Determination of 6 Rubber Additives in Rubber by UPLC

Rubber sample strips (thickness:ca. 2 mm, width:ca. 1 mm) of 1.000 g were taken and extracted ultrasonically with 50 mL of a mixed solution of CH₃CN and CH₂Cl₂ with the volume ratio of 6:1 for 60 min. The solution was filtered through 0.45 μm filtering membrane and the filtrate was used for UPLC analysis. ZORBAX Eclipse XDB-C₁₈ column (4.6 mm×100 mm, 1.8 μm) was used as stationary phase, and a mixed solution of CH₃CN and 12.5 mmol·L^-1 NaH₂PO₄ (pH 4.0) with the volume ratio of 40:60 was used as mobile phase in isogradient elution, in the course of which the 6 rubber additivesi.e., the anti-aging agent 6PPD (N-(1,3-dimethylbuty)-N'-phenyl-phenylenediamine), the anti-charring agnet CTP (N-cyclohexylthiophthalimide) and 4 vulcanizing agents TBBS (N-tert-butyl-2-benzothiazole), MBTS (2,2-dibenzothiazole disulfide), CBS (N-cyclohexyl-2-benzothiazole sulfenamide) and DCBS (N,N-dicyclohexyl-2-benzothiazole sulfenamide) were separated and their absorbances measured spectrophotometrically at different wavelengths of 290 nm (for 6PPD) and of 226 nm (for the remainder). Linearity ranges of the standard curves of the 6 rubber additives were found same between 5.0 mg·L^-1 and 500.0 mg·L^-1; their detection limits (3S/N) were found in the range of 0.3-2.5 mg·L^-1. Test for recovery was made by standard addition method, giving recoveries ranged from 82.8% to 107%. Values of RSDs (n=5) were found all less than 5.0%.