Disclosed herein are a device and method for accurately extracting individual organic acid and/or Total Volatile Fatty Acid (VFA), ammonium (NH4+) and buffering inorganic carbon compound or hydrogen carbonate (HCO3−) concentrations trends from an active Anaerobic Digestion (AD) process. The substantially real-time individual and/or total VFA, NH4+ and HCO3− information allows the AD operator to effectively operate the system at optimal efficiency and ensure that VFA and NH4+ concentrations do not reach toxic levels that can potentially cause the AD process to fail. The general health of an AD digester and process may be determined by using a ratio of total organic acids to total inorganic carbon as determined by the method.