THE UNCERTAINTY IN REE DETERMINATION IN URINE BY ETV-ICP-MS:A NEW APPROACH TO DATA EVALUATION

摘要

Aim of this work was to develop an analytical method for the determination of REEs in urine of non-exposed subjects, since there are few reliable data for the endogenous concentrations of these elements in literature. Generally, the endogenous concentrations of REEs in body fluids are very low, and only the most sensitive analytical techniques can be used to determine these elements at ng/L concentrations. In the literature there are several examples of determination of REE in biological fluids, using different techiniques. Among them, NAA is one of the most used, but not suitable for routine analyses, while ET-AAS, that is generally one of the best technique used for trace metal determination in biological samples, has insufficient sensitivity for the determination of REEs. Some examples are reported using ICP-MS with a preconcentration step before the measurement in biological fluids or an acid decomposition procedure followed by a concentration step on resins capable of determining few ng/L of REE. We considered the use of ETV-ICP-MS coupling. This coupling permits both the water and the matrix of the sample to be removed before introducing the analyte into the detector (MS) so that spectral and non-spectral interferences are significantly reduced. This technique is often used for many analytes in different matrices but, if applied to REEs, it lacks sensitivity and is characterized by memory effects because they form stable oxides and refractory carbides during the atomization in the graphite tube. Recently, Buseth et al. reported the possibility to employ ETV-ICP-MS for the determination of REEs in human tissues and body fluids after microwave dissolution of the sample. Several Authors have recently studied the role of modifiers in ETV-ICP-MS for the determination of refractory elements such as La and U or of some elements that can form carbides, such as B, La and U, Zr, V and Cr, Mo and W, Y and REEs. Several papers have been published by Huang et al. considering the use of PTFE slurry as in-situ fluorination agent for refractory elements. The purpose of this work was to investigate the applicability of a fluorination agent (CHF_(3)) used as a chemical modifier, in order to allow the determination of REE in urine samples without any preconcentration step and at concentration levels like those one in samples from healthy subjects. This procedure was evaluated according to the procedures recommended by ISO and Eurachem/CITAC Guides for estimating measurement uncertainty. The knowledge of the uncertainty associated to the measurement result, in fact, permits to have an essential information in order to evaluate the reliability of the analytical result and their fitness to purpose in particular during the definition of reference values.