Abstract: A 10 mL portion of 1 M NaOH was added to 8-hydroxyquinoline (quinolin-8-ol; I) prepared in HCl of pH 3, or in KCl/H3BO3/NaOH buffers of pH 8 or 10 and the total volume was diluted to 25 mL. Streams (3.2 ml/min) of p-aminophenol (PAP) (100 µg/ml) and 0.004 M KIO4 were mixed in a reactor coil (45 cm x 0.8 mm i.d.) and the benzoquinoneimine, formed in situ fed into a second reactor coil (400 cm x 0.8 mm i.d.) with 0.4 M NaOH (3.2 ml/min) into which a 500 µL portion of I in an appropriate buffer had been injected. The resultant indophenol dye (structure illustrated) was measured at 610 nm in a 50 µL flow cell (1 cm path). The calibration graph was linear from 2-8 µg/ml I and the detection limit was 7.6 ng/ml. The RSD (n = 4) was 0.06% for 4 µg/ml I. Recoveries of 98-102% were obtained at pH 3, 8 or 10. Sensitivity is lower (ε = 9500) for the reaction of I with PAP than reported for batch procedures which employ reactions of I with orthanilic acid (ε = 26 500) or diazotized 4-aminoacetophenone (ε = 33 700).

Abstract: The design, construction and operation are described of a flow-through amperometric cell with a small Pt-wire working electrode and sub µL geometric volume and wherein the counter, working and reference electrodes are electrolytically connected by means of a Nafion solid polymer electrolyte. The cell was tested in a flow injection system with use of quinolin-8-ol (I), 4-methylcatechol (II) and K4Fe(CN)6 as model analytes. Calibration graphs were rectilinear from 0.2 to 0.6 µM up to 100 µM. In the determination of I at the 10 and 100 µM levels the coefficient of variation were 4.3 and 1.1% respectively (n = 10). Electrode activity decreased by 10 to 15% during a day's use but this could be restored by cyclic polarization of the working electrode between +1.6 and -0.2 V (vs. Ag - AgCl) for 15 min at 50 mV s-1. The detector has been applied in the HPLC determination of I, catechol and II on a Separon SGX C-18 column (15 cm x 3 mm) with aqueous 4% dioxan as mobile phase. AB An amperometric cell with a small platinum wire working electrode, a submicroliter geometric volume, and a solid polymer electrolyte (Nafion) was constructed and tested. The cell permits sensitive and reliable detection even in mobile phases of negligible elec. conductivity, (e.g., distilled water or nonpolar organic solvents). The sensitivity is substantially higher than that attained with similar cells containing large-area working electrodes; typical limits of detection amt. to analyte concentrations. between 10^-7 and 10^-6 mol/L, corresponding to subnanogram amounts in common HPLC sample volumes The detector response exhibits satisfactory linearity, a linear dynamic range of at least three concentration. decades, and a good precision, with relative standard deviations of 1 to 5%. This cell substantially widens the possibilities of amperometric detection, permitting direct application, for example, to normal-phase HPLC or to methods with programmed composition of the mobile phase (gradient elution).

Abstract: A high-performance liquid chromatography method for the separation of 8-hydroxyquinoline (I) [148-24-3] and three of its halogenated derivatives and their fluorescence detection after post-column derivatization to the corresponding metal chelates is described. Quinine sulfate in 0.1N H2SO4 was used as reference of fluorescence intensity. The column was packed with Iatrobeads 6CP-2010 resin. Excitation spectra of the metal chelates showed two maxima, 270-280 and 380-400 nm. All chelates exhibited more intense fluorescence when excited at longer wavelengths. The fluorescence intensities of Mg 8-hydroxyquinoline [14639-28-2] and Mg 5-chloro-8-hydroxyquinoline [41584-60-5] increased with pH, the optimum pH being 9.5, since >pH 12 a white ppt. of Mg(OH)2 was formed. Mg concentration affected the fluorescence intensity; at least 10^-3 M Mg(II) was required to obtain intense fluorescence when the final concentration. of 8-hydroxyquinoline was 10^-6 M.