Reasons for the low content detected by gas chromatography

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The reasons for low gas chromatography analysis results can be categorized into five main areas: sampling issues, column problems, detector problems, carrier/gas issues, and operational condition problems. The details are as follows: Category of reason, Specific manifestations, Impact on results. Sampling issues: 1. Insufficient sample volume (blockage or leakage of the injection needle resulting in a reduced actual sample volume); 2. Poor sampling repeatability (insufficient skill in manual sampling, leading to variations in the sample volume). An insufficient injection volume directly results in a weak detector response signal, leading to lower values; poor repeatability causes data fluctuations, with some results being low. Column issues: 1. Column aging and contamination (loss of the stationary phase or adsorption of impurities after long-term use); 2. Inappropriate column selection (failure to match the polarity and boiling point of the components to be analyzed). Aging/pollution reduces the separation efficiency, resulting in a decrease in the peak area of the component being analyzed; improper selection leads to abnormal retention times and reduced response values. Detector issues: 1. Reduced detector sensitivity (filament aging over time, fatigue of the photomultiplier tube); detector failures (circuit faults, broken filaments). Reduced sensitivity prevents the effective detection of components at low concentrations, resulting in lower values. Failures cause the detector to fail to respond or to respond abnormally. Carrier gas/auxiliary gas issues: 1. Unstable carrier gas flow rate (too high/low flow rates affect component separation and detection); 2. Insufficient pressure of the auxiliary gases (hydrogen, nitrogen). Unstable flow rates can cause peak distortion and changes in retention time, leading to lower results; insufficient auxiliary gas pressure can affect the performance of the detector (such as the flame intensity of a FID). Operation condition issues: 1. Improper temperature settings (inappropriate column temperature, injection port temperature, and detector temperature); 2. Inaccurate instrument calibration (data deviations due to lack of regular calibration). Improper temperature can affect the volatilization/separation of components, resulting in a decrease in peak area; inaccurate calibration can cause the results to be systematically low.