A simple preconcentration and clean-up liquid-liquid-liquid microextraction of aromatic amines is described in this paper. The compounds were extracted from 2.0µl aqueous samples (donor phase) into an organic phase, layered on the donor phase, and then back extracted to a microdrop of aqueous receiving phase, suspended in the organic phase. After extraction, the microdrop was injected into the HPLC system directly for analysis. Optimal conditions of the extraction were donor phase (a): 2 ml of water sample adjusted to pH 13 with NaOH-NaCl; organic phase (o), 150ml ethyl acetate; and 1 receiving phase (a) of 2µl aqueous solution at pH 2.1. The a→o extraction time was 15min and for o→a, 30s. 212 18-Crown-6 ether, which can complex with amine, was added to the aqueous receiving phase to improve the extraction performance. Enrichment factors ranged from 218 (for 4-nitroaniline) to 378 (for 4-chloro-2-aniline). The calibration curve 2 for these anilines was linear within the range 2.5ng/ml-2.5mg/ml (r 50.998). Detection limits ranged from 0.85 to 1.80ng/ml (at S/N53). This procedure can be a selective preconcentration method for aromatic amines present in water samples. 2002 Elsevier Science B.V. All rights reserved.

Large-volume sample stacking (LVSS) is an effective on-capillary sample concentration method in capillary zone electrophoresis, which can be applied to the sample in a low-conductivity matrix. NaOH solution is commonly used to back-extract acidic compounds from organic solvent in sample Fretreatment. The effect of NaOH as sample matrix on LVSS of haloacetic acids was investigated in this study. It was found that the presence of NaOH in sample did not compromise, but rather help the sample stacking performance if a low pH background electrolyte (BGE) was used. The sensitivity enhancement factor was higher than the case when sample was dissolved in pure water or diluted BGE. Compared with conventional injection (0.4% capillary volume), 97-120-fold sensitivity enhancement in terms of peak height was obtained without deterioration of separation with an injection amount equal to 20% of the capillary volume. This method was applied to determine haloacetic acids in tap water by combination with liquid-liquid extraction and back-extraction into NaOH solution. Limits of detection at sub-ppb levels were obtained for real samples with direct UV detection.

The total concentrations (ΣPBDE) of 15 polybrominated diphenyl ethers, BDEs 17, 28, 47, 49, 66, 71, 85, 99, 100, 138, 153, 154, 183, 190, and 209, and a predominant polybrominated biphenyl (PBB) congener, 2,2´,4,4´,5,5´-polybrominated biphenyl (PBB-153) were determined in six natural matrix Standard Reference Materials (SRM) provided by the National Institute of Standards and Technology (NIST). The ΣPBDE concentrations (±one standard deviation) in SRM 1945 (whale blubber), SRM 1946 (fish tissue), SRM 1947 (fish tissue), and SRM 1974b (mussel tissue) were ±126, 7±79, 3±134, 5, and 7.9±0.2ng/g of wet wt, respectively. The ΣPBDE concentrations were 54±2 and 163±4ng/g of dry wt for SRM 2977 (mussel tissue) and SRM 2978 (mussel tissue), respectively. Among the three kinds of marine animals, mussel tissue had the lowest total concentration of PBDEs. These values can provide an informal reference or benchmark to laboratories who measure these compounds.

An easy, simple, and highly efficient on-line preconcentration method for acidic compounds in capillary electrophoresis was investigated. It combined two on-line concentration techniques, field-amplified sample injection (FASI) and sweeping. A low-pH (2.5) background electrolyte was used to suppress the electroosmotic flow (EOF), obviating the need of a coated capillary, as well as to neutralize the weakly acidic analytes. After injection of a plug of water inside the separation capillary, negative voltage was applied to initialize FASI for a much longer time than usual. The anions experienced a high electric field and moved quickly to the boundary of the water and the low-pH nonmicellar electrolyte. When the anions encountered the low-pH electrolyte, they were neutralized and a focused sample zone was formed. Then both inlet and outlet vials were changed to those Containing the lowp Hmicellar background electrolyte. As negative voltage was applied, the anionic micelles moved into the capillary, and sweeping and separation began. The novelty in the present procedure is that a low-pH buffer is used to suppress the EOF and also the ionization of the analytes, without need of any other additives or use of a coated capillary. This method afforded 100 000-fold improvement in peak heights for some phenoxy acidic herbicides. The detection limits for these compounds could be low as 100pg/mL.

A preconcentration technique, which involves liquid–liquid–liquid microextraction, was developed to determine phenoxy herbicides in bovine milk. A layer of organic phase was impregnated into the pores of a 3.5cm long porous hollow fiber, while the internal volume of the fiber was filled with NaOH solution (the acceptor solution) that was connected directly to the needle of a microsyringe. The fiber was then immersed into 8ml of acidified milk sample. When the sample solution was stirred, acidic analytes were extracted into the organic phase and back extracted simultaneously into the alkaline acceptor medium as the analytes were protonated at low pH and deprotonated at high pH. After extracting for a prescribed time, 5ml acceptor solution was taken back into the syringe and injected directly into a HPLC system for quantification. The analytes were extracted quantitatively from the sample solution into the acceptor solution with a large enrichment factor of 900. Due to its low cost, the hollow-fiber extraction device was disposed of after a single extraction that eliminated the possibility of carry over effects. In addition, because a small volume of organic solvent was required and little waste is generated, the procedure is environmentally friendly, and is compatible with the "green chemistry" concept.