Dissolved organic nitrogen calibration

The ability to make analytical measurements depends intimately on the availability of well-defined standards and calibrants. Many measurements of analytes in seawater (such as dissolved organic carbon and dissolved organic nitrogen) cannot be compared among laboratories because of the lack of appropriate reference materials and blanks for instrument calibration and testing. Intercomparison exercises are critical (NRC, 1993, p. 75). 

Szathmary and Luhmann [50] described a sensitive and automated gas chromatographic method for the determination of miconazole in plasma samples. Plasma was mixed with internal standard l-[2,4-dichloro-2-(2,3,4-trichlorobenzyloxy) phenethyl]imidazole and 0.1 M sodium hydroxide and extracted with heptane-isoamyl alcohol (197 3) and the drug was back-extracted with 0.05 M sulfuric acid. The aqueous phase was adjusted to pH 10 and extracted with an identical organic phase, which was evaporated to dryness. The residue was dissolved in isopropanol and subjected to gas chromatography on a column (12 m x 0.2 mm) of OV-1 (0.1 pm) at 265 °C, with nitrogen phosphorous detection. Recovery of miconazole was 85% and the calibration graph was rectilinear for 0.25 250 ng/mL. 

Equivalent amounts of TIE and TDI (50 mmoles each) were dissolved in an organic solvent like 2-butanone (l.lM cone- ) and to this solution was added O.lg of dibutyltin dilaurate as a catalyst. The mixture was heated under nitrogen at 75 0 for 2 hrs. and the polymer was recovered by precipitation into acetone followed by reprecipitation into diethyl ether from chloroform. It was dried under a vacuum to yield a quantitative conversion to polymer. From GPG the Mn = 7 500 and Mw = 46,900, calibrated with respect to polystyrene. 

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