Reverse flow injection analysis method for catalytic spectrophotometric determination of iron in estuarine and coastal waters: A comparison with normal flow injection analysis

• Published in: Talanta (Oxford) 2012-05, Vol.93, p.86-93
• Main Authors: Huang, Yongming, Yuan, Dongxing, Dai, Minhan, Liu, Yaoxing
• Format: Article
• Language: English
• Subjects: Analytical chemistry; Brackish; Calibration; Carriers; Catalysis; Catalysts; Catalytic spectrophotometry; Chemistry; Estuaries; Estuarine and coastal waters; Exact sciences and technology; Flow injection analysis; Flow Injection Analysis - methods; Fresh Water - chemistry; General, instrumentation; Iron; Iron - analysis; Limit of Detection; Reverse flow injection analysis; Sea water; Spectrometric and optical methods; Spectrophotometry; Spectrophotometry - methods; The Pearl River Estuary; Water - chemistry
• ISSN: 0039-9140; 1873-3573
• DOI: 10.1016/j.talanta.2012.01.050

► Catalytic spectrophotometry was coupled to reverse flow injection analysis for iron determination. ► Double carrier streams were used in reverse flow injection analysis. ► An intercomparison experiment with normal flow injection analysis was conducted. ► The concentrations of total dissolvable iron in surface seawater of the Pearl River Estuary were obtained and non-conservative mixing processes were revealed. ► The rFIA method was more sensitive, faster and more environment-friendly. A method for determining iron in seawater had been developed by coupling reverse flow injection analysis (rFIA) and catalytic spectrophotometric detection with N,N-dimethyl-p-phenylenediamine dihydrochloride (DPD). With a seawater sample or a standard solution as the carrier, the mixture of DPD and buffer was injected into the carrier stream quantitatively and discretely. After mixing with H2O2, the DPD was oxidized to form two pink semiquinone derivatives that were monitored at 514nm wavelength with a reference at 700nm. The method detection limit was 0.40nmolL−1, lower than half of that of normal flow injection analysis (nFIA) method. The sample throughput was 10h−1 with triplicate determination, compared with 4h−1 for nFIA-DPD method. The analysis results of the certified seawaters CASS-4 (12.33±0.18nmolL−1) and NASS-5 (3.47±0.23nmolL−1) well agreed with the certified values (12.77±1.04 and 3.71±0.63nmolL−1, respectively). The typical precision of the method for a 2.97nmolL−1 iron sample was 4.49% (n=8). Interferences from copper and salinity were investigated. An instrument was assembled based on the proposed method and applied successfully to analyze total dissolvable iron (TDFe) in surface seawater samples collected from the Pearl River Estuary, the results of which revealed non-conservative behavior of TDFe during the estuarine mixing. Results for these samples with both rFIA-DPD and nFIA-DPD methods showed good agreement with each other. The proposed method was superior to the currently used nFIA-DPD method, particularly when it is adapted for field and in situ deployment, due to its lower reagent consumption, higher sample throughput and keeping the manifold tubing clean.