Table 1.

Validation parameters for the analysis of dihydrothymine and the DPD activity.

ParameterRecovery (n = 10),1 %PrecisionApparent recovery,2 %
Intraassay (n = 10)Interassay (n = 5)Intraassay (n = 10)Interassay (n = 5)
Mean (SD)CV, %Mean (SD)CV, %Mean (SD)CV, %Mean (SD)Mean (SD)
Dihydrothymine (1 μmol/L)80.6 (2.7)3.30.94 (0.03)3.20.99 (0.04)4.294.4 (3.2)99.4 (4.2)
Dihydrothymine (5 μmol/L)91.9 (2.8)3.05.12 (0.05)1.05.08 (0.24)4.7102.4 (1.0)101.6 (4.7)
Dihdyrothymine (10 μmol/L)96.7 (3.0)3.210.06 (0.25)2.59.98 (0.17)1.7100.6 (2.5)99.9 (1.7)
DPD activity (nmol/mg/h)36.13 (0.43)7.16.47 (0.47)7.3
DPD activity (nmol/mg/h)46.48 (0.25)3.96.91 (0.45)6.5
DPD activity (nmol/mg/h)56.36 (0.27)4.36.36 (0.31)4.9
  • 1 Recovery of dihydrothymine, without correction with the internal standard.

  • 2 The apparent recovery was defined as the percentage of the ratio of the calculated concentration and the nominal concentration.

  • 3 The reaction mixtures and the samples were incubated for 15 min; the amount of dihydrothymine produced by DPD was near the LOQ level.

  • 4 The reaction mixtures and the samples were incubated for 90 min.

  • 5 The reaction mixtures and the samples were incubated for 180 min.