Jakub Schůrek

Institute of Chemical Technology Prague, Praha, Praha, Czech Republic

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Publications (5)5.51 Total impact

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    ABSTRACT: A series of twelve breast milk samples were analysed by gas chromatography-mass spectrometry (GC/MS) operated in selected ion monitoring mode for 3-chloropropane-1,2-diol (3-MCPD). Whilst none of the samples contained 3-MCPD above the limit of detection of 3 microg kg(-1) milk, all contained high amounts of 3-MCPD esterified with higher fatty acids. The levels of 3-MCPD released by hydrolysis of these esters (bound 3-MCPD) ranged from the limit of detection (300 microg kg(-1), expressed on a fat basis) to 2195 microg kg(-1); with a mean level of bound 3-MCPD of 1014 microg kg(-1), which corresponded to 35.5 microg kg(-1) milk. The presence of bound 3-MCPD was confirmed using orthogonal gas chromatography coupled with high-speed time-of-flight mass spectrometry analysis for four randomly selected breast milk samples. Six breast milks collected from one of the nursing mothers 14-76 days after childbirth contained bound 3-MCPD within the range of 328-2078 microg kg(-1) fat (mean 930 microg kg(-1) fat). The calculated bound 3-MCPD content of these samples was within the range of 6 and 19 microg kg(-1) milk (mean of 12 microg kg(-1) milk). The major types of 3-MCPD esters were the symmetric diesters with lauric, palmitic, and oleic acids, and asymmetric diesters with palmitic acid/oleic acid among which 3-chloro-1,2-propanediol 1,2-dioleate prevailed.
    Full-text · Article · Jul 2008 · Food Additives and Contaminants - Part A Chemistry, Analysis, Control, Exposure and Risk Assessment
  • J. Schůrek · J.P. Rabová · J. Hajšlová

    No preview · Article · Jan 2008 · Chemicke Listy
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    ABSTRACT: Introduction Ambient desorption ionization mass spectrometry (MS) is a rapidly growing area representing an attractive alterna-tive to conventional analytic approaches. Recently intro-duced ionization techniques, such as direct analysis in real time (DART) 1 , desorption electrospray ionization (DESI) 2 or atmospheric pressure solids analysis probe (ASAP) 3 , allow direct examination of various types of samples in the open atmosphere and at ground potential. Little or no sample tre-atment prior to analysis is required. Additionally, time-con-suming separation of sample components, which is usually employed by chromatographic methods, can be omitted with ambient MS. 4 The ionization process with DART is based on interac-tions of metastable atoms of gas with atmosphere (H 2 O, O 2) and sample components. The gas (usually helium) flows th-rough a tube divided into several compartments. In a discharge chamber, ions, electrons and metastables are formed. In the next step, charged species are removed from the gas stream and heated gas promotes the desorption process. Ionization of the sample occurs in the area between the ion source and a mass spectrometer inlet (sampling gap). DART provides rela-tively simple mass spectra characterized mainly by [M + H] + and [M] + in positive-ion mode or [M – H] – and [M] – in nega-tive-ion mode. 1 It is worth to notice, that DART technique has common features with atmospheric pressure chemical ionization (APCI) as the formation of metastables take place in an electrical discharge. 1,4 DART ion source can be hyphenated to any type of mass spectrometer. However, when coupled to a high-resolution time-of-flight mass spectrometer (TOFMS), accurate mass measurement is enabled, allowing the confirmation of target analyte identity and calculations of elemental compositions of "unknowns". For correct identification of "unknowns", it is essential to gain knowledge about the examined matrix to allow discrimination of potential compounds suggested by the software. Until now, very few papers dealing with applications of DART have been published. 5-9 In following examples, the potential of DART–TOFMS technique for qualitative and quantitative analysis of (i) pesticide residues, in particular case, strobilurins in wheat grains, (ii) thiabendazole on cut-flower leaves, and (iii) rapid screening of brominated flame retardants (BFRs) in in-door dust extract, will be demon-strated. Experimental C h e m i c a l s Pesticide standards (≥ 99 %) were obtained from Dr. Ehrenstorfer (Germany), decabromodiphenyl ether (BDE-209) standard (≥ 98 %) was provided by Cambridge Isotope Laboratories (USA). Solvents used for sample extractions and preparations of standard solutions were HPLC-grade. Poly(ethylene glycol) 600 was from Sigma-Aldrich (Ger-many), anhydrous Na 2 SO 4 was supplied by Merck (Ger-many). S a m p l e P r e p a r a t i o n (i) An amount of 12.5 g of milled wheat grains was spiked with an internal standard (prochloraz) at a concent-ration of 250 ng g –1 and extracted by shaking with 50 ml of ethyl acetate and 10 g of anhydrous Na 2 SO 4 . The suspension was filtered and the volume was reduced by evaporation to 25 ml. Similarly, wheat grain extracts spiked with strobilurins (azoxystrobin, kresoxim methyl, pyraclostrobin, trifloxystro-bin, dimoxystrobin and picoxystrobin) in the range from 12 to 1200 ng g –1 were prepared. Wheat grains with incurred residues of azoxystrobin, kresoxim methyl and pyraclostro-bin (reference material) were processed as described above. (ii) Flowers (roses) were purchased from local florists shop. The leaf was separated from the rest of flower and its surface was directly analyzed. (iii) In-door dust containing BFRs (mainly BDE-209) was extracted using ASE 300 pressurized liquid extraction system (Dionex, USA): a hexane–acetone (1 : 1, v/v) mixture was used for extraction. The residues of extract were dissol-ved in isooctane.
    Full-text · Article · Jan 2008

  • No preview · Article · Jan 2008
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    ABSTRACT: A wide range of estrogenic contaminants has been detected in the aquatic environment. Among these, natural and synthetic steroid estrogens, typically present in municipal sewage-treatment plant (STP) effluents, are the most potent. In this study a new GC-MS method has been developed for direct analysis of five major steroid estrogens (estrone, 17beta-estradiol, 17alpha-ethinylestradiol, dienestrol, and diethylstilbestrol) in river sediments. Four GC-MS systems used for analysis of underivatized analytes in purified extracts were compared. Relatively low detection limits (1.5-5 ng g(-1) dried sediment) and good repeatability of GC splitless injection (RSD 1-2%) were achieved by use of a system combining low-pressure gas chromatography with a single-quadrupole mass analyzer (LP-GC-MS). Use of orthogonal gas chromatography (GCxGC) hyphenated with high-speed time-of-flight mass spectrometry (HSTOF-MS) enabled not only significantly better resolution of target analytes, and their unequivocal identification, but also further improvement (decrease) of their detection limits. In addition to these outcomes, use of this unique GCxGC-TOF-MS system enabled identification of several other non-target chemicals, including pharmaceutical steroids, present in purified sediment extracts.
    Full-text · Article · Mar 2007 · Analytical and Bioanalytical Chemistry