Trueness [13] was quantified, analysing a certified reference material (NIST 2383), through z-score (z = (Clab − Ccert )/u2 lab + u2 cert ), where Clab and Ccert are the laboratory and assigned analyte concentration values, respectively, ulab is the laboratory combined standard uncertainty, assumed similar to ucert (more unfavourable situation), and ucert is the combined standard certified reference material uncertainty.