Sampling of Volatiles in Closed Systems: A Controlled Comparison of Three Solventless Volatile Collection Methods

Complex inter-organismal communication among plants, insects, and microbes in natural and agricultural ecological systems is typically governed by emitted and perceived semiochemicals. To understand and ultimately utilize the role of volatile semiochemicals in these interactions, headspace volatiles are routinely collected and analyzed. Numerous collection systems are available (e.g., static or dynamic; adsorption or absorption) where the choice of technique should be dependent upon the plant, insect, or microbial ecological system studied, the information sought, and the limitations of each method. Within these constraints, it remains necessary that each method detects and provides the accurate in situ, or in vitro, volatile profile of the studied system. Herein, we analyzed and compared the pros and cons of three solventless, thermal desorption systems (SPME, Tenax/cold trap, SPDE) using a synthetic standard blend of compounds mimicking a simple natural blend (benzaldehyde, b-caryophyllene, (Z)-3-hexenol, 6-methyl-5-hepten-2-one, and limonene). Direct splitless injection and Super Q collections of the standard blend were used as controls. The results indicated that related qualitative, as well as quantitative differences, could be correlated with adsorbent sampling capacity and structural bias. The results for Tenax/cold trap and SPDE also were affected by sampled headspace volumes. All solventless techniques exhibited high analytical reproducibility, with SPME and SPDE providing ease of use, low cost, and minimal instrument modifications. The more complex Tenax/cold trap technique provided higher collection efficiency. Using these results, we provide guidance for technique selection for chemical communication applications.

Volatile compounds profiling by using proton transfer reaction-time of flight-mass spectrometry (PTR-ToF-MS). The case study of dark chocolates organoleptic differences

Direct-injection mass spectrometry (DIMS) techniques have evolved into powerful methods to analyse volatile organic compounds (VOCs) without the need of chromatographic separation. Combined to chemometrics, they have been used in many domains to solve sample categorization issues based on volatilome determination. In this paper, different DIMS methods that have largely outperformed conventional electronic noses (e-noses) in classification tasks are briefly reviewed, with an emphasis on food-related applications. A particular attention is paid to proton transfer reaction mass spectrometry (PTR-MS), and many results obtained using the powerful PTR-time of flight-MS (PTR-ToF-MS) instrument are reviewed. Data analysis and feature selection issues are also summarized and discussed. As a case study, a challenging problem of classification of dark chocolates that has been previously assessed by sensory evaluation in four distinct categories is presented. The VOC profiles of a set of 206 chocolate samples classified in the four sensory categories were analysed by PTR-ToF-MS. A supervised multivariate data analysis based on partial least squares regression-discriminant analysis allowed the construction of a classification model that showed excellent prediction capability: 97% of a test set of 62 samples were correctly predicted in the sensory categories. Tentative identification of ions aided characterisation of chocolate classes. Variable selection using dedicated methods pinpointed some volatile compounds important for the discrimination of the chocolates. Among them, the CovSel method was used for the first time on PTR-MS data resulting in a selection of 10 features that allowed a good prediction to be achieved. Finally, challenges and future needs in the field are discussed.

Current awareness. Current literature in mass spectrometry

In order to keep subscribers up-to-date with the latest developments in their field, John Wiley & Sons are providing a current awareness service in each issue of the journal. The bibliography contains newly published material in the field of mass spectrometry. Each bibliography is divided into 11 sections: 1 Books, Reviews & Symposia; 2 Instrumental Techniques & Methods; 3 Gas Phase Ion Chemistry; 4 Biology/Biochemistry: Amino Acids, Peptides & Proteins; Carbohydrates; Lipids; Nucleic Acids; 5 Pharmacology/Toxicology; 6 Natural Products; 7 Analysis of Organic Compounds; 8 Analysis of Inorganics/Organometallics; 9 Surface Analysis; 10 Environmental Analysis; 11 Elemental Analysis. Within each section, articles are listed in alphabetical order with respect to author (3 Weeks journals - Search completed at 7th. Mar. 2001)