Herbicide mobility acids

A triple-quadrupole mass spectrometer with an electrospray interface is recommended for achieving the best sensitivity and selectivity in the quantitative determination of sulfonylurea herbicides. Ion trap mass spectrometers may also be used, but reduced sensitivity may be observed, in addition to more severe matrix suppression due to the increased need for sample concentration or to the space charge effect. Also, we have observed that two parent to daughter transitions cannot be obtained for some of the sulfonylurea compounds when ion traps are used in the MS/MS mode. Most electrospray LC/MS and LC/MS/MS analyses of sulfonylureas have been done in the positive ion mode with acidic HPLC mobile phases. The formation of (M - - H)+ ions in solution and in the gas phase under these conditions is favorable, and fragmentation or formation of undesirable adducts can easily be minimized. Owing to the acid-base nature of these molecules, negative ionization can also be used, with the formation of (M - H) ions at mobile phase pH values of approximately 5-7, but the sensitivity is often reduced as compared with the positive ion mode. 

Lord and Pawliszyn" developed a related technique called in-tube SPME in which analytes partition into a polymer coated on the inside of a fused-silica capillary. In automated SPME/HPLC the sample is injected directly into the SPME tube and the analyte is selectively eluted with either the mobile phase or a desorption solution of choice. A mixture of six phenylurea pesticides and eight carbamate pesticides was analyzed using this technique. Lee etal. utilized a novel technique of diazomethane gas-phase methylation post-SPE for the determination of acidic herbicides in water, and Nilsson et al. used SPME post-derivatization to extract benzyl ester herbicides. The successful analysis of volatile analytes indicates a potential for the analysis of fumigant pesticides such as formaldehyde, methyl bromide and phosphine. 

Guillaume, Y.C. et al.. Chiral discrimination of phenoxypropionic acid herbicides on teicoplanin phase effect of mobile phase modifier, Chromatographia, 55, 143, 2002. 

CE offers unsurpassed efficiency in chiral separations. As enantiomers have identical electrophoretic mobilities, some chiral complexing reagents must be added to the separation buffer to form diastereo-meric complexes in dynamic equilibrium. One of the most popular procedures is the addition of CDs to the separation buffers. The outstanding chiral separation ability of the CE systems is accredited for phenoxy acid herbicides and triazole fungicides, which possess at least one chiral center. Addition of CDs can also be used for separating positional isomers as complex mixtures of vmsubstituted naphthalene mono- to tetrasulfonic acids by CE (Figure 5). 

Mobile phases Eor RP-LC, mixtures of an aqueous component and organic solvents are invariably used. The aqueous component is eventually buffered (e.g., phosphate buffers l-10mmoll for triazines and phenylureas) or acid additivated (e.g., 0.1% phosphoric acid for chlorophenoxy acidic herbicides or 0.1-0.4% for phenoxyacetic herbicides). The organic solvents are mainly methanol, acetonitrile, or their mixtures. For NP-LC, hexane, dichloromethane, ethanol, and iso-propanol are frequently used. 

Alkyl-glucoside monomer, S = phenoxy acid herbicide, H, = solute apparent mobility, /igp = solute electrophoretic mobility, neo - electro-osmotic mobility... 

Acid amide herbicides are nonionic and moderately retained by soils. The sorption of several acid amide herbicides has been investigated (369). Acetochlor [34256-82-1] is sorbed more than either alachlor or metolachlor, which are similarly sorbed by a variety of soils. Sorption of all the herbicides is well correlated to soil organic matter content. In a field lysimeter study, metolachlor has been found to be more mobile and persistent than alachlor (370) diphenamid [957-51-7] and napropamide [15299-99-2] have been found to be more readily leached (356). 

The effect of the mobile phase modifier was investigated for a series of phen-oxypropionic acid (PEA) herbicides on a teicoplanin CSP [85, 86] an increasing enantioselectivity was found with increasing MeOH content in the mobile phase, attributed to restriction of the solute association with the TE CSP, which led to favorable stereoselective interactions. 

Other herbicidal phenoxyacetic and phenoxypropionic acids have some properties similar to those of (2,4-dichlorophenoxy)acetic acid, but often have quite different species selectivity. Some of the differences can be explained on the basis of molecular stability, persistence, or mobility in the toxic form, as well as on the basis of differences in solubility and in absorption through leaves or roots. 

Typically, only 0.01-10% of the mass of pesticide compounds applied to fields is detected in streams [91]. The remaining 90-99% of pesticides adsorb to soil, percolate into groundwater, or volatilize [79]. The major degradates of the most heavily used herbicides found in surface water have not been studied widely. Many chemical properties of pesticides affect the amounts transported to streams. In general, acetanilide herbicides are more soluble in water, and thus more mobile than are the triazines [92], The solubilities of sulfonated degradates of acetanilides (ethane sulfonic acid, or ESA), can be 10 times the solubility of the parent compound [93]. The greater mobilities of the degradates of the acetanilides (amide family) can explain these com-... 

---