Chelating agent differences in ferrous iron determinations

Abstract

Experiments were conducted to test the ability of ferrous iron (Fe²⁺) chelating agents to discriminate between Fe²⁺ and ferric iron (Fe³⁺), to determine ranges of Fe²⁺ detection in reactions, to determine interactions of chelating agents with phosphorus (P) which is common in plant tissue, and to evaluate some of the complexities of methodology for Fe²⁺ determinations. PDTS [ferrozine; 3‐(2 pyridyl)‐5,6‐bis (4‐phenyl‐sulfonic acid)‐l,2,4‐triazine] reacted with only small amounts of Fe³⁺, had a fairly wide range of Fe²⁺ detection (0–200 μg), P did not interfere with the reaction, and methodology was relatively simple. TPTZ [2,4,6‐tripyridyl‐s‐triazine] was very specific for Fe²⁺, did not react with Fe³⁺, had a relatively narrow range of Fe²⁺ detection (0–40 μg), P did not interfere with the reaction, and methodology was relatively simple. BPDS [4,7‐diphenyl 1.10‐phenanthrolinedisulfonic acid] reacted with a small amount of Fe³⁺, had a fairly wide range of Fe²⁺ detection (40–200 μg), did not react with low levels of Fe²⁺ (<40 μg), P did not interfere with the reaction, and the methodology was relatively simple. OPh [1,10‐o‐phenanthroline] reacted extensively with Fe³⁺, had a wide range of Fe²⁺ detection (0–200 μg), P did not interfere with the reaction, and methodology was relatively simple. BDTPS [2,4‐bis(5,6‐diphenyl‐1,2,4‐triazine‐3‐yl)‐pyridinetetrasulfonic acid], BPT [4,7‐diphenyl‐1,10‐phenanthroline], and PDT [3‐(2pyridyl)‐5,6‐diphenly‐1,2,4‐triazine] were considered, but the literature indicated that P interferred with BDTPS and BPT reactions, citrate interferred with the BPT reactions, and the methodologies for PDT and BPT were relatively complex (required special separations and extractions). PDTS was the best of the chelating agents tested for Fe²⁺ determinations. OPh plus hydroxylamine (OPhH) was the best of the chelating agents for the determination of total Fe.

Key words:

• Iron nutrition
• Iron analysis
• Chelating agent interactions