The LOD and LOQ were evaluated according to the procedure proposed by International Union of Pure and Applied Chemistry (IUPAC) (Currie, 1995) and the US Environmental Protection Agency (US EPA, 2003) based on the constant error model described by Currie (Currie, 1968). LOD is defined as the minimal concentration of an analyte that can be reliably detected or differentiated from the background for a given matrix by a given analytical method. The LOQ is defined as the minimal concentration of an analyte that can be reliably quantified with a certain degree of reliability within a given matrix by a given analytical method. The LOD is determined from the analysis of at least seven replicate samples containing the target analyte at an estimate of the detection limit. The LOD is calculated as