Development and Validation of an LC-MS/MS Method and Comparison with a GC-MS Method to Measure Phenytoin in Human Brain Dialysate, Blood, and Saliva

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, r^2	r^2blood = 0.998 (n = 2); r^2dialysate = 0.999 (n = 8); r^2saliva = 0.999 (n = 2)	r^2blood = 0. 996 (n = 3); r^2dialysate = 0.997 (n = 6); r^2saliva = 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