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Automation is a key demand in modern analytical chemistry. Automated analytical schemes facilitate samples handling, and enable effective processes such as dilution, extraction, derivatization, and preconcentration to be carried out. Flow (FI) and sequential injection (SI) analysis are well-established and mature automated analytical techniques with more than 18,000 publications so far in all areas of analytical science. FI and SI offer significant advantages such as low instrumental and operational cost, widely available instrumentation, and effective automation of critical steps in the analytical process. Until recently, the main disadvantage of FI and SI was the inability of simultaneous determinations of more than two analytes in a single run. Due to the low pressure operation of these techniques, it was impossible for them to be coupled to conventional particulate-based separation columns that enable chromatographic separations. This drawback was overcome by the introduction of monolithic stationary phases. Monolithic columns are prepared from organic and silica monomers. Silica-based monoliths have small-sized skeletons and a bimodal pore size distribution with microm-sized throughpores and nm-sized mesopores. This gives silica-based monoliths favorable properties for high-efficiency fast separations, such as low-pressure drop across the column, fast mass transfer kinetics and a high binding capacity. They consist of a single rigid porous rod, enabling higher flow rates than particulate columns at reasonable back-pressures. These unique features of monolithic columns enabled their incorporation in low/moderate pressure setups, such as FI and SI, expanding dramatically their possibilities.

Abstract:The present study reviews more than twenty years (1985-present) of published research on the development and application of analytical procedures for the determination of chlorine dioxide, a widely used disinfectant and bleaching agent. The review covers a variety of techniques including batch and automated spectrophotometry and fluorimetry, electroanalysis and chromatography. The analytical figures of merit to the methods are presented, while critical discussion regarding their advantages and disadvantages is addressed.

A simple and rapid flow-injection (FI) method is reported for the simultaneous spectrophotometric determination of Fe(II) and Fe(III) in pharmaceutical products. The method is based on the reaction of Fe(II) with 2,2'-dipyridyl-2-pyridylhydrazone (DPPH) in acidic medium to form a water-soluble reddish complex (lambdamax=535 nm). Fe(III) reacts with DPPH under flow conditions only after its on-line reduction by ascorbic acid (AsA). Both analytes were determined in the same run via a double-injection valve, which enabled the simultaneous injection of two sample volumes in the same carrier stream (,,single-line double-injection" approach). The two well-defined peaks produced corresponded to total iron [Fe(II)+Fe(III)] and Fe(II). Speciation of the analytes in their mixtures was achieved by multiple regression analysis. The calibration curves obtained were linear over the ranges 0-30 and 0-50 mg L(-1) for Fe(II) and Fe(II), respectively, and the precision [s(r)=1.0% for Fe(II) and 1.5% for Fe(III)] was satisfactory. The method proved to be selective and adequately sensitive (cL=0.25 and 0.17 mg L(-1) for Fe(III) and Fe(II), respectively, in mixtures). Application of the method to the analysis of pharmaceutical samples resulted in excellent accuracy; the percent mean recoveries were in the range 99.0-102.0% for both Fe(II) and Fe(III) and the mean relative error was e(r)=1.0%.