A variable-volume sample injector design is presented and evaluated for performing sample introduction protocols for carrying out miniaturised isotachophoresis (ITP) separations. The microdevice design features a wide bore sample loop channel connected to a narrower bore separation channel via a short injection channel angled at 45°. An additional side arm channel located at the injection point enabled a range of injection strategies, using a gravity-fed system, to be implemented and assessed. A model analyte was used to demonstrate the versatility of the injector design for low and high sample loading regimes suitable for concentrated and dilute sample solutions, respectively.