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  • 1.
    Amini, Nahid
    Stockholm University, Faculty of Science, Department of Analytical Chemistry.
    Novel Solid Phase Extraction and Mass Spectrometry Approaches to Multicomponent Analyses in Complex Matrices2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Analysis of compounds present in complex matrices is always a challenge, which can be partly overcome by applying various sample preparation techniques prior to detection. Ideally, the extraction techniques should be as selective as possible, to minimize the concentration of interfering substances. In addition, results can be improved by efficient chromatographic separation of the sample components. The elimination of interfering substances is especially important when utilizing mass spectrometry (MS) as a detection technique since they influence the ionization yields. It is also important to optimize ionization methods in order to minimize detection limits.

    In the work this thesis is based upon, selective solid phase extraction (SPE) materials, a restricted access material (RAM) and graphitized carbon black (GCB) were employed for clean up and/or pre-concentration of analytes in plasma, urine and agricultural drainage water prior to liquid chromatography/mass spectrometry (LC/MS). Two SPE formats, in which GCB was incorporated in µ-traps and disks, were developed for cleaning up small and large volume samples, respectively. In addition, techniques based on use of sub-2 µm C18 particles at elevated temperatures and a linear ion trap (LIT) mass spectrometer were developed to improve the efficiency of LC separation and sensitivity of detection of 6-formylindolo[3,2-b]carbazole (FICZ) metabolites in human urine.

    It was also found that GCB can serve not only as a SPE sorbent, but also as a valuable surface for surface-assisted laser desorption ionization (SALDI) of small molecules. The dual functionality of GCB was utilized in a combined screening-identification/quantification procedure for fast elimination of negative samples. This may be particularly useful when processing large numbers of samples. SALDI analyses of small molecules was further investigated and improved by employing two kinds of new surfaces: oxidized GCB nanoparticles and silicon nitride.

  • 2.
    Amini, Nahid
    et al.
    Stockholm University, Faculty of Science, Department of Analytical Chemistry.
    Crescenzi, Carlo
    Feasibility of an on-line restricted access material/liquidchromatography/tandem mass spectrometry method in the rapid and sensitive determination of organophosphorustriesters in human blood plasma2003In: Journal of chromatography. B, ISSN 1570-0232, E-ISSN 1873-376X, Vol. 795, no 2, p. 245-256Article in journal (Refereed)
    Abstract [en]

    A rapid on-line solid phase extraction/liquid chromatography/tandem mass spectrometry (SPE/LC/MS/MS) method usingrestricted access material (RAM) was developed for the simultaneous determination of eight organophosphorus triesters inuntreated human blood plasma. In a process involving column-switching techniques, the analytes were enriched on the RAMcolumn, separated using a C-18 analytical column and detected with LC/MS. Tandem mass spectrometrywas used to characterizeand quantify the analytes. To elucidate the fragmentation pathway of a number of the analytes, MS3 experiments using an iontrap mass spectrometer were performed. The matrix effects associated with using APCI and ESI interfaces were investigated.The recoveries obtained were in the range 60–92% (R.S.D. < 6%), with estimated detection limits between 0.2 and 1.8 ng/mlof plasma, and the total analysis time was 27 min.

  • 3.
    Amini, Nahid
    et al.
    Stockholm University, Faculty of Science, Department of Analytical Chemistry.
    Shariatgorji, Mohammadreza
    Stockholm University, Faculty of Science, Department of Analytical Chemistry.
    Crescenzi, Carlo
    Thorsén, Gunnar
    Stockholm University, Faculty of Science, Department of Analytical Chemistry.
    Screening and Quantification of Pesticides in Water Using a Dual-Function Graphitized Carbon Black Disk2010In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 82, no 1, p. 290-296Article in journal (Refereed)
    Abstract [en]

    A simple platform for combining solid phase extraction (SPE) and surface-assisted laser desorption ionization mass spectrometry (SALDI-MS) of extracted analytes, using disks prepared by embedding graphitized carbon black (GCB-4) particles in a network of polytetrafluoroethylene (PTFE), is presented. The system provides a convenient approach for rapid SALDI-MS screening of substances in aqueous samples, which can be followed by robust quantitative and/or structural analyses by liquid chromatography (LC)/MS/MS of positive samples. The extraction discs are easily transferred between gaskets where the sample extraction and desorption of selected samples is performed and the mass spectrometer. The SPE and SALDI properties of the new GCB-4 disc have been characterized for 15 pesticides with varying chemical properties, and the screening strategy has been applied to the analysis of pesticides in agricultural drainage water. Atrazine and atrazine-desethyl-2-hydroxy were detected in the sampled water by SALDI-MS screening and subsequently confirmed and quantified using LC/MS/MS.

  • 4.
    Amini, Nahid
    et al.
    Stockholm University, Faculty of Science, Department of Analytical Chemistry.
    Shariatgorji, Mohammadreza
    Stockholm University, Faculty of Science, Department of Analytical Chemistry.
    Thorsen, Gunnar
    Stockholm University, Faculty of Science, Department of Analytical Chemistry.
    SALDI-MS Signal Enhancement Using Oxidized Graphitized Carbon Black Nanoparticles2009In: Journal of the American Society for Mass Spectrometry, ISSN 1044-0305, E-ISSN 1879-1123, Vol. 20, no 6, p. 1207-1213Article in journal (Refereed)
    Abstract [en]

    The signal intensity of low-molecular-weight compounds analyzed using surface-assisted laserdesorption/ionization time-of-flight mass spectrometry (SALDI-TOF-MS) was significantlyenhanced when oxidized graphitized carbon black (GCB) particles were used as the desorption/ionization surface. The surface of oxidized GCB contains more carboxylic acid groupsthan non-oxidized GCB. Carboxylic acid groups enhance the efficiency of the ionizationprocess and the desorption of more hydrophobic compounds. A common pharmaceuticalcompound, propranolol, was successfully extracted from Baltic Sea blue mussels and quantifiedusing oxidized GCB as the SALDI surface, whereas deuterated propranolol was used asthe internal standard. The calibration curve showed a wide linear dynamic range of response(0.1–20 g/mL) and good reproducibility (RSD 10%). It was not possible to detectpropranolol in Baltic Sea blue mussels when non-oxidized GCB was used as the SALDI surface.

  • 5.
    Shariatgorji, Mohammadreza
    et al.
    Stockholm University, Faculty of Science, Department of Analytical Chemistry.
    Amini, Nahid
    Stockholm University, Faculty of Science, Department of Analytical Chemistry.
    Ilag, Leopold L.
    Stockholm University, Faculty of Science, Department of Analytical Chemistry.
    Silicon nitride nanoparticles for surface-assisted laser desorption/ionization of small molecules2009In: Journal of nanoparticle research, ISSN 1388-0764, E-ISSN 1572-896X, Vol. 11, no 6, p. 1509-1512Article in journal (Refereed)
    Abstract [en]

    Conventional matrix-assisted laser desorption/ionization mass spectrometry is limited to analyses of higher molecular weight compounds due to high background noise generated by the matrix in the lower mass region. Surface-assisted laser desorption/ionization (SALDI) mass spectrometry is an alternative solution to this problem. Nanoparticles, structured silicon surfaces and carbon allotropes are commonly used as SALDI surfaces. Here, for the first time, we demonstrate the application of silicon nitride nanoparticles as a suitable medium for laser desorption/ionization of small drug molecules.

  • 6.
    Shariatgorji, Mohammadreza
    et al.
    Stockholm University, Faculty of Science, Department of Analytical Chemistry.
    Amini, Nahid
    Stockholm University, Faculty of Science, Department of Analytical Chemistry.
    Thorsen, Gunnar
    Stockholm University, Faculty of Science, Department of Analytical Chemistry.
    Crescenzi, Carlo
    Stockholm University, Faculty of Science, Department of Analytical Chemistry.
    Ilag, Leopold
    Stockholm University, Faculty of Science, Department of Analytical Chemistry.
    µ-trap for the SALDI-MS screening of organic compounds prior to LC/MS analysis2008In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 80, no 14, p. 5515-5523Article in journal (Refereed)
    Abstract [en]

    A procedure for rapidly screening and quantitatively analyzing organic molecules is presented, in which a miniaturized solid-phase extraction (SPE) cartridge containing 0.6 mg of graphitized carbon black (the GCB-mu-trap) is used for sample pretreatment. Then surface-assisted laser desorption ionization dine-of-flight mass spectrometry (SALDI-TOF-MS) screening is followed by liquid chromatography/mass spectrometry (LC/MS) for robust quantitative analysis of samples containing analytes of interest. Liquid samples with volumes up to 100 mL were extracted using the GCB-mu-trap, and SALDI screening was performed by transferring a few particles of the GCB 4 sorbent from the mu-trap onto a stainless steel plate. Analytes were then simply ionized and desorbed by irradiating the GCB 4 particles without any further pretreatment. GCB 4 was found to be an excellent surface for the SALDI analysis of small molecules, providing spectra with very clean backgrounds. The small size of the cartridge (micropipet filter tip) results in enrichment of the analytes on a small surface area, affording low SALDI-TOF-MS detection limits. Furthermore, the removal of just a few particles from the p-trap does not significantly affect the subsequent quantitative determination. This approach offers considerable reductions in analytical costs by eliminating unnecessary SPE-LC/MS analyses.

  • 7.
    Spacil, Zdenek
    et al.
    Stockholm University, Faculty of Science, Department of Analytical Chemistry.
    Shariatgorji, Mohammadreza
    Stockholm University, Faculty of Science, Department of Analytical Chemistry.
    Amini, Nahid
    Stockholm University, Faculty of Science, Department of Analytical Chemistry.
    Solich, Petr
    Department of Analytical Chemistry, Faculty of Pharmacy, Charles University in Prague, Heyrovskeho 1203, 500 05 Hradec Kralove, Czech Republic.
    Ilag, Leopold L.
    Stockholm University, Faculty of Science, Department of Analytical Chemistry.
    Matrix-less laser desorption/ionisation mass spectrometry of polyphenols in red wine2009In: Rapid Communications in Mass Spectrometry, ISSN 0951-4198, E-ISSN 1097-0231, Vol. 23, no 12, p. 1834-1840Article in journal (Refereed)
    Abstract [en]

    Matrix-assisted laser desorption/ionisation (MALDI) of small molecules is challenging and in most cases impossible due to interferences from matrix ions precluding analysis of molecules <300-500 Da. A common matrix such as ferulic acid belongs to an important class of compounds associated with antioxidant activity. If the shared phenolic structure is related to the propensity as an active MALDI matrix then it follows that direct laser desorption/ionisation should be possible for polyphenols. Indeed matrix-less laser desorption/ionisation mass spectrometry is achieved whereby the analyte functions as a matrix and was used to monitor low molecular weight compounds in wine samples. Sensitivity ranging from 0.12-87 pmol/spot was achieved for eight phenolic acids (4-coumaric, 4-hydroxybenzoic, caffeic, ferulic, gallic, protocatechuic, syringic, vanillic) and 0.02 pmol/spot for trans-resveratrol. Additionally, 4-coumaric, 4-hydroxybenzoic, caffeic, ferulic, gallic, syringic, vanillic acids and trans-resveratrol were identified in wine samples using accurate mass measurements consistent with reported profiles based on liquid chromatography (LC)/MS. Minimal sample pre-treatment make the technique potentially appropriate for fingerprinting, screening and quality control of wine samples. Copyright © 2009 John Wiley & Sons, Ltd.

  • 8.
    Wincent, Emma
    et al.
    Stockholm University, Faculty of Science, Department of Genetics, Microbiology and Toxicology.
    Amini, Nahid
    Stockholm University, Faculty of Science, Department of Analytical Chemistry.
    Luecke, Sandra
    Glatt, H.
    Bergman, Jan
    Crescenzi, Carlo
    Stockholm University, Faculty of Science, Department of Analytical Chemistry.
    Rannug, Agneta
    Rannug, Ulf
    Stockholm University, Faculty of Science, Department of Genetics, Microbiology and Toxicology.
    The suggested physiologic aryl hydrocarbon receptor activator and cytochrome P4501 substrate 6-formylindolo[3,2-b]carbazole is present in humans2009In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 284, no 5, p. 2690-2696Article in journal (Refereed)
    Abstract [en]

    Dioxins and other polycyclic aromatic compounds formed during the combustion of waste and fossil fuels represent a risk to human health, as well as to the well being of our environment. Compounds of this nature exert carcinogenic and endocrine-disrupting effects in experimental animals by binding to the orphan aryl hydrocarbon receptor (AhR). Understanding the mechanism of action of these pollutants, as well as the physiological role(s) of the AhR, requires identification of the endogenous ligand(s) of this receptor. We reported earlier that activation of AhR by ultraviolet radiation is mediated by the chromophoric amino acid tryptophan (Trp), and we suggested that a new class of compounds derived from Trp, in particular 6-formylindolo[3,2-b]carbazole (FICZ), acts as natural high affinity ligands for this receptor. Here we describe seven new FICZ-derived indolo[3,2-b]carbazole-6-carboxylic acid metabolites and two sulfoconjugates, and we demonstrate the following. (i) FICZ is formed efficiently by photolysis of Trp upon exposure to visible light. (ii) FICZ is an exceptionally good substrate for cytochromes P450 (CYP) 1A1, 1A2, and 1B1, and its hydroxylated metabolites are remarkably good substrates for the sulfotransferases (SULTs) 1A1, 1A2, 1B1, and 1E1. Finally, (iii) sulfoconjugates of phenolic metabolites of FICZ are present in human urine. Our findings indicate that formylindolo[3,2-b]carbazols are the most potent naturally occurring activators of the AhR signaling pathway and may be the key substrates of the CYP1 and SULT1 families of enzymes. These conclusions contradict the widespread view that xenobiotic compounds are the major AhR ligands and CYP1 substrates.

1 - 8 of 8
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