Preparation of covalent organic framework based on room temperature solution-suspension approach and its application to solid-phase microextraction of pyrethroids in tea

doi:10.3724/SP.J.1123.2020.12012

Abstract

Abstract:

Pyrethroids (PYs) have been widely used to control pests and prevent diseases in tea gardens. However, with the increasingly stringent pesticide testing standards in the import and export trade of tea, there is an urgent need for methods to detect trace amounts of PYs in tea. In this study, a covalent organic framework (COF) material TpBD with excellent thermal/chemical stability, high porosity, and a large specific surface area was prepared by a room-temperature solution-suspension approach (SSA). TpBD-coated solid phase microextraction (SPME) fibers were fabricated by coating the material on etched stainless-steel fibers by a simple physical coating method. The fibers were used in combination with gas chromatography-tandem mass spectrometry (GC-MS/MS) to establish a highly sensitive method for the detection of PYs. The enrichment factors of this method for cyfluthrin, cypermethrin, flucythrinate, fenvalerate, and deltamethrin were 702-2687. The method showed low LODs (0.1-0.5 ng/L), wide linear ranges (0.2-800 ng/L), good linearities (correlation coefficients (R)≥0.9991) and acceptable repeatabilities (RSD≤11.0%, n=3). Green tea and oolong tea samples were analyzed using the developed method, and trace levels of the five PYs were successfully detected. The recoveries of the spiked PYs in the real green tea and oolong tea samples were in the range of 80.2%-109.5%. Experimental results showed that the established analytical method is suitable for the determination of PY pesticides in tea. Furthermore, the TpBD material was successfully prepared by the SSA method, demonstrating that the method has good universality and excellent potential for the simple synthesis of other COF materials.

Key words: gas chromatography-tandem mass spectrometry (GC-MS/MS), solid phase microextraction (SPME), covalent organic frameworks (COFs), pyrethroids (PYs), tea

CLC Number:

O658

YU Qidong, ZHANG Lan, ZHANG Wenmin, YANG Jiangfan. Preparation of covalent organic framework based on room temperature solution-suspension approach and its application to solid-phase microextraction of pyrethroids in tea[J]. Chinese Journal of Chromatography, 2021, 39(4): 349-356.

Figures/Tables 10

Table 1 Retention times, qualitative ions, and quantitative ions of the five pyrethroids (PYs)

Compound	Retention time/min	Qualitative ions (m/z)	Quantitative ion (m/z)
Cyfluthrin (CYF)	17.49	206, 199, 226	206
Cypermethrin (CYP)	17.81	181, 152, 180	181
Flucythrinate (FLU)	19.35	199, 157, 451	199
Fenvalerate (FEN)	21.45	225, 167, 419	225
Deltamethrin (DEL)	25.45	253, 172, 181	253

Fig. 1 Schematic illustrations for the preparation of (a) the TpBD via room-temperature solution-suspension approach (SSA) and (b) the TpBD-SPME fibers TpBD: β-ketoenamine-linked covalent organic framework (COF); Tp: 2,4,6-triformylphloroglucinol; BD: benzidine; RT: room temperature; HF: hydrogen fluoride.

Fig. 2 (a) Powder X-ray diffraction (PXRD) patterns and (b) Fourier transform-infrared (FT-IR) spectra of TpBD with the different reaction times

Fig. 3 (a) PXRD patterns and (b) FT-IR spectra of TpBD after treatment with different solvents for 24 h, and (c) thermal stability and (d) N2 adsorption-desorption isotherms of TpBD The inset in Fig. 3d shows the pore size distributions of TpBD. THF: tetrahydrofuran; MeOH: methanol; EtOH: ethanol; DCM: dichloromethane; ACN: acetonitrile; CP: acetone; BET: Brunauer-Emmett-Teller surface area.

Fig. 4 SEM images of (a) the etched stainless steel fiber, (b) TpBD coated fiber, (c) the cross section of the TpBD fiber, and (d) TpBD material

Fig. 5 Effects of (a) extraction temperatures, (b) extraction times, (c) desorption temperatures and (d) desorption times on the extraction efficiencies of the five PYs (500 ng/L) (n=3)

Table 2 Linear ranges, correlation coefficients (R), limits of detection (LODs),precisions and enrichment factors (EFs) of the five PYs

Analyte	Linear range/(ng/L)	R	LOD/ (ng/L)	RSD (n=3)/%			EF
				Single fiber		Fibers of batch-to-batch
				Intra-day	Inter-day	Fibers of batch-to-batch
CYF	0.2-800	0.9995	0.1	5.5	4.9	8.9	1740
CYP	0.8-800	0.9997	0.3	4.3	4.1	6.6	1513
FLU	0.5-800	0.9995	0.1	5.5	5.4	8.7	1082
FEN	1-800	0.9998	0.3	3.2	5.4	11.0	2687
DEL	1-800	0.9991	0.5	3.9	8.7	9.6	702

Table 3 Comparison of the proposed method with other reported methods

Coating	Linear range/ (μg/L)	LOD/ (ng/L)		Analytical technique	Reference
MWCNTs	1-50	120-	165	GC-MS	[20]
MWCNTs/Ppy	1-10000	120-	430	GC-ECD	[21]
Hydrazone COF	1-1000	110-	230	GC-ECD	[15]
ZIF-90-NPC	0.3-50	100-	500	GC-μECD	[22]
TpBD	0.0002-0.8	0.1-	0.5	GC-MS/MS	this work

Table 4 Recoveries and RSDs of the five PYs spiked in green tea and oolong tea samples (n=3)

Compound	Spiked level/ (ng/L)	Green tea		Oolong tea
Compound	Spiked level/ (ng/L)	Recovery/ %	RSD/ %	Recovery/ %	RSD/ %
CYF	5	92.7	8.5	82.2	8.0
	20	105.7	7.9	102.2	7.9
	100	99.6	7.8	91.4	2.9
CYP	5	81.8	9.5	88.0	9.1
	20	104.8	9.1	80.7	7.1
	100	89.8	8.2	93.5	1.2
FLU	5	94.8	7.9	105.9	5.9
	20	106.1	8.2	80.9	8.6
	100	88.1	3.0	86.5	3.2
FEN	5	92.1	7.3	89.4	5.4
	20	105.6	7.5	85.4	9.1
	100	94.7	3.2	91.4	4.2
DEL	5	109.5	6.7	107.7	7.5
	20	89.7	8.4	80.3	4.9
	100	81.4	5.3	88.3	7.8

Fig. 6 Chromatograms of the five PYs (20 ng/L) in green tea and oolong tea samples

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