Abstract
Other than their inherent accuracy, analytical robustness and nondestructive features, instrumental neutron activation analysis (INAA) and particle-induced X-ray emission (PIXE) are both multi-elemental techniques that complement – and partially overlap – each other with respect to a vast majority of elements of interest in environmental studies and life sciences at large. Analytical accuracy notwithstanding, INAA and PIXE ask for different sample-preparation procedures and rely on dissimilar energy-related profiles, which can lead to some divergence in their operational outputs. Especially interesting are the elements determined by either technique, in that they can provide what one might call an index of intrinsic reliability as to an elemental pool. This paper presents an evaluation of the relative performance of INAA and PIXE on measurements in atmospheric biomonitors, namely epiphytic lichens of the Parmelia genus. The study is based upon 4 elements – Fe, Mn, Rb (customary crustal references) and K (an indicator of physiological status) – in lichen samples from 58 sites in mainland Portugal. Distribution-free statistics – rank-order correlations and enhanced-sign tests – were used for checking the degree of association between concentration patterns (variables) and any significant differences between individual values (variates), respectively. The results show that (i) for all elements, the area-wide patterns by either technique display similar trends; and (ii) for all elements but rubidium, no statistically sound evidence for relative bias – consistently higher or lower values by one technique – could be found. As far as this investigation goes, the techniques may be used interchangeably for determining Fe, K and Mn in Parmelia spp. samples.
Published Version
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