ANALYSIS OF NEUTRAL NITROGEN-COMPOUNDS IN DIESEL OIL BY DIRECT-INJECTION HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY MASS-SPECTROMETRY ULTRAVIOLET SPECTROMETRY METHODS

An analytical methodology has been developed for the direct analysis o f neutral nitrogen compounds in diesel oil by HPLC with subsequent det ection using MS and/or photodiode-array UV spectrometry. By diluting d iesel oils with one volume of hexane, diesel samples could be injected directly onto an alumina analytical column and then eluted with a gra dient mobile phase consisting of hexane and dioxane. Nitrogen compound s were selectively retained on the alumina column, eluted using LC, an d then detected by particle beam LC-MS or UV at 254, 270 and 290 nm. T wo Brazilian and one Arabian diesel distillates were investigated. Alk ylcarbazoles and alkylindoles were identified as the major neutral nit rogen components. Structural identification was accomplished by combin ation of electron impact MS and UV analyses. The concentration of carb azoles and indoles was estimated using calibration standards of carbaz ole and indole, respectively.