Diatom oxylipins, as key infochemicals, play a significant role in driving biological interactions during coastal diatom blooms and may influence biogeochemical cycles throughout the bloom's life cycle. Oxylipins occur in three forms in water, with particle-adsorbed oxylipins in the phycosphere reaching micromolar levels, making them particularly impactful in ecological contexts. In this study, we focused on polyunsaturated aldehydes (PUAs), a crucial class of oxylipins, and developed a method for rapidly quantifying particle-adsorbed PUAs during diatom blooms. The method involves measuring diatom particle volumes through sedimentation and centrifugation, simulating the natural processes of sedimentation and compaction. We observed that particle volumes varied between 12% and 49%. To avoid the formation of new PUAs, we optimized a derivatization process using 5% sulfuric acid-dissolved 2,4-dinitrophenylhydrazine (DNPH), replacing the traditional neutral buffer. Using ultra-high-performance liquid chromatography (UHPLC) paired with multiple reaction monitoring (MRM) in tandem mass spectrometry, we were able to achieve rapid separation and accurate quantification of PUAs within just 5 minutes. This method was applied to monitor the growth stages of three common red tide diatom strains in laboratory-simulated blooms. Our results revealed that the particle-adsorbed PUAs concentrations in all three strains reached micromolar levels, ranging from 0.4 to 69 μmol·L-1. Notably, Skeletonema costatum exhibited similar trends between particle-adsorbed and particulate PUAs, with concentrations rising significantly during the stationary phase after being low in the exponential phase. In contrast, Thalassiosira rotula showed a decline in particle-adsorbed PUAs concentrations during the stationary phase compared to the exponential phase. Additionally, the composition of particle-adsorbed PUAs varied, with Skeletonema costatum being dominated by heptadienal in the exponential phase. This study provides important insights for the in situ monitoring of diatom oxylipins and their potential ecological impacts.