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The chemical activity of organic chemicals directs their diffusion and partitioning and is consequently crucial for their transport, distribution, and toxic effects. A silicone membrane equilibrator is introduced for measuring the chemical activity of nonpolar organic chemicals in lipid-rich samples: (I) A 6 m poly(dimethylsiloxane) (PDMS) microtube (300 [micro]m i.d., 640 [micro]m o.d.) was placed in a sample, and a sample--PDMS equilibrium was reached within 10 min for 12 polycyclic aromatic hydrocarbons (PAHs) acting as model compounds. (II) A plug of 100 [micro]L of methanol was pushed through the tube to equilibrate it with the PDMS and thus the sample. (III) This yielded an undiluted methanol extract that was injected into a high-performance liquid chromatograph (HPLC) with multiband fluorescence detection. Quantification limits expressed as unitless chemical activities ranged from 6 x [10.sup.-9] to 5 x [10.sup.-8], and relative standard deviations were from 6% to 19%. Chemical activities of PAHs in mussels from two polluted sites were measured between [10.sup.-7] and [10.sup.-5], activity coefficients for PAHs in vegetable and fish oils hardly differed between oils. This method can be used for internal exposure measurements, for monitoring product safety/conformity, and process control. The method can also be applied to measure total analyte concentrations in lipid-rich samples and oils.

A new negligible depletion extraction procedure was proposed for equilibrium sampling of 4-tert-octylphenol (OP) and 4-nonylphenol (NP) into a thin film of 1-octanol supported on a hollow fiber membrane. This thin liquid film extraction technique was directed at the determination of (1) freely dissolved concentrations, (2) distribution coefficients to 1-octanol ([D.sub.ow]), and (3) binding to dissolved organic matter ([D.sub.DOC]). The sampling device was prepared by dipping pieces of polypropylene microporous hollow fiber membrane (10-mm length, 30-[micro]m wall thickness, 240-[micro]m inner diameter) into 1-octanol for a few seconds to impregnate the pores of the hollow fiber wall. After stirring in 100 mL of sample solution for 24 h, the sampling device was harvested and desorbed with 30 [micro]L of methanol, of which 20 [micro]L was injected for HPLC analysis. With the measured [D.sub.ow] of a chemical and its equilibrium concentration in the 1-octanol sampling phase ([C.sub.octanol]), the freely dissolved concentration ([C.sub.free]) was calibrated based on [C.sub.free] = [C.sub.octanol]/[D.sub.ow]. Measured log [D.sub.ow] values of OP (4.32 [+ or -] 0.06) and NP (4.79 [+ or -] 0.02) were independent of the chemical concentration, only minimally affected by the environmentally relevant pH, buffering capacity, and salinity of samples, and agreed well with reported values. Log [D.sub.DOC] values of OP (4.89 [+ or -] 0.43) and NP (5.14 [+ or -] 0.37), determined in Aldrich humic acid solution, agreed with reported partition coefficients to organic carbon (log [K.sub.oc]) for particles in river water and effluent wastewater. Short equilibration times and high enrichment factors were obtained for both analytes due to the high surface to volume ratio of the new sampler. The technique was successfully applied to determine [C.sub.free] of OP and NP in real water samples and to study their association with humic acids and bovine albumin.

The freely dissolved concentration ([C.sub.free]) of pollutants is generally believed to be bioavailable and thus responsible for toxic effects. The [C.sub.free] of organic weak acids and bases consists of a dissociated and a nondissociated fraction. By using chlorophenols as model compounds, a negligible-depletion extraction technique, equilibrium sampling through membranes (ESTM), was developed for the measurement of the nondissociated part of the [C.sub.free]. Polypropylene hollow fiber membranes (280-[micro]m i.d., 50-[micro]m wall thickness, 0.1-[micro]m pore size, 15-cm length) were impregnated with undecane in the pores in the fiber wall as liquid membrane and filled with buffer solution in the lumen as acceptor. Then, the hollow fiber membranes were placed into the sample (donor) for an equilibrium extraction after sealing the two ends. The chlorophenol concentrations in the acceptor were then determined by direct injection into a HPLC system. Finally, the [C.sub.free] of the nondissociated and the dissociated species of a chlorophenol were calculated based on its measured concentration in the acceptor, its p[K.sub.a] value, and the measured pH in sample and acceptor. Theoretically calculated distribution coefficients (D = 8-970) agree well with the experimental enrichment factors ([E.sub.e(max)] = 6-1124), and the equilibration time was observed to increase with increasing distribution coefficients (hours to days). The freely dissolved concentration of five chlorophenols, with a wide range of p[K.sub.a] (4.9-9.2) and log [K.sub.ow] (2.35-5.24), were successfully determined in model solutions of humic acids and at low-ppb levels in fiver and leachate water.

A new, fast, and automated sample pretreatment technique for determination of lipophilic organic compounds in aqueous samples has been developed and applied to the determination of polychlorinated biphenyls (PCBs) in environmental river water. It is based on miniaturized microporous membrane liquid-liquid extraction coupled on-line to gas chromatography (GC) with electron capture detection. The heart of the system that simultaneously connects the sample pretreatment step to the final GC analysis has been named the extracting syringe (ESy). The ESy carries a miniaturized membrane extraction card attached to an electrically and mechanically designed installment and is mounted directly over a GC injector for fully automated injection of the extract. A method was developed to extract 10 PCB congeners from 1-mLwater samples (after addition of 40% acetonitrile) with an extraction time of 10 min. The optimized methodology showed good linearity (in the dynamic concentration range of 5 ng [L.sup.-1]-1 [micro]g [L.sup.-1]), enrichment factors of 33-40 times, repeatable extractions (RSD 2-5%, n = 4), and low detection limits (2-3 ng [L.sup.-1]). Acetonitrile had to be added to the samples in order to overcome the influence of PCB adsorption on the repeatability of extraction and enrichment and to minimize the overall memory effect (OME). OME and carryover depended not only on the concentration of the organic solvent added to the sample and that used in the washing procedure but also on whether the extracting card was changed or not. When an optimized washing procedure was applied, the OME was ~0.2% at high concentrations (i.e., 1 [micro]g [L.sup.-1]). When each extraction took place in a new extraction card, no OME was detected. Additionally, no significant adsorption onto glass surfaces or a matrix effect on extraction was noticed. The main features of this methodology are good extraction repeatability, low detection limits at short extraction time, and the unsurpassed characteristic of no detectable OME in the entire system when each sample is processed in a new card. The total consumption of organic (nonchlorinated) solvents is less than 5 ml per sample.

Membrane extraction is a family of techniques that can be applied to many extraction problems. These techniques require very little solvent and provide remarkable cleanup efficiency. Figures 1 and 2 [...]

A new automated procedure for analyzing complex samples has been developed utilizing microporous membrane liquid-liquid extraction (MMLLE) combined with capillap gas chromatography. Some local anaesthetics were used as model compounds in aqueous solution as well as in blood plasma. The MMLLE procedure was performed in a flow system with the sample fed to the donor side of the hydrophobic microporous membrane and with an organic solvent (hexane) in the pores and as the acceptor solution. The analytes in a small volume of sample (< 1 mL) were extracted into the organic acceptor phase which was transferred into the gas chromatographic system by utilizing a loop-type interface compatible with large-volume (300 [Mu]L) injection. High selectivity and low carry-over effects were obtained with the system. The detection limits were 0.5-1 ng/mL using 0.5 mL of human plasma, and the precision was [approximately]5%. The effects of pH, flow rates, and adsorption of the analytes were evaluated.

The determination of the basic drug Amperozide, one of its main metabolites, and a third related compound in human blood plasma is described. All three compounds include an amine functionality. The process is governed by a modified ASTED instrument (Gilson). The dialysis unit is exchanged for a supported liquid membrane (SLM), which gives a simultaneous cleanup and enrichment of the analytes. The ASTED is coupled to column liquid chromatographic equipment with UV detection. An efficient cleanup is achieved, and there is no visible difference between the chromatograms after enrichment of a plasma blank and an aqueous blank. To increase the recovery, the same sample can be passed by the membrane several times, while the receiving phase is kept stagnant. An enrichment with three passages takes 15-20 min. The limit of detection for Amperozide in blood plasma is then [approximately]30 ng/mL. The use of the SLM technique for estimation of the degree of protein binding is discussed. Preliminary results agree reasonably with measurements with other techniques. The optimization of the enrichment with supported liquid membranes is described and different membrane supports are compared.

To obtain a high degree of selectivity in sample preparation, supported liquid membrane (SLM) extraction was combined with immunologic recognition. The SLM employs a hydrophobic polymer for supporting the immobilization of an organic solvent, thus forming a nonporous membrane. Said membrane separates the aqueous sample on one side (donor) from a receiving aqueous phase on the other (acceptor). The extraction involves the partitioning of neutral compounds between the sample solution, continuously pumped alongside the membrane, and the membrane. From the membrane, reextraction takes place into a second aqueous phase containing antibodies specific for the target compound(s). Hence, there is a formation of an antibody-antigen complex at the heart of the sample preparation (ImmunoSLM). When the immunocomplex forms, the antigen can no longer redissolve in the organic membrane, thus being trapped in the acceptor. Consequently, the concentration gradient of free antigen over the membrane is ideally unaffected, this being the driving force for the process. With a surplus of antibody, the concentration of analyte in the receiving phase will easily exceed the initial sample concentration. In this work, the so formed immunocomplex was quantified on-line, using a fluorescein flow immunoassay in a sequential injection analysis (SIA) setup. The outlined ImmunoSLM-SIA scheme was successfully applied for the extraction of 4-nitrophenol from spiked water solutions as well as from a spiked wastewater sample, indicating that the immunoextraction can be suitable when dealing with difficult matrixes.

The asymmetry of chromatographic peaks is important in the assessment of chromatographic efficiency and resolution. In textbooks, peak asymmetry (sometimes called symmetry, symmetry factor, tailing factor, or skew) is determined [...]

Discusses the suggestion made by the American, European and Japanese pharmacopoeias on hot to calculate the asymmetry of chromatographic peaks. Interpretation of the quotient as the observed width of the peak divided by what would have been determined if no asymmetry occurred; Assessment of the validity of the calculation.