Direct aqueous injection with backflush thermal desorption for wastewater monitoring by online GC-MS

A gas chromatography—mass spectrometry system with a novel injector type, which is designed for direct aqueous injection of wastewater, is presented. The system is used for online monitoring of the influent of the wastewater treatment plant at BASF’s main chemical production site in Ludwigshafen, Germany. The purpose of monitoring is to protect the biological treatment process and the receiving water body, the Rhine. The modular system is primarily based on commercial equipment, but utilizes a special injection system, which is connected to a Deans switch. The two-stage injector consists of a programmable temperature vaporizer (PTV) injector with a small volume insert for vaporization and a dual sorbent packed second PTV for analyte adsorption/desorption. The Deans switch allows a backflush/thermal desorption operation which enables the direct injection of filtered, crude wastewater. About 170 volatile and semivolatile compounds are calibrated with approximate detection limits of 1 mg/L, which are sufficient for the analysis of untreated wastewater. The quantitative results are transferred to a database which is connected to a process control system. If the wastewater does not meet the required specification, an alarm is generated and the wastewater is diverted into a storage basin. Special software programs and routines allow for reliable, unattended operation and remote instrument control. Data quality is automatically controlled in each run and through the daily analysis of quality control samples. The current design allows for analysis of volatile compounds, such as methanol, whereas an earlier injector setup restricted the range of analytes to less volatile compounds (of size C₄ or greater).