Usporedba dinamičke analize para iznad otopine i mikroekstrakcije analita na čvrstoj fazi za plinskokromatografsko određivanje BTEX-a u urinu

The aim of this study was to compare two extraction procedures: dynamic headspace-purge and trap (PT) and headspace solid-phase microextraction (HS-SPME) for gas chromatographic determination of benzene, toluene, ethylbenzene, and isomeric xylenes (BTEX) in urine with photoionization (PID) and mass spectrometric (MS) detection, respectively. Both methods showed linearity in the range of interest [(50-2000) ng L-1], good accuracy (80% to 100 %), and repeatability (RSD≤11 %). Detection limits were in the low ng L-1 level for both methods, although slightly greater sensitivity was found for the PT method. In comparison with PT, HS-SPME was simpler and required less time for analysis. Although the analytical features of both examined methods are appropriate for biomonitoring of environmental exposure to BTEX, only the HS-SPME-GC-MS method is recommended for routine analysis of BTEX in urine. The method was applied for the quantitative analysis of BTEX in urine samples collected from non-smokers (n=10) and smokers (n=10).Cilj ovog rada bio je usporediti dva postupka ekstrakcije za plinskokromatografsko određivanje benzena, toluena, etilbenzena i izomera ksilena u urinu. Uspoređene su dinamička analiza para iznad otopine (tzv. purge and trap) uz fotoionizacijski detektor i mikroekstrakcija analita na čvrstoj fazi uz detektor spektrometar masa. Rezultati upućuju na linearnost odziva detektora u ispitivanome koncentracijskom području [(50- 2000) ng L-1], zadovoljavajuću točnost (80 %-100 %) i ponovljivost (RSD ≤11 %). Postignute su niske granice detekcije za obje metode. Mikroekstrakcija analita na čvrstoj fazi uz detektor spektrometar masa pokazala se jednostavnijom i bržom za izvođenje pa se preporučuje za rutinsko određivanje BTEX-a u urinu. Metoda je primijenjena za analizu tih spojeva u uzorcima urina nepušača (n=10) i pušača (n=10)

C-axis lattice dynamics in Bi-based cuprate superconductors

We present results of a systematic study of the c axis lattice dynamics in single layer Bi2Sr2CuO6 (Bi2201), bilayer Bi2Sr2CaCu2O8 (Bi2212) and trilayer Bi2Sr2Ca2Cu3O10 (Bi2223) cuprate superconductors. Our study is based on both experimental data obtained by spectral ellipsometry on single crystals and theoretical calculations. The calculations are carried out within the framework of a classical shell model, which includes long-range Coulomb interactions and short-range interactions of the Buckingham form in a system of polarizable ions. Using the same set of the shell model parameters for Bi2201, Bi2212 and Bi2223, we calculate the frequencies of the Brillouin-zone center phonon modes of A2u symmetry and suggest the phonon mode eigenvector patterns. We achieve good agreement between the calculated A2u eigenfrequencies and the experimental values of the c axis TO phonon frequencies which allows us to make a reliable phonon mode assignment for all three Bi-based cuprate superconductors. We also present the results of our shell model calculations for the Gamma-point A1g symmetry modes in Bi2201, Bi2212 and Bi2223 and suggest an assignment that is based on the published experimental Raman spectra. The superconductivity-induced phonon anomalies recently observed in the c axis infrared and resonant Raman scattering spectra in trilayer Bi2223 are consistently explained with the suggested assignment.Comment: 29 pages, 13 figure