Bubble enclosures in polar ice cores represent the only direct paleoatmospheric archive. To constrain past methane sources the isotopic composition (13C and D) of CH4 in high temporal resolution and with high precision is needed. dD(CH4) is of special interest in order to constrain the origin of additional atmospheric methane during rapid warming events (Dansgaard/Oeschger events).We developed an online gas chromatography isotope ratio monitoring mass spectrometry technique (GC-irmMS) based on developments by Merritt et al. (1995) and Rice et al. (2001). The method includes gas extraction from ice, preconcentration, chromatographic separation and pyrolysis (P) of methane. Internal isotopic calibration is implemented using synthetic air and pure methane. The reproducibility of these two standards for amounts of methane typical for 500 g of glacial ice (approx. 1 nmol CH4) is better than 5 permil and 3 permil, respectively. A new tool to process raw data is presented. Differences in accuracy and precision arising from different peak integration methods are discussed.