Direct multi-element analysis of biological samples in dry matrix spots by PIXE

The dried matrix spot (DMS) method, initially developed for neonatal blood screening, has gained prevalence in various research fields for its efficiency in handling small sample volumes and its adaptability to diverse analytical techniques. This study presents the results of the first systematic investigation of direct multi-element analysis in DMS of human blood and plasma samples with Particle Induced X-ray Emission (PIXE). Internal standard addition was used to address the issue of DMS heterogeneity and to eliminate the need for determining the sample volume equivalent, allowing a single-spot (single-punch) measurement. The method was tested for linearity, accuracy, precision and limit of detection (LOD) using reference materials. It was applied to samples from healthy volunteers and compared to analysis results obtained by ICP-OES showing good agreement. Sample volumes as low as 50 μL were sufficient for the quantification of Na, Mg, P, S, K, Ca, Fe, and Zn in whole blood, and Na, Mg, P, S, K, and Ca in plasma samples without significant matrix effects being observed. Chlorine, which is also an electrolyte element present in high enough concentrations for determination by PIXE, was not addressed in this study due to a lack of reference materials. The results highlight PIXE as a viable alternative to other techniques that are sensitive to matrix issues, require larger sample volumes and/or sample treatment. Overall, this work establishes DMS sampling as being suitable for direct multi-element analysis of biological samples by PIXE, offering detection limits at the mg/L level which is sufficient for determination of electrolyte and essential trace elements and paving the way for its broader application in clinical and research settings.