[Ion chromatography-pulsed amperometry method for determination of trace hydrogen sulfide in air]

Hydrogen sulfide (H₂S) is a pervasive gaseous pollutant that emits the characteristic odor of rotten gas, even at low concentrations. It is generated during various industrial processes, including petroleum and natural gas refining, mining operations, wastewater treatment activities, and refuse disposal practices. According to statistics from the World Health Organization (WHO), over 70 occupations are exposed to H₂S, rendering it a key monitoring factor in occupational disease detection. Although H₂S has legitimate uses in the chemical, medical, and other fields, prolonged exposure to this gas can cause severe damage to the respiratory and central nervous systems, as well as other organs in the human body. Moreover, the substantial release of H₂S into the environment can lead to significant pollution. This noxious substance has the potential to impair soil, water, and air quality, while disrupting the equilibrium of the surrounding ecosystems. Therefore, sulfide has become one of the most commonly measured substances for environmental monitoring worldwide. Achieving the stable enrichment and accurate detection of low-level H₂S is of great significance. Common methods for detecting this gas include spectrophotometry, chemical analysis, gas chromatography, rapid field detection, and ion chromatography. Although these methods provide relatively reliable results, they suffer from limitations such as high detection cost, low recovery, lack of environmental friendliness, and imprecise quantification of low-concentration H₂S. Furthermore, the sampling processes involved in these methods are complex and require specialized equipment and electrical devices. Additionally, approximately 20% of the sulfides in a sample are lost after 2 h in a conventional alkaline sodium hydroxide solution, causing difficulties in preservation and detection. In this study, an accurate, efficient, and cost-saving method based on ion chromatography-pulse amperometry was developed for H₂S determination. A conventional IonPac AS7 (250 mm×4 mm) anion-exchange column was employed, and a new eluent based on sodium hydroxide and sodium oxalate was used to replace the original sodium hydroxide-sodium acetate eluent. The main factors influencing the separation and detection performance of the proposed method, including the pulse amperage detection potential parameters and integration time, as well as the type and content of additives in the stabilizing solution, were optimized. The results showed that the proposed method had a good linear relationship between 10 and 3000 μg/L, with correlation coefficients (r²) of up to 0.999. The limits of detection (S/N=3) and quantification (S/N=10) were 1.53 and 5.10 μg/L, respectively. The relative standard deviations (RSDs) of the peak area and retention time of sulfides were less than 0.2% (n=6). The new method exhibited excellent stability, with up to 90% reduction in reagent costs. Compared with conventional ion chromatography-pulse amperometry, this method is more suitable for detecting low concentrations of sulfides in actual samples. Sulfides in a 250 mmol/L sodium hydroxide-0.8% (mass fraction) ethylenediaminetetraacetic acid disodium salt solution were effectively maintained for over 10 h. The new stabilizer significantly improved the reliability of both large-scale and long-term detection. The recovery of the proposed method was investigated by combining the system with a badge-type passive sampler. This sampling method requires no power devices; it is inexpensive, simple to operate, and can realize long-term sampling without the need for skilled personnel. Moreover, it can overcome the influence of short-term changes in pollutant concentration. The sampling results have high reference value for large-scale intervention-less pollutant monitoring in ultraclean rooms, museum counters, and other places. The results demonstrated that the recovery of the proposed method was greater than 95% for the blank sample and 80% for the sample plus standard solution. Finally, the newly established method was applied to determine H₂S levels in air samples collected via passive sampling at school garbage stations. The measured results did not exceed the national limit.