The GC-CP interface is a bench-top Gas Chromatograph and gas conversion continuous flow interface for a 20-20 or GEO series isotope ratio mass spectrometer.

When combined with the 20-22s novel 120° high dispersion ion optics, the interface provides
The capability of measuring D/H, ¹³C/¹²C, ¹⁵N/¹⁴N and ¹⁸O/¹⁶O ratios in compounds separated by GC. The GC-CP interface is fully integrated with Hewlett Packard and other gas chromatograph to preserve chromatography during the gas conversion process, ensuring that sample peaks are well resolved when they reach the stable isotope analyser.

In combustion mode, peaks eluting from the capillary GC enter the combustion tube and are converted over and oxidative surface (at 800°C) to CO₂, N₂, NO_x and H₂O. An elemental copper stage reduces NO_x, a Nafion dryer removes water vapour and a simple liquid nitrogen trap focuses CO₂ (when measuring N₂ to prevent CO formation in the mass spectrometer ion source). A further GC plot column can be used to separates CO₂ from N₂ (allowing dual isotope analysis).

In pyrolysis mode, peaks eluting from the capillary GC enter the pyrolysis tube (1200°C). The pyrolysis products, CO, N₂, and H₂ are purified by chemical processes. A Nafion dryer guards against any water vapour contamination (e.g. if the pyrolysis chemicals become exhausted). A post reaction Poraplot-Q or Molsieve 5a open tubular column are used to separate analyte gases from minor biproducts of thermal decomposition.

| Specifications | Isotope Ratio Mass Spectrometers|