Fig. 1. Diagram of the custom-built polysulfone gas extractor. Seawater is directed by a stream selection valve into the extractor, where it is mixed with phosphoric acid, bubbled with helium and sent for analysis by a quadropole mass spectrometer. The liquid level is maintained between two quartz optical liquid detectors. The seawater/acid mixture is periodically drained off through the drain port when its level reaches the top detector.