Novel ship-based and submersible Membrane Inlet-Photo-Ionization Mass Spectrometer (MI-PIMS) for on-line detection of environmental pollutants and explosives in sea water

The trace analysis of anthropogenic pollutants in seawater, such as Polycyclic Aromatic Hydrocarbons (PAH) from oil spills and TNT from dumped ammunition, is crucial in marine sciences. After the World Wars, large quantities of ammunition were dumped in European coastal waters, posing a threat to marine ecosystems. Continuous monitoring is necessary. A new online analysis method combines direct water sampling via a membrane inlet with a mobile Photoionization Mass Spectrometer (MI-PIMS). The system samples seawater into a membrane extraction unit, where organic contaminants penetrate a PDMS membrane and are transported to a TOFMS. Laser pulses ionize target molecules using Resonance-Enhanced Multiphoton Ionization (REMPI), enabling real-time measurements of pollutants at ng/L levels. The mobile MI-PIMS system was initially tested in the Warnow Estuary in Rostock, Germany, and showed high sensitivity in detecting oil spills and PAH. For explosive detection at ammunition dump sites, TNT and other explosives penetrate the PDMS membrane, where laser pulses induce the formation of NO2 and its decomposition to NO molecules. These serve as sensitive markers for explosives. A shipborne MI-PIMS system examined bottom water from the Baltic Sea and successfully detected TNT at ppb concentrations. In detail, trinitrotoluene (TNT) as well as other nitrated organic explosives are penetrating the MI-PIMS system´s PDMS-membrane. 226 nm Nd:YAG-OPO-pulses are inducing a photolytic formation of NO2 from any nitroorganic explosive. The NO2 molecule subsequently undergoes instantaneous predissociation, forming nitrous oxide molecules (NO) which are efficiently ionized by the same laser pulse in a 1+1-REMPI process. A submersible MI-PIMS system, mounted on a remotely operated underwater vehicle (ROV), is being developed to test for TNT traces at ammunition dump sites and identify leaking shells.