was quantified by the structural similarity index (SSIM).