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

Dicamba is a moderately volatile herbicide used for post-emergent control of broadleaf weeds in corn, soybean, and a number of other crops. With increased use of dicamba due to the release of dicamba-resistant cotton and soybean varieties, growing controversy over the effects of spray drift and volatilization on non-target crops has increased the need for quantifying dicamba collected from water and air sampling. Therefore, this study was designed to evaluate stable isotope-based direct quantification of dicamba from air and water samples using single-quadrupole liquid chromatography-mass spectrometry (LC-MS). The sample preparation protocols developed in this study utilize a simple solid-phase extraction (SPE) protocol for water samples and a single-step concentration protocol for air samples. The LC-MS detection method achieves sensitive detection of dicamba based on selected ion monitoring (SIM) of precursor and fragment ions and relies on the use of an isotopically labeled internal standard (IS) (D3-dicamba), which allows for calculating recoveries and quantification using a relative response factor (RRF). Analyte recoveries of 106-128% from water and 88-124% from air were attained, with limits of detection (LODs) of 0.1 ng mL-1 and 1 ng mL-1, respectively. The LC-MS detection method does not require sample pretreatment such as ion-pairing or derivatization to achieve sensitivity. Moreover, this study reveals matrix effects associated with sorbent resin used in air sample collection and demonstrates how the use of an isotopically labeled IS with RRF-based analysis can account for ion suppression. The LC-MS method is easily transferrable and offers a robust alternative to methods relying on more expensive tandem LC-MS/MS-based options.

Applicability of multisyringe chromatography coupled to on-line solid-phase extraction to the simultaneous determination of dicamba, 2,4-D, and atrazine.

Simultaneous determination of three herbicides (dicamba, 2,4-D, and atrazine) has been achieved by on-line solid-phase extraction (SPE) coupled to multisyringe chromatography (MSC) with UV detection. The preconcentration conditions were optimized; a preconcentration flow rate of 0.5 mL min(-1) and elution at 0.8 mL min(-1) were the optimum conditions. A C(18) (8 mm i.d.) membrane extraction disk conditioned with 0.3 mol L(-1) HCl in 0.5% MeOH was used. A 3-mL sample was preconcentrated, then eluted with 0.43 mL 40:60 water-MeOH. A C(18) monolithic column (25 mm × 4.6 mm) was used for chromatographic separation. Separation of the three compounds was achieved in 10 min by use of 0.01% aqueous acetic acid-MeOH (60:40) as mobile phase at a flow rate of 0.8 mL min(-1). The limits of detection (LOD) were 13, 57, and 22 µg L(-1) for dicamba, 2,4-D, and atrazine, respectively. The sampling frequency was three analyses per hour, and each analysis consumed only 7.3 mL solvent. The method was applied to spiked water samples, and recovery between 85 and 112% was obtained. Recovery was significantly better than in the conventional HPLC-UV method. These results indicated the reliability and accuracy of this flow-based method. This is the first time this family of herbicides has been simultaneously analyzed by on-line SPE-MSC using a monolithic column.

The evaluation of carbon nanotubes as a sorbent for dicamba herbicide.

The potential of carbon nanotubes (CNTs) as a novel sorbent for extraction of dicamba, a highly polar acidic herbicide, from aqueous samples was evaluated. The sorption capacity of CNTs increases remarkably with decreasing sample pH. The solution of ACN and ammonia (80:20 v/v) was found to be the most effective as the eluent for desorption from a 0.2 g CNT cartridge. The method was tested for river water samples with the LOD of 2 microg/L (for 100 mL sample) and compared with C18 bonded silica.