ABSTRACT
RATIONALE: The offline coupling of high-performance thin-layer chromatography (HPTLC) with atmospheric solids analysis probe mass spectrometry (ASAP-MS) was evaluated for the characterization of polymeric additives in gasoline. METHODS: A protocol was developed to optimize the ion signal. A glass capillary was moistened with deionized water, and then dipped into silica gel scratched from an HPTLC plate. The capillary tube was fixed to the ASAP holder and introduced into the ionization source for analysis by MS. Silica gel, reversed-phase C18 and cellulose stationary phases were evaluated. RESULTS: The effect of the stationary phase and the nature of analyte were evaluated using polypropylene glycol and polyisobutylene succinimide polyamine as analyte molecules. The optimal ionization conditions are significantly different between ASAP and HPTLC/ASAP-MS analyses. In particular, a higher desorption gas temperature was required to produce ions from the silica gel HPTLC plate. The presence of the stationary phase reduces the internal energy of the ions and limits the fragmentation. CONCLUSIONS: HPTLC/ASAP-MS is a very fast and efficient technique for the analysis of polymers in formulated fuels. Good ionization efficiency was obtained with all investigated stationary phases.
ABSTRACT
Polyalphaolefins (PAOs) are saturated alpha olefin oligomers used as a base stock oil for synthetic lubricants. The synthetic base stocks are manufactured from linear alpha olefins by catalytic oligomerization processes. The aim of this work was the characterization of different PAO grades, synthesized from different linear alpha olefins using two oligomerization processes, acid and metallocene catalyses. Negative ion atmospheric pressure photoionization (APPI) coupled with ion mobility spectrometry-mass spectrometry (IMS-MS) permitted the detection of intact PAO adducts with either chloride, bromide or iodide ions using halogenated solvents (e.g. dichloromethane, dibromomethane and diiodomethane) and toluene as the dopant. The best signal-to-noise ratio was obtained with dichloromethane. The APPI mass spectra displayed characteristic ion distributions for high viscosity PAO grades. The mass shift between two adjacent ions permitted the identification of repeating units and consequently the monomers of alpha olefins used to manufacture the PAO. For low PAO grades, the halide anion adducts were not detected as they are less stable. The IMS-MS data, as well as the correlated variables, i.e. the drift time and full width at half maximum (FWHM) of the IMS peaks, can be used to differentiate polyalphaolefins of the same grade but differently synthesized.
ABSTRACT
Polyalphaolefins (PAOs) are polymers produced from linear alpha olefins through catalytic oligomerization processes. The PAOs are known as synthetic high-performance base stock fluids used to improve the efficiency of many other synthetic products. In this study, we report the direct characterization of PAOs using atmospheric solid analysis probe (ASAP) coupled with ion mobility spectrometry-mass spectrometry (IMS-MS). We studied different PAOs grades exhibiting low- and high-viscosity index. Specific adjustments of the ASAP source parameters permitted the monitoring of ionization processes as three mechanisms could occur for these compounds: hydride abstraction, nitrogen addition, and/or the formation of [M-2H]+⢠ions. Several series of fragment ions were obtained, which allowed the identification of the alpha olefin used to synthesize the PAO. The use of the ion mobility separation dimension provides information on isomeric species. In addition, the drift time versus m/z plots permitted rapid comparison between PAO samples and to evidence their complexity. These 2D plots appear as fingerprints of PAO samples. To conclude, the resort to ASAP-IMS-MS provides a rapid characterization of the PAO samples in a direct analysis approach, without any sample preparation. Graphical Abstract á .
ABSTRACT
Kahweol and cafestol are two diterpenes that exist mainly as esters of fatty acids in green coffee oil. To recover them under their free form they have to be either saponified or trans-esterified. These two compounds are well known to be sensitive to heat, and reagents, therefore experimental conditions used in the transesterification reaction are critical. In this paper, a Doehlert experimental design plan is used to optimize the transesterification conditions using some key variables such as the temperature of the reaction, the reagent base concentration and the duration of the reaction. Therefore, the optimal parameters determined from the Doehlert design are equal to 70 °C, temperature of the reaction; 1.25 mol L(-1) concentration of the reagent base; and 60 min reaction time. The contour plots show that the extracted quantity of kahweol and cafestol can depend greatly from the experimental conditions. After transesterification, the free form of the diterpernes is extracted from the lipid fraction using liquid-liquid extraction and analyzed using GC-FID without prior derivatization. The amount of kahweol and cafestol obtained from green coffee oil obtained by cold mechanical press of Catuai coffee bean is equal to 33.2±2.2 and 24.3±2.4 g kg(-1)oil, respectively. In an attempt to streamline the process, the transesterification reaction is performed in an in-flow chemistry reactor using the optimal conditions obtained with the Doehlert experimental design. The amount of kahweol and cafestol obtained from the same green coffee oil is equal to 43.5 and 30.072 g kg(-1)oil, respectively. Results are slightly higher compared to the ones obtained with the batch procedure. This can be explained by a better mixing of the coffee oil with the reagents and a faster transesterification reaction.
