Organic acids as the modifier to determine Zn, Cd, Tl and Pb in soil by slurry sampling electrothermal vaporization inductively-coupled plasma mass spectrometry

Ultrasonic slurry sampling electrothermal vaporization inductively-coupled plasma mass spectrometry (USS-ETV-ICP-MS) has been applied to the determination of Zn, Cd, Tl and Pb in several soil samples. A mixture of 1% m/v EDTA and 1.5% m/v of ascorbic acid was used as the modifier to enhance the ion signals. The influences of instrument operating conditions and slurry preparation on the ion signals were reported. In this study, a relatively low vaporization temperature was used which separated the analyte from the major matrix components and improved the ion signals significantly. With ETV sample introduction device, spectroscopic and nonspectroscopic interferences were alleviated significantly. Since the sensitivities of Zn, Cd, Tl and Pb in various soil slurries and aqueous solution were different, standard addition method and isotope dilution method were used for the determination of Zn, Cd, Tl and Pb in these soil samples. This method has been applied to the determination of Zn, Cd, Tl and Pb in NIST SRM 2711 Montana soil reference material and several soil samples collected from Kaohsiung area. The analysis results were agreed with the certified values. The precision between sample replicates was better than 9% with USS-ETV-ICP-MS method. Detection limits estimated from standard addition curves were about 260¯620, 3¯5, 0.3¯1 and 9¯20 ng g-1 for Zn, Cd, Tl and Pb, respectively, in different samples.