Characterization of Nano-Gravimetric-Detector Response and Application to Petroleum Fluids up to C34.

A nano-gravimetric detector (NGD) for gas chromatography is based on a nanoelectromechanical array of adsorbent-coated resonating double clamped beams. NGD is a concentration-sensitive detector and its sensitivity is analyte-dependent based on the affinity of the analyte with the porous layer coated on the NEMS surface. This affinity is also strongly related to the NGD temperature (NGD working temperature can be dynamically set up from 40 to 220 °C), so the sensitivity can be tuned through temperature detector control. An adsorption-desorption model was set up to characterize the NGD response on a large set of n-alkanes from C10 to C22 at different NGD temperatures. For fast identification of petroleum mixture based on chromatogram fingerprint, a general strategy for NGD temperature program design was developed leading to a constant relative response factor between 0.96 and 1.03 for all the alkanes, and then chromatograms are very similar to those obtained with a flame ionization detector (FID). The analysis of a real petroleum fluid was also performed and compared to FID results: quantitative results obtained for all the analytes were satisfactory according to precision (<5%) and accuracy (average relative error = 4.3%). Based on such temperature control strategy, NGD sensitivity and the dynamic linear range can be adjusted and detection limits at a picogram level can be easily achieved for all n-alkanes.

Corona charged aerosol detector non-uniform response factors of purified alcohol ethoxylated homologues using liquid chromatography.

Surfactants are used in various applications: cosmetics, pharmaceuticals, petrochemicals, environmental, etc. Many of these compounds are polydisperse, and because of this intrinsic polydispersity, it is essential to have a universal detector with a uniform response to quantify them in a simple way. Indeed, Charged Aerosol Detector (CAD) was presented as a universal detector with a uniform response. Thus, in the present study, the CAD response, in a High-Performance Liquid Chromatography - CAD configuration (HPLCCAD), was evaluated using purified alcohol ethoxylated surfactants. A semi-preparative liquid chromatography step using a Hydrophilic interaction chromatography (HILIC) bare silica column (150 mm, 4.6 mm, 2.6 µm) was implemented to prepare eleven homologues of BrijC10, a nonionic surfactant. These homologues differed only by the number of ethylene oxide units. BrijC10 homologues were analyzed by HPLCCAD, using a HILIC bare silica column (150 mm, 2.1 mm, 2.6 µm) to determine the HPLCCAD response factors of purified homologues. From the calibration curves (from 100 to 500 mg.kg-1), their response factors were estimated: differences in response factors were observed and a maximum difference in response factors of 3.6 was obtained. Thus, it could be concluded that CAD hyphenated to HILIC separation did not present a uniform response for this homologue's distribution.

Chromatographic behavior and characterization of polydisperse surfactants using Ultra-High-Performance Liquid Chromatography hyphenated to High-Resolution Mass Spectrometry.

Surfactants are widely used in various petrochemical applications. Thus, it is essential to have highly efficient analytical tools to monitor the different classes of surfactants commonly used. Three among the four known classes of surfactants were studied in the present work: anionic (i.e. alkylbenzene sulfonate, alkyl ether carboxylic acid), nonionic (i.e. alkylcyclohexyl alcohol ethoxylated, alkyl alcohol ethoxylated) and cationic (i.e. alkyl trimethylammonium). Thanks to high-resolution mass spectrometry (HRMS), a useful mass list was created including 119 m/z values (error in mass around 5 ppm). This list was the foundation of a HRMS database, which, for the sake of simplicity, will be further denoted only "database". To avoid ion competition and streamline attribution of structural formulas for isobar molecules, a suitable chromatographic method was used before MS. The retention behavior of six surfactants (trimethyloctadecylammonium bromide, myristyltrimethylammonium bromide, Brij®C10, Triton X-100 reduced, glycolic acid ethoxylate lauryl ether, 4-dodecylbenzenesulfonic acid) was evaluated under three separation modes: reversed-phase liquid chromatography (RPLC), hydrophilic interaction chromatography (HILIC) and mixed-mode chromatography (combination of anion-exchange and reversed-phase mechanisms). In RPLC mode, six columns were tested including C4, C18, C30, polar-embedded C18, PFP and phenyl chemistries. Two HILIC columns were also tested including bare silica and urea chemistries. An anion-exchange combined with RPLC mechanism was investigated as mixed-mode mechanism. Using ammonium formate at 10 mM as buffer provided the best signal in HRMS. In liquid chromatography, acid conditions (pH 3.5) were preferred, to avoid peak tailing due to residual silanols. The mixed-mode separation mode clearly appears as the best compromise for the characterization of the three surfactants classes. Nevertheless, the orthogonality observed for the separations obtained in HILIC and RPLC modes offers some possibilities for further multidimensional separations.