Determination of Cr(Ⅲ) and Cr(Ⅵ) in Cigarettes by Ion Chromatography Hyphenated with Inductively Coupled Plasma Mass Spectrometry

A portion (0.200 0 g) of cut tobacco packed in the cigarette was taken and extracted with 20 mL of 100 mmol·L^-1 EDTA solution (pH 7.5) in a water bath at 50℃ for 3 h; an aliquot (5 mL) of the extract was purified by passing through a microcolumn packed with carbon black. The eluate was taken as the sample solution of cut tobacco. To prepare the sample solution of particulate matter in smoke of cigarette, 20 cigarettes were smoked by a rotary smoking machine, and the particulates in the smoke were collected by static trapping. 20 mL of 100 mmol·L^-1 EDTA solution (pH 7.5) were used to wash down the particulates from the collection tube and transferred to a 20 mL volumetric flask, which was then extracted and purified under the same way as described above. Smoking of a whole cigarette was done under the standard smoking condition, and the cigarette ash and butt obtained were extracted with 20 mL of EDTA solution (pH 7.5) in the same way, and 5 mL of the extract were filtered through 0.45 μm filter membrane and the filtrate was taken as the sample solution of cigarette ash and butt. The 3 sample solutions were then separated respectively by IC using IonPac AG11-HG column as stationary phase and 50 mmol·L^-1 NH₄NO₃ solution (pH 6.8) as mobile phase for elution. Cr(Ⅲ) and Cr(Ⅵ) in the eluate were finally determined by ICP-MS under the prescribed instrumental condition. Linear relationships between values of peak areas and mass concentrations of Cr(Ⅲ) and Cr(Ⅵ) were found in the ranges of 0.15 to 1 500 μg·L^-1 and 0.06 to 600 μg·L^-1, with detection limits (3S/N) of 0.15 μg·L^-1 and 0.06 μg·L^-1, respectively. Test for recovery was carried out by standard addition method, and values of recovery were 95.2%-98.6% for Cr(Ⅲ) and 90.6%-96.8% for Cr(Ⅵ). Precision of the method was tested by replicate determinations on a same sample, values of RSDs (n=7) of the peak areas obtained were 3.3% for Cr(Ⅲ) and 4.8% for Cr(Ⅵ). It was shown that the main source of Cr in cigarettes was the cut tobacco and that the Cr was mainly in its trivalent state. And during smoking, Cr(Ⅲ) compounds were easily transferred into the partioulates of the smoke, due to their relatively low melting point, and either were trapped by the stub-filter or entered into the mainstream smoke; while most of the Cr(Ⅵ) was remained in the ash.