Stir membrane liquid-liquid microextraction

In this article, a novel liquid phase microextraction technique, called stir membrane liquid-liquid microextraction (SM-LLME), is presented. The new approach combines the advantages of liquid phase microextraction and stirring in the same unit allowing the isolation and preconcentration of the analytes in a simple and efficient way. In the construction of the unit, a polymeric membrane is employed to protect the small volume of the extractant phase. The extraction technique is characterized for the resolution of a model analytical problem: the determination of five selected chlorophenols in water. A two-phase extraction mode is used for the extraction of the analytes with an organic solvent in which an in situ derivatization reaction takes place. The analytes are finally analyzed by gas chromatography/mass spectrometry. All the variables involved in the extraction process have been clearly identified and optimized. The new extraction mode allows the determination of chlorophenols with limits of detection in the range from 14.8 ng/L (for 2,4,5-trichlorophenol) to 22.9 ng/L (for 3-chlorophenol) with a relative standard deviation lower than 8.7% (for 2,6-dichlorophenol).     

Simultaneous determination of histamine and spermidine by second-derivative synchronous fluorescence spectrometry

The method is based on formation of the fluorescent condensation products with o-phthaldialdehyde; 0.5–2000 ng ml^?1 histamine and 3–700 ng ml^?1 spermidine can be quantified, with relative standard deviations of 2–3%. Histamine/spermidine ratios of 2.5:1–1:30 can be handled. A selectivity study is reported.     

Multidetection flow-injection techniques for manipulation of sensitivity : Amplification and dilution methods

Different multidetection flow-injection techniques are considered for the manipulation of analytical sensitivity and for broadening the determination range of an analyte with maximum accuracy. Conventional spectrophotometric detection in linear or cyclic flow systems and a diode-array detector for monitoring several wavelengths simultaneously are used. The formaldehyde/pararosaniline/sulfite system is used for studying these techniques.     

Coupling continuous flow systems to instruments based on discrete sample introduction

The interfaces between low-pressure continuous sample treatment systems and high-level information instruments such as gas chromatographs, capillary electrophoresis equipment and graphite furnace atomic spectroscopic instruments, which are characterized by conventional discrete sample introduction devices, are presented. The present and future developments are discussed of (directly) linking real samples and those analytical equipments with the main objective of avoiding or minimizing manually implemented preliminary operations of the analytical process.     

Titration of thiosemicarbazones with Cu(II) and vice versa by use of a copper selective electrode in acetone-water mixture: Determination of the conditional formation constants of the cupric thiosemicarbazonates

The titration technique of seven thiosemicarbazones by complexation with cupric ion and with the help of a copper selective electrode has been carried out. The conditional formation constants for these chelates are determined by the Ringbom and Harju method.     

Ion mobility spectrometry of volatile compounds from Iberian pig fat for fast feeding regime authentication

Characteristic ion mobility spectra for volatile compounds present in fat were used to authenticate the feeding regime of Iberian pigs. Volatile compounds were obtained by heating the solid samples at 150 degrees C for 40 min. This produced a headspace that was introduced in the spectrometer ionization chamber by means of a highly purified nitrogen stream. The spectra thus, obtained for the fat samples were processed chemometrically in order to assess their usefulness for discriminating meat from free-range pigs fed on pasture and acorns and confined pigs fed with commercial feed including high-oleic acid products. Principal component analysis was used as both an exploratory tool and a variable reduction method, and linear discriminant analysis was employed to classify 65 subcutaneous fat samples according to pig feeding regime. Only 2.3% of the samples from pigs reared in confinement were misclassified. 95.5% of the free-range samples were correctly predicted.     

Simple and rapid instrumental characterization of sensory attributes of virgin olive oil based on the direct coupling headspace-mass spectrometry

A methodology for obtaining reliable qualitative and quantitative information about negative (fusty, muddy sediment, musty, rancid and vinegary) and positive (fruity) sensory attributes of virgin olive oils (lampante and extra) has been developed. The procedure implies the joint use of a headspace autosampler, a mass spectrometer and an adequate chemometric data treatment. For this purpose, soft independent modelling of class analogy (SIMCA) and partial least squares (PLS) regression approaches were used for attribute identification and quantification, respectively. InStep application was employed to generate a decision tree by the combination of both models in order to provide the joint prediction of the sensory attributes of a given virgin olive oil and their respective intensities by means of a single output result. The good prediction results obtained when the decision tree generated were applied to a new set of virgin olive oil samples (viz, a specificity of 100%, an average sensitivity of 86% and a RMSEP<0.8% in the quantification task) reveals its potential applicability in routine analysis.