Long-Term Stability of Hydromorphone in Human Plasma Frozen at −20°C for Three Years Quantified by LC-MS/MS

Figure 4

Calibration data of hydromorphone and hydromorphone-D3 used as the internal standard for the range of 0.3 to 20 ng/mL. The black circles represent the calibration samples, and the red line represents the calibration curve determined by linear regression. The response was calculated from the area under the curve of the hydromorphone peak (AUC_HM), the area under the curve of the internal standard peak (AUC_IS), and the concentration of the internal standard (C_IS): response = AUC_HM/AUC_IS  C_IS.