Separation of 18 modern plant protectants using cyclodextrin modified micellar electrokinetic chromatography including an ion-pairing reagent

Abstract

Abstract.A cyclodextrin-modified micellar electrokinetic chromatography separation for 18 different pesticides (metsuifuron-methyl, rimsulfuron, thifensulfuron-methyl, desethylatrazine, desisopropylatrazine, atrazine, simazine, terbuthylazine, 2,4-D, MCPR MCPB, dicamba, linuron, alachlor, metolachlor, orbencarb, propiconazole, prochloraz) from eight different substance classes with very varying chemical and physical properties is presented. In particular acidbase characteristics and water-octanol distribution coefficients diverge in wide ranges. 3-cyclodextrin was successfully employed as a modifier in separating the hydrophobic analytes. Peak distortion of some neutral analytes, which is devoted to the methanol content of the sample zone, was reduced by increasing the SDS concentration. Methanol in the sample is necessary for a better solubility of the hydrophobic pesticides. Few optima of SDS concentration exist allowing the separation of sulfonylureas as well as phenoxy acids and hydrophobic pesticides. An improved resolution of the sulfonylureas was achieved with tetramethylammonium chloride, which was used as an ion-pairing reagent.' Final operating conditions for the separation of all these plant protectant compounds by MEKC in just one single run are a 27mmolL -1 phosphate buffer, pH 8.03, with 95mmolL-1SDS, 5rmnolL =1 /3-cyclodextrin and 10 mmolL -1 tetramethylammonium-chloride.Key words: capillary electrophoresis, micellar electrokinetic chromatography, multi-residue-analysis, pesticide analysis. * To whom correspondence should be addressedThe relevance of high performance capillary electrophoresis (HPCE) applied in multi-residue methods for trace analysis of plant protectants in environmental samples has attained growing interest in the past few years. With a few exceptions authors restrict themselves to one class of pesticides, such as triazines [1-3], hydroxy-or methoxymetabolites of triazines, either alone or in combination with their parent compounds [4][5][6][7], phenoxy acids [8-11 ], phenylurea-[12], sutfonylurea-[13, 14J or dipyridylium-pesticides [15,16]. The application of capillary zone electrophoresis (CZE) dominates over micellar electrokinetic chromatography (MEKC). For neutral analytes or more complex pesticide mixtures MEKC is selected [17][18][19][20][21][22]. HPCE is more versatile than HPLC and GC since there is nearly no restriction to certain pesticide classes and therefore derivatization becomes unnecessary. Within the HPCE-techniques MEKC is more likely to separate complex substance mixtures than CZE, which is restricted to charged substances. This is due to various surfactants and modifiers that can be selected and combined in MEKC to optimize separation.In the field of multi-residue separation several successful attempts are published which show the general viability of MEKC technique. These approaches, however, were confined to mixtures of hydrophilic and moderately hydrophobic pesticides [18,21] including one hydrophobic pesticide at maximum [22]. If more than one hydrophobic ...

Separation and analysis of triazine herbcide residues by capillary electrophoresis

“…Several MEKC methods regarding the determination of triazines in different matrices have been published (Loos and Niessner, ; Dinelli et al , ; Desiderio and Fanali, ; Kubilius and Bushway, ; Lanças and Ruggiero, ; Stutz and Malissa ; Penmetsa et al , ; Yu and Cole, ; Carabias‐Martínez et al , ). This is due to the variety of surfactants and modifiers that can be selected and combined in MEKC to optimize separation.…”

The effect of operating variables in microemulsion electrokinetic capillary chromatography

“…Cyclodextrins are generally water-soluble and have a low UV activity which permit use of low UV wavelengths for sensitive detection [40]. The extreme water-insolubility of some species in sample mixtures necessitates use of cyclodextrin additives with micellar buffers to achieve resolution and in this case, insoluble compounds should dissolve better in the microemulsion [41]. 13-Cyclodextrin was chosen for this study, and the maximum amount of CD which could be dissolved in the standard microemulsion was 25 mM, higher concentration were found to be cloudy after 30 min of sonication.…”

Analytical tools for the analysis of β-carotene and its degradation products

“…Therein, CDs possess a rigid hydrophobic cavity providing a favorable and water-protective microenvironment for β-carotene, whereas hydroxyl groups of the glucose moieties protrude into the circumfluent bulk solution and ensure the water wettability of CD [ 98 , 99 ]. Although frequently applied as chiral selectors, CDs have also been used to generally improve the solubility of hydrophobic compounds in aqueous solutions [ 100 ]. Different carotenoids have been tested for their capability to form host-guest complexes with CD variants.…”