Table 2. Validation results of PPD in human urine.

Intra- and interday Accuracy and Precision in human urine
	nominal conc. [µmol/L]	mean calc. conc.[µmol/L]	Accuracy (bias %)		Precision (% CV)
			MALDI-MS/MS / HPLC-UV		MALDI-MS/MS / HPLC-UV
Intra-day (n = 3)	1000	960	−3.9	2.7	24.1	10.5
	750	745	−0.6	−9.4	9.9	5.2
	500	512	2.5	2.2	8.9	8.8
	250	261	4.4	9.2	13.2	1.8
	150	157	4.5	4.7	2.4	9.4
	100	91	−8.9	n.d.	9.5	n.d.
	50	51	2.1	n.d.	16.2	n.d.

Inter- and intraday accuracy and precision measurements (n = 3 for each value). The mean relative error of each concentration is expressed as % bias and the reproducibility is depicted as the coefficient of variation (% CV). Intraday accuracy and precision were also determined on the HPLC-UV system.