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Rapidly expanding biogeochemical applications based on compound specific isotope ratios require instrumentation versatility to meet different analytical challenges. Here we present features and benefits of using the following GC injection techniques: on-column injection, Large Volume Injection (LVI) Programmed Temperature Vaporization (PTV) technique, Static Headspace Sampling (SHS) injection and conventional Split/Splitless injection. We will demonstrate capability of Thermo Scientific™ GC IsoLink™ II IRMS System to support these injection techniques to properly transfer a representative portion of the sample to the analytical column while avoiding discrimination and isotopic effects.On-column injection is applied for analysis of thermally labile or unstable compounds, as well as for samples with large analyte-boiling-point differences. It can be advantageous in a wide area of applications, i.e. for investigations of alkenones and alkanes from soils and sediments. We will present an optimized GC-IRMS analytical setup for stable carbon isotope ratios analysis of saturated hydrocarbons.The LVI PTV is an injection technique which allows the introduction of larger volumes of samples in the GC injector which can be particularly useful for analysis of organic pollutants present in very small quantities. Here we present an optimized methodology for analysis of very small amounts of saturated hydrocarbons.The SHS injection via split/splitless injector eliminates the need for direct liquid sample injection, reducing column contamination and improving analyte separation and reproducibility of isotope data. Here we demonstrate excellent precision and accuracy for GC-C-IRMS analysis of VOCs by using an optimized method for SHS, including improved sensitivity and lower detection limits.Finally, we also present an optimized workflow for the analysis of PAHs by GC-IRMS with conventional Splitless injection, including characterization of PAHs standards and data evaluation.