Simultaneous Determination of Cr³⁺ and Cr⁶⁺ in Cigarette Tipping Paper by High Performance Liquid Chromatography after Dispersion Liquid-Liquid Micro-Extraction

2 g of the sheared cigarette tipping paper sample was extracted ultrasonically with 20 mL of water for 30 min. An aliquot of 8 mL of the solution was taken, and 100 μL of 200 mmol·L^-1 sodium diethyldithiocarbamate (chelating agent) solution was added for reaction at 45℃ for 10 min under the system acidity of pH 6.0. After reaction, 60 μL of n-dodecyl alcohol (extractant) and 100 μL of methanol (dispersant) were added. After vortex and centrifugation, the upper organic phase was taken and made its volume up to 0.5 mL with methanol, then filtered into chromatographic bottle for testing. ZORBAX SB-C₁₈ column was used as stationary phase, and a mixture of methanol and water with different volume ratios was used as mobile phase for gradient elution. The separated target compounds were detected by diode-array detector at 258 nm. The results showed that the linear ranges of standard curves of Cr³⁺ and Cr⁶⁺ were 2.00-100.00 μg·L^-1, with detection limits (3S/N) of 3, 6 μg·kg^-1, respectively. Test for recovery was made on the actual sample by standard addition method, giving results in the ranges of 90.7%-105% for Cr³⁺ and 84.1%-106% for Cr⁶⁺, and RSDs (n=7) of the determined values were in the ranges of 4.2%-7.3% for Cr³⁺ and 4.5%-7.6% for Cr⁶⁺. The enrichment factors of Cr³⁺ and C⁶⁺ were 25.6 and 9.5, respectively. This method was applied to analysis of the 5 actual samples, and Cr³⁺ and Cr⁶⁺ were both detected in 4 samples, with the detection amounts of Cr⁶⁺ higher than those of Cr³⁺.