The chromatography column exhibits poor separation efficiency after aging

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Our analysis laboratory has an old chromatograph, the Shimadzu GC2014C, which is used to analyze oxygen and nitrogen in hydrogen. The problem is that the hydrogen produced by ion-exchange membrane electrolyzers is not dried, so it may contain some water vapor; when sampling using a six-way valve, this water can be carried into the chromatography column. Over time, the oxygen and nitrogen peaks become indistinguishable from each other, which in turn causes the column to degrade. After degradation, the baseline of the chromatogram shifts, and the oxygen and nitrogen peaks remain separated; it takes a few days before the peak patterns return to normal. Where is the problem? The following are the operating principle and conditions: 9.1 Principle: This method uses high-purity hydrogen as the carrier gas, and a 5A molecular sieve is employed to separate the gases, thereby isolating the oxygen and nitrogen components. Detection is carried out using a thermal conductivity cell detector, with quantification performed via external standard method. 137 Q/BH J JY 73-2022 Q/BH J JY 73-2022 9.2 Instruments and materials a) Gas chromatograph b) Chromatography data processing workstation. c) Chromatography column: stainless steel column, 2 meters in length and 4 millimeters in inner diameter (filled with a stationary phase of 5A molecular sieve, 60–80 mesh); d) High-purity hydrogen gas: purity ≥99.99%. e) Standard gas: 0.1% hydrogen, 1.0% oxygen. 9.3 Analysis steps 9.3.1 Operating conditions (can be adjusted according to specific circumstances): Carrier gas: hydrogen; Detector type: Thermal Conductivity Cell Detector (TCD). Pressure before the column: around 0.2 Mpa. Column temperature: 50°C; Inlet temperature: 80°C; Detector temperature: 120°C; Thermal conductivity cell current: 120 mA.