Solid-Phase Extraction and Large-Volume Sample Stacking-Capillary Electrophoresis for Determination of Tetracycline Residues in Milk

Table 1

Optimal conditions determined with Box–Behnken design.

Exp.	Control factors			Enrichment factors				Output variable
	Injection time (min)	Reverse potential (kV)	Applied time (min)	TC	CT	OT	DT	Sum
1	−1	−1	0	25.4	49.0	38.9	42.2	155.45
2	1	0	1	0.0	0.0	0.0	0.0	0.0
3	0	1	−1	41.2	58.0	46.1	49.1	194.34
4	0	0	0	20.4	43.7	55.7	1.2	121.02
5	1	0	−1	44.8	71.1	55.5	47.2	218.76
6	1	1	0	2.5	17.1	29.1	61.5	110.20
7	−1	0	1	0.0	0.0	0.0	0.0	0.0
8	0	−1	1	10.5	9.0	13.4	21.4	54.27
9	0	0	0	26.8	61.3	47.8	41.0	176.84
10	0	−1	−1	9.6	51.3	32.7	60.5	154.04
11	0	1	1	0.0	0.0	0.0	26.8	10.83
12	−1	0	−1	11.8	29.0	42.2	59.0	142.00
13	−1	1	0	0.0	0.0	0.0	0.0	0.0
14	0	0	0	0.0	0.0	10.8	0.0	26.75
15	1	−1	0	31.1	54.0	52.4	48.4	185.94