Quick, easy, cheap, effective, rugged and safe strategy for quantifying cadmium polluted rice

Figures & data

Figure 1. UV spectrum and transmission electron microscope map (inset) of 20 nm Au solution.

Figure 2. Steps for detecting Cd in rice samples by strip.

Table 1. Time optimization of extraction Cd from rice.

Extract time (min)	1	3	9	20	1	3	9	20
Cadmium in rice^a (ng/g)	Cd extracted (ng/g)				Extraction efficiency (%)
827.8	790.6	826.3	822.8	826.6	95.5	99.8	99.4	99.9
337.3	324.9	333.7	335.5	359.7	96.3	98.9	99.5	106.6
3	3.2	3.2	3.2	3.4	106.3	105.2	106.0	114.0

^aCadmium concentration in rice were detected by the ICP-MS.

Table 2. Dilute acid extraction cadmium from rice and extraction by SPE column.

Sample	Cadmium concentration in rice (ng/g)	Acid extraction efficiency (%)	Extraction efficiency by extraction column (%)
1	3.0	105.2	98.3
2	15.5	99.3	97.7
3	56.8	96.8	99.0
4	103.7	97.5	99.4
5	148.0	98.9	99.2
6	183.0	97.7	99.5
7	327.0	99.2	97.3
8	337.3	98.9	97.0
9	827.8	99.8	96.2

Table 3. Optimization of elution method.

Acid type	Acid concentration	Elution method	Elution efficiency (%)
Perchloric acid	0.025 M	Vigorously shaking	1.6
Perchloric acid	0.05 M	Vigorously shaking	1.7
Perchloric acid	0.1 M	Vigorously shaking	1.0
Perchloric acid	0.2 M	Vigorously shaking	48.3
Perchloric acid	0.3 M	Vigorously shaking	46.0
Perchloric acid	0.4 M	Vigorously shaking	50.2
Perchloric acid	0.5 M	Vigorously shaking	54.6
Perchloric acid	0.5 M	Static extraction	24.4
Nitric acid	0.5 M	Vigorously shaking	7.6

Table 4. The elution of Cd from SPE column.

Sample	Cadmium concentration (ng/g)	Elution efficiency (%)	Final extraction efficiency (%)
1	3.0	66.2	68.5
2	15.5	50.1	48.6
3	56.8	54.6	52.3
4	103.7	58.0	56.2
5	148.0	50.6	49.6
6	183.0	58.5	56.9
7	327.0	59.4	57.3
8	337.3	51.8	49.7
9	827.8	56.7	54.4

Table 5. The pretreatment of spiked rice samples.

Spiked cadmium (ng/g)	0	20	50	100	200	500	800
Acid extraction efficiency (%)	106.3	99.6	99.8	98.8	98.5	98.4	98.1
Extraction efficiency by extraction column (%)	98.2	99.9	99.7	99.1	98.5	97.7	96.5
Elution efficiency (%)	65.6	52.7	53.3	54.6	53.5	57.3	53.2
Final extraction efficiency (%)	68.5	52.4	53.0	53.5	51.9	55.1	50.4

Figure 3. The detection results of Cd in rice by immunochromatography (a) and the standard curve (b).

Table 6. Real rice samples kindly provided by the National Center for Food Safety Risk Assessment were detected by the immunochromatography assay and ICP-MS and the data unit is mg/kg.

Sample number	ICP-MS	Strip	Sample Number	ICP-MS	Strip	Sample Number	ICP-MS	Strip
1	0.0026	0.02^a	11	0.029	0.035	21	0.12	0.16
2	0.0026	0.02	12	0.032	0.048	22	0.12	0.15
3	0.005	0.02	13	0.042	0.054	23	0.14	0.24
4	0.0055	0.02	14	0.07	0.10	24	0.17	0.18
5	0.0056	0.02	15	0.077	0.12	25	0.18	0.16
6	0.0062	0.02	16	0.087	0.11	26	0.23	0.31
7	0.011	0.02	17	0.089	0.12	27	0.29	0.38
8	0.012	0.02	18	0.099	0.12	28	0.30	0.36
9	0.018	0.030	19	0.099	0.13	29	0.33	0.50
10	0.025	0.034	20	0.11	0.13	30	0.64	0.70

^aThe detection results of rice samples by the immunochromatography assay which were lower than the detection limit were all assigned as 0.02 mg/kg.

Table 7. Real rice samples obtained from different supermarkets in Hunan province were detected by the immunochromatography assay and ICP-MS and the data unit is mg/kg.

Sample number	ICP-MS	Strip	Sample number	ICP-MS	Strip	Sample number	ICP-MS	Strip
1	0.024	0.036	9	0.44	0.83	17	0.14	0.20
2	0.14	0.17	10	0.83	0.85	18	0.022	0.038
3	0.34	0.29	11	0.16	0.20	19	0.11	0.15
4	0.027	0.027	12	0.094	0.12	20	0.022	0.029
5	0.061	0.072	13	0.28	0.37	21	0.080	0.11
6	0.045	0.055	14	0.15	0.19	22	0.016	0.020^a
7	0.095	0.10	15	0.29	0.29	23	0.10	0.13
8	0.057	0.067	16	0.098	0.079

^aThe detection results of rice samples by the immunochromatography assay which were lower than the detection limit were all assigned as 0.02 mg/kg.

Table 8. Real rice samples kindly provided by Huaan Magnech Bio-Tech Co., Ltd. were detected by the immunochromatography assay and ICP-MS and the data unit is mg/kg.

Sample number	ICP-MS	Strip	Sample number	ICP-MS	Strip
1	0.25	0.22	10	0.15	0.26
2	0.11	0.11	11	0.2	0.26
3	0.08	0.095	12	0.17	0.23
4	0.2	0.25	13	0.17	0.23
5	0.16	0.17	14	0.18	0.16
6	0.14	0.18	15	0.25	0.33
7	0.2	0.20	16	0.23	0.31
8	0.18	0.15	17	0.23	0.31
9	0.19	0.27	18	0.23	0.21

Figure 4. The detection results of Cd in rice by immunochromatography and ICP-MS. Error bars represent SD (n = 3).