3.4. Preparation of Calibration Standards and Spiked Quality control Samples

Calibration standards for NDMA, NDEA, DIPNA, and EIPNA were prepared by aliquoting the working standard solutions in DMSO to yield final concentrations of 25 (LOQ of NDMA and NDEA), 50 (LOQ of DIPNA and EIPNA), 100, 250, 500, 1000, and 5000 ng/mL. Spiked QC samples for NDMA and NDEA were prepared by adding the working standard solutions to the nitrosamine-free losartan API at concentrations of 25, 250, and 1000 ppb, representing QC at LOQ (LOQ QC), medium QC (MQC), and high QC (HQC) samples, respectively. For DIPNA and EIPNA, spiked QC samples were prepared at concentrations of 50 (LOQ), 250, and 1000 ppb, representing LOQ QC, MQC, and HQC, respectively.