Table 2.

Stability f or the assay of DA in urine sample (n = 5).

Concentration found (ng mL−1) (mean ± SD)	Concentration added (ng mL−1) (mean ± SD)
	0.1	1.0	10.0
Freeze and thaw stability
At the beginning	0.0946 ± 0.0061	0.959 ± 0.047	9.68 ± 0.35
After three freeze-thaw cycle	0.0990 ± 0.0065	0.995 ± 0.052	10.01 ± 0.57
Bias (RE%)	4.6	3.8	3.4
Short-term room temperature stability
At the beginning	0.0946 ± 0.0061	0.959 ± 0.047	9.68 ± 0.35
After 4 h at room temperature	0.0983 ± 0.0042	0.991 ± 0.042	9.90 ± 0.46
Bias (RE%)	3.9	3.4	2.3
Long-term cold storage stability
At the beginning	0.0946 ± 0.0061	0.959 ± 0.047	9.68 ± 0.35
After 15 days at -20 °C	0.1004 ± 0.0039	1.012 ± 0.038	10.12 ± 0.42
Bias (RE%)	6.1	5.5	4.5

^a Bias (RE%)= (C_actual −C_calculated)/C_actual (%).