Simultaneous determination of nitrapyrin and its metabolite residues in food crops by derivatization with gas chromatography-triple quadrupole mass spectrometry

doi:10.3724/SP.J.1123.2019.11030

Abstract

Abstract:

A method based on precolumn derivatization along with gas chromatography-triple quadrupole mass spectrometry (GC-MS/MS) was developed for the determination of nitrapyrin and its metabolite, 6-chloropicolinic acid, in crops. The samples were extracted by acid acetonitrile, and subjected to precolumn derivatization using a sulfoacid. The quantification of the analytes was performed by the internal standard method. Good linear relationships between the peak areas and mass concentrations of the analytes were obtained in the range of 0.025-0.2 mg/L with correlation coefficients greater than 0.995 (n=6). The limits of quantification (LOQs) were 0.05 mg/kg. The recoveries of the analytes in crops at three spiked levels (0.05, 0.1, and 0.2 mg/kg) were in the range of 80.4%-98.4%, with relative standard deviations between 1.0% and 10.1% (n=6). This new method satisfies the related regulations for the determination of nitrapyrin and its metabolite in crops.

Key words: gas chromatography-triple quadrupole mass spectrometry (GC-MS/MS), nitrapyrin, 6-chloropicolinic acid, crops

SUN Linghui, CHEN Jie, XU Juan, LI Minqing, CHEN Wenrui. Simultaneous determination of nitrapyrin and its metabolite residues in food crops by derivatization with gas chromatography-triple quadrupole mass spectrometry[J]. Chinese Journal of Chromatography, 2020, 38(6): 695-701.

Figures/Tables 9

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No.	Compound	Retention time/min	Quantitative ion pair (m/z)	Quantitative ion pair collision energy/V	Qualitative Ion pair (m/z)	Qualitative ion pair collision energy/V
* 6-Chloro-2-picolinic acid methyl ester is a derivative of the metabolite of nitrapyrin.
1	nitrapyrin	7.97	113/78	16	195.9/135	16
					195.9/195.9	5
2	6-chloro-2-picolinic acid methyl ester^*	7.32	193.9/133	16	112/76	10
					141/113	4
3	pyridine-2-carboxylic acid methyl ester	6.13	107.1/79	4	79.1/52	16
					78.1/51	10

No.	Compound	Retention time/min	Quantitative ion pair (m/z)	Quantitative ion pair collision energy/V	Qualitative Ion pair (m/z)	Qualitative ion pair collision energy/V
* 6-Chloro-2-picolinic acid methyl ester is a derivative of the metabolite of nitrapyrin.
1	nitrapyrin	7.97	113/78	16	195.9/135	16
					195.9/195.9	5
2	6-chloro-2-picolinic acid methyl ester^*	7.32	193.9/133	16	112/76	10
					141/113	4
3	pyridine-2-carboxylic acid methyl ester	6.13	107.1/79	4	79.1/52	16
					78.1/51	10

Compound	Matrix	Linear equation	r²	LOD/(mg/kg)	LOQ/(mg/kg)
Y: peak area of product ion/peak area of internal standard×mass concentration of internal standard; X: mass concentration, g/L. Linear range: 0.025-0.4 mg/L.
Nitrapyrin	wheat	Y=2.20×10^-3X-1.57×10^-2	0.9953	0.01	0.05
	sorghum	Y=2.40×10^-3X+1.00×10^-3	0.9977
	maize	Y=2.50×10^-3+1.12×10^-2	0.9990
	popcorn	Y=2.50×10^-3X-6.50×10^-3	0.9988
6-Chloropicolinic acid	wheat	Y=5.60×10^-3X-2.21×10^-2	0.9999	0.001	0.05
	sorghum	Y=5.30×10^-3X+2.90×10^-3	0.9999
	maize	Y=2.90×10^-3X+5.50×10^-3	0.9995
	popcorn	Y=2.40×10^-3X+2.80×10^-3	0.9995

Compound	Matrix	Linear equation	r²	LOD/(mg/kg)	LOQ/(mg/kg)
Y: peak area of product ion/peak area of internal standard×mass concentration of internal standard; X: mass concentration, g/L. Linear range: 0.025-0.4 mg/L.
Nitrapyrin	wheat	Y=2.20×10^-3X-1.57×10^-2	0.9953	0.01	0.05
	sorghum	Y=2.40×10^-3X+1.00×10^-3	0.9977
	maize	Y=2.50×10^-3+1.12×10^-2	0.9990
	popcorn	Y=2.50×10^-3X-6.50×10^-3	0.9988
6-Chloropicolinic acid	wheat	Y=5.60×10^-3X-2.21×10^-2	0.9999	0.001	0.05
	sorghum	Y=5.30×10^-3X+2.90×10^-3	0.9999
	maize	Y=2.90×10^-3X+5.50×10^-3	0.9995
	popcorn	Y=2.40×10^-3X+2.80×10^-3	0.9995

Compound	Added/(mg/kg)	Wheat		Sorghum		Maize		Popcorn
Compound	Added/(mg/kg)	Recovery/%	RSD/%	Recovery/%	RSD/%	Recovery/%	RSD/%	Recovery/%	RSD/%
Nitrapyrin	0.05	96.4	7.0	84.8	8.7	95.9	9.0	84.4	8.8
	0.1	84.1	2.1	83.1	1.4	89.0	6.5	89.2	8.2
	0.2	92.0	4.2	85.3	4.1	84.5	1.0	92.0	3.6
6-Chloropicolinic acid	0.05	80.4	3.4	88.7	10.1	98.4	2.4	86.7	8.0
	0.1	88.0	5.4	90.8	5.7	93.8	5.0	94.4	4.8
	0.2	90.0	1.8	91.1	2.6	87.4	4.4	83.9	1.9