Simultaneous screening for marbofloxacin and ofloxacin residues in animal-derived foods using an indirect competitive immunoassay

Figures & data

Figure 1. Chemical structures of MBF (a) and OFX (b).

Figure 2. UV–vis spectra of MBF, BSA, and MBF–BSA.

Table 1. Specificity of the MBF antibody.

Compound	IC50 ± CV (ng mL^−1) (n = 5)	Cross-reactivity (%)
Marbofloxacin	0.36 ± 0.012	100
Ofloxacin	0.87 ± 0.056	41.38
Difloxacin	149.99 ± 5.75	0.24
Enrofloxacin	250.01 ± 16.25	0.14
Ciprofloxacin	>1000	<0.01

Note: CV, coefficient of variation.

Figure 3. Effects of coating buffer (a) pH value in the assay buffer, (b) ionic strength in the assay buffer on ELISA performance, (c) and inhibition curves for MBF and OFX by ELISA under optimal conditions (d).

Table 2. Results of the spiked test.

Analyte	Sample	Spiked level (ng mL^−1)	Mean recovery (%)	CV (%)
				Intra-day (n = 5)	Inter-day (n = 15)
Marbofloxacin	Milk	0.1	84.35	4.82	9.41
		0.4	87.95	5.79	10.40
		1.6	93.91	6.26	8.98
	Porcine muscle	0.1	81.35	7.06	9.67
		0.4	86.83	4.98	9.85
		1.6	92.54	6.54	11.67
Ofloxacin	Milk	0.5	85.97	5.39	10.25
		2	89.75	6.09	10.08
		8	94.26	4.54	8.57
	Porcine muscle	0.5	80.52	4.96	12.06
		2	87.73	6.23	9.78
		8	95.46	7.02	8.43

Figure 4. Comparative detection of MBF and OFX between the ELISA and HPLC–MS/MS.