Table 8.

Stability testing. QC samples were tested for stability after 3 freeze-thaw cycles. They were also tested overnight at the indicated temperatures. A 3- and 7- day postextraction study were also performed at 2–8°C.

Drug/Metabolite	F/T 3 cycles		Overnight stability (%)			Postpreparation stability
	QC	% Diff	RT	4°C	−20°C	Init % diff nom	% Diff init day 3	% Diff init day 7
Amphetamine∗	QC 75	0.69	2.48	4.91	3.63	8.95	−1.33	0.61
	QC 800	6.92	6.21	8.19	0.45	−0.69	0.16	−1.78
Methamphetamine	QC 75	−2.38	1.39	-0.23	0.72	−1.25	2.61	6.13
	QC 1800	1.12	2.62	1.95	4.85	−2.22	−4.26	−1.39

^∗ Indicates high QC of 800.