Capillary electrophoresis-electrospray mass spectra of the herbicides paraquat and diquat

Abstract

The positive ion electrospray mass spectra of the quaternary ammonium salt herbicides paraquat and diquat are examined by on-line separation with capillary electrophoresis (CE) and by direct infusion of the analytes. The analytes are separated by CE in 7-10 min at pH 3.9 in 50% methanol-water by using several different separation buffer electrolytes. The capillary electrophoresis-electrospray ionization (CE-ES) mass spectra of paraquat and diquat consist primarily of doubly charged molecular ions, singly charged molecular ions, and singly charged deprotonated ions. The direct infusion spectra consist primarily of doubly charged molecular ions and singly charged deprotonated ions. The relative abundances of the doubly charged and deprotonated ions depend strongly on the presence or absence of ammonium ion in the CE separation buffer or the direct infusion solution. A deprotonation mechanism is proposed in which the free base ammonia is the deprotonating agent in the desolvating charged droplets or in the gas phase. The analytical potential of the CE-ES electrospray approach for environmental analyses is evaluated in terms of the precision of replicate injections, linear concentration range, and estimated detection limit.

Reduction of cationic free-base meso-tris-N-methylpyridinium-4-yl porphyrins in positive mode electrospray ionization mass spectrometry

“…Ions formed by one electron reduction from nonmetallated dicationic species in solution were previously observed in positive-mode electrospray mass spectrometry for ionic compounds such as diquaternary pyridinium salts [11][12][13] and free-base N-alkylpyridiniumyl porphyrin salts [14]. One-and two-electron reductions of the cations of metallated N-alkylpyridiniumyl porphyrin salts were also reported, when electrospray was used in the positive mode [15][16][17].…”

A Simple High Performance Liquid Chromatography/Ionspray Tandem Mass Spectrometry Method for the Direct Determination of Paraquat and Diquat in Water

“…8,9,13,14 Both Yoshida et al 11 and Barceló et al 12 have reported methods using HPLC/MS with thermospray ionization, while both Song and Budde 8 and Moyano et al 9 developed methods incorporating capillary electrophoresis with electrospray mass spectrometry. HPLC separation methods that incorporate nonvolatile buffers or ion-pair reagents cannot be used with mass spectrometry.…”

“…These compounds are not easily analysed by GC without an extensive sample preparation and derivatization procedure. 4 High performance liquid chromatography (HPLC) [5][6][7] or capillary electrophoresis (CE) 5,8,9 are the methods of choice for these ionic species. The United States Environmental Protection Agency method (EPA method 549.1) for paraquat and diquat in water requires ion-pair extraction to concentrate the sample prior to analysis using HPLC with diode-array detection.…”

Analysis of Dabsyl-Cl Derivated Amino Acids by High Performance Liquid Chromatography and Tandem Mass Spectrometry

“…Although a better separation technique with capillary electrophoresis (CE) has been attempted (Terabe et al, 1991), the selectivity with UV or fluorescent spectrometry still has its limitations. Mass spectrometry (MS) has been employed successfully with CE in the analysis of phenolic compounds (Lafont et al, 1999), herbicides (Song & Budde, 1996), drugs and their metabolites (Lu et al, 1996), and carboxylic acids (Johnson et al, 1999) with the advantage of high selectivity and sensitivity. It was not until recently that CE-MS was claimed to be effective in the analysis of underivatized amino acids (Soga & Heiger, 2000).…”