Mária Chalányová

Liquid chromatographic method development for determination of fungicide epoxiconazole enantiomers by achiral and chiral column switching technique in water and soil

High-performance liquid chromatography (HPLC) in both chiral isocratic and achiral-chiral column switching mode was employed for optimization of separation conditions, separation and determination of fungicide epoxiconazole in real samples. Two enantiomers of commercially available triazole fungicide epoxiconazole (BAS 480 F), first registered in 1993, were resolved for the first time on a microcrystalline cellulose triacetate (MCTA). A low-cost home-packed chiral column (150x3 mm, 15-25 microm, MCTA, Merck) enabled baseline enantiomeric resolution of two enantiomers of the fungicide epoxiconazole produced commercially. The effects of concentration of organic modifiers (methanol, ethanol) in mobile phase, flow-rate and temperature were studied. The isocratic chiral HPLC method allows determination of the enantiomers in tap and surface water within the range 1-1000 mg/l by direct injection (20 microl) of the sample. Using the achiral (C18)-chiral (MCTA) column-switching technique and 1-ml sample volume, injection of 0.050 mg/l of epoxiconazole enantiomers can be conveniently determined by UV detection at 230 nm. The same method applied to methanolic soil extracts allows determination of 0.2 mg/kg of epoxiconazole enantiomers in addition to the other 10 commonly used pesticides in fortified soils.

Preparative capillary isotachophoresis as a sample pretreatment technique for complex ionic matrices in high-performance liquid chromatography

Abstract Preparative capillary isotachophoresis (ITP) was studied for sample pretreatment in the high-performance liquid chromatography (HPLC) of ionogenic analytes present in complex ionic matrices (urine and humic substances). Sulphanilate, methyl (4-aminobenzenesulphonyl)carbamate (asulam), 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-methyl-4-chlorophenoxyacetic acid (MCPA) served as model analytes. A high sample load of the ITP pretreatment was achieved by performing the preparative separations in tubes of 2.0 and 1.0 mm I.D. in the column-coupling configuration of the separation unit. The ITP separation according to ionic mobilities was combined with gradient elution HPLC in the ion-suppression mode to achieve highly dissimilar (orthogonal) separation systems in both techniques. The pretreatment provided the sample fraction for the HPLC analysis containing in addition to the analyte (sulphanilate) only ca. 2–3% of the urine matrix (spread along the complete elution profile) when a pair of discrete spacers defined the trapped constituents. Under these conditions the limit of detection for sulphanilate in urine could be reduced by more than two orders of magnitude. A high recovery of the pretreatment procedure [99 ± 1.5% for a 1.7 ppm (w/w) concentration of sulphanilate] was typical. For asulam, 2,4-D and MCPA present in a humic matrix it was shown that the ITP pretreatment may also be effective for multi-residue procedures while favourable analytical characteristics of the pretreatment such as recovery and efficient sample clean-up are maintained.

Some theoretical and practical aspects in the separation of humic substances by combined liquid chromatography methods

Permanent need to understand nature, structure and properties of humic substances influences also separation methods that are in a wide scope used for fractionation, characterization and analysis of humic substances (HS). At the first glance techniques based on size-exclusion phenomena are the most useful and utilized for relating elution data to the molecular mass distribution of HS, however, with some limitations and exceptions, respectively, in the structural investigation of HS. The second most abundant separation mechanism is reversed-phase based on weak hydrophobic interactions beneficially combined with the step gradients inducing distinct features in rather featureless analytical signal of HS. Relatively great effort is invested to the developments of immobilized-metal affinity chromatography mimicking chelate-forming properties of HS as ligands in the environment. Surprisingly, relatively less attention is given to the ion-ion interactions based ion-exchange chromatography of HS. Chromatographic separation methods play also an important role in the examination of interactions of HS with pesticides. They allow us to determine binding constants and the other data necessary to predict the mobility of chemical pollutants in the environment. HS is frequently adversely acting in analytical procedures as interfering substance, so more detailed information is desired on manifestation of its numerous properties in analytical procedures. The article topic is covered by the review emphasizing advances in the field done in the period of last 10 years from 2000 till 2010.

Dependence of preferential solvation of liquid chromatographic sorbents in mixed eluents on pressure

Abstract Pronounced baseline perturbations were observed in alternating recycling liquid chromatographic experiments when mixed eluents and a refractometric detector were applied. These perturbations were caused by local variations in the effluent composition most probably due to changes in the extent of preferential salvation of the column packings with pressure. Experimental support of this hypothesis is presented and the possible practical aspects of this phenomenon are briefly discussed.

Reversed phase liquid chromatography trace analysis of pesticides in soil by on‐column sample pumping large volume injection and UV detection

The idea of utilization of one hydraulic line of a common commercial HPLC pump for direct on-column sample pumping injection of large sample volumes, 20 mL, was further investigated with the aim to develop multicomponent pesticides trace residues HPLC method in gram soil samples. Target pesticides group involve asulam, atrazine, 2,4-D, PCA, propazine, simazine, 4-chloro-2-methylphenoxyacetic acid, 2-(4-chloro-2-tolyloxy) propionic acid, chlortoluron, metoxuron, epoxiconazole. The results proved the applicability of this approach in experiments with mixtures of analytes at low ng/mL levels. Analysis of 20 mL of soil leachates and extracts of fortified soil samples containing these pesticides at the 10-50 ng/g level (in dry soil) revealed good figures of merit, also in the presence of large excess of humics. LODs achieved by detection at 220 nm evaluated from calibration runs of spiked soil extracts by Hubaux et al. method ranged from 5-12 ng per injected volume. For 20 mL large volume injection it represents 0.25-0.6 ng/mL of diluted soil extract, or 2.5-6 ng/mL of crude extract, or 6-5 ng/g dry soil. Recoveries of pesticides at concentration levels approaching half of maximum allowable concentration of pesticides in soil (100 ng/g) ranged from 85 to 98% with acceptable reproducibility, except asulam and metoxuron.

Effect of Pressure on Preferential Sorption within Column Packing: Possible Explanation of some Unexpected Results in GPC with mixed Eluents

Abstract It is shown that pressure affects the extent of preferential sorption of mixed eluent components on the surface of GPC column packing. In some systems, this may result in base line perturbations and possibly also in changes of size, shape and position of sample peaks when pressure is changed within column either due to variation in the flow rate or as a result of partial blocking of column end fittings and connecting capillaries. The described phenomenon could lead to erroneus GPC results. On the other hand, it may help to explain some unexpected and artificial results obtained in GPC separations with mixed eluents.

The posibility of soil micromycetes produced the abscisic acid

The typical soil micromycetes Aspergillus niger and Cladosporium cladosporioides from the family moniliaceae were investigated with emphasis on production of ABA into the culture medium. The both fungi were cultivated in a static liquid Czapek — Dox medium and agar Czapek — Dox medium. Aspergillus niger and Cladosporium cladosporioides showed ability to produce ABA. Analytical detection of ABA from the culture medium was performed by TLC combinated with biotest and HPLC with spectroscopy.

RPHPLC analysis of some nitrophenols

Problem of nitrophenols group analysis as well as separation to individuals is still attracting attention of research and practicing chemists, environmental chemists and the others. Chromatographic behaviour in RPHPLC systems expressed by such parameters as retention time, sorption capacity, selectivity and/or elution order was studied for group of 8 nitrophenols: 2,4,6-trinitrophenol, 2-nitrophenol, 3-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol, 2,5-dinitrophenol, 2,6-dinitrophenol and 4-nitro-3-cresol. Condition for baseline separation of almost all of these nitrophenols on Separon SGX C18 were chosen. Sorption capacities were tested for 4 different RP materials. The data will be used for devising of Solid Phase Extraction (SPE) and/or column switching schema in RPHPLC sample pretreatment.

Analysis of mercury(II), methylmercury and phenylmercury by RPHPLC with micellized dithizone post-column derivatization photometric detection

Post-column derivatization detection system based on dithizone solubilized in cetyltrimethyl-ammonium hydrogenesulfate micellar media at pH 2.0 was devised and evaluated for selective detection of mercury(II), methylmercury and phenylmercury in reversed-phase HPLC system with photometric detection at 500 nm. This reagent solution is fully compatible with acidic organo-aqueous mobile phases generally used in RPHPLC. With the aid of the detection systematic study of the retention behaviour of three mercury species on octadecylsilica sorbent was carried out. Influence of pH, acetonitrile volume fraction, complex forming additives was investigated in detail. In mobile phase consisting of 5–30% of acetonitrile in water at pH 2.0 and 2·10−4 mol·I−1 DCTA linear calibration curves were measured in range 20–1000 ppb with correlation coefficient better than 0.99. Detection limits were 1–5 ng for this three mercury species. Interferences of copper(II) and silver(I) are negligible.