Flow-Injection Inductively Coupled Plasma Mass Spectrometer Incorporated with an Ultrasonic Nebulizer-Membrane Dryer: Application to Trace Lead Detection in Aqueous Solution and Seawater

Abstract

Flow-injection (FI) incorporated with inductively coupled plasma mass spectrometry (ICP-MS) was used to determine lead in aqueous solutions and seawater. Lead was retained in the form of Pb-DDPA complex in a sorbent microcolumn packed with C₁₈-bonded silica, and then carried to an ultrasonic nebulizer with methanol as eluent. The ultrasonic nebulizer removed about 66% of methanol solvent vapors from entering the detector. A multi-tube Nafion® membrane dryer, installed along the passage prior to the ICP torch, further removed 50% of methanol. Reducing the amount of methanol solvent significantly improved the signal-to-background ratio of the detector. Accordingly, when the sample was loaded for 15 and 60 s, respectively, Pb detection limits were determined to be 0.162 and 0.028 ng/L, one to two orders of magnitude lower than those reported. The enrichment factors were also measured to be 7 and 28, with the sampling frequencies of 31 and 21 h⁻¹, respectively. The method was applied for the determination of Pb in a reference seawater. The obtained result was 0.013 ± 0.001 ng/mL, consistent with the certified value of 0.013 ± 0.005 ng/mL.