This article introduces the improved response for active compounds using the Direct Connect Liners technique. The Direct Connect Liners is a commonly used inlet for trace compound analysis and splitless injection technique. This technique is rugged, robust, and sensitive as a large portion of the sample is delivered to the column. The key to the technique is vaporization in the inlet, facilitated by the inlet liner. Liners are typically made of straight, deactivated borosilicate glass with a tapered bottom to prevent contact with the metal baseplate of the inlet. Liners with tapers at the bottom and the top are also popular as they provide better containment of the injected sample. This is important for difficult or active compounds that tend to be lost or irreversibly adsorbed in the inlet. These compounds are often highly polar and are typically acidic or basic compounds. In theory, the response factor should be constant and independent of the amount injected. Typically, the response factor (detector signal per weight of compound injected) is smaller at lower concentrations than at higher concentrations. The lowered response is more apparent at small concentrations.
Agilent Technologies introduces Direct Connect Liners designed for the 6890 Gas Chromatograph to address the issue of low response factors for active, polar compounds. Standard liners often cause analyte loss due to adsorption, particularly at low concentrations. The Direct Connect design minimizes this loss by directly connecting the capillary column to the liner, reducing the volume where adsorption can occur.
| Compatible Instrument | 6890 GC |
|---|---|
| Part Number (Single Taper) | G1544-80730 |
| Part Number (Double Taper) | G1544-80700 |
Active compounds, especially highly polar and acidic or basic ones like 2,4-dinitrophenol, which tend to be lost or irreversibly adsorbed in standard liners.
They are best suited for relatively clean samples such as water extracts, though they have worked successfully for solid waste methods with user evaluation.