Speciation of Inorganic Arsenic in Waters by Potentiometric Flow Analysis with On‐Line Preconcentration

Abstract

A potentiometric flow system has been developed for the direct determination of arsenic(V) in water samples after on-line preconcentration in a minicolumn packed with a new adsorbent material selective to As(V). Iron oxyhydroxide embedded in silica gel was synthesized and used simultaneously as adsorbent material in the minicolumn and as selective component in a tubular potentiometric electrode. In the first step, the sample solution is mixed on-line with phosphate buffer of pH 7 and pumped through the minicolumn to adsorb As(V). The insertion of the minicolumn in the mobile section of a homemade injector-commutator allows to relocate the minicolumn to desorb the retained As(V) in the second step. The desorption is maximum in the presence of 0.1 M phosphate of pH 12. Maximum response of the tubular selective membrane is achieved in phosphate buffer of pH 7. On-line oxidation of As(III) to As(V) by iodine (I 3 À ) in the presence of phosphate buffer of pH 7 allows the determination of total As as As(V) and then the speciation of inorganic arsenic, since As(III) can be estimated as the difference between total As and As(V). In the optimized experimental conditions, a linear range of 40 -500 mg L À1 for As(V), and detection limits of 30.6 and 38.6 mg L À1 for As(V) and total As, respectively, were obtained.The flow system has been successfully applied to the determination of inorganic arsenic species in groundwater samples collected in areas affected by arsenic contamination. Relative standard deviation of replicated determinations of As in groundwater samples was always below 5%.

Specific Determination of As(V) by an Acid Phosphatase−Polyphenol Oxidase Biosensor

“…Under these experimental conditions, the in-situ detection of As(V) provided a 2 ppb LOD and a LR of 5−592 ppb. It should be noted that this LOD value is close to those recently reported with the ICP-MS method (0.5 ppb) or is more sensitive than the molybdene blue method (20 ppb) 6 and the potentiometric flow method (30.6 ppb) 3 (A) Inhibition calibration curves for the detection of arsenate with different concentrations of phenyl phosphate: (a) 2, (b) 5, (c) 10, (d) 20, and (e) 2 μM using the incubation method ( E app = −0.2 V, in 0.1 M acetate buffer pH 6.0, 10 mM MgCl 2 ).…”

Recent developments in electrochemical flow detections—A review

“…Tubular detectors, where the flow channel is made in the bulk material of an ion-selective electrode (ISE) membrane electroactive material, are considered convenient to use and simple to prepare in a laboratory. The design is used both for solid-state heterogeneous membranes [22][23][24] and a monocrystalline LaF 3 membrane for a fluoride-sensitive electrode [25,26], but also for polymeric poly(vinyl chloride) (PVC) plasticized membranes, most often deposited on the solid support of a conductive composite of epoxy resin and graphite [27,28]. This configuration additionally facilitates, for instance, obtaining of detectors with two identical indicating electrodes, enabling increased response sensitivity by applying an electronic summing device [24].…”

“…Taking into account importance of speciation in modern inorganic analysis, surprisingly limited attention is focused on this aspect of flow potentiometry, which is principally most suitable method for speciation analysis. Application of iron oxyhydroxide embedded in silica gel as a membrane material of solid-state ISE allows flow determination of As(V), and in the flow system with oxidation of As(III) allows simultaneous determination of both arsenic forms at different oxidation states [23].…”

Tubular potentiometric detector used to determine As(V) in sediment extracts by flow injection

“…Potentiometric methods are only occasionally used, for instance, to detect titration end points for high As concentrations [10], although their use in water by coupling to preconcentration systems based on iron oxyhydroxides embedded in silica gel has recently been reported [11]. Notwithstanding, potentiometric detectors have the advantage of being sensitive over a wide concentration range and the use of a tubular electrode in flow injection analysis avoids altering the hydrodynamic conditions of the system [12][13][14][15].…”