HPLC ndash MS MS analysis

2.4.2. HPLC–MS/MS analysis
2.5. Quantification and method validation
The concentrations of target A 841720 in water samples were quantified by using internal standard method based on six points (5, 25, 50, 100, 250, 500 μg/L) calibration curve. The correlation coefficient (R2) of 25 calibration curves was more than 0.9. Standards addition method was used to assess the effect of different water matrices. Three kinds of water (groundwater/GW, wastewater/WW, river water/RW) were spiked with 25 target antibiotics at two concentration levels (10, 100 ng/L for GW; 100, 1000 ng/L for WW; 20, 200 ng/L for RW). Each sample was spiked and analyzed in triplicate (used to calculate the relative standard deviation/RSD), the same non-spiked sample was analyzed in duplicate to measure the background concentrations. Limit of detection (LOD) was determined from a connective tissue low concentration standard and calculated using a signal-to-noise ratio (S/N) of 3. All the details above could be found in Supporting Information, Table S2.