Temperature-Dependent Lipid Conversion and Nonlipid Composition of Microalgal Hydrothermal Liquefaction Oils Monitored b
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Temperature-Dependent Lipid Conversion and Nonlipid Composition of Microalgal Hydrothermal Liquefaction Oils Monitored by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry Nilusha Sudasinghe 1 & Harvind Reddy 2,4 & Nicholas Csakan 3,5 & Shuguang Deng 2 & Peter Lammers 3,5 & Tanner Schaub 1
# Springer Science+Business Media New York 2015
Abstract We illustrate a detailed compositional characterization of hydrothermal liquefaction (HTL) oils derived from two biochemically distinct microalgae, Nannochloropsis gaditana and Chlorella sp. (DOE 1412), for a range of reaction temperature as observed by high-resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). The unique capability to unequivocally derive molecular formulae directly from FT-ICR MS-measured mass-to-charge ratio (for several thousand compounds in each oil) shows that lipids are completely reacted/converted for any reaction temperature above 200 °C and reveals the formation of nonlipid reaction products with increasing temperature. Specifically, lipid-rich oil is obtained at low reaction temperature (96 and >80 % of the total mass spectral signal for
Chlorella sp. and N. gaditana HTL oils, respectively, in both ionization modes. A variety of nonlipid reaction products from HTL processing at different reaction temperatures were identified by their heteroatom class. Residual lipids in the oils were identified as a given lipid class by matching the assigned elemental compositions to an in-house assembled lipid database derived from Lipid Maps (Nature, Lipidomics Gateway) as previously described [21]. Tandem mass measurement was performed for selected species in each abundant compound class for structural identification where possible. For this process, ions of interest were first isolated and signals from isobars within 1 Da of the selected ion mass were determined. If no significant/high-abundance interfering peaks were observed, MSn fragmentation was performed in the linear ion trap by collision-induced dissociation (CID) with high-resolution/accurate mass measurement FT-ICR MS detection of the fragment ions. The MSn spectra were evaluated by manual inspection and elemental composition of fragment ions was determined directly from sub-part-per-million mass measurement accuracy. These data represent a detailed qualitative analysis where comparison of individual compound signals is possible between samples, but compound-to-compound signal magnitudes are not comparable due to a lack of available analytical standards for each of the 1,000+ compounds observed. FAME and FFA Quantitation Acid- and base-catalyzed FAME analyses were performed for Chlorella sp. and N. gaditana biomass and their HTL oils produced at reaction temperatures range from 180 to 300 °C. For acid-catalyzed FAME analysis, 5 mL of 0.4 % sulfuric acid was added to 50 mg of sample and vortexed for 30 s. Then, the sample was placed in a hot water bath at 75 °C for 1 h and vortexed in 20-min intervals. One milliliter of deionized w
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