“One-pot” preparation of aminated carbon nanotube-modified magnetic nanoparticles and their application to the quantification of phenoxyacetic acid herbicides in cereal and vegetable samples

doi:10.3724/SP.J.1123.2021.12008

Abstract

Abstract:

Phenoxyacetic acid herbicides (PAs) are widely used to control the growth of broad-leaf weeds in corn, tobacco, etc. The presence of PAs in plants even at low concentrations (at the ng/L to μg/L scale) may induce severe effects and lead to human health risks. Hence, a sensitive and reliable method for the determination of PAs at trace levels in cereals and vegetables is highly desired. Magnetic solid-phase extraction (MSPE) has attracted considerable attention on account of its benefits such as ease of separation, less solvent consumption, and good service life. In this study, aminated carbon nanotube-modified magnetic nanoparticles (NH₂-CNTs@M) were prepared by a convenient and simple “one-pot” strategy and employed as the adsorbent for the MSPE of PAs in crops. The fabrication procedure is very convenient. In detail, the aminated carbon nanotubes, Fe(Ⅱ), Fe(Ⅲ), and isopropanol were mixed in one pot with mechanical stirring and reacted for 2.0 h at 80 ℃. The spectroscopic properties, morphology, and magnetic properties of the synthetic adsorbent were characterized by Fourier Transform-infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results revealed that the size of Fe₃O₄, diameter of NH₂-CNTs, and the magnetic saturation values of NH₂-CNTs@M were 30 nm, 40 nm, and 44.2 emu/g, respectively. Additionally, the results of FT-IR and TEM characterization confirmed the successful fabrication of NH₂-CNTs@M by this “one-pot” hydrothermal approach. The NH₂-CNTs@M displayed satisfactory capability to capture PAs through π-π, hydrophobic, and hydrogen-bonding interactions. To realize the best extraction performance, the key parameters, including the amount of adsorbent, formic acid concentration in the eluent, adsorption and desorption time, sample pH, and ionic strength in the sample matrices, were inspected and studied in detail. The optimal conditions were as follows: amount of NH₂-CNTs@M, 30 mg; desorption solvent, 0.5 mL acetonitrile containing 2.0% (v/v) formic acid; adsorption and desorption times, 8.0 and 3.0 min, respectively; the sample pH was adjusted to 6.0, and no salt was added to the sample. Under the optimized extraction conditions, a sensitive, quick, and environmentally friendly method for the determination of the studied PAs in cereal and vegetable samples was established by the combination of NH₂-CNTs@M/MSPE with high performance liquid chromatography-diode array detection (HPLC-DAD). The enrichment factors for the studied PAs varied from 73 to 90. The limits of detection (S/N=3) for the PAs in the cereal and vegetable matrixes were in the ranges of 0.32-1.6 μg/kg and 0.53-1.6 μg/kg, respectively; and the limits of quantification (S/N=10) for the PAs in the cereal and vegetable matrixes were 0.94-4.8 μg/kg and 1.6-4.8 μg/kg. The developed method also showed wide linear ranges and good precision. Finally, the established NH₂-CNTs@M/MSPE-HPLC-DAD approach was applied to measure trace levels of PAs in cereals and vegetables, and good fortified recoveries (72.3% to 113%) and repeatability (RSDs below 10%) were obtained. The established approach has several advantages over the existing methods, such as high analytical speed, low LODs, and eco-friendliness.

Key words: aminated carbon nanotubes, magnetic solid-phase extraction (MSPE), high performance liquid chromatography (HPLC), phenoxyacetic acid, herbicides, cereals, vegetables

CLC Number:

O658

HUANG Youfang, LIU Jun, HUANG Xiaojia. “One-pot” preparation of aminated carbon nanotube-modified magnetic nanoparticles and their application to the quantification of phenoxyacetic acid herbicides in cereal and vegetable samples[J]. Chinese Journal of Chromatography, 2022, 40(10): 900-909.

Figures/Tables 10

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Sample	Target	Linear range^a/ (μg/kg)	r²	LOD/ (μg/kg)	LOQ/ (μg/kg)	RSDs/%(n=4)
						Intra-day		Inter-day
						10 μg/kg	200 μg/kg	10 μg/kg	200 μg/kg
Cereal	NPOA	5.0-500.0	0.9927	1.6	4.8	9.2	6.1	8.2	7.5
	POA	1.0-500.0	0.9938	0.32	0.94	8.4	9.7	8.1	6.0
	CPOA	5.0-500.0	0.9925	1.6	4.8	5.6	3.9	6.3	3.8
	2,4-D	5.0-500.0	0.9978	1.4	4.3	8.2	5.4	6.5	6.6
	MCPA	5.0-500.0	0.9963	1.5	4.4	8.2	6.7	7.1	7.3
Vegetable	NPOA	5.0-500.0	0.9982	1.6	4.8	3.4	7.8	8.8	7.5
	POA	5.0-500.0	0.9988	1.3	3.9	4.4	9.2	7.1	9.2
	CPOA	2.0-500.0	0.9987	0.53	1.6	4.7	4.4	7.2	2.9
	2,4-D	2.0-500.0	0.9993	0.63	1.9	8.7	1.9	3.3	10
	MCPA	2.0-500.0	0.9992	0.60	1.8	4.2	1.4	8.1	1.2

Sample	Target	Linear range^a/ (μg/kg)	r²	LOD/ (μg/kg)	LOQ/ (μg/kg)	RSDs/%(n=4)
						Intra-day		Inter-day
						10 μg/kg	200 μg/kg	10 μg/kg	200 μg/kg
Cereal	NPOA	5.0-500.0	0.9927	1.6	4.8	9.2	6.1	8.2	7.5
	POA	1.0-500.0	0.9938	0.32	0.94	8.4	9.7	8.1	6.0
	CPOA	5.0-500.0	0.9925	1.6	4.8	5.6	3.9	6.3	3.8
	2,4-D	5.0-500.0	0.9978	1.4	4.3	8.2	5.4	6.5	6.6
	MCPA	5.0-500.0	0.9963	1.5	4.4	8.2	6.7	7.1	7.3
Vegetable	NPOA	5.0-500.0	0.9982	1.6	4.8	3.4	7.8	8.8	7.5
	POA	5.0-500.0	0.9988	1.3	3.9	4.4	9.2	7.1	9.2
	CPOA	2.0-500.0	0.9987	0.53	1.6	4.7	4.4	7.2	2.9
	2,4-D	2.0-500.0	0.9993	0.63	1.9	8.7	1.9	3.3	10
	MCPA	2.0-500.0	0.9992	0.60	1.8	4.2	1.4	8.1	1.2

Compound	Spiked/ (μg/kg)	Rice				Millet						Wheat flour
Compound	Spiked/ (μg/kg)	Found/ (μg/kg)	Recovery/ %	RSD/ %		Found/ (μg/kg)		Recovery/ %		RSD/ %		Found/ (μg/kg)		Recovery/ %		RSD/ %
NPOA	0	ND			7.02						ND
	10.0	9.33	93.3	6.3	15.9		89.2		3.0		9.57		95.7		9.7
	50.0	38.7	77.3	8.6	48.6		107		4.8		43.1		86.1		5.3
	200	197	98.6	5.4	178		89.1		8.4		163		81.7		5.7
POA	0	ND			5.42						ND
	10.0	8.38	83.8	6.1	15.3		98.9		1.7		8.49		84.9		7.4
	50.0	56.0	112	2.1	47.4		94.8		8.2		46.2		92.3		2.5
	200	172	85.9	7.1	199		99.6		7.2		147		73.6		4.0
CPOA	0	ND			ND						ND
	10.0	8.02	80.2	6.8	10.1		101		8.9		7.94		79.4		4.7
	50.0	36.6	73.1	6.0	45.1		90.1		5.5		45.1		90.1		10
	200	151	75.6	2.8	167		83.6		3.9		150		75.0		7.7
2,4-D	0	ND			ND						ND
	10.0	7.66	76.6	9.2	7.67		76.7		5.7		10.6		106		5.5
	50.0	52.5	105	4.8	38.3		76.6		8.5		37.9		75.9		6.9
	200	187	93.3	8.4	155		77.4		2.7		185		92.6		5.2
MCPA	0	ND			ND						ND
	10.0	9.94	99.4	8.9	8.09		80.9		7.8		8.81		88.1		9.3
	50.0	42.8	85.5	9.0	41.4		82.7		9.5		39.6		79.2		8.3
	200	169	84.7	3.3	157		78.3		7.1		163		81.6		6.2

Compound	Spiked/ (μg/kg)	Rice				Millet						Wheat flour
Compound	Spiked/ (μg/kg)	Found/ (μg/kg)	Recovery/ %	RSD/ %		Found/ (μg/kg)		Recovery/ %		RSD/ %		Found/ (μg/kg)		Recovery/ %		RSD/ %
NPOA	0	ND			7.02						ND
	10.0	9.33	93.3	6.3	15.9		89.2		3.0		9.57		95.7		9.7
	50.0	38.7	77.3	8.6	48.6		107		4.8		43.1		86.1		5.3
	200	197	98.6	5.4	178		89.1		8.4		163		81.7		5.7
POA	0	ND			5.42						ND
	10.0	8.38	83.8	6.1	15.3		98.9		1.7		8.49		84.9		7.4
	50.0	56.0	112	2.1	47.4		94.8		8.2		46.2		92.3		2.5
	200	172	85.9	7.1	199		99.6		7.2		147		73.6		4.0
CPOA	0	ND			ND						ND
	10.0	8.02	80.2	6.8	10.1		101		8.9		7.94		79.4		4.7
	50.0	36.6	73.1	6.0	45.1		90.1		5.5		45.1		90.1		10
	200	151	75.6	2.8	167		83.6		3.9		150		75.0		7.7
2,4-D	0	ND			ND						ND
	10.0	7.66	76.6	9.2	7.67		76.7		5.7		10.6		106		5.5
	50.0	52.5	105	4.8	38.3		76.6		8.5		37.9		75.9		6.9
	200	187	93.3	8.4	155		77.4		2.7		185		92.6		5.2
MCPA	0	ND			ND						ND
	10.0	9.94	99.4	8.9	8.09		80.9		7.8		8.81		88.1		9.3
	50.0	42.8	85.5	9.0	41.4		82.7		9.5		39.6		79.2		8.3
	200	169	84.7	3.3	157		78.3		7.1		163		81.6		6.2

Compound	Spiked/ (μg/kg)	Cucumber 1				Cucumber 2						Loofah
Compound	Spiked/ (μg/kg)	Found/ (μg/kg)	Recovery/ %	RSD/ %		Found/ (μg/kg)		Recovery/ %		RSD/ %		Found/ (μg/kg)		Recovery/ %		RSD/ %
NPOA	0	ND			ND						ND
	10.0	8.45	84.5	2.8	7.68		76.8		8.6		7.23		72.3		2.2
	50.0	56.5	113	7.3	56.5		80.2		6.6		37.0		73.9		5.1
	200	196	97.9	7.6	196		92.4		3.2		162		80.8		6.5
POA	0	5.34			ND						ND
	10.0	16.0	107	8.8	8.58		85.8		6.5		8.97		89.7		6.6
	50.0	49.2	87.8	3.2	39.7		79.3		9.6		49.7		99.3		3.8
	200	157	75.9	6.7	168		84.2		8.0		153		76.5		8.8
CPOA	0	5.42			ND						ND
	10.0	13.5	81.2	8.4	8.36		83.6		5.9		7.92		79.2		7.3
	50.0	37.2	74.5	9.4	46.1		92.2		5.6		37.6		75.2		5.8
	200	184	92.2	4.0	168		84.2		5.8		161		80.6		1.9
2,4-D	0	ND			ND						ND
	10.0	9.97	99.7	7.4	10.4		104		5.9		10.9		109		5.4
	50.0	40.6	81.1	8.3	38.0		75.9		6.7		40.3		80.6		3.4
	200	175	87.5	1.9	152		76.1		6.1		204		102		3.8
MCPA	0	ND			ND						ND
	10.0	10.4	104	5.9	11.2		112		9.4		10.2		102		6.6
	50.0	38.0	75.9	6.7	40.5		80.9		5.1		42.3		84.6		8.4
	200	152	76.1	6.1	160		79.9		5.8		176		88.0		1.0