WANG Lijuan, ZHANG Jin, LIU Qin, QU Yin, TIAN Xin, BAO Xiangchun
The accurate determination of vanadium (V), chromium (Cr) and arsenic (As) contents in aluminum and aluminum alloys is of great significance for the production and application of aluminum and aluminum alloys. When the silicon content (mass fraction, the same below) in aluminum and aluminum alloys was less than 0.5%, the sample was dissolved with mixed acid (VHCl∶VHNO3∶VH2O=10∶1∶10). When the silicon content was not less than 0.5%, the sample was dissolved with 200 g/L sodium hydroxide solution followed by acidification with mixed acid. In the tandem quadrupole (MS/MS) mode, the mass-to-charge ratio (m/z) of the primary mass filter (Q1) was set to 51, 52, and 75. Then, NH3 and O2 were successively introduced into the collision/reaction cell. 35Cl16O+ reacted with NH3 through redox reaction to form polyatomic ions with m/z values not equal to 51. 52Cr+ and 75As+ reacted with O2 to form 52Cr16O+ and 75As16O+, respectively. The interfering ions 35Cl16OH+ and 40Ar35Cl+ could not react with O2. Therefore, the m/z of the second mass filter (Q2) were set to 51, 68, and 91. Only 51V+, 52Cr16O+, and 75As16O+ passed through and were detected by the detector, thereby avoiding the mass spectrometric interference of 35Cl16O+,35Cl16OH+, and 40Ar35Cl+. Accordingly, the method for the determination of V, Cr and As in aluminum and aluminum alloys by inductively coupled plasma tandem mass spectrometry (ICP-MS/MS) was established. The flow rates of NH3 and O2 were optimized: the flow rate of NH3 was set at 0.40 mL/min and the flow rate of O2 were selected at 1.20 mL/min. The linear relationship was good for the mass concentration in range of 0.25-50.00 ng/mL, and the correlation coefficients were higher than 0.999 5. When the sample was dissolved with mixed acid, the limits of detection for testing elements were 0.024-0.12 μg/g, and the limits of quantification were 0.080-0.39 μg/g. When the sample was dissolved with 200 g/L sodium hydroxide solution, the limits of detection for testing elements were 0.064-0.17 μg/g, and the limits of quantification were 0.22-0.56 μg/g. The aluminum alloy standard sample was determined according to the experimental method, and the found results were basically consistent with the certified values. The contents of V, Cr and As in aluminum and aluminum alloys with different silicon contents were determined. The relative standard deviations (RSD, n=11) of determination results were between 1.4% and 9.4%, and the spiked recoveries were between 95% and 115%.
