Luteolin and apigenin, extracted from Reseda luteola L., were spectrophotometrically and fluorimetrically studied. The spectra were investigated as a function of pH in methanol/water solutions (1/2, v/v) in the 2-12 pH range. The absorption spectra markedly shifted to the red by increasing the pH. Three acid-base dissociation steps were detected for luteolin (pK (a) = 6.9; 8.6; 10.3) and two for apigenin (pK (a) = 6.6; 9.3). Fluorescence emission was very weak or undetectable (Phi (F) < 10(-4)) in acidic solution, but increased in intensity with increasing the pH. Both molecules exhibited a great propensity towards complex formation with metal ions, with association constants on the order of 10(5)-10(7) for the first complexation step; in the presence of excess Al(3+) ions, multiple equilibria were detected. A marked fluorescence enhancement was observed upon complexation with Al(3+) ions (Phi (F) approximately 1 for luteolin and approximately 10(-2) for apigenin).

The possibility of applying headspace microextraction into a single drop for the determination of alcohols in aqueous solutions is demonstrated. A drop of ethylene glycol containing butan-2-one as an internal standard is used for extraction. The analytes are extracted by suspending a 1 ml extracting drop directly from the tip of a microsyringe fixed above an extraction vial with a septum such that the needle passes through the septum and the needle tip appears above the surface of the solution. After the extraction is finished the drop is retracted back into the needle and injected directly into a GC column. Optimization of experimental conditions (sampling time, sampling temperature, stirring rate and ionic strength of the solution) with respect to the extraction efficiency were investigated and the linear range and the precision were examined. This headspace single drop microextraction method was applied to the analysis of beer.

The tremendous potential of room temperature ionic liquids as an alternative to environmentally harmful ordinary organic solvents is well recognized. Due to their unique properties, such as low volatility, tunable viscosity and miscibility, and electrolytic conductivity, ionic liquids have attracted extensive attention and gained popularity in many areas of analytical chemistry including modern sample preparation techniques. In this review the advantages and limitations of application of ionic liquids as solvents/sorbents for microextraction are critically discussed. Topics covered include solid-phase microextraction, single drop microextraction, dispersive liquid-liquid microextraction and hollow-fiber liquid-phase microextraction. The compatibility of the ionic liquid-based microextraction with different analytical techniques such as gas chromatography, high-performance liquid chromatography, electrothermal or flame atomic absorption spectrometry and some others is also discussed. Finally, the main practical applications on this topic are summarized.

Saffron is a yellow substance which is extracted from the stigmas ofCrocus sativus L. and is used in painting, cooking and medicine. In this paper six components (transandciscrocins) with carotenoid structures were separated from natural saffron by HPLC and were characterised by their absorption and emission spectra. Photochemical and thermal processes which degrade the dye were also investigated. The effect of light promoted thecis⇄transisomerization, while the thermal effect detached the glycosyl moieties.

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Summary. Dispersive liquid-liquid microextraction in combination with an in situ derivatization is suggested for parabens sampling and preconcentration. The derivatization was carried out with acetic anhydride under alkaline conditions maintained using dipotassium hydrogen phosphate. The effects of an extraction solvent type, extraction and disperser solvents volume, extraction time, and ionic strength of the solution on the extraction efficiency were investigated. Chlorobenzene containing n-hexadecane as internal standard was used as an extracting solvent and acetone was used as a disperser solvent. The calibration graphs were linear up to 10 mg mL −1 , correlation coefficients were 0.997-0.999, enrichment factors were from 70 for methylparaben to 210 for butylparaben, and detection limits were 22, 4.2, 3.3, and 2.5 μg L −1 for methylparaben, ethylparaben, propylparaben, and butylparaben, respectively. Repeatabilities of the results were acceptable with relative standard deviations up to 11%. A possibility to apply the proposed method for parabens determination in water samples was demonstrated.

Two microextraction techniques--liquid phase microextraction based on solidification of a floating organic drop (LPME-SFO) and dispersive liquid-liquid microextraction combined with a solidification of a floating organic drop (DLLME-SFO)--are explored for benzene, toluene, ethylbenzene and o-xylene sampling and preconcentration. The investigation covers the effects of extraction solvent type, extraction and disperser solvents' volume, and the extraction time. For both techniques 1-undecanol containing n-heptane as internal standard was used as an extracting solvent. For DLLME-SFO acetone was used as a disperser solvent. The calibration curves for both techniques and for all the analytes were linear up to 10 microg/mL, correlation coefficients were in the range 0.997-0.998, enrichment factors were from 87 for benzene to 290 for o-xylene, detection limits were from 0.31 and 0.35 microg/L for benzene to 0.15 and 0.10 microg/L for o-xylene for LPME-SFO and DLLME-SFO, respectively. Repeatabilities of the results were acceptable with RSDs up to 12%. Being comparable with LPME-SFO in the analytical characteristics, DLLME-SFO is superior to LPME-SFO in the extraction time. A possibility to apply the proposed techniques for volatile aromatic hydrocarbons determination in tap water and snow was demonstrated.

Abstract:A hollow fibre liquid phase microextraction for gas chromatographic determination of some p-hydroxybenzoic acid esters has been developed. Chlorobenzene containing tetradecane as internal standard was used for the extraction. Optimized extraction was carried out at room temperature for 40 min in the presence of 0.4 g mL -1 NaCl in the sample solution. Calibration was linear up to 30 mg L -1 . Correlation coefficients were 0.996 -0.998. Enrichment factors were 21, 95 and 154, and detection limits were 0.20, 0.03 and 0.01 µg mL -1 for methylparaben, ethylparaben and propylparaben, respectively. Reproducibility was acceptable with relative standard deviations up to 11.7%. The technique was tested for water and urine analysis.