Optimization of a Simultaneous Extraction and Detection Method for n-Alkanes and Polycyclic Aromatic Hydrocarbons in Marine Sediments

n-alkanes and polycyclic aromatic hydrocarbons (PAHs) serve as key molecular indicators for reconstructing a marine paleoclimate, tracing organic matter sources, and evaluating anthropogenic pollution. Current literature still employs separate pretreatment and detection methods for these two substance categories. For co-extraction, highly polar mixed solvents such as chloroform–methanol or chloroform–acetone are typically used, resulting in numerous co-extracted impurities that reduce quantitative accuracy. n-hexane–acetone (4:1, V/V) was employed as the extraction solvent with lower polarity. This approach minimized co-extracted impurities while ensuring recovery rates of all components, thereby enhancing detection accuracy. Gas chromatography-mass spectrometry (GC-MS) was used to effectively separate all 53 compounds under the same temperature program, with a total detection time of only 80 min. A new method was established for the simultaneous extraction and detection of 53 compounds in marine sediments, encompassing 34 n-alkanes and 16 PAHs, along with PAH surrogates including naphthalene-D₈, anthracene-D₁₀, and p-terphenyl-D₁₄. Methodological evaluation results indicated that 50 compounds exhibit good linearity within the range of 10 ng/mL to 20 μg/mL, with correlation coefficients exceeding 0.999. The method detection limits (MDLs) for n-alkanes ranged from 0.04 to 1.35 ng/g, while the method quantification limits (MQLs) ranged from 0.16 to 5.40 ng/g. For PAHs, the MDLs ranged from 0.14 to 0.43 ng/g, with MQLs from 0.56 to 1.72 ng/g. At three spiking levels (1×, 2×, and 8× the MQL), the recovery rates for target compounds ranged from 60% to 130%, with relative standard deviations (RSDs) ranging from 0.22% to 7.04% (n = 6). The MDLs and MQLs for both substance categories were below standard method requirements, and recovery rates met standard criteria. This work is applicable to the simultaneous extraction and detection of n-alkanes and PAHs in marine sediments.