Table 2.

Summary of stability of morphine and codeine under various storage conditions (n = 3).

Compound	Condition	Concentration (ng/mL)	RSD	RE
		Added	(%)	(%)
Morphine	Three freeze–thaw cycles	50	2.5	−10.1
		200	1.4	−8.9
		1600	4.3	−12.5
	Autosampler ambient 12 h	50	2.1	−10.5
		200	1.3	−6.2
		1600	3.5	−9.2
Codeine	Three freeze–thaw cycles	50	3.2	−8.9
		200	3.3	−11.2
		1600	3.0	−14.1
	Autosampler ambient 12 h	50	3.3	−11.1
		200	3.2	−12.9
		1600	3.3	−14.4