Theodoros Potouridis

Analysis of carbonyl compounds via headspace solid-phase microextraction with on-fiber derivatization and gas chromatographic–ion trap tandem mass spectrometric determination of their O-(2,3,4,5,6-pentafluorobenzyl)oxime derivatives

An improved method for the analysis of carbonyls is described utilizing a headspace solid-phase microextraction (HS-SPME) step and on-fiber derivatization with O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) hydrochloride. Thermal desorption of the oxime derivatives formed on the fiber is followed by gas chromatographic separation coupled to an ion trap tandem mass spectrometer (GC-ITMS). Selecting specific fragment ions within the electron ionization (EI(+)) mass spectra of these oxime derivatives as precursor ions for MS-MS fragmentation provides a suitable method for the target analysis of individual carbonyl classes, such as alkanals, (E)-2-alkenals, (E,E)-2,4-alkadienals, and others. Retention indices on polar as well as on apolar stationary phases along with EI(+) mass spectra patterns are presented for a large set of oxime derivatives, giving valuable information needed for unambiguous assignment of substances in complex sample matrices. The fast sample preparation and derivatization step via HS-SPME can be automated and is applicable to a variety of biological samples and foodstuffs, allowing rapid and sensitive screening analyses of important aldehydic biomarkers and aroma active compounds.

Pitfalls encountered during quantitative determination of 3-alkyl-2-methoxypyrazines in grape must and wine using gas chromatography–mass spectrometry with stable isotope dilution analysis. Comprehensive two-dimensional gas chromatography–mass spectrometry and on-line liquid chromatography-multidimensional gas chromatography–mass spectrometry as potential loopholes

The analysis of 3-alkyl-2-methoxypyrazines in Vitis vinifera grape must or wine at the low nanogram per liter level failed in several situations when applying a one-dimensional gas chromatographic analysis with mass spectrometric detection (GC-MS). Sample preparation methods such as headspace solid phase microextraction or solid phase extraction were convenient procedures, however lacking extraction selectivity for complex matrices. Analysis by comprehensive two-dimensional gas chromatography with mass spectrometric detection clearly demonstrated the potential for co-elution in such matrices and the risk for erroneous results when applying one-dimensional GC-MS. In one example, matrix problems would have been a challenge even for a comprehensive two-dimensional chromatographic approach with MS detection (GC×GC-MS). A solution to matrix problems was found by protonating the 3-alkyl-2-methoxypyrazines in acidic pH and sample clean-up using solid phase extraction with a mixed-mode polymeric cation-exchange sorbent. Quantification was performed by a stable isotope dilution assay, following analysis by on-line coupled high performance liquid chromatography with multidimensional gas chromatography and detection with mass spectrometry (on-line LC-MDGC-MS). This new approach allowed trace-level analysis of 3-alkyl-2-methoxypyrazines in grape musts and wines and is described for V. vinifera Sauvignon blanc, following 3-alkyl-2-methoxypyrazines concentrations during ripening and in the processed wines.

Analysis of aldehydes via headspace SPME with on-fiber derivatization to their O-(2,3,4,5,6-pentafluorobenzyl)oxime derivatives and comprehensive 2D-GC-MS

A method for the analysis of the homologous series of alkanals, (E)-2-alkenals, and (E,E)-2,4-alkadienals is described utilizing a headspace solid-phase microextraction (HS-SPME) step and on-fiber derivatization with O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) hydrochloride. Oxime derivatives formed on the fiber are desorbed in the gas chromatographic injector and analyzed by comprehensive 2-D GC coupled to quadrupole MS (GC x GC-qMS). Selecting specific fragment ions within the electron impact mass spectra of the oxime derivatives provides a suitable method for the target analysis of these aldehyde classes, which furthermore benefits from the increased separation efficiency by GC x GC. The analysis of higher molecular weight aldehydes is described in wine and grape seed oil as examples. Quantification of the aldehydes utilizes a stable isotope dilution analysis (SIDA) assay with octan-d(16)-al as isotopomeric internal standard. Besides the selectivity and sensitivity of aldehyde analysis using PFBHA derivatives, critical aspects on background level contamination and repeatability of the sample preparation method are discussed. Optimization of GC x GC-qMS parameters allowed a considerable saving of the cryogenic medium, involving additional (unmodulated) conditioning runs, rendering the method more amenable to routine analysis.

Long-term effects of nanoscaled titanium dioxide on the cladoceran Daphnia magna over six generations

We investigated the impact of nanoscaled titanium dioxide (nTiO2) on Daphnia magna populations in a multi-generational study over six generations (F0-F5). Each generation was exposed for 21 days to nTiO2 (AEROXIDE(®) TiO2 P25, primary particle size 21 nm) while mortality, individual growth, reproduction and population growth rates (PGR) were assessed as endpoints. The size distribution of nTiO2 in the single test media was analysed by dynamic light scattering (DLS) and transmission electron microscopy (TEM). nTiO2 concentrations were measured using ICP-MS. Mortality and individual growth of D. magna were significantly affected with increasing exposure duration and concentration. Daphnids demonstrated decreasing reproduction over generations in all treatment groups (1.19-6 mg/L) but not in the control. At concentration levels of 1.78 mg/L chronic exposure resulted in a population collapse after five generations. This study indicates that multi-generational studies are suitable for evaluating long-term effects of nanoparticles since they reflect potential effects more accurately than single generation tests.

Effect-directed identification of endocrine disruptors in plastic baby teethers.

Concerns have been raised regarding the human health effects of endocrine disrupting chemicals (EDCs), many of which are associated with and leaching from plastics. As infants are particularly vulnerable to EDCs, we have investigated whether plastic teethers for babies represent a relevant source of exposure. Applying effect‐directed analysis, we use bioassays to screen teethers, toys used to soothe a babys teething ache, for endocrine activity and chemical analysis to identify the causative compounds. We detected significant endocrine activity in two of 10 plastic teethers. Those samples leached estrogenic and/or antiandrogenic activity as detected in the Yeast Estrogen Screen and Yeast Antiandrogen Screen. After sample fractionation, gas chromatography–mass spectrometry non‐target screening revealed that methyl‐, ethyl‐ and propylparaben were responsible for the observed estrogenic and antiandrogenic activity in one product. The second product is likely to contain at least six different antiandrogenic compounds that remain so far unidentified. This study demonstrates that plastic teethers can be a source of infant exposure to well‐established and unknown EDCs. Because of their limited value to the product, but potential toxicity, manufacturers should critically revisit the use of parabens in plastic teethers and further toys. Moreover, plastic teethers might leach EDCs that escape routine analysis and, thus, toxicological evaluation. The resulting uncertainty in product safety poses a problem to consumers, producers and regulators that remain to be resolved. Copyright

Analysis of alkyl esters of p -hydroxybenzoic acid (parabens) in baby teethers via gas chromatography-quadrupole mass spectrometry (GC-qMS) using a stable isotope dilution assay (SIDA)

Alkyl esters of p-hydroxybenzoic acid (parabens) are well-known to be used as preservatives in pharmaceuticals, cosmetics, and food products due to their antimicrobial effect. However, parabens are also known to act as endocrine disruptors. Thus, if manufactures of consumer goods use parabens particularly in products for infants and young children, this application should be considered as critical and should be thoroughly investigated, at least if an intake into the body cannot be excluded. The present work describes an analytical method for the analysis of methyl-, ethyl- and n-propylparaben (MeP, EtP and n-PrP) in plastic and gel material from baby teethers filled with cooling gel. Measurements were performed with gas chromatography-quadrupole mass spectrometry (GC-qMS) on N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) derivatized parabens. Samples were prepared applying ultrasonic assisted extraction (UAE) using methanol as the solvent. For quantification, a stable isotope dilution assay (SIDA) was used that showed good recoveries for spiked gel material, which ranged from 82 to 119%. The baby teether analyses showed that parabens were present in all considered plastic and gel samples. Furthermore, in all gel samples (2E,4E)-hexa-2,4-dienoic acid (sorbic acid) was identified as an additional preservative.

Exploring 2-aminoacetophenone contents in sparkling wines based on analytical data and statistical modelling

The influence of the second fermentation step on sparkling wine aroma was investigated with respect to the content of 2-aminoacetophenone (AAP) as an indicator substance for the atypical ageing off-flavour (ATA). AAP contents of aged sparkling wines and their corresponding base wines (Riesling and Chardonnay variety) were determined by means of multidimensional gas chromatography using a stable isotope dilution assay. The majority of sparkling wines were lower in AAP in comparison with their corresponding base wines. Explorative and predictive statistical analyses of the resulting AAP content in sparkling wines were performed concerning the influence of the parameters lees contact time, yeast strain, base wine AAP concentration and total phenolic contents. Both statistical approaches yielded good fits with AAP concentration of the base wine being the predominant factor. Although it was possible to explain the changes in AAP concentrations on the basis of how total phenolics changed during second fermentation, predicted AAP trends did not hinge upon the amount of total phenolics present in a base wine. Unpressurised model fermentations were a promising technological alternative to study the development of AAP in sparkling wines. Altogether, this study presents a multidisciplinary approach to master the challenging task of ATA risk assessment in base wines, which at present rather accesses the sparkling wine producer’s individual experience.

Using ICP-qMS to trace the uptake of nanoscale titanium dioxide by microalgae–potential disadvantages of vegetable reference material

AbstractAs nanoscale materials have gained in economic importance over recent years, concerns about accumulation in the environment and, consequently, analysis of nanoparticles in biological material have increasingly become the focus of scientific research. A nanomaterial used in a wide range of food, consumer and household products is titanium dioxide (nTiO2). Monitoring of nTiO2 via determination of elemental titanium (Ti) can be very challenging because of a variety of possible interferences. This work describes problems during the development of a quantification method for titanium dioxide (TiO2) using inductively coupled plasma-quadrupole mass spectrometry (ICP-qMS). To evaluate the analytical method, certified vegetable reference material NCS DC 73349 was used. Interestingly, measurements of NCS DC 73349 seemed to result in acceptable recovery values—however, this was without considering interferences or conceivable differences in the natural isotopic abundance of the certified titanium calibration solution and NCS DC 73349. Actually, recoveries were lower than initially assumed. The potential interferences causing augmented recovery could be attributed to the presence of the elements sulfur (S) and phosphorus (P), which were able to form oxide ions and nitrogen-interfering species. The effect of such interfering cluster ions could be prevented by dry ashing as a sample preparation step, to evaporate S and P, before digestion with aqua regia in a high-pressure asher (HPA). Final practicability of the analysis method was proved by monitoring the uptake of nTiO2 by the microalgae Scenedesmus acutus in an environmental exposure study. Figureᅟ

Ion Trap Mass Spectrometric Effect Leading to Peak Suppression and Solvent-Free Peak Focusing due to Co-Chromatography

Abstract During the enantioselective analysis of whisky lactones after headspace in-tube extraction and gas chromatography with mass spectrometric detection using an ion trap mass analyzer (ITMS), an unusual effect led to peak suppression for one of the four enantiomers of whisky lactones. Using the ITMS in the selective ion monitoring (SIM) mode, one of the four targeted whisky lactone enantiomers could not be detected due to an abundant co-eluting matrix compound. For troubleshooting, detection with a quadrupole MS proved the presence of the missing enantiomer peak. A hypothetical explanation of this phenomenon is at present based on the different ion scanning mechanism of the two MS instruments. Considering the irregular sampling during the discontinuous scanning process of the ITMS being dictated by the ion current, this might have led to the suppression of the analyte. Furthermore, a solvent trapping effect of the target analyte with a co-chromatographing abundant matrix compound created a peak distortion (focusing) of the minor whisky lactone enantiomer. In our case, the inexplicably missing enantiomer peak triggered this investigation, but such matrix effects could easily be overseen with ITMS (SIM) detection, then eventually causing false-negative results.