“一锅法”制备氨基碳纳米管功能化磁性纳米粒子及其在谷物和蔬菜中苯氧羧酸类除草剂测定中的应用

doi:10.3724/SP.J.1123.2021.12008

摘要/Abstract

摘要：

有效萃取是分析复杂样品中苯氧羧酸类除草剂(PAs)残留的关键步骤。为此,该文利用“一锅法”水热技术快速、简便地制备了氨基碳纳米管功能化磁性纳米粒子(NH₂-CNTs@M)并作为磁固相萃取(MSPE)的萃取介质,用于萃取谷物和蔬菜样品中痕量PAs。研究利用多种手段对NH₂-CNTs@M的形貌、尺寸、磁性性质等进行了表征,结果表明Fe₃O₄的粒径、氨基化碳纳米管的直径以及NH₂-CNTs@M的磁饱和值分别为30 nm、40 nm和44.2 emu/g。详细考察了制备条件和萃取参数对NH₂-CNTs@M/MSPE萃取性能的影响,结果表明,NH₂-CNTs@M/MSPE可通过π-π、疏水和氢键作用有效富集目标化合物,最佳萃取条件如下:吸附剂用量为30 mg,解吸溶剂为含2.0%(v/v)甲酸的乙腈溶液,吸附时间和解吸时间分别为8.0 min和3.0 min,基底pH值为6.0,不调节基底的离子强度。将NH₂-CNTs@M/MSPE与高效液相色谱-二极管阵列检测技术(HPLC-DAD)联用,建立了谷物和蔬菜中PAs的灵敏检测方法。谷物和蔬菜基质中苯氧羧酸类除草剂的检出限(LOD, S/N=3)分别为0.32~1.6 μg/kg和0.53~1.6 μg/kg,定量限(LOQ, S/N=10)分别为0.94~4.8 μg/kg和1.6~4.8 μg/kg。在两种实际样品中不同浓度下的加标回收率分别为73.1%~112%和72.3%~113%。与现有方法相比,所建方法具有萃取速度快、灵敏度高和环境友好等特点。

关键词: 氨基化碳纳米管, 磁固相萃取, 高效液相色谱, 苯氧羧酸, 除草剂, 谷物, 蔬菜

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

中图分类号:

O658

黄幼芳, 刘珺, 黄晓佳. “一锅法”制备氨基碳纳米管功能化磁性纳米粒子及其在谷物和蔬菜中苯氧羧酸类除草剂测定中的应用[J]. 色谱, 2022, 40(10): 900-909.

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.

图/表 10

图1 NH2-CNTs@M的制备流程图

Fig. 1 Schematic for preparation of aminated carbon nanotube-modified magnetic nanoparticles (NH2-CNTs@M)

图2 NH2-CNTs的用量对5种目标物萃取性能的影响

Fig. 2 Effect of the amount of NH2-CNTs on the extraction performance of the five targets Conditions: amount of sorbent, 30.0 mg; desorption solvent, 0.5 mL acetonitrile (ACN) containing 1.0% (v/v) formic acid (FA); adsorption and desorption times, 10.0 min and 5.0 min, respectively. No salt was added to the sample and the pH of the sample was not adjusted. The spiked mass concentration of each compound was 100 μg/L. NPOA: 2-nitrophenoxyacetic acid; POA: phenoxyacetic acid; CPOA: 4-chlorophenoxyacetic acid; 2,4-D: 2,4-dichlorophenoxyacetic acid; MCPA: 2-methyl-4-chlorophenoxyacetic acid.

图3 NH2-CNTs@M的(a)红外光谱图、(b)扫描电镜图、(c)透射电镜图和(d)磁化曲线

Fig. 3 (a) FT-IR spectra, (b) SEM image, (d) TEM image, and magnetization curves of NH2-CNTs@M

图4 吸附剂用量对5种目标物萃取性能的影响(n=3)

Fig. 4 Effect of the amount of adsorbent on the extraction performance of the five targets (n=3) Conditions: desorption solvent, 0.5 mL ACN containing 1.0% (v/v) FA; adsorption and desorption times, 10.0 min and 5.0 min, respectively; no salt was added to the sample, and the pH of the sample was not adjusted. The spiked mass concentration of each compound was 100 μg/L.

图5 (a)解吸溶剂种类和(b)甲酸含量、(c)吸附时间、(d)解吸时间、(e)基底pH值、(f)离子强度对PAs萃取性能的影响(n=3)

Fig. 5 Effects of (a) type of desorption solvent, (b) FA content in desorption solvent, (c) adsorption time, (d) desorption time, (e) sample pH, and (f) ionic strength on the extraction performance toward PAs (n=3) Conditions: a. amount of sorbent, 30.0 mg; FA content in the eluent, 1.0% (v/v); adsorption and desorption times, 10.0 min and 5.0 min, respectively; the pH of the matrix was not adjusted, and no salt was added to the sample; b. the elution solvent was ACN, and the other conditions were the same as those in (a); c. 0.5 mL ACN containing 2.0% FA was used as the desorption solvent, and the other conditions were the same as those in (b); d. the adsorption time was 8.0 min, and the other conditions were the same as those in (c); e. the desorption time were 3.0 min, and the other conditions were the same as those in (d); f. the sample matrix pH was adjusted to 6.0, and the other conditions were the same as those in (e). The spiked mass concentration of each compound was 100 μg/L.

表1 所建立方法对PAs的分析性能

Table 1 Analytical performance of the proposed method toward PAs

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

表2 谷物样品中PAs的测定及加标回收率结果(n=3)

Table 2 Results of determination and spiked recoveries of PAs in cereal samples (n=3)

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

表3 蔬菜样品中PAs的测定及加标回收率结果(n=3)

Table 3 Results of determination and spiked recoveries of PAs in vegetable samples (n=3)

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

图6 大米和黄瓜样品中PAs的色谱图

Fig. 6 Chromatograms of the PAs in rice and cucumber samples a. real sample treated with NH2-CNTs@M/MSPE; b. spiked sample with each target at 200 μg/kg and treated with NH2-CNTs@M/MSPE. Conditions: sorbent amount, 30.0 mg; desorption solvent, 0.5 mL ACN containing 2.0%FA; adsorption and desorption times, 8.0 min and 3.0 min, respectively; sample matrix pH, 6.0.

表4 所建方法与文献报道的PAs检测方法的对比

Table 4 Comparison of proposed method with reported methods for the analysis of PAs

Method	Sample	Compounds	Extraction time/min	Organic solvent consumption	LODs/ (μg/kg)	Recoveries/ %	Ref.
SPME/HPLC-UV	cereal	POA, CPOA, MCPA, NPOA, 2,4-D	80	0.39 mL MeOH	0.36-0.66	70.0-117	[2]
SPME-HPLC-UV	cereal	2,4-D	34	0.2 mL ACN	2.1	92.9-112	[23]
SPE/HPLC-MS/MS	cereal	POA, CPOA, MCPA, NPOA, 2,4-D	15	1.6 mL ACN	1.0-2.0	80.0-115	[10]
TFME/SESI-IMS	cereal	2,4-D	38	0.2 mL MeOH	0.09-0.3	82.0-115	[24]
MSPE-LLME/HPLC-MS/MS	cereal	2,4-D, MCPA, CPOA	17	4.0 mL MeOH	0.19-0.80	83.9-103	[15]
MSPE/HPLC-DAD	cereal	POA, CPOA, MCPA, NPOA, 2,4-D	11	0.49 mL ACN	0.32-1.6	73.1-112	this work
SPE/HPLC-DAD	vegetable	2,4-D, MCPA	31	0.95 mL MeOH	0.1-0.5	86.1-103	[11]
D-μ-SPE/HPLC-UV	vegetable	2,4-D	36	1.5 mL ACN	7.0	88.0-94.0	[12]
FSPE/HPLC-MS/MS	vegetable	MCPA	>25	2.85 mL MeOH	55	81.1-106	[25]
QuEChERS/HPLC-MS/MS	vegetable	MCPA	-	9.9 mL ACN	0.22-0.60	83.4-107	[26]
MSPE/HPLC-DAD	vegetable	POA, CPOA, MCPA, NPOA, 2,4-D	11	0.49 mL ACN	0.53-1.6	72.3-113	this work

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