Table 2.
Comparison of the GC-MS [8] versus LC-MS/MS method.
| Criterion | GC-MS | LC-MS/MS |
|---|---|---|
| Retention time | PHT 15.12 min, IS MPPH 16.15 min | PHT and PHT-D10 2.8 min |
| Selectivity/sensitivity (absence of PHT) | Good peak differentiation and quantification of PHT. All blank samples were negative (no presence of PHT) | All blank samples were negative (no presence of PHT) |
| Recovery | 94.1% for QC2 (100 ng/mL) | 89.5% for QC1 (10 ng/mL) |
| 94.3% for QC5 (1000 ng/mL) | 97.1% for QC3 (1600 ng/mL) | |
| LOD (calculated as S/N ratio of 4 : 1) | 15 ng/mL | <1 ng/mL |
| LOQ (calculated as 5 times the response/blank) | 50 ng/mL | 10 ng/mL |
| Accuracy | The calibrator values showed min–max percent deviations of 1–20% for Cal 1 (50 ng/mL) to Cal 6 (1200 ng/mL) | The calibrator values showed min–max percent deviations of 1–8% for Cal 1 (10 ng/mL) to Cal 8 (2000 ng/mL) |
| Regression coefficient, r2 |
r
2
blood = 0.998 (n = 2) r2dialysate = 0.999 (n = 8) r2saliva = 0.999 (n = 2) |
r
2
blood = 0. 996 (n = 3) r2dialysate = 0.997 (n = 6) r2saliva = 0.995 (n = 3) |
| Calibration range | 50–1200 ng/mL | 10–2000 ng/mL |
| Run time per analysis | 30 min | 7 min |
| Injection volume of the sample | 2.0 µL | 10 µL |
| Sample preparation time | 5 h for 25 samples | 6 h for 182 samples |
| Stability of the processed samples | Dried extracts were stable for ≥4 weeks (min/max deviation 4%). No effect by reinjection and storage (33 h) on the autosampler | Reinjection after 7 days showed no difference in accuracy |
| Sample volume needed | 50 µL | 25 µL |