Method for Detecting Drag Reducer Additives in Gasoline

A method for detecting polymer-based drag reducer additives in gasoline. One embodiment of the invention is a method for detecting the concentration of polymer-based drag reducer additives in gasoline, the method including the following: (a) placing a gasoline sample in a receptacle having at least two adjacent clear sides and irradiating one of the two clear sides of the receptacle with a pulsed laser beam, the pulsed laser beam having a wavelength in the ultra violet region shorter than 300 nm; (b) detecting laser-induced fluorescence wavelength resolved spectrum at 90° angle relative to the incident laser beam and through a slit defined in a diffraction screen, the diffraction screen being placed at a pre-defined first distance from the receptacle; (c) adjusting the position of the receptacle and slightly de-focusing the collimating lenses so that the low resolution fluorescence wavelength-resolved spectrum of the gasoline sample appears with a first peak at about 380 nm and a second peak at about 430 nm; (d) recording the laser-induced fluorescence wavelength-resolved spectra of the gasoline sample within a defined time-gate starting at the end of the temporal span of the laser pulse; and (e) comparing the percentage intensity of the first peak relative to the second peak for the laser-induced fluorescence spectrum near 380 nm of the gasoline sample to that of a gasoline sample free of any polymer-based drag reducer additives. In another embodiment of the method, the location of the diffraction-screen is at the pre-defined distance of between 0.5 mm to 2 mm from the side of the receptacle. In another embodiment of the method, the time-gate in step (d) is of 3 ns width and starting immediately after the end of the laser pulse.