Abstract:

Many amine pollutants exist in the atmosphere. Lower aliphatic amines promote the formation and growth of particles into PM_2.5, which damages the heart, lungs, and kidneys of the human body. PM_2.5, a common atmospheric particulate pollutant with complex compositions, is the main cause of haze weather. Therefore, measuring the contents of lower aliphatic amines and cations in PM_2.5 is of great significance for monitoring environmental air quality and protecting human health. This study established a suppressed ion-chromatographic method with conductivity for the simultaneous detection of four lower aliphatic amines (methylamine, dimethylamine, trimethylamine, and ethylamine) and five cations (Na⁺, N ${\mathrm{H}}_4^{+}$, K⁺, Mg²⁺, and Ca²⁺) in PM_2.5. The effective separations of several groups of substances that are difficult to separate, such as K⁺ and methylamine, dimethylamine, and ethylamine, were achieved by optimizing the chromatographic conditions. The results were then used to assess the pollution caused by small particles in the air. A medium-flow sampler loaded with a quartz filter membrane was used to collect PM_2.5 particles in the atmosphere. The sample flow rate was 100 L/min, and the sampling time was 24 h. Half of the filter membrane was cut and shredded into 10 mL of ultrapure water for two cycles of ultrasonic extraction over 60 min. After membrane filtration, the extract was analyzed using ion chromatography (IC). Three cation-exchange columns (IonPac^TM CS17, IonPac^TM CS16, and SH-CC-9) were compared, and the SH-CC-9 column (200 mm×4.6 mm) was ultimately used for separation under a column temperature of 30 ℃, detector temperature of 35 ℃, and injection volume of 25 μL. An aqueous solution of methyl sulfonic acid (MSA) was used as the mobile phase at a flow rate of 1.1 mL/min. Under these conditions, other aliphatic amine ions in air (triethanolamine, diethylamine, triethylamine, isopropylamine, propylamine, N,N-dimethylformamide, and N,N-dimethylacetamide) did not interfere with the separation and detection of the nine target ions. The nine ions showed good linear relationships within the corresponding concentration range, with linear correlation coefficients (r) no less than 0.997. The limits of detection (LODs) were 0.02-1.90 μg/L, and the limits of quantification (LOQs) were 0.07-6.32 μg/L. The relative standard deviations (RSDs) for the determination of six parallel samples were less than 2%, and the sample recoveries were between 93.2% and 104%. The established IC method was used to detect 189 PM_2.5 samples collected from the atmosphere, and all nine ions were successfully detected. Among these ions, Na⁺, N ${\mathrm{H}}_4^{+}$, and Ca²⁺ showed high concentrations. The contents of the four lower aliphatic amines were low; however, the ethylamine content in some samples was high. The results indicate that the proposed method meets the quantification requirements for cations and lower aliphatic amines in PM_2.5, with simple processing, high sensitivity, and good accuracy. It can quickly and accurately detect a large number of samples and be used to assess the pollution of small particles in the air as well as trace pollution sources to protect human health.

Key words: ion chromatography (IC), lower aliphatic amines, cations, PM_2.5