Determination of Acidic Pesticides in Water by a Benchtop Electrospray Liquid Chromatography Mass Spectrometer

Abstract

A very sensitive and specific analytical procedure for determining 20 acidic pesticides in aqueous environmental samples using pneumatically assisted electrospray (ES) LC/MS is presented. This procedure involves passing 1-and 4-L river water and drinking water samples, respectively, through a 1-g graphitized carbon black (GCB) extraction cartridge. By exploiting the presence of positively charged active centers on the GCB surface, isolation of the acidic pesticides from base/neutral species was made possible by differential elution. Recoveries of the analytes were higher than 85%, irrespective of the aqueous matrix in which they were dissolved. Adoption of the ion pair technique by addition of 0.1 mmol/L K2HPO4 and 0.2 mmol/L tetrabutylammonium fluoride to the mobile phase allowed analytes to be analyzed as preformed ions. A conventional 4.6-mm-i.d. reversed-phase LC C-18 column operating with a 1 mL/min flow of the mobile phase was used for chromatographing the analytes. A flow of 30 μL/min of the column effluent was diverted to the ES source, while the rest of the mobile phase was delivered to a UV detector set at 220-nm wavelength. The effects of the nature of the ion pair forming agent and its counterion as well as its concentration in the mobile phase on the response of the ES/MS detector were investigated. The effects of varying the skimmer cone voltage on the production of diagnostic fragments and the response of the MS detector were also evaluated. For the analytes considered, the response of the mass detector was linearly related to the amount of the analytes injected between 2.5 and 200 ng. A certain variation of the ion signal for the analytes considered occurred after several hours of continuous use of the LC/ES/MS instrumentation. For routine use, then, analyte quantitation could be better performed by the UV trace method while entrusting unambiguous identification of the analytes to the MS detector. The limits of sensitivity (signal-to-noise ratio = 3) of the method for the pesticides considered in drinking water and surface water samples were estimated to be about 2-6 and 8-25 ng/L, respectively

Particle discriminator interface for nanoflow ESI-MS

“…Typical solution flow rates for LC-MS are on the order of 100 -2000 L/min. It has been common practice to split the LC flow, to reduce the volume of sample entering the electrospray source region [8], but recently new ion sources have been developed that allow stable operation with solution flow rates of greater than 2 mL/min [9]. The development of high flow rate electrospray ion sources has primarily been driven by the LC market because of the lack of LC systems available for routine operation at lower solution flow rates.…”

Analysis of Triazines and Associated Metabolites with Electrospray Ionization Field-Asymmetric Ion Mobility Spectrometry/Mass Spectrometry

“…A sample handling scheme involving solid-phase extraction (SPE) with graphitized carbon black followed by liquid chromatography (LC) with ultraviolet (UV) and massselective detection has been presented for dealing with pesticides, including atrazine. [6][7][8] In these studies, SPE concentration factors were of the order of 10 4 . The intrinsic sensitivity of the mass spectrometer (MS) was about 20 ppb; including SPE the LOD was 3 to 30 ppt depending on the nature of the aqueous matrix 6 (even LOD as low as 0.2 ppt has been reported 9 ).…”

“…[6][7][8] In these studies, SPE concentration factors were of the order of 10 4 . The intrinsic sensitivity of the mass spectrometer (MS) was about 20 ppb; including SPE the LOD was 3 to 30 ppt depending on the nature of the aqueous matrix 6 (even LOD as low as 0.2 ppt has been reported 9 ). It was suggested 6 that the best setup for the final analysis would be an LC-MS system which includes a UV detector, the UV trace best aimed for quantitation, and the MS (possibly including collision-induced dissociation or tandem MS) providing for unambiguous identification.…”

Stable gradient nanoflow LC-MS

“…and electrospray ionization-mass spectrometry (ESI-MS) has evolved substantially since its initial implementation in the 1980s [1]. Traditional LC systems operated at solvent flow rates that were orders of magnitude higher (hundreds of L/min to mL/min) than those used for mass spectrometry (tens of L/ min), resulting in the need for solvent flow splitters [2]. Some of the subsequent improvements were focused on the use of nebulizer gases [3] and heating [4,5] for stabilization of the electrospray process to accommodate higher LC solvent flows.…”