A sensitive flow-injection analysis method with iminodiacetate chelation and spectrophotometric detection for on board determination of trace dissolved aluminum in seawater

Abstract

A flexible, flow injection analysis method for shipboard use was developed for the on-line determination of trace dissolved aluminum (dAl) in seawater. The analytical system included a Towed Fish underway sampler and a modified flow injection analysis system with a solid phase extraction-spectrophotometric detection device. Determination was based on the spectrophotometric detection of a complex of chrome azurol S and dAl. In this study, the dAl in the samples was efficiently extracted onto an SPE cartridge, packed with iminodiacetate chelating resin. The extracted dAl was rapidly eluted with hydrochloric acid and reacted with the reagents to form a complex, which was detected at 620 nm with a 30 mm flow cell. Compared with the commonly used methods, the proposed method offered the benefits of improved sensitivity, negligible salinity effect and low cost. The experimental parameters were optimized based on a univariate experimental design, and the matrix effect of seawater was preliminarily investigated. The proposed method had high sensitivity with a detection limit of 0.80 nmol L⁻¹. The linearity range was 1.0 to 250 nmol L⁻¹ with a 120 s sample loading time and the upper limit was extended to 1.0 μmol L⁻¹ when choosing longer sample loading times. The recoveries were between 96.8 and 99.8% and the relative standard deviation was 2.6% (n = 8) for an aged seawater sample spiked with 5.0 nmol L⁻¹ dAl. The analytical results obtained with the proposed method showed good agreement with those using a reference method. The proposed method has been successfully applied to a shipboard underway analysis of dAl in the Jiulongjiang Estuary, Fujian, China.