Investigation of the Effect of Impurities on Gas Chromatographic Analysis of Natural Gas in Processing Plants in Rivers State

Gas chromatographic analysis is the primary technique for determining the compositional quality of natural gas streams, providing essential data for custody transfer, process control, and pipeline integrity management. This study investigates the effect of common impurities on the accuracy and reproducibility of gas chromatographic analysis at processing plants in Rivers State, specifically at the Rumuola Gas Processing Plant and the Trans-Amadi Industrial Gas Facility. The research employs an experimental methodology, preparing certified reference gas mixtures spiked with controlled concentrations of hydrogen sulphide, water vapour, mercury vapour, and compressor oil mist, and analysing them using the on-line process gas chromatographs installed at the study plants. The study quantifies the bias introduced into component concentration measurements by each impurity type and evaluates the effectiveness of sample conditioning systems in removing impurities before chromatographic analysis. Findings indicate that mercury vapour at concentrations as low as 50 micrograms per cubic metre causes measurable interference in C6+ heavy component analysis, while inadequate coalescing filters in sample systems allow hydrocarbon liquids to contaminate carrier gas lines, causing baseline drift. Recommendations include regular replacement of sample conditioning system consumables, installation of mercury removal units upstream of sample probes, and adoption of GPA 2261 standards for gas chromatographic analysis in Nigerian processing facilities. This study strengthens the evidence base for improving analytical quality control in the Nigerian gas processing sector. Keywords: gas chromatography, impurities, natural gas analysis, Rivers State, sample conditioning.