Fig. 5From: Screening freshness of seafood by measuring trimethylamine (TMA) levels using helium-plasma ionization mass spectrometry (HePI-MS)A plot of signal intensity (m/z 25–200) versus time. At 0.7 min, a shrimp sample was inserted to the ambient-pressure ion source. After recoding spectra for 1.2 min, the sample was treated with lime juice. Panels a, b, and c show average mass spectra recorded before adding the sample, after adding the sample, and after adding lime juice, respectivelyBack to article page