Reactive unsaturated aldehydes produced by marine diatoms upon cell damaged interfere negatively with the reproduction success of their grazers. In this paper, a method based on headspace solidphase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS) was developed for analysis of six aldehydes: [(E)-2-hexenal, heptanal, (E)-2-heptenal, (E,E)-2,4-heptadienal, (E)-2-decenal, (E,E)-2,4-decadienal] in two laboratory cultured diatoms (Skeletonema costatum and

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... os Muelleri). HS-SPME experimental conditions including SPME fiber types, extraction time and temperature, desorption time and temperature were optimized. Under the optimal experimental conditions, limits of detection for six aldehydes were both in the range of 0.1-2 µg/L. The relative standard deviations ranged from 7.2 to 13.9%. Recoveries were in the range of 60.6-85.7%. The concentrations of six aldehydes in Skeletonema costatum were 0.359, 0.038, 0.028, 0.183, 0.023, and 0.058 ng/10 6 cells respectively. The six aldehydes were not found in Chaetoceros Muelleri. The study shown here provided a simple, fast and sensitive method for the analysis of aldehydes in diatoms.