2.8. Method detection limit
The limit of detection (LOD) of the proposed methodology was determined at the lowest concentration of each analyte. The limit of quantification (LOQ) and limit of detection (LOD) were determined based on the standard deviation of eight measurements of the spiked blank urine samples [18]. The limit of detection (LOD) was calculated by adding 3× the standard deviation of the response lowest concentration of the calibration curve. Accordingly, the limit of quantification (LOQ) was equal to 3× the LOD.
2.9. Stability of THMs in urine samples—storage effect
A stability experiment was performed to evaluate the stability of THM in stored urine samples during time of sampling and storage at −80 °C. In an attempt to simulate as much as possible realistic sampling conditions, a pooled urine sample (with negligible THM measured concentrations) was placed in sampling vials. Samples were spiked with a concentration of THM in a final concentration of 10 μg L−1 for each analyte (four analytes). They were kept in the −80 °C freezer, and at specific time intervals, vials were sacrificed and samples were analyzed for THM.