Analysis of Volatile Organic Compounds in Cinnamomum camphora Leaves by Direct Thermal Desorption–Gas Chromatography/Mass Spectrometry (DTD-GC/MS)

This study established a novel detection method for volatile organic compounds in forest therapy tree species based on direct thermal desorption technology. The optimized parameters included 20 mg sample loading, 110 °C desorption temperature, 30 min desorption time, and 1:30 split ratio. The optimal loading was 5–65 mg to balance the separation resolution and detection sensitivity. Desorption temperature significantly affected component detection: terpenoids accounted for the highest proportion (82.0%) at 90 °C; alkanes surged to 53.3% at 150 °C; acids (19.0%) and esters (19.4%) became dominant; and ascorbyl dipalmitate (17.3%) exceeded linalool (14.6%) at 180 °C. Chemotype analysis revealed that camphor-type leaves were dominated by camphor (72.8%) while linalool-type leaves by linalool (54.3%). Compared with steam distillation, DTD increased the camphor/linalool extraction efficiency while eliminating solvent contamination. Relative to dynamic headspace sampling, DTD mitigated the environmental interference and reduced the pretreatment time. The study confirmed that 110 °C is the optimal temperature for maximized characterization of terpenoids (63.3%), providing technical support for selecting high-terpenoid-emitting trees in forest therapy and evaluating the therapeutic efficacy. It also reveals the linkages between leaf volatiles and stand-level air composition and promotes the development of dynamic forest VOC databases.