Browsing by Subject "liquid chromatography-tandem mass spectrometry"

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  • Pusfitasari, Eka Dian (Helsingin yliopisto, 2019)
    Urine can be used to determine human exposure to nerve agents through the analysis of specific biomarkers. Isopropyl methylphosphonic acid (IMPA) is an important marker of sarin nerve agent, a highly toxic chemical regulated under the Chemical Weapons Convention (CWC). A methodology for sensitive, reliable, and selective determination of IMPA in urine matrix was developed and validated, using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The sample preparation method employs normal phase–solid phase extraction (NP-SPE) using silica based cartridge. Before conducting IMPA analysis, the instrument performance was controlled using a quality control sample. Three different ion sources, namely electrospray ionization (ESI), Unispray, and atmospheric pressure chemical ionization (APCI), were compared in order to define the best method for trace analysis of targeted IMPA. Parameters affecting the ionization process such as cone voltage, capillary voltage, impactor pin voltage, corona voltage, and mobile phase flow rate were optimized. Negative ion mode was selected as the best method for IMPA identification in all three ion sources, and multiple reactions monitoring (MRM) was employed to improve sensitivity and selectivity. The APCI source was shown to be the least sensitive and least efficient ionization technique for IMPA identification. In contrast, using ESI and Unispray resulted in satisfactory data with excellent limit of detection (LOD), limit of quantification (LOQ), precision, and accuracy. The two latter ion sources share the same values of those parameters, i.e. 0.44 ng/mL, 1.46 ng/mL, < 4% precision bias, < 5% accuracy bias, for ESI; and 0.42 ng/mL, 1.38 ng/mL, < 4% precision bias, < 4% accuracy bias, for Unispray. Nonetheless, the Unispray shows better performance in comparison to ESI in producing higher signal intensity/peak area and has lower matrix effect.
  • Martens, Helge; Tillmann, Urban; Harju, Kirsi; Dell'Aversano, Carmela; Tartaglione, Luciana; Krock, Bernd (2017)
    Alexandrium ostenfeldii is a toxic dinoflagellate that has recently bloomed in Ouwerkerkse Kreek, The Netherlands, and which is able to cause a serious threat to shellfish consumers and aquacultures. We used a large set of 68 strains to the aim of fully characterizing the toxin profiles of the Dutch A. ostenfeldii in consideration of recent reports of novel toxins. Alexandrium ostenfeldii is known as a causative species of paralytic shellfish poisoning, and consistently in the Dutch population we determined the presence of several paralytic shellfish toxins (PST) including saxitoxin (STX), GTX2/3 (gonyautoxins), B1 and C1/C2. We also examined the production of spiroimine toxins by the Dutch A. ostenfeldii strains. An extensive liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis revealed a high intraspecific variability of spirolides (SPX) and gymnodimines (GYM). Spirolides included 13-desMethyl-spirolide C generally as the major compound and several other mostly unknown SPX-like compounds that were detected and characterized. Besides spirolides, the presence of gymnodimine A and 12-Methyl-gymnodimine A was confirmed, together with two new gymnodimines. One of these was tentatively identified as an analogue of gymnodimine D and was the most abundant gymnodimine (calculated cell quota up to 274 pg cell(-1), expressed as GYM A equivalents). Our multi-clonal approach adds new analogues to the increasing number of compounds in these toxin classes and revealed a high strain variability in cell quota and in toxin profile of toxic compounds within a single population.