Analysis of Biodiesels Using LC–MS

Experimental Conditions

The method was developed using a Thermo Scientific Accela high speed LC and the MSQ Plus single quadrupole. This system had a pressure tolerance of 15000 psi enabling flexible control of the chromatographic parameters.

The integrated cone wash delivered a continuous 80 μL/min of methanol to the skimmer cone, eliminating any possible deposition and blockage at the entrance cone. Direct infusion of samples and standards was used for instrument tuning and optimization of the MS parameters.

The biodiesel sample was mixed in winter diesel at 5% (BD5). They were diluted in methanol to 100 mg/mL and further diluted to 1 mg/mL in 10 mM LiI in methanol. Tricaprin and monoolein were diluted in methanol to 10 mg/mL solutions. They were further diluted in methanol in series to the final concentration of 10 mM LiI and 0.005, 0.010, 0.050, 0.1, 2.5 and 5 mg/mL of tricaprin and 10 mM of LiI and 0.001, 0.005, 0.01, 0.05, 0.1, 0.5, 1, 2.5 and 5 mg/mL of monoolein.

Results

A clean separation of the sample was obtained within 20 minutes [see Figure 1(a)]. The mass spectrum in Figure 1(b) illustrates that there were many low molecular weight (MW) components, as well as many high MW components. Essentially, the low MW components came out in the first part of the chromatogram (there are more than 20 different identifiable compounds before 13 min), while the higher MW components came out in the second part (>14 min). In this separation, the MS was more sensitive to this type of biodiesel sample than a PDA detector. While we saw more than 15 peaks in the TIC acquired by the MSQ Plus, there were only three identifiable UV peaks in the 205 nm trace. They represented the major FAMEs components in biodiesel.

Figure 1

The above results cannot be achieved without the cone-wash feature (exclusively available on the MSQ Plus) because the cone wash removes any possible residue deposition to the entrance cone of the MSQ Plus, keeping it from clogging.

Conclusions

Preliminary studies of biodiesel samples by a high speed LC–MS system demonstrate that LC–MS can reduce the analysis time to 20 minutes and also reveals information about higher MW compounds in biodiesel while still detecting many low MW chemicals, including FAMEs, at high sensitivity. The patented cone-wash integrated into the electrospray source of the mass spectrometer allowed for the uninterrupted analysis of complicated sample matrices and kept the interface clean from contamination. The methodology described in this publication can be used to characterize chemicals in a wide range of petroleum and petrochemical analyses.

Jennifer Huang, Ray Chen, Daniela Cavagnino and Ed Long, Thermo Fisher Scientific, San Jose, California, USA.

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