Optimization of SPME-Arrow-GC/MS Method for Determination of Free and Bound Volatile Organic Compounds from Grape Skins.

(1) Background: Solid phase microextraction (SPME)-Arrow is a new extraction technology recently employed in the analysis of volatiles in food materials. Grape volatile organic compounds (VOC) have a crucial role in the winemaking industry due to their sensory characteristics of wine.; (2) Methods: Box-Behnken experimental design and response surface methodology were used to optimise SPME-Arrow conditions (extraction temperature, incubation time, exposure time, desorption time). Analyzed VOCs were free VOCs directly from grape skins and bound VOCs released from grape skins by acid hydrolysis.; (3) Results: The most significant factors were extraction temperature and exposure time for both free and bound VOCs. For both factors, an increase in their values positively affected the extraction efficiency for almost all classes of VOCs. For free VOCs, the optimum extraction conditions are: extraction temperature 60 °C, incubation time 20 min, exposure time 49 min, and desorption time 7 min, while for the bound VOCs are: extraction temperature 60 °C, incubation time 20 min, exposure time 60 min, desorption time 7 min.; (4) Conclusions: Application of the optimized method provides a powerful tool in the analysis of major classes of volatile organic compounds from grape skins, which can be applied to a large number of samples.

Strategies for Accurate Quantitation of Volatiles from Foods and Plant-Origin Materials: A Challenging Task.

The volatile fraction of foods and of plant-origin materials provides functional information on sample-related variables, and gas-phase extractions are ideal approaches for its accurate chemical characterization. However, for gas-phase sampling, the usual procedures adopted to standardize results from solvent extraction methods are not appropriate: headspace (HS) composition depends on the intrinsic physicochemical analyte properties (volatility, polarity, partition coefficient(s)) and matrix effects. Method development, design, and expression of the results are therefore challenging. This review article focuses on volatile vapor-phase quantitation methods (internal standard normalization, standard addition, stable isotope dilution assay, multiple headspace extraction) and their suitability in different applications. Because of the analyte informative role, the different ways of expressing results (normalized chromatographic area, percent normalized chromatographic areas, and absolute concentrations) are discussed and critically evaluated with examples of quality markers in chamomile, process contaminants (furan and 2-methylfuran) in roasted coffee, and key-aroma compounds from high-quality cocoa.

Determination of selenium in dietary supplements by optical emission spectrometry after alkaline dissolution and subsequent headspace solid phase microextraction.

Headspace solid phase microextraction (HSSPME) of chemically generated selenium hydride from alkaline solution followed by thermal desorption (TD) coupled directly to a microwave plasma (MWP) source has been examined for the optical emission spectrometric (OES) determination of Se. Various chemical and operating parameters including the NaBH(4) and HCl concentrations as well as the fiber exposure time and desorption temperature have been optimized. Alternatively, continuous hydride generation (HG) from alkaline medium and inductively coupled plasma (ICP) may be used for Se determination by OES. With the procedure developed, the determination of Se in dietary supplements at the tens of µgg(-1) level and an accuracy of 3-6% could be performed even in the presence of the 1000-fold excess of Fe and Cu. Additionally, Se was determined in the NIST 8418 material (Wheat gluten) with a certified concentration of Se of 2.58 ± 0.19 µgg(-1), and a value of 2.45 ± 0.25 µgg(-1) was found using HG-HSSPME-MWP-OES. The detection limit for Se (3.2 ng ml(-1)) with the proposed procedure was comparable to those obtained with HG-ICP-OES and the calibration curve was linear of about 2 orders of magnitude.

Development of a negligible depletion-solid phase microextraction method to determine the free concentration of chlorpromazine in aqueous samples containing albumin.

The addition of proteins to in vitro systems influences the free concentration of the test compound in the medium. The objective of this study was to set up a negligible depletion-solid phase microextraction method, coupled to high-performance liquid chromatography (nd-SPME-HPLC) to measure the free concentration of chlorpromazine (CPZ) in medium containing albumin. The nd-SPME method was optimized for coating thickness (polyacrylate coating) and exposure time, and potential effects from the addition of bovine serum albumin (BSA) were studied. It was shown that the addition of albumin did not cause fouling or influenced the uptake kinetics of CPZ into the fiber. At a realistic in vivo albumin concentration of 40 g/L of albumin, 94% of CPZ was protein bound. This is in line with findings in vivo, reporting a protein binding for CPZ of 92-99%. The nd-SPME-HPLC method described in this study can be used to measure the free concentration of chlorpromazine in medium containing proteins. These findings can be used to correct in vitro data for protein binding of chlorpromazine and this information is essential for the extrapolation to in vivo data.