Browsing by Subject "Gas chromatography"

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Enzymatically formed fatty acid hydroperoxides determined through GC‐MS analysis of enantiomeric excess of hydroxy fatty acids after reduction and ibuprofen derivatization
(2025) Hotz, Lisa; Zartmann, Anne; Noack, Isabelle; Drees, Luca J.; Kuschow, Meret K.; Heinrich, Markus R.; Janssen, Hans‐Gerd; Hammann, Simon
Unsaturated fatty acids are susceptible to lipid oxidation through autoxidation, photooxygenation or enzymatical oxidation. A characteristic feature of enzyme‐catalyzed oxidation is the high regio‐ and stereospecificity of the formed fatty acid hydroperoxides. In this study, we present a method to quantify enzymatic lipid oxidation through reducing hydroperoxy fatty acid methyl esters to hydroxy fatty acid methyl esters and derivatizing them with enantiopure (S)‐ibuprofen, allowing the resolution of the enantiomer pairs as diastereomers via achiral GC‐MS. After application to enantiopure reference fatty acids, the approach was applied to autoxidation products of linoleic acid, and the expected racemic mixtures of the 9‐ and 13‐hydroperoxide derived hydroxy fatty acids were detected. On the other hand, when linoleic acid was oxidized using soybean lipoxygenase, clear enantiomeric excess of the (13S) enantiomer could be detected, proving the applicability of this method to detect enzymatic oxidation through enantiomeric excess.
A fast gas chromatography coupled with electron capture negative ion mass spectrometry in selected ion monitoring mode screening method for short‐chain and medium‐chain chlorinated paraffins
(2022) Schweizer, Sina; Schulz, Tobias; Vetter, Walter
Rationale: Chlorinated paraffins (CPs) are a group of anthropogenic pollutants that consist of complex mixtures of polychlorinated n-alkanes of different chain lengths (~C10 to C30). Persistence, bioaccumulation, toxicity, and long-range transport of short-chain chlorinated paraffins (SCCPs, C10- to C13-CPs) have prompted their classification as persistent organic pollutants (POPs) by the Stockholm Convention in 2017. Due to the varying chain lengths and chlorination degrees, quantification of SCCPs and medium-chain chlorinated paraffins (MCCPs, C14- to C17) using gas chromatography coupled with electron capture negative ion mass spectrometry in selected ion monitoring mode (GC/ECNI-MS-SIM) is not only challenging but also very time consuming. In particular, up to eight GC runs per sample are required for the comprehensive GC/ECNI-MS-SIM quantification of SCCPs and MCCPs. These efforts are high especially if the samples do not contain CPs above the limit of detection (LOD), subsequently. Methods: We developed a semi-quantitative and sensitive method for the examination of SCCPs and MCCPs in one GC run. This GC/ECNI-MS-SIM screening method was based on the recording of Cl− (m/z 35 and 37), Cl2− (m/z 70 and 72), and HCl2− (m/z 71 and 73) isotope ions and evaluation of the ratios between them. Results: Correctness of the results of the screening method was verified by analysis of edible oils with and without CPs, CP standards, as well as a technical CP mixture. Polychlorinated biphenyls (PCBs) and other polyhalogenated aromatic compounds, as well as brominated flame retardants, do not form all of the fragment ions analyzed by the screening method. Conclusions: After the screening, only CP-positive samples may need to be measured in detail. Measurement time will already be gained in the case of ~10% samples without CPs.
GC/EI-MS method for the determination of phytosterols in vegetable oils
(2021) Schlag, Sarah; Huang, Yining; Vetter, Walter
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.
Previtamin D2, vitamin D2, and vitamin D4 amounts in different mushroom species irradiated with ultraviolet (UV) light and occurrence of structurally related photoproducts
(2024) Sommer, Katrin; Hillinger, Marissa; Vetter, Walter
Mushrooms are rich in ergosterol and ergosta‐5,7‐dienol, which can be partly converted into vitamin D2 and D4 through ultraviolet (UV) light exposure. Typically, mushrooms have very low vitamin D contents, but it can be increased by UV irradiation. This process generates additional photoisomers scarcely studied in mushrooms due to analytical challenges. Here, we developed a new solid phase extraction (SPE) method to separate vitamin D2, vitamin D4, and other tri‐ and pentacyclic photoisomers from the much higher abundant ergosterol. Subsequent GC/MS analysis enabled the detection of ten photoisomers in eight UV‐treated mushroom species, including vitamin D2 (previtamin D2, tachysterol2, two suprasterol2 and trans‐vitamin D2 isomers) and vitamin D4 (previtamin D4). Quantitated vitamin D2 contents of 10–540 µg/100 g dry weight agreed well with the sparse literature data available for the investigated mushroom species. In addition, previtamin D2 (nd–1950 µg/100 g dry weight) and vitamin D4 (10–140 µg/100 g dw) were quantified in the samples. The content and photoproduct compositions varied considerably between different mushroom species. Practical applications: The novel SPE method can be applied to study the vitamin D and photoisomer content of mushrooms.