Abstract:

p-Phenylenediamine compounds （PPDs） are widely used as anti-aging agents and antioxidants in rubber industry. However， environmental concerns have arisen regarding the toxicity of their quinone derivatives （PPD-Qs）. Fine particulate matter （PM_2.5） serves as a crucial vector enabling PPDs and PPD-Qs to enter the human body via respiratory exposure pathway. Therefore， accurate monitoring of PPDs and PPD-Qs in PM_2.5 is essential. In this research， a high performance liquid chromatography-tandem mass spectrometry （HPLC-MS/MS） approach was established to quantify seven PPDs and seven PPD-Qs in PM_2.5. Samples were collected on quartz fiber filters with a diameter of 90 mm. The filter was cut into strips and subsequently spiked with 2 ng of 6PPD-d₅ and 6PPD-Q-d₅ internal standards. The target compounds were extracted with 10 mL of acetonitrile containing 1% （volume fraction） ammonia solution and 20 μmol/L glutathione （GSH）， and purified via a modified QuEChERS pretreatment method. Specifically， after salting out with 0.5 g of NaCl and 1.0 g of MgSO₄， the supernatant was subjected to dispersive solid-phase extraction for cleanup. In this process， 0.5 g of MgSO₄， 100 mg of octadecylsilane （C₁₈）， and 100 mg of N-propylethylenediamine （PSA） were employed as sorbents. Subsequently， 5 mL of the cleaned-up supernatant was evaporated to near dryness and then redissolved in 0.2 mL of a methanol-water mixture （1∶1， volume ratio） for instrumental determination. The compounds were separated on a Waters ACQUITY UPLC HSS T₃ column（100 mm×2.1 mm，1.8 μm） with mobile phases consisting of a 5 mmol/L ammonium formate aqueous solution containing 0.1% formic acid and methanol. Identification and quantification of the compounds were carried out under positive electrospray ionization in multiple reaction monitoring mode. The results indicated that all analytes exhibited good linear relationships within the range of 0.05-20.0 ng/mL， with correlation coefficients （r） exceeding 0.999. The method detection limits （MDLs） and method quantification limits （MQLs） of the compounds were within the ranges of 0.003-0.07 pg/m³ and 0.01-0.2 pg/m³， respectively. At three spiked levels of low， medium and high， the recoveries of the compounds were in the range of 66.3% to 119.0% ， and the relative standard deviations （RSDs） ranged from 1.5% to 13.2% （n=6）. Ultimately， the developed method was employed for the analysis of PPDs and PPD-Qs in PM_2.5 samples collected from Baotou during January and February 2025. The results indicated that seven PPDs and five PPD-Qs were detected， with mass concentrations ranging from 2.26 to 251.2 pg/m³ and 2.36 to 105.4 pg/m³， respectively. The proposed method is characterized by its simplicity， environmental friendliness and accuracy， making it suitable for the rapid quantitative analysis of PPDs and PPD-Qs in PM_2.5.

Key words: high performance liquid chromatography-tandem mass spectrometry （HPLC-MS/MS）, fine particulate matter （PM_2.5）, p-phenylenediamine compounds （PPDs）, p-phenylenediamine quinones （PPD-Qs）