A method and system for determining the purity and authenticity of a substance being transported in a container. A method includes increasing an upstream NOx level based on an initial upstream NOx level in an exhaust system, and detecting an NH3 storage condition based on a difference in a downstream NOx level before and after the upstream NOx level is increased. A differential amplifier drive signal is produced in response to the received supply voltage signal, the received differential input signal, and the received differential control signal. The tag, tag CRC, data, and data CRC are pipelined from DRAM in four frames, each having multiple clock cycles.