Frédéric Begnaud

Good quantification practices of flavours and fragrances by mass spectrometry.

Over the past 15 years, chromatographic techniques with mass spectrometric detection have been increasingly used to monitor the rapidly expanded list of regulated flavour and fragrance ingredients. This trend entails a need for good quantification practices suitable for complex media, especially for multi-analytes. In this article, we present experimental precautions needed to perform the analyses and ways to process the data according to the most recent approaches. This notably includes the identification of analytes during their quantification and method validation, when applied to real matrices, based on accuracy profiles. A brief survey of application studies based on such practices is given. This article is part of the themed issue ‘Quantitative mass spectrometry’.

Effects of variation in modulator temperature during cryogenic modulation in comprehensive two-dimensional gas chromatography.

Many modulation systems in comprehensive 2D GC (GC x GC) are based on cryogenic methods. High trapping temperatures in these systems can result in ineffective trapping of the more volatile compounds, whilst temperatures that are too low can prevent efficient remobilisation of some compounds. To better understand the trapping and release of compounds over a wide range of volatilities, we have investigated a number of different constant temperature modulator settings, and have also examined a constant temperature differential between the cryo-trap and the chromatographic oven. These investigations have led us to modify the temperature regulation capabilities of the longitudinally modulated cryogenic system (LMCS). In contrast to the current system, where the user sets a constant temperature for the cooling chamber, the user now sets the temperature difference between the cryo-trap and the chromatographic oven. In this configuration, the cooling chamber temperature increases during the chromatographic run, tracking the oven temperature ramp. This produces more efficient, volatility-dependent modulation, and increases the range of volatile compounds that can be analysed under optimal trap-and-release conditions within a single analytical run. This system also reduces cryogenic fluid consumption.

Extraction, thermal cleanup, and GC/MS quantification with disposable solid extractants: Application to hydrophobic analytes in aqueous surfactant solutions

Fragranced consumer products are generally formulated together with surfactants. In application, these products are often highly diluted with water. Analyzing trace amounts of fragrance ingredients in such mixtures is challenging and usually requires either time-consuming sample cleanup or extensive cleaning of the trapping device to avoid memory effect and cross-contamination between samples. To overcome these limitations, a new disposable extraction device has been developed to be used in combination with a thermodesorption-GC-MS unit. Made of PDMS foam cylinders, it efficiently extracts trace amounts of hydrophobic compounds from complex aqueous solutions and provides an online sample cleanup, thanks to the controlled desorption temperature, which allows retaining the low volatile constituents of the matrix within the absorptive foam. Combined with a stable isotope dilution assay, accurate quantifications of Cetalox(®), Muscenone™, Helvetolide(®), Polysantol(®), Dartanol, and Myrrhone(®) from aqueous solution containing surfactant and from water from the aeration tank of a sewage plant were successfully conducted. LOQ varied between 1 and 25 ppb (20% confidence interval, α = 0.1).

Novel concept of multidimensional gas chromatography. New capabilities for chiral analysis and olfactometric detection

Abstract In multidiumensional gas chromatography (MDGC), the analyte transfer from the first to the second column is usually achieved using either a valve, or a pneumatic switcher. Both systems have significant drawbacks (degradation of analytes, switchercomplexity, etc.). A new design, based on the double-cool-strand interface (DCSI) overcomes these limitations due to: 1) simplicity and low coest, 2) no degradation of labile compounds, 3) no dead volume, 4) optimised chiral MDGC conditions with a single oven, 5) higher sensitivity and peak resolution. Examples illustrate the suitability of this technique when various detection means are hyphenated to MDGC: FID, mass spectrometry and olfactometric detection. In addition, the use of the new interface in conjunction with a chiral colum allows the odour evaluation of enantiomers with an interval of several minutes. Such a possibility that may not be achieved with previous interfaces, allows the panellist to recover from the first stimuli prior to smelling the second one. This is particularly important for long-lasting compounds, such as mercaptans, as exemplified with 3-methyl-3-mercapto-1-hexanol found in human sweat.

TransFEr: a new device to measure the transfer of volatile and hydrophobic organic chemicals across an in vitro intestinal fish cell barrier

Transfer of compounds across cellular barriers is a critical step of compound uptake into organisms. Using in vitro barrier systems to evaluate such transfer is attractive because of the higher throughput and reduced resource needs compared to animal studies. Thus far, however, studying the transfer of hydrophobic and volatile compounds was hampered by the unavailability of in vitro exposure systems that allow for stable and predictable chemical exposure concentrations. To overcome this limitation, we constructed a novel exposure chamber, TransFEr, and tested it with an in vitro epithelial barrier model using the rainbow trout (Oncorhynchus mykiss) intestinal cell line, RTgutGC. Key features of the chamber are its closed design and rotatable silicon segments, which can serve for chemical dosing and sampling. Using the fragrance damascone beta (log KOW: 3.7, log HLC: −3.9) as a pilot chemical, we were able to demonstrate that our exposure chamber provides for stable chemical exposure concentrations and full mass balance. The RTgutGC epithelium served as barrier for damascone beta transfer, which we attribute to chemical retention and biotransformation in the intestinal cells. Nevertheless, substantial transfer of the chemical across the epithelium occurred. When a chemical sink, i.e. a silicon segment, was included in the basolateral chamber to mimic blood constituents binding in vivo, transfer was about three-fold enhanced. We suggest that the presented methodology can help to obtain insights into chemical uptake mechanisms via the intestinal or other epithelia of fish and other animals for hydrophobic and volatile chemicals.