The 2,3-diaminonaphthalene (DAN) assay is routinely used in the determination of nitrite/nitrate levels in biological fluids and cellular extracts as one indicator of nitric oxide activity. The assay, as reported by Misko, uses the reaction of DAN with NO2- under acidic conditions to form a detectable fluorescent naphthotriazole. The reaction proceeds at acidic pH at room temperature. Fluorescence is monitored following the addition of NaOH, which raises pH, resulting in lower background and increased sensitivity (Ex/Em: ~365/415nm). However, detection at 450nm is recommended to avoid fluorescent blanks and increase sensitivity. The fluorescent background of DAN is low for maximum sensitivity. Detection limits of NO achieved by this method are in the high-pM range. 2,3-Diaminonaphtaline (DAN) is used as a derivatisation-reagent for the determination of selenium at low detection limits. The 4,5-benzopiaselenol-complex can be quantified by photometry or GC.