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Braunschweig, Juliane ; Bosch, Julian ; Heister, Katja ; Kuebeck, Christine ; Meckenstock, Rainer U.:
Reevaluation of colorimetric iron determination methods commonly used in geomicrobiology.
In: Journal of Microbiological Methods.
Bd. 89
(2012)
Heft 1
.
- S. 41-48.
ISSN 0167-7012
Abstract
The ferrozine and phenanthroline colorimetric assays are commonly applied for the determination of ferrousand total iron concentrations in geomicrobiological studies. However, accuracy of both methods depends onslight changes in their protocols, on the investigated iron species, and on geochemical variations in sampleconditions. Therefore, we tested the performance of both methods using Fe(II)(aq), Fe(III)(aq), mixed valencesolutions, synthetic goethite, ferrihydrite, and pyrite, as well as microbially-formed magnetite and a mixtureof goethite and magnetite. The results were compared to concentrations determined with aqua regia dissolutionand inductively coupled plasma atomic emission spectroscopy (ICP-AES). Iron dissolution prior to thephotometric assays included dissolution in 1 M or 6 M HCl, at 21 or 60 °C, and oxic or anoxic conditions. Resultsindicated a good reproducibility of quantitative total iron determinations by the ferrozine and phenanthrolineassays for easily soluble iron forms such as Fe(II)(aq), Fe(III)(aq), mixed valence solutions, andferrihydrite. The ferrozine test underestimated total iron contents of some of these samples after dissolutionin 1 M HCl by 10 to 13%, whereas phenanthroline matched the results determined by ICP-AES with a deviationof 5%. Total iron concentrations after dissolution in 1 M HCl of highly crystalline oxides such as magnetite,a mixture of goethite and magnetite, and goethite were underestimated by up to 95% with both methods.When dissolving these minerals in 6 M HCl at 60 °C, the ferrozine method was more reliable for total ironcontent with an accuracy of ±5%, related to values determined with ICP-AES. Phenanthroline was more reliablefor the determination of total pyritic iron as well as ferrous iron after incubation in 1 M HCl at 21 °Cin the Fe(II)(aq) sample with a recovery of 98%. Low ferrous iron concentrations of less than 0.5 mM wereoverestimated in a Fe(III) background by up to 150% by both methods. Heating of mineral samples in 6 MHCl increased their solubility and susceptibility for both photometric assays which is a need for total iron determinationof highly crystalline minerals. However, heating also rendered a subsequent reliable determinationof ferrous iron impossible due to fast abiotic oxidation.Due to the low solubility of highly crystalline samples, the determination of total iron is solely possible afterdissolution in 6 M HCl at 60 °C which on the other hand makes determination of ferrous iron impossible. Therecommended procedure for ferrous iron determination is therefore incubation at 21 °C in 6 M HCl, centrifugation,and subsequent measurement of ferrous iron in the supernatant.The different procedures were tested during growth of G. sulfurreducens on synthetic ferrihydrite. Here, thephenanthroline test was more accurate compared to the ferrozine test. However, the latter provided easyhandling and seemed preferable for larger amounts of samples.
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| Publikationsform: | Artikel in einer Zeitschrift |
|---|---|
| Begutachteter Beitrag: | Nein |
| Zusätzliche Informationen: | BAYCEER109779 |
| Institutionen der Universität: | Forschungseinrichtungen > Forschungszentren > Bayreuther Zentrum für Ökologie und Umweltforschung - BayCEER Forschungseinrichtungen Forschungseinrichtungen > Forschungszentren |
| Titel an der UBT entstanden: | Ja |
| Themengebiete aus DDC: | 500 Naturwissenschaften und Mathematik |
| Eingestellt am: | 07 Aug 2015 06:59 |
| Letzte Änderung: | 07 Aug 2015 06:59 |
| URI: | https://eref.uni-bayreuth.de/id/eprint/17662 |