Use of Solvent Adduct Ions To Confirm Structure of Selected Herbicides with Thermospray Liquid Chromatography/Mass Spectrometry

Abstract

Conventional positive-ion and negative-ion modes (PI and NI ,respectively), the use of ammonium acetate and ammonium formate and the addition of 2% chloroacetonitrile in the liquid chromatographic eluent using filament-on thermospray LC-MS have been applied for the determination of selected herbicides. By using acetonitrile-water and 0.05 M ammonium acetate mixtures, the chlorotriazine herbicides showed [M + (CH 3 CN)H] + and [M -H] -ions as base peaks in PI and NI modes, respectively. When ammonium formate and ammonium acetate were added to methanol-water eluent, the phenylurea herbicides exhibited in PI mode a relevant peak between 50-70% relative intensity corresponding to [M + (CH 3 OH)NH 4 ] + and [M + (CH 3 COOH)NH 4 ]+, respectively, whereas the base peak was [M + NH 4 ] + in both cases. The formation of [M + HCOOHNH 4 ] + was incidently observed in PI when ammonium formate was used. With this ionizing additive and NI the chlorinated phenoxyacid herbicides exhibited [M + HCOO] -as base peak, thus allowing a complementary structural information to [M + CH 3 COO] -, a typical ion obtained whenammonium acetate was added as ionizing additive. The addition of 2% chloroacetonitrile to acetonitrile-water eluent showed in NI mode a [M + Cl] -ion as base peak instead of [M + CH 3 COO] -or [M + HCCO] -ions in combination with other main ions which were assigned to [M -H] -and [M + H] -. Applications are reported for the determination of phenylurea and chlorinated phenoxyacid herbicides in spiked water samples by using PI and NI modes, respectively.

Dilute-and-shoot-based direct nano-electrospray ionization tandem mass spectrometry as screening methodology for multivitamins in dietary supplement and human urine

“…In addition, the use of disposable NS capillary minimizes the possibility of contamination and carry-over effect. Moreover, while ion adducts are more pronounced in NS ionization, the present work uses them as further confirmation of detected metabolites, as previous studies have proved their usefulness, even to the extent of quantification [54] , [55] .The merit of the method also lies within the singularity of the NS tip. Conventional LC-MS methods require each run to consume a new volume of sample for a single purpose.…”