We present an optimized method for compound-specific stable carbon isotope (δ¹³C) analysis of n-alkanes. For sample preparation, the traditionally used Soxhlet extraction was replaced by accelerated solvent extraction (ASE). δ¹³C values of individual n-alkanes - measured using gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) - were first drift-corrected with regularly discharged pure CO ₂ pulses as reference gas and, secondly, corrected for the amount dependence of the δ¹³C values by co-analyzing standards with varying analyte concentrations. Finally, the δ¹³C values were calibrated against two internal standards. The improved method was applied to selected sediment samples from a palaeoenvironmental study in subtropical NE Argentina. The measured δ¹³C values of all long-chain n-alkanes (nC₂₇, nC₂₉, nC₃₁ and nC₃₃), representing biomarkers for terrestrial plants, correlate significantly with the δ¹³C of bulk organic matter (δ¹³C _TOC). The latter is hence corroborated as a proxy for C3-C4 vegetation changes. Furthermore, the δ¹³C variations reveal higher amplitudes for nC₃₁ and nC₃₃ than for nC ₂₇ and nC₂₉, indicating that the former n-alkanes mainly derive from C3 and/or C4 grasses, whereas the latter homologues mainly derive from C3 plants (trees and shrubs). Except for the lowermost part of the sediment core, the δ¹³C values of the mid-chain alkanes nC₂₃ and nC₂₅ do not reflect the terrestrial δ¹³C pattern, thus indicating that they are probably mainly of lacustrine origin.