Determination of Acid Herbicides Using Modified QuEChERS with Fast Switching ESI⁺/ESI^– LC-MS/MS

Abstract

A method for the determination of 35 acid herbicides in food matrices was developed, validated, and implemented. It utilizes a modified QuEChERS extraction procedure coupled with quantitation by liquid chromatography tandem mass spectrometry (LC-MS/MS). The acid herbicides analyzed are all organic carboxylic acids, including the older chlorophenoxy acid herbicides such as 2,4-dichlorophenoxyacetic acid (2,4-D), dicamba, 4-chlorophenoxyacetic acid (4-CPA), quinclorac, and many of the newer imidazolinone herbicides such as imazethapyr and imazaquin. In the procedure, 10 mL of water is added to 5 g of sample and then extracted with 1% formic acid in acetonitrile for 1 min. The acetonitrile phase is salted out of the extract by adding sodium chloride and magnesium sulfate, followed by centrifugation. The acetonitrile is diluted 1:1 with water to enable quantitation by LC-MS/MS using fast switching between positive and negative electrospray ionization modes. The average recoveries for all the compounds except aminocyclopyrachlor were 95% with a precision of 8%. The method detection limits for all residues were less than 10 ng/g, and the correlation coefficients for the calibration curves was greater than 0.99 for all but two compounds tested. The method was used successfully for the quantitation of acid herbicides in the FDA's total diet study. The procedure proved to be accurate, precise, linear, sensitive, and rugged.

Dissipation and Residues of Dichlorprop-P and Bentazone in Wheat-Field Ecosystem

“…Besides that, to develop a reliable multi-residue method that can sufficiently extract acidic pesticides from cereals, the pH of the extraction is also important and should be suitably controlled. There are many published methods [ 33 , 34 , 35 ] for the analysis of acidic herbicides in cereals and related matrices recommended extraction with acidified solvent because acidic herbicides were more stable at low pH. Other authors reported that extract acidic herbicides with alkaline hydrolysis which could break up any covalent bond between the matrix components and acidic pesticides [ 36 ].…”

Evaluation of a Stable Isotope-Based Direct Quantification Method for Dicamba Analysis from Air and Water Using Single-Quadrupole LC–MS

“…Sub-picogram level detection of dicamba from water was also reported using paired-ion electrospray ionization (ESI) mass spectrometry [ 14 ]. Furthermore, several MS-based dicamba analytical methods have been reported for food items [ 17 , 18 ], water and agricultural cleanouts [ 13 , 14 , 16 , 19 , 20 , 21 , 22 ], air samplers [ 6 , 23 , 24 ], crops like apple, pepper, brown rice, and soybean [ 25 ], tobacco [ 26 ], barley [ 27 ], soybean [ 28 ], rice [ 29 ], as well as in other agricultural commodities [ 30 ]. Most of these protocols rely on triple quadrupole and/or higher resolution MS instruments, although quantification procedures using LC–diode array detection (DAD) [ 24 ] and single-quadrupole LC–MS [ 6 , 31 ] have been reported.…”

Multifamily Determination of Phytohormones and Acidic Herbicides in Fruits and Vegetables by Liquid Chromatography–Tandem Mass Spectrometry under Accredited Conditions

“…It is easy to find monofamily methods for the determination of phytohormones (auxins [ 10 , 11 ], cytokinins [ 12 , 13 ], gibberellins [ 14 , 15 ]) or methods specifically developed for the analysis of acidic herbicides [ 16 , 17 , 18 ] in the literature. Some scientific publications have even jointly analyzed various families of phytohormones [ 19 , 20 , 21 , 22 , 23 , 24 ].…”