Sterols are a highly complex group of lipophilic compounds present in the unsaponifiable matter of virtually all living organisms. In this study, we developed a novel gas chromatography with mass spectrometry selected ion monitoring (GC/MS-SIM) method for the comprehensive analysis of sterols after saponification and silylation. A new referencing system was introduced by means of a series of saturated fatty acid pyrrolidides (FAPs) as internal standards. Linked with retention time locking (RTL), the resulting FAP retention indices (RIFAP) of the sterols could be determined with high precision. The GC/MS-SIM method was based on the parallel measurement of 17 SIM ions in four time windows. This set included eight molecular ions and seven diagnostic fragment ions of silylated sterols as well as two abundant ions of FAPs. Altogether, twenty molecular ions of C27- to C31-sterols with 0–3 double bonds were included in the final method. Screening of four common vegetable oils (sunflower oil, hemp oil, rapeseed oil, and corn oil) enabled the detection of 30 different sterols and triterpenes most of which could be identified.
Graphical abstract
Halogenated natural products (HNPs)
and persistent organic pollutants
(POPs) were quantified in South African sardines (Sardinops
sagax) from one site in the South Atlantic Ocean and
one in the Indian Ocean. At both sites, HNPs [2,3,3′,4,4′,5,5′-heptachloro-1′-methyl-1,2′-bipyrrole
(Q1), mixed halogenated compound 1 (MHC-1), 2,4,6-tribromoanisole
(2,4,6-TBA), 2′-MeO-BDE 68 (BC-2), and 6-MeO-BDE 47 (BC-3)]
were 1 order of magnitude higher concentrated than anthropogenic POPs
[mainly polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane
(DDT), ∼3 ng/g lipids]. MHC-1 and Q1 were the major HNPs in
the samples from both sites, contributing with up to 49 and 52 ng/g
lipids, respectively. The same 1,1-dichloro-2,2-bis(4-chlorophenyl)ethane
(p,p′-DDE)/PCB ratio suggested
that the major POPs were evenly distributed at both sites. Different
ratios of Q1/MHC-1 in the samples from the Indian (∼2:1) and
South Atlantic (∼1:1) Oceans indicated that the occurrence
of HNPs in seafood is difficult to predict and should be investigated
more in detail. The PCB levels in sardines were found to pose no risk
to human consumers, whereas HNPs could not be evaluated because of
the lack of toxicological data.
Phytosterols were analyzed in 34 different quinoa accessions,
which
were obtained from the same field trial. Twenty different sterols
were detected, and 17 could be structurally assigned by means of gas
chromatography with mass spectrometry. Sterols were quantitated in
selected ion monitoring mode (GC/MS-SIM) with the novel internal standard
3-O-tert-butyldimethylsilyl-cholestanol
(cholestanyl-TBDMS). GC/MS-SIM response factors of minor sterols were
determined after enrichment by countercurrent chromatography. The
total sterol contents varied from 120 to 180 mg/100 g of seeds, which
is higher than has been described in quinoa before. This was due to
the fact that Δ7-sterols (e.g., Δ7-sitosterol, spinasterol,
and Δ7-avenasterol) were quantitated for the first time in quinoa
and contributed ∼64% to the total sterol content. Clustering
allowed distributing of the 34 different quinoa accessions into four
distinct groups on the basis of the different sterol patterns.
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