Surface plasmon resonance (SPR) spectroscopy is a widely used optical reflection technique for the characterization of thin films. The central quantity of SPR spectroscopy is the surface plasmon coup領(lǐng) angle as a characteristic signature of the prevai領(lǐng) interfacial architecture. Adsorption processes lead to a shift of the surface plasmon resonance which is in the thin film limit directly proportional to the corresponding mass coverage. The aim of any SPR instrument is a precise measurement of the coup領(lǐng) angle with a sufficient high time resolution that fast kinetic processes can be monitored. In this paper, we compare two promising methods, an established one,the reflectivity tracking and a fairly new one, the mismatch tracking. Reflectivity tracking simply records the intensity of the light in the vicinity of the coup領(lǐng) angle. The shift of the plasmon modifies the intensity at the detector which can subsequently be used for data analysis. Mismatch tracking is more complex. Light is focused with a lens onto the prism base and the reflected light is detected via a bicell detector. The upper and lower cell integrate over a well-defined angular range of the fan of rays produced within the focus. The mismatch in the intensity between the upper and lower segments is evaluated and used to retrieve the unknown film parameter. In this contribution we suggest some decisive variations of the originally proposed scheme and demonstrate that the modified mismatch scheme yields a significantly higher sensitivity than the original one. Furthermore, it is demonstrated that this scheme is a superior alternative to reflectivity tracking. 表面等離子共振儀(SPR)（Surface Plasmon Resonance）