Cyclic Flow-Injection Analysis for the Repetitive Determination of Zinc with 2-(5-Bromo-2-pyridylazo)-5-[N-n-propyl-N-(3-sulfopropyl)amino]phenol and EDTA

Abstract

Cyclic methods of analysis can lead to many advantages, such as low consumption of reagents, minimization of waste, high sample throughput, simple equipment, extended running hours and no contamination of the environment. Flow-injection analysis (FIA) is considered to be a most suitable technique for cyclic methods, i.e., the outlet from the flow-through cell is fed continuously back to the reservoir using a single-line flow system. On this cyclic FIA, the chemical reaction can be easily controlled by fixing the flow rate of a circulating reagent carrier solution and by the constant introduction of a sample solution to the carrier stream. Reproducible mixing of the sample and the reagents can be achieved within the closed flow system, resulting in a highly precise and reproducible signal response. Since the reaction products accumulate in the circulated flow system, a gradual built-up of the background signal produces a continuous baseline shift that limits the useful detection scale. Therefore, elimination of the accumulated reaction products and regeneration of the main reagent are required to maintain a long-running flow system. Some reports have been published concerning cyclic FIA using kinetic (reaction rate) methods 1-4 or the skillful application of electrolysis for removing metal ions. 5,6 Other reports include the incorporation of an immobilized enzyme column for its effective use. The high cost of enzymes justifies attempts to regenerate and reuse them in the system. [7][8][9][10][11] Among the analytical methods, although spectrophotometry is the most commonly used in FIA, there appears to be little in the literature concerning cyclic FIA with spectrophotometric detection. To reuse chromogenic reagents effectively, a rapid regeneration system for them is desired under circulating flow conditions.In a rapid communication, 12 we have proposed a new concept to eliminate the reaction products in a cyclic FIA system. The adoption of a complexing agent (inhibitor) together with a chromogenic reagent makes it possible to regenerate and reuse the main reagent repeatedly. To recognize the new concept and to further test its applicability, a cyclic FIA system has been proposed for the determination of zinc. In order to improve the manipulation and the sensitivity, a water-soluble pyridylazo derivative, 2-(5-bromo-2-pyridylazo)-5-[N-n-propyl-N-(3-sulfopropyl)amino]phenol (5-Br-PAPS), 13-17 is used as a chromogenic reagent. Hayashibe et al. 18 have shown that 5-Br-PAPS is a selective and sensitive reagent for zinc (ε = 1.4 × 10 5 dm 3 mol -1 cm -1 , at 554 nm), and successfully applied it to the determination of zinc in serum using conventional FIA without any preconcentration or separation procedure. The aim of the work described here is a cyclic FIA system for the repetitive determination and/or monitoring of zinc using 5-Br-PAPS and EDTA by spectrophotometry. Experimental ReagentsAll chemicals used were of analytical-reagent grade, and water was purified in a Millipore Milli-Q system. A zinc standard solution...

Spectrophotometric Flow Injection Methods for Zinc Determination in Pharmaceutical and Biological Samples

“…[5][6][7] Flow-injection analysis with spectrophotometric detection has been used for determining Zn(II), and offers some advantages, such as low instrumental cost and a large variety of organic reagents that form coordination compounds with the metal cation. [8][9][10][11] Additionally, FIA offers low consumption of the sample and the reagent, high sample throughput, reproducibility and degree of flexibility, and, finally, it may be easily automated. 5 Recently, a significant number of studies using FIA have used solid-liquid phase extraction to concentrate and/or to remove matrix interference or other species.…”