2. Experimental
2.1. Reagents and instrumentation
All solvents were reagent grade or better. Strongly basic anion
exchanger Dowex 1 8, AC and filter were used to prepare HA
(detailed experimental conditions are listed in Supporting
Information). A PerkinElmer AAnalyst™ 900 atomic absorption
spectrometer were used. The optimal operating conditions of
GF-AAS and measurement parameters are listed in Table S1. The
tailored design multicolumn solid phase extraction device is
shown in Fig. S1.