Development of a portable setup and a multicommuted flow analysis procedure for the photometric determination of Fe(III) and Fe(II) in fresh water

Diagram of the set-up and switching pattern of the pumps. •Iron speciation in fresh waters.•Portable equipment, based on flow analysis system and photometric determination.•Electric batteries that allow the functioning of the system for 55h.•Reagent solutions with lifetime of 10 days.•Appropriate for work at field condition being tolerant to the temperature variation. In this work, a portable instrument setup comprising a LED based photometer, a multicommuted flow analysis module, and a procedure for the determination of Fe(III) and Fe(II) in fresh water are described. The photometric procedure was based on the reaction of Fe(III) with SCN−. An oxidizing step using a K2S2O8 solution was included to allow iron (II) determination. The compound was monitored using a blue LED (λ=474nm) as a radiation source. The robustness of the equipment setup and analytical procedure for work in adverse operational conditions was ascertained by carrying out the assays without controlling the temperature of the laboratory, which varied daily from 22°C to 35°C. Baseline drift and noise increases were not observed. Furthermore, reagent solutions presented a 10 days lifetime. Accuracy assessed by employing FAAS and o-phenantroline photometric procedure as reference methods indicated that there was no significant difference at a 95% confidence level. Useful features included linear responses ranging from 0.1 up to 2.0mgL−1 Fe(II) (r=0.997) and Fe(III) (r=0.999), respectively; detection limits of 0.08mgL−1 Fe (II) and 0.06mgL−1 Fe (III), respectively; a coefficient of variation of 1.7% (n=7) for both analytes; reagent consumption of 4.8mg KSCN and 0.8mgK2S2O8 per determination; a sampling throughput of 64 determination per hour; and a waste generation of 1.42mL per determination. The weight of the equipment, including solenoid micro-pumps, photometer, electric batteries and the metallic box used for its accommodation was approximately 3kg. The electric battery used to feed the setup worked 55h without reloading, while the reagent solutions had a lifetime of 10 days.