Fatty acid biomarkers in sediment samples via ultra-high resolution and accuracy time-of-flight mass spectrometry

Abstract

This study proposes a new and fast protocol using ultra-high resolution (Rp of 100,000) and accuracy (⩽1ppm) mass spectrometry in a “zig-zag” time-of-flight analyzer with electrospray ionization in the negative ion mode (ESI(−)-UHR TOF-MS) for direct screening of free fatty acids (FA) in sediments. As a proof-of-concept study, the profiles of FA in surface sediments from contrasting environments, including estuarine, coastal, and polar samples, and a sedimentary core were assessed. The profiles of saturated FA from C12–C36 revealed a strong even-over-odd preference with specific distributions for each selected environment. The terrigenous/aquatic ratio (TAR) and average chain length (ACL) proxies were calculated based on results obtained by ESI(−)-UHR TOF-MS and GC–MS for all the samples to validate the proposed protocol. Applying the paired t-test at a confidence level of 95%, we found a t-statistic equal to 2.05 for TAR and 2.01 for ACL, which are lower than the critical value of t. Thus, there is no significant difference between the results obtained by the two techniques at a confidence level of 95%. In addition, ESI(−)-UHR TOF-MS exhibited lower limits of quantification for free FA (10ng/ml) compared to those obtained by GC–MS for fatty acid methyl esters (FAME) (50ng/ml). Direct ESI(−)-UHR TOF-MS offers therefore a reliable, fast, and relatively simple MS protocol to obtain free FA profiles from sediments. The results strongly suggest that the method presented herein has future geochemical applications in the rapid screening of FA biomarkers in sediment samples, reducing both sample preparation as well as analysis time.