Analysis of Common Problems and System Maintenance Guide for Gas Chromatographs
1. Comprehensive Diagnosis and Solutions for Peak Absence Phenomenon
One of the most troubling issues encountered during gas chromatography analysis is the absence of peaks. This situation may be caused by failures in multiple links, requiring systematic troubleshooting and diagnosis.
First, check the flame status of the FID detector. A extinguished flame is the most intuitive reason, possibly due to insufficient gas supply, ignition device failure, or low detector temperature. The detector temperature must be maintained above 150°C to ensure continuous combustion, especially after analyzing high-boiling-point components when carbon buildup may cause extinction.
Issues with the injection system should not be overlooked either. Improperly set vaporization chamber temperatures can prevent samples from fully vaporizing, particularly for high-boiling compounds. It is recommended to set the vaporization chamber temperature at least 20-30°C higher than that of the highest boiling point component in the sample. Additionally, aging injector seals or contaminated liners can lead to sample loss manifested as absent peaks or unstable peak areas.
Problems related to chromatographic columns mainly include low column temperatures and blockages at column heads. When column temperatures are below certain components' boiling points within a sample, these components will condense at the head of the column instead of moving with carrier gas. Furthermore, leaks caused by improper installation or non-volatile impurities introduced during sampling can also result in peak absence phenomena.
2. Investigation into Causes for Reduced Peak Response and Countermeasures
When all chromatographic peaks show significant declines in response values, it often indicates systemic problems that require comprehensive inspection. The injection system issues are among those most commonly observed; worn injection needles can lead to inaccurate sampling volumes—especially after prolonged use with automatic samplers where needle rod sealing decreases causing sample leakage. Regular replacement of injection needles is advised along with checking post-injection leakage conditions; excessive split ratios represent another common issue—particularly when analyzing trace components—as overly large split ratios can cause much of a sample's volume being diverted away leading to significantly reduced detection sensitivity. Detector status directly affects response values: For NPD detectors contamination or aging rubidium beads will reduce responses manifesting as simultaneous reductions in peak heights across all nitrogen- and phosphorus-containing compounds; this necessitates replacing rubidium beads while ensuring high-purity gases are used accordingly as inappropriate settings on detector temperatures could impact responses too—excessively high temps lower ionization efficiency whereas excessively low ones might induce condensation effects on components themselves.