An analyzer based on Quantum Cascade Laser (QCL) has been developed for chemical sensing of gaseous nitrogen compounds (NO, NO₂, N₂O and NH₃). The QCL can emit coherent lights in the Mid-infrared (Mid-IR) region where these nitrogen compounds exhibit strong absorption tendency. Therefore, it is possible to detect very low concentration gas. QCL can also give a super fine resolution of the spectrum in this region. Therefore, utilization of this spectrometer can reduce the interference caused by the spectral overlap of coexisting gases in automobile engine exhaust. In the previous study, the fundamental concept of development along with some basic performance of the analyzer had been reported. In this study, improvement of performance has been attempted. Especially, the cell design, response time of NH₃, broadening the measurement ranges, and increasing the data sampling speed have been considered. In addition the measurement accuracies and stabilities are also confirmed with some real engine exhaust with NH₃ injection in the tailpipe. Very low detection limit (≺1 ppm) and faster response (≺1s) have been achieved with the analyzer.