The current international reference method (IP585/10) for the determination of rapeseed methyl ester (RME) in jet fuel [aviation turbine fuel (AVTUR), current specifications U.S. ASTM 1655 and DEF STAN 91-91] uses gas chromatography−mass spectrometry (GC−MS). The fuel matrix requirements demand that a slow temperature gradient method (50 min) must be used. The fuel matrix also limits the application of this approach in relation to the detection and quantification of low-carbon-number fatty acid methyl esters (FAMEs), e.g., coconut methyl ester (CME), C8−C14 from coconut oil, a feedstock for FAME production in the Pacific Rim region. A 3 min ultrahigh-performance supercritical fluid chromatography− mass spectrometry (UHPSFC−MS) method has been developed for the analysis of RME and CME. This is compared to the existing reference method and an adapted form of the reference GC−MS method for the detection of low-carbon-number FAMEs. The UHPSFC−MS method is approximately 20 times faster than the ASTM reference method, affords a comparable linear dynamic range for the detection of total FAME content up to 100 ppm with a linear correlation (R 2 > 0.99 for RME), and is more suitable for the detection and quantification of lower chain length methyl esters.
The Songkhla Lake Basin (SLB) located in Southern Thailand, has been increasingly polluted by urban and industrial wastewater, while the lake water has been intensively used. Here, we aimed to investigate cyanobacteria and cyanotoxins in the SLB. Ten cyanobacteria isolates were identified as Microcystis genus based on16S rDNA analysis. All isolates harbored microcystin genes, while five of them carried saxitoxin genes. On day 15 of culturing, the specific growth rate and Chl-a content were 0.2–0.3 per day and 4 µg/mL. The total extracellular polymeric substances (EPS) content was 0.37–0.49 µg/mL. The concentration of soluble EPS (sEPS) was 2 times higher than that of bound EPS (bEPS). The protein proportion in both sEPS and bEPS was higher than the carbohydrate proportion. The average of intracellular microcystins (IMCs) was 0.47 pg/cell on day 15 of culturing, while extracellular microcystins (EMCs) were undetectable. The IMCs were dramatically produced at the exponential phase, followed by EMCs release at the late exponential phase. On day 30, the total microcystins (MCs) production reached 2.67 pg/cell. Based on liquid chromatograph-quadrupole time-of-flight mass spectrometry, three new MCs variants were proposed. This study is the first report of both decarbamoylsaxitoxin (dcSTX) and new MCs congeners synthesized by Microcystis.
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