Table 4. Recovery by LC–MS/MS and UHPLC of plasma samples fortified with a standard solution of Nτ-methylhistidine or Nπ-methylhistidine at three spiking levels.
| Recovery | |||||||||
| Low | Middle | High | |||||||
| Recovery ratio (%) |
RSD (%) |
Recovery ratio (%) |
RSD (%) |
Recovery ratio (%) |
RSD (%) |
||||
| Nτ-Methylhistidine | |||||||||
| LC–MS/MS (m/z 170.20>96.10) |
94.67 | 14.57 | 93.93 | 6.01 | 90.81 | 7.30 | |||
| LC–MS/MS (m/z 170.20>124.10) |
100.14 | 13.60 | 93.11 | 2.92 | 88.00 | 8.68 | |||
| UHPLC | 99.19 | 3.57 | 97.31 | 5.78 | 98.10 | 2.06 | |||
| Nπ-Methylhistidine | |||||||||
| LC-MS/MS (m/z 170.20>96.10) |
94.07 | 30.97 | 102.04 | 9.22 | 94.03 | 15.65 | |||
The recovery ratio represents the mean value of three replicates. RSD (%) = (standard deviation / measured mean value) × 100. The three spiking levels were set to 5, 10, and 20 μmol/L (Nτ-methylhistidine) and 2.5, 5, and 10 μmol/L (Nπ-methylhistidine).