Sequential injections as an alternative to gradient exploitation for implementing differential kinetic analysis in a flow injection system

Abstract

A novel flow-based strategy for implementing simultaneous determinations of different chemical species reacting with the same reagent(s) at different rates is proposed and applied to the spectrophotometric catalytic determination of iron and vanadium in Fe-V alloys. The method relies on the influence of Fe(II) and V(IV) on the rate of the iodide oxidation by Cr(VI) under acidic conditions; the Jones reducing agent is then needed. Three different plugs of the sample are sequentially inserted into an acidic KI reagent carrier stream, and a confluent Cr(VI) solution is added downstream. Overlap between the inserted plugs leads to a complex sample zone with several regions of maximal and minimal absorbance values. Measurements performed on these regions reveal the different degrees of reaction development and tend to be more precise. Data are treated by multivariate calibration involving the PLS algorithm. The proposed system is very simple and rugged. Two latent variables carried out ca 95% of the analytical information and the results are in agreement with ICP-OES.

Stopped-in-loop flow analysis system for successive determination of trace vanadium and iron in drinking water using their catalytic reactions☆

“…Fortes et al [20,21] reported a novel flow-based strategy for implementing simultaneous catalytic spectrophotometric determinations of vanadium and iron in Fe-V alloys.…”

Advanced Stopped-in-Loop Flow Analysis with a Reagents-Merging Zones Technique for a Catalytic Successive Determination of Vanadium and Iron

“…However, the sensitivities of the proposed method for the successive determination of vanadium and iron were better than those of a catalytic spectrophotometric method for the simultaneous determination of mg L -1 levels of vanadium and iron. 22 The sample throughput of this method was 13 samples h -1 (275 s per one determination of vanadium or iron). The a. Abbreviations (SPV, SP, SV1 -SV5, SWV1, SWV2, HC1 -HC5, HL, and CS) as in Fig.…”

“…However, the number of papers on flow injection spectrophotometry for the simultaneous/successive determination of two different metal ions (including two oxidation states of a metal) in the same sample is limited. For instance, binary mixtures of iron(III)/vanadium(V), 18 iron(III)/chromium(VI), 18 and vanadium(IV)/vanadium(V), 19 were selectively determined using the redox reactions, and also catalytic methods for iron/ copper 20,21 and vanadium/iron 22,23 were proposed. In recent years, our research group has proposed alternative concepts for flow injection analysis (FIA) systems, called stopped-in-loop flow analysis (SILFA) 24 and stopped-in-dualloop flow analysis (SIDLFA) 25 to reduce reagent consumption compared with conventional FIA.…”

Differential Reaction-Rate Methods in Flow Analysis

“…To this end, different sample aliquots were sequentially inserted into the reagent carrier stream [41], and the resulting zones underwent severe overlap yielding a complex sample zone with regions of maximal and minimal local concentrations. Precise absorbance values associated to these regions were attained.…”