Polish researchers have optimized and applied a hyphenated technique for iron speciation based on high performance liquid chromatography using a short cation-exchange column coupled with inductively coupled plasma optical spectrometry.
Iron constitutes approximately 45% of mass of the earth and is spread in earth's crust and soils. Its amounts in soils are relatively significant and can reach up to several percent mainly occurring in two oxidation states: Fe(II) and Fe(III). These species have different roles and pathways in the biogeochemical processes in the environment, and therefore need to be distinguished. Iron is also an essential element for life and therefore an essential element in food. Especially in developing countries with high iron deficiency among the population, supplementation of iron is of special concern. Fortification approaches aiming at modified crops that can effectively accumulate iron from the soil are investigated in order to improve human nutrition. Knowledge about iron uptake and distribution within different plant parts in the form of Fe(II) and Fe(III) complexes calls for iron speciation analysis. Most often used methods for iron speciation are based on colorimetry using specific reagents such as 1,10-phenantroline or ferrozine. Unfortunately, colorimetric methods are not very sensitive and also lack selectivity.The new study:
In order to improve selectivity and sensitivity of iron speciation analysis researchers from Poland have optimized a method based on high performance liquid chromatography with a short cation-exchange column coupled to inductively coupled plasma optical emission spectrometry (LC-ICP-OES). Fe(III) and Fe(II) species were separated on the column with the mobile phase containing pyridine–2,6–dicarboxylic acid (PDCA) as complexing agent. The mobile phase was optimized with respect to composition and concentration. It was noticed that using NaOH/Na2SO4 instead of KOH/K2SO4 ensured more stable work of the HPLC system. On the other hand the high content of sodium compounds in the mobile phase called for regular cleaning of the ICP torch and the cone. Using the short CG5A column, adequate separation of Fe(II) and Fe(III) was obtained within 240 s at an eluent flow rate of 0.5 ml/min.
The selection of the Fe II 238.204 nm line and attenuated radial plasma view for detection was based on the best match of the obtained working range with expected concentration of the samples. The detection limits for samples diluted 50 times were 41 mg/kg and 50 mg/kg, respectively for Fe(III) and Fe(II) and the upper limit of the working range was 12,500 mg/kg. In absence of any certified reference material for iron speciation, the method was validated by using the spike recovery test. All recoveries were in the acceptable range, i.e. 81-120% and 92-104% for Fe(III) and Fe(II), respectively.
The method was applied for the analysis of soil, sediments and archaeological pottery. These samples were extracted with 2 mol/L hydrochloric acid at 80°C in a reflux system. After cooling, the extract was filtered and made up to volume with water. Soil and sediment samples contained between 1.2 and 33 g/kg Fe, pottery samples ranged between 15.9 and 18.7 g/kg. In most of the samples, there was a dominance of Fe(III).
The original publication
Aleksandra Orłowska, Jedrzej Proch, Przemysław Niedzielski, A Fast and Efficient Procedure of Iron Species Determination Based on HPLC with a Short Column and Detection in High Resolution ICP OES
, Molecules, 28 (2023) 4539. DOI: 10.3390/molecules28114539
J. Proch, P. Niedzielski, Iron Species Determination by High Performance Liquid Chromatography with Plasma Based Optical Emission Detectors: HPLC–MIP OES and HPLC–ICP OES
. Talanta, 231 (2021) 122403. DOI: 10.1016/j.talanta.2021.122403
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last time modified: July 10, 2023