Evidence for thermal decomposition contributions to the mass spectra of chlorinated phenoxyacid herbicides obtained by particle beam liquid chromatography mass spectrometry

Abstract

The spectral quality of a group of chlorinated phenoxyacid herbicides has been shown to degrade under certain conditions upon introduction into the mass spectrometer by a particle beam interface. Experiments were performed to investigate these changes in spectra. Normalized ion chromatograms were generated for the herbicides, and the results showed a broadening of the profiles of some ions, indicating a longer residence time in the ion source. These ions were postulated as coming from the ionization of thermal degradation products from the herbicides. The generation of these ions was dependent on ion source temperature, analyte concentration, and, by implication, ion source cleanliness. Tandem mass spectrometry experiments were performed on these ions from the herbicides and ions from the corresponding phenols. The tandem mass spectra of the ions from the herbicides were similar to the tandem mass spectra of the ions from the phenols. Therefore, it appears that the particle beam mass spectra of the chlorinated phenoxyacid herbicides are composite spectra with contributions from the gas phase ionization of the parent herbicides and thermal decomposition products.

Identification of Carbamates by Particle Beam/Mass Spectrometry

“…Thermal decomposition is commonly known to occur in GC/MS of carbamates (see, e.g., Refs 3 and 4) and it has also been reported to occur in PBMS of some carbamates ;13 therefore, the ion source temperature may be a critical parameter. In addition, the ion source temperature might give rise to "tailingÏ of the chromatographic peak ; this phenomenon was conÐrmed by the present experiments, as reported by Betowski et al 37 The tailing is attributed to retarded evaporation of the analyte upon ion source wall impact of the particle beam, as it is corroborated by a decrease in the chromatographic peak width with an increase in the source temperature.37 A selection of 19 carbamates were used to study the e †ect of the source temperature (range 125È 250 ¡C at 25 ¡C intervals) on the ammonia PCI mass spectra ; FI experiments were performed with three injections of 500 ng of each compound. Two typical examples of the inÑuence of thermal degradation on spectra are shown in Fig.…”

The role of column liquid chromatography-mass spectrometry in environmental trace-level analysis. Determination and identification of pesticides in water

“…This was convincingly shown for organophosphorus pesticides, carbamates and their TPs [42], triazines and phenylureas [43,44] and chlorinated phenoxy acids [45,46]. One case has been reported in which the LC-based introduction of the analytes, phenoxy acid herbicides, caused a reduction of the spectral quality due to thermal decomposition [46], while Honing et al [47] noted similar phenomena for carbamates. In the latter study, experimental conditions such as ion-source pressure and temperature in flow-injection analysis (FIA) -PB-MS were found to be important parameters with the strongest effects being observed for carbofuran.…”

Electron capture ionization of explosives with a microflow rate particle beam interface

“…As pointed out by Jones et a1. [12] and also discussed in recent papers [6,13], the way heat is transferred to the solute particles and how the particles interact with the hot source surface is still a question. The vaporization process is tolerated poorly by many heat-sensitive compounds, and explosives fall into this category.…”