Determination of selenium sulfide using 1,3-dibromo-5,5-dimethylhydantoin (DBH). Analytical methods of pharmacopeias with DBH in respect to environmental and economical concern Part 11.
USP 2000 (The United States Pharmacopeia, Rockville, MD, 24th ed., 2000, pp. 1514-1515) and PH. EUR. 1997 (European Pharmacopoeia, 3rd ed., Council of Europe, Strasbourg, 1997, p. 1459) dissolve selenium sulfide by boiling with fuming nitric acid for about 1 h. After cooling to room temperature and dilution with water nitrous acid and nitrogen oxides are removed with urea also by boiling before the iodometric titration is performed. This method can be importantly simplified and improved, when using 1,3-dibromo-5,5-dimethylhydantoin (DBH) in glacial acetic acid in presence of solid potassium bromide. Selenium sulfide is dissolved during 5-10 min at room temperature. The excess of DBH and bromine can be removed with 5-sulfosalicylic acid also without boiling. The point of the indicator change for the iodometric titration is improved in comparison to the method of the pharmacopeias, because the colloidal solution of selenium mostly coagulates. Also the sulfur content of selenium sulfide can be determined with DBH.
Evaluation of 1.0 mm i.d. column performances on ultra high pressure liquid chromatography instrumentation.
The present study focuses on the evaluation of 1.0 mm i.d. (internal diameter) columns on a commercial Ultra-High Pressure system. These systems have been developed specifically to operate columns with small volumes, typically 2.1 mm i.d., by reducing extra-column volume dispersion. The use of columns with smaller i.d. results in a reduced solvent consumption and required sample volume. The evaluation of the columns was carried out with samples containing neutral and pharmaceutical compounds. In isocratic mode, the extra-column volume produced additional band broadening leading to poor performances compared to equivalent 2.1 mm i.d. columns. By increasing the length of the column, the influence of the extra-column bandspreading could be reduced and 75,000 plates were obtained when four columns were coupled. In gradient mode, the effect of the extra-column contribution on efficiency was limited and about 80% of the performance of the 2.1 mm i.d. columns was obtained. Optimum conditions in gradient mode were further investigated by changing flow rate, gradient time and column length. A different approach of the calculation of peak capacity was also considered for the comparison of the influence of these different parameters.
Identification of Dihydroxy Aromatic Compounds in a Low-Temperature Pyrolysis Coal Tar by Gas Chromatography−Mass Spectrometry (GC−MS) and Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS)
Dihydroxy aromatics in coal tar undergo rapid coupling reactions with each other and with some coal-derived species during coal pyrolysis and liquefaction. However, only limited information on the structure of dihydroxy aromatics is known. In this study, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and gas chromatography−mass spectrometry (GC−MS) were used to characterize the dihydroxy aromatics in a low-temperature pyrolyzed coal tar and its distillate and residue fractions. Negative-ion electrospray ionization (ESI) FT-ICR MS spectra of coal-tar-derived samples had low molecular masses and narrow mass ranges. Negative-ion ESI is extremely selective for the dihydroxy aromatics present in coal tar. The O2 class species had the highest ion intensity among the species in the negative-ion FT-ICR mass spectrum for each sample. Dihydroxy compounds with an aromatic core structure of benzene, indan, biphenyl (and/or acenaphthene), and naphthalene were identified in the distillate fract...