Direct Mass Spectrometric Analysis of Hydrogen Sulfide in Complex Oil Samples

Due to the high viscosity and bulk complexity of crude oil samples, it poses a grand challenge to determine hydrogen sulfide (H₂S) in them. Although many methods have been developed for the analysis of H₂S in complex systems, these methods generally have complex processes, large analysis error and low sensitivity. In the study, based on the reaction between triazine and H₂S by generating thiadiazine, a small volume of complex crude oil sample was introduced directly into a triazine solution using acetonitrile as solvent for transferring H₂S into detectable species by organic mass spectrometry. The experimental parameters of solution composition, acetic acid content, reaction time and reaction temperature were optimized, and the method of paper spray ionization-mass spectrometry (PSI-MS) was established for rapid analysis of H₂S in complex crude oil samples. An optimal performance was achieved when the reaction of triazine and H₂S was carried out at 30 ℃ for 2 h with acetonitrile containing 0.1% acetic acid as solvent. The standard curve for the quantitative analysis of H₂S was constructed according to the linear relationship between MS signal intensity of resulting thiadiazine and the concentration of H₂S, which was applied for actual crude oil samples from different sources. The results showed that the linear range and the limit of detection (LOD) were 0.1-1 000 μg/L and 0.041 μg/L with intra-day precision of 3.04% and inter-day precision of 3.18%, respectively. The PSI-MS was also employed to determine H₂S in different actual crude oil samples, and the spiked recovery was 91.7%-103.5% with relative standard deviation (RSD) of 1.2%-4.5%. This method has the advantages of easy operation, low cost, high sensitivity and less contamination to mass spectrometer, which is promising for the direct and fast analysis of H₂S in complex crude oil samples.