Catalytically enhanced spectrophotometric determination of manganese in seawater by flow‐injection analysis with a commercially available resin for on‐line preconcentration

Abstract

The sensitive, laboratory-and ship-based, flow-injection (FI) method for the determination of dissolved manganese in seawater developed by Resing and Mottl (Anal. Chem. 1992;64:2682-2687) has been significantly modified and improved by incorporating five significant changes. The three major changes are the use of a commercially available iminodiacetate (IDA) resin (Toyopearl AF-chelate 650M) in place of 8-hydroxyquinoline for on-line preconcentration of manganese and matrix removal, the addition of nitrilotriacetic acid as an activator ligand which increases sensitivity by a factor of 7 and decreases the limit of detection, and the on-line buffering of acidified samples before column loading. Two minor improvements include use of the more soluble sodium periodate in place of potassium periodate and elimination of Brij-35 surfactant. To accommodate these changes, the pH of samples was adjusted to 8.5 (vs. 7.8), a higher acid concentration was required to elute the Mn from the IDA resin, and stronger reaction buffer was required to neutralize the acid. The accuracy of the method was evaluated with the use of NASS-4 standard seawater and by a comparison study of samples from the California coast that were analyzed by this method and an FI method coupled to inductively coupled plasma sector field mass spectrometry detection. The detection limit and precision of the method depend on the amount of sample preconcentrated onto the column. By preconcentrating 1.6 mL of sample, a detection limit of 0.03 nM (3 times the standard deviation of a blank) and precision of 3.2% (as percent relative standard deviation) were obtained. The method was used on board ship to determine dissolved manganese in coastal waters off Oregon and Washington.

Determination of total dissolved cobalt in UV‐irradiated seawater using flow injection with chemiluminescence detection

“…On the other hand, FI methods that have used IDA-Toyopearl as the chelating resin have included a column-conditioning step using a buffer with a pH similar to that of the in-line buffered seawater sample to ensure an optimum pH in the resin column before sample preconcentration (Aguilar-Islas et al 2006;Brown and Bruland 2008). The column-conditioning step removes any residual acid that remains from the previous sample elution step and ensures that the resin is no longer in the protonated form, which might otherwise reduce retention of the analyte and thereby lessen the sensitivity of the method.…”

“…Commercially available chelating resins are arguably preferable since the quality of the resins is reproducible, and such resins have been successfully used in FI systems (e.g., AguilarIslas et al 2006;Lohan et al 2006) and combined with ICP-MS detection (Lohan et al 2005;Sohrin et al 2008;Milne et al 2010). Commercially available resins that have been used for the analysis of trace metals in seawater include an NTAtype chelating resin for Fe and Cu (Lohan et al 2005), an EDTA-type resin for Al, Cd, Co, Cu, Fe, Mn, Ni, Pb, and Zn (Sohrin et al 2008), and Toyopearl AF-Chelate 650M resin, which contains tridentate iminodiacetate functional groups, for Al, Cd, Co, Cu, Mn, Ni, Pb, and Zn (Warnken et al 2000;Ndung'u et al 2003;Aguilar-Islas et al 2006;Brown and Bruland 2008;Milne et al 2010).…”

“…Flow injection systems can also be coupled with towed, trace metal-clean sampling devices, enabling the near-realtime determination of trace metals in surface ocean waters (e.g., Bowie et al 2002;Bruland et al 2005). In addition, FI methods are ideal for kinetic catalytic methods that use the analyte of interest as a reaction catalyst, resulting in highly sensitive analytical techniques (Resing and Mottl 1992;Measures et al 1995;Aguilar-Islas et al 2006). Previously developed FI methods for the determination of dissolved cobalt in coastal and estuarine waters have used the Trautz-Schorigen reaction (TSR), which involves the oxidation of either gallic acid (3,4,5-trihydroxybenzoic acid; Sakamoto-Arnold and Johnson, 1987) or pyrogallol (Cannizzaro et al 2000) with hydrogen peroxide in the presence of cobalt as a catalyst to produce chemiluminescence emission in the visible region.…”

Flow injection analysis as a tool for enhancing oceanographic nutrient measurements—A review

“…A more sensitive method FIA-SP for determining Mn at low oceanic concentrations by pre-concentrating Mn on 8-HQ resin at pH 8.5 and involved the catalytic oxidation of malachite green by periodate and manganese was reported by Resing and Mottl [237]. Aguilar-Islas et al [239] added nitrilotriacetic acid as an activator ligand to this FIA-SP method, which increased the reaction rate and resulted in better sensitivity, and use a commercially available Toyopearl resin for pre-concentration. Mn is eluted from the resin and mixes with periodate/buffer and sodium periodate producing malachite green that is detected spectrophotometrically at 620 nm.…”

“…Mn is eluted from the resin and mixes with periodate/buffer and sodium periodate producing malachite green that is detected spectrophotometrically at 620 nm. The average blank for this method was 0.07 ± 0.01 nM (n = 4) with a detection limit of 0.03 nM [239]. The accuracy of the method was tested using NASS-4 (National Research Council, Canada) certified reference material, with concentrations of 6.7 ± 0.2 nM determined, which was within 3% of the certified value of 6.9 ± 0.4 nM [239].…”