Inert non-adsorbing crimpable capillaries and device for adjusting gas flow in isotope ratio analysis

A gas transfer system for transferring gas 14 into an analytical instrument 15 for isotope ratio analysis. The system comprises a capillary 2 and a crimping device 20, adapted to receive the capillary and adjust gas flow into the analytical instrument by crimping the capillary. The internal surface of the capillary is coated to prevent or minimize adsorption of water to its surface. The coating is sufficiently free of contaminants that the isotopic composition of gas passing through the capillary does not change. The coating can be silicon based. Also provided is a device for regulating gas flow in a gas inlet system of an analytical instrument, comprising a body member having an internal gas flow channel, and a clamping member for adjusting a gas flow through the channel. A non-crimpable capillary can be connected to this device.