Determination of polar aniline derivatives in aqueous environmental samples using on-line liquid chromatographic preconcentration techniques

Molecular recognition and self-assembly special feature: Multipoint molecular recognition within a calix[6]arene funnel complex

A multipoint recognition system based on a calix[6]arene is described. The calixarene core is decorated on alternating aromatic subunits by 3 imidazole arms at the small rim and 3 aniline groups at the large rim. This substitution pattern projects the aniline nitrogens toward each other when Zn(II) binds at the Tris-imidazole site or when a proton binds at an aniline. The XRD structure of the monoprotonated complex having an acetonitrile molecule bound to Zn(II) in the cavity revealed a constrained geometry at the metal center reminiscent of an entatic state. Computer modeling suggests that the aniline groups behave as a tritopic monobasic site in which only 1 aniline unit is protonated and interacts with the other 2 through strong hydrogen bonding. The metal complex selectively binds a monoprotonated diamine vs. a monoamine through multipoint recognition: coordination to the metal ion at the small rim, hydrogen bonding to the calix-oxygen core, CH/pi interaction within the cavity's aromatic walls, and H-bonding to the anilines at the large rim.

Recent developments in polymer-based sorbents for solid-phase extraction

A review with 136 references on the principles and recent developments in the solid-phase extraction based on polymer sorbents is presented. New polymer-based materials, chromatographic modes, experimental configurations are described and their advantages for a rapid sample preparation of certain classes of compounds with different functional groups are discussed and compared to silica-based sorbents.

Gas chromatographic determination of aromatic amines in water samples after solid-phase extraction and derivatization with iodine. II. Enrichment

A procedure for the enrichment of aromatic amines via solid-phase extraction was developed. A HR-P phase based on styrene-divinylbenzene was used for the investigations, generally followed by derivatization with iodine and determination via GC-ECD. The recoveries of 53 aromatic amines in a drinking water matrix at pH 9 were determined. Most anilines showed relative recoveries between 80-120% with relative standard deviations of< or = 5% at concentration levels between 10 and 20 micrograms 1(-1). The comparison with a wastewater matrix led to similar results. The enrichment procedure was applied to real samples, e.g., samples of ammunition wastewater.

Determination of carbaryl and some organophosphorus pesticides in drinking water using on-line liquid chromatographic preconcentration techniques

Reversed-phase high-performance liquid chromatography (HPLC) was adapted for the determination of trace concentrations of carbaryl and seven organophosphorus pesticides in drinking water. Between 100 and 300 ml of water sample is passed through a 1.5-cm precolumn, packed with C18-bonded silica or styrene-divinylbenzene copolymer (PRP-1) sorbent at a flow-rate of 3 ml/min. The HPLC system is then switched to an acetonitrile-water gradient elution programme. The analytes that have been concentrated on the precolumn are eluted and separated on a 15-cm C18 analytical column and are determined by measuring their UV absorption at 254 nm. This wavelength was selected as the optimum for the simultaneous determination of these pesticides. The preconcentration yields of the examined solutes obtained with the two types of precolumn are almost identical. Band broadening is avoided by a suitable choice of the C18 precolumn and the analytical column. With 200 ml of tap water, the recoveries for most of the examined pesticides were ca. 90%, except for carbaryl (54%). The detection limits are in the range 0.03-0.2 micrograms/l.

Determination of phenoxyacid herbicides in drinking water at the ppt-level by liquid chromatography and on-line selective preconcentration

On-line precolumn sample handling using an anion-exchanger is applied to preconcentrate phenoxyacid herbicides in aqueous samples prior to their LC separation. Since direct percolation of large sample volumes through the ion-exchanger has to be avoided owing to the high content of inorganic anions in natural waters, a two-step preconcentration is carried out: phenoxyacids are concentrated in their neutral (acidic) form by percolation of natural samples at pH 1 first through a precolumn packed with the copolymer-based PRP-1 sorbent. Then, the PRP-1 precolumn is coupled on-line with a second one packed with the anion-exchanger and 3 ml of deionised water with 35% of acetonitrile allows the phenoxyacids to be desorbed from the PRP-1 sorbent and reconcentrated on the anion-exchanger in their ionic form. The content of the anion-exchanger is analysed on-line by coupling with a C18 analytical column and elution is made with a water-acetonitrile gradient. Detection limits in drinking water from a 500-ml sample are between 15 and 35 ng/l (ppt) and identity of phenoxyacids is reinforced by the fact that analytes are preconcentrated by the anion-exchanger. This methodology can be fully automated.