To establish an LC-MS/MS method for determining the concentrations of imipenem and cilastatin in human plasma, for monitoring clinical therapeutic drug concentrations, and to investigate the effects of adding stabilizers during the sample pretreatment on mass spectrometry signal intensity.
After protein precipitation, the sample was subjected to gradient elution using an Agilent TC-C18 (2) (150 mm×4.6 mm, 5 µm) column with a mobile phase system of 0.15% formic acid in water and methanol. The electrospray ionization (ESI) mass spectrometer was operated in positive ion mode using multiple reaction monitoring (MRM): m/z 300.1 → 141.9 (imipenem),m/z 359.7 → 97.0 (cilastatin) and m/z 384.1 → 141.1 (meropenem, internal standard). The samples containing and without 3-(N-morpholino) propane sulfonic acid (MOPS) as stabilizers were pretreated and continuously analyzed to compare the changes in mass spectrometry signal intensity.
Both imipenem and cilastatin showed good linearities in the concentration ranges of 0.1-100.0 μg·mL-1 (r>0.99). The intra-day and inter-day accuracy ranges from 95.3% to 108.5%, the precision (RSDs) were less than 9.3%, the extraction recovery rate ranges from 77.4% to 84.3%, and the matrix effect ranges from 97.1% to 111.2%. Imipenem in plasma samples was stable at room temperature for 3 h, at 4 ℃ for 6 h, and at -80 ℃ for 12 d, while it was significantly degraded at -20 ℃ for 12 d. Cilastatin was stable under a variety of conditions. The method was robust to changing conditions of column temperature ±5 ℃, flow rate ±0.1 mL·min-1, formic acid concentration in the aqueous phase ±0.025%, and ion source temperature ±50 ℃. The samples containing stabilizers exhibited significant ion inhibition on mass spectrometry after continuous injection, while samples without stabilizers had no significant effect on the signal intensity of mass spectrometry.
The method is simple and accurate and can be used for clinical drug monitoring of imipenem and cilastatin. Nonvolatile salt stabilizers such as MOPS can reduce mass spectrometry sensitivity, and the absence of such stabilizers is more suitable for long-term analysis by LC-MS/MS.
| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |