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Fe3O4/SiO2/PPy nanocomposite was synthesized, characterized and coated onto a steel wire as a reliable SPME fiber coating.The fiber was used for HS- and DI-SPME-GC-FID analysis of endogenous aldehydes in human urine, without derivatization.The methods showed good RSDs, wide LDRs and low LODs, while HS-SPME-GC-FID found to be more sensitive and precise.The short chain alkyl aldehydes, especially hexanal and heptanal, in urine are considered as potential biomarkers of several diseases and their determination in biological fluids has gained a great attention in recent years. Magnetic iron oxide core-shell silica (Fe3O4/SiO2) nanoparticles was synthesized and embedded in polypyrrole (PPy) during the in-situ electropolymerization on the surface of a stainless-steel wire. The Fe3O4/SiO2/PPy coated steel wire was used as a novel and effective solid-phase microextraction (SPME) fibre. It was employed for the extraction and preconcentration of hexanal and heptanal through direct-immersion (DI-) and headspace (HS-) SPME sampling strategies, followed by GC-FID quantification. The prepared nanocomposite fiber was characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). All influential variables on the extraction efficiency of the DI- and HS-SPME sampling modes were studied and optimized. The calibration curves showed acceptable linearity (R2 > 0.99) over the range of 0.01–10 μg mL−1 for the DI-SPME-GC-FID and 0.01–15 μgmL-1 for HS-SPME-GC-GID methods. The limit of detections (LODs) corresponding to the analytes amounts for which signal-to-noise ratios were equal to 3, estimated to be 0.1 and 0.5 ng mL-1, for hexanal and heptanal using HS-SPME-GC-FID, respectively. The LODs for DI-SPME-GC-FID method were 0.1 and 1.0 for hexanal and heptanal. For six replicated analyses of 0.5 μg mL-1 of the analytes, the relative standard deviations (RSDs) were calculated 6.5–6.6% and 5.1–5.3%, for DI-SPME and HS-SPME, respectively. The two developed methods were successfully applied for analysis of hexanal and heptanal in urine samples without derivatization step. The HS-SPME-GC-FID sampling/determination strategy showed better analytical figures of merit and longer lifetime for the prepared nanocomposite fiber.