Thermospray herbicides

Phenylurea herbicides (urons). Dinocap, Dinoseb, Benomyl, Carbendazim and Metamitron in Waters [e.g. determination of phenylurea herbicides by reverse phase HPLC, phenylurea herbicides by dichloromethane extraction, determination by GC/NPD, phenylurea herbicides by thermospray LC-MS, Dinocap by HPLC, Dinoseb water by HPLC, Carbendazim and Benomyl (as Carbendazim) by HPLC], 1994... 

D Barcelo, J Albaiges. Characterization of organophosphorus compounds and phenylurea herbicides by positive and negative ion thermospray liquid chromatography-mass spectrometry. J Chromatogr 474 163-173,1989. 

Volmer et al. [11] evaluated the performances of both thermospray and electrospray ion sources for determining trace levels of sulphonylurea herbicides in water. In terms of specificity, they concluded that the latter source, in combination with a tandem mass spectrometer, was superior to the former one. 

An interlaboratory comparison of the performance of thermospray and PBI LC-MS interfaces for the analysis of chlorinated phenoxyacid herbicides was reported by Jones et al. [94]. Except for Silvex, statistically significant differences were observed in the results from the two interfaces. PBI LC-MS exhibited a high positive bias, but a better %RSD at the highest concentration (500 pg/ml). A comparison of the official US-EPA method 515.1 for CPA analysis with on-line solid-phase extraction (SPE) in combination with GC with electron-capture detection (GC-ECD), LC-UV, and PBI LC-MS was reported by Bruner et al. [95]. In this method, liquid-liquid extraction (LLE), as prescribed in the US-EPA method, was replaced by SPE for sample preconcentration. In the LC methods, no derivatization was necessary. Detection limits were in the range of 0.07-0.8 ng/1 for GC-ECD, 0.7-7 ng/1 for PBI-LC-MS, and 6-80 ng/1 for LC-UV. The most accurate methods were LC-UV and GC-ECD, although PBI LC-MS is still more accurate than the US-EPA 515.1 method. 

Pesticides. There are numerous references to the use of HPLC/MS for the analysis of pesticides and herbicides [14, 16-20]. Some major classes of pesticides and herbicides including carbamate, triazines, organophosphorus, and phenolic acid have been analyzed by HPLC/MS using Cl or ion evaporation ionization. While these ionization techniques often resulted in excellent sensitivity (thermospray/MS full scan detection limits of 1-10 ng), usually only [M+H] and/or [M+NH4] ions were formed. This limitation can be overcome using tandem4MS [20], moving belt [17], and most recently through the use of particle beam HPLC/MS. 

Voyksner, R. D. McFadden, W. H. Lammert, S. A. Application of Thermospray HPI.C/MS/MS for the Determination of Triazine Herbicides A Chemical Analysis Series on Application of New Mass Spectrometry Techniques in Pesticide Chemistry Rosen, J., 1987 Vol. 91, Chapter 17, p 247. 

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

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 aoetonitrile-vater and 0.05 M anmonium acetate mixtures, the chlorotriazine herbicides shoved [M + (Cl CN) ] and... 

MAIN IONS AND RELATIVE ABUNDANCES OF THREE HERBICIDES IN THERMOSPRAY LIQUID CHROMATOGRAPHY-MASS SPECTROMETRY USING DIFFERENT ELUENT MIXTURES AND FILAMENT ON... 

A method that uses high performance liquid chromatography/ mass spectrometry (HPLC/MS) for the analysis of chlorinated phenoxyacid herbicides is described. During method development different techniques were used to increase both the sensitivity and the specificity of thermospray HPLC/MS for chlorinated acid herbicides. These included the operation of the instrument in the negative chemical ionization (NCI) mode initiated by discharge and the use of a wire-repeller in the ion source for efficient extraction of positive ions. Single quadrupole repeller-induced and multiple quadrupole collision activated dissociation (CAD) experiments were also performed to increase the structural information of the mass spectra. 

Eight of the nine compounds are chlorinated phenoxyadds dalapon is a chlorinated aliphatic acid. The positive ion thermospray mass spectra of these pesticides are summarized in Table I. The base peak in all cases is the (M+NH4)+ ion for 2,4-DB the (M+H) ion is present No ions were detected for dalapon. Since the protonated molecule is present for 2,4-DB this compound has the highest apparent proton affinity among these herbicides. 

Thermospray LC/MS has been extensively used for the study of sulfonylurea herbicides (1-2). These compounds are thermally labile and can not be successfully analyzed by conventional GC/MS. Early applications of thermospray LC/MS included metabolite identification and product chemistry studies. We have recently evaluated the use of thermospray LC/MS for multi-sulfonylurea residue analysis in crops and have found the technique to meet the criteria for multiresidue methods. LC/MS offers both chromatographic separation and universal mass selectivity. Our study included optimization of the thermospray ionization and LC conditions to eliminate interferences and maximize sensitivity for trace level analysis. The target detection levels were SO ppb in crops. Selectivity of the LC/MS technique simplified sample extraction and minimized sample clean up, which saved time and optimized recovery. Average recovery for these compounds in crop was above 85%. 

General LC/MS Conditions for Sulfonylurea Multiresidue Analysis. We have developed general thermospray LC/MS conditions for the purpose of separating and detecting six different sulfonylurea herbicides. These conditions can be used as a guide fra- a variety of LC/MS residue applications which may require the analysis of one or more of these herbicides. Our procedure includes GLEAN (chlorsulfuron), ALLY (metsulfuron methyl), HARMONY (thiameturon) and EXPRESS cereal herbicides, CLASSIC (chlorimuron ethyl) soybean herbicide and OUST (sulfometuron-methyl) noncrop land herbicide. (Structure 1)... 

Figure 1 shows the LC/MS thermospray total ion chromatogram of 0.25 p.g standard mixture of the six sulfonylurea herbicides. Gradient HPLC conditions were used to separate the six compounds in less than 25 minutes total run time. The mobile phase composition was kept isocratic at 30% acetonitrile/.05M formic acid for the first 15 minutes to separate the four herbicides HARMONY, ALLY, OUST and GLEAN. A gradient from 30% acetonitrile to 60% in 10 minutes was then used to elute EXPRESS and CLASSIC. An acidified mobile phase is used with sulfonylureas to keep them in the undissociated form which is retained on the HPLC column (3). Organic acids are recommended for use with LC/MS to prevent the formation of deposits in the mass spectrometer source and to prevent clogging of the thermospray interface probe tip. In this work we used formic acid. 

Figure 1. Thermospray LC/MS total ion chromatogram of 0.25 (ig standard mixture of six sulfonylurea herbicides.

A typical thermospray ionization mass spectrum for a sulfonylurea contains a weak protonated molecular ion and three to four characteristic fragment ions. Figure 2 shows the thermospray positive ion mass spectrum for HARMONY. The spectrum contains a protonated molecular ion at m/z 388, the sulfonamide ammonium adduct ion at m/z 239 and the protonated triazine urea fragment ion at m/z 184. At the same time, Figure 3 shows the positive ion thermospray mass spectrum for LONDAX. It contains the protonated pyrimidine amine at m/z 156, the protonated pyrimidine urea is at m/z 199 and the sulfonamide ammonium adduct ion at m/z 247. LONDAX (bensulfuron methyl) is a sulfonylurea rice herbicide and it elutes between EXPRESS and CLASSIC if we use the LC conditions outlined in Figure 1. HARMONY and LONDAX thermospray spectra were generated with the thermospray vaporizer tip temperature at 150°C and the source block temperature at 320°C. 

Figure 5. Effect of thermospray vaporizer tip temperature on the total ion signal for a sulfonylurea herbicide.

The thermospray LC/MS with selected ion monitoring is applicable to multiresidue sulfonylurea herbicides. This method offers simultaneous extraction and analysis of three herbicide compounds in a fast and efficient way, in addition to good recovery. 

L. M. Shalaby, Trace Level Analysis of Thermally Labile Herbicides by on-Line Thermospray LC/MS, 33rd Annual Conference on Mass spectrometry and Allied Topics, San Diego, CA, 1985... 

Thermospray ionization was especially applied between 1987 and 1992 in combination with LC-MS for a wide variety of compound classes, e.g. pesticides and herbicides, drugs and metabolites, alkaloids, glycosides and several other natural products, as well as peptides. 

There are many studies available concerning the characterization of interface and ionization performance for the thermospray LC-MS analysis of pesticides, herbicides and insecticides, the improvement of detection limits and information content of the mass spectra. Compound classes most frequently studied are the carbamates, organophosphorous pesticides, triazine and phenylurea herbicides, chlorinated phenoxy acetic acids, and sulphonylureas. 

Carbamate, methyl -urea and oxime pesticides and herbicides AgO.IM NH,0 CCH, Large dynamic range of 10 Thermospray HPLC-MS Ippb [25]... 

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