Feasibility Study for Determination of Trace Iron in Red Sandstone via O-Phenanthroline Spectrophotometry
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis article is devoted to the development of a method for the spectrophotometric determination of iron in geological samples. Phenanthroline was used as the photometric reagent.
The reviewer's main criticism concerns the scientific novelty of the proposed method. The article contains virtually no literature review, but the authors state (line 110) that "In rock and mineral analysis, o-phenanthroline spectrophotometry is commonly employed to quantify iron." The reviewer fully agrees with this statement. Therefore, a detailed discussion of the specific shortcomings of previously published methods for spectrophotometric determination of iron is required, along with an explanation of how the authors' proposed approach is superior. These advantages are unclear from the current version of the article.
A second significant criticism concerns the presence of a significant amount of poorly soluble silica in the analyzed sample. To confirm the accuracy of iron determination in such a complex sample, the authors should analyze a certified reference material and demonstrate that the results obtained correspond to the sample's certified concentration of Fe2+ and Fe3+.
In my opinion, the article in its current form should not be published in the journal Apllied Sciences.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe article is mainly devoted to the issues of analytical chemistry – the development of a methodology for the determination of total iron and iron (II) in sandstone samples. It consistently examines the stages of dissolution, complexation, and measurement of the analytical signal by molecular absorption analysis. The Fe2+ complex with ortho-phenanthroline is used as a basis. The authors reviewed and justified the choice of the type and quantity of reagents, studied the metrological characteristics of the technique. The results obtained using the authors' methodology are compared with alternative methods. The second part of the work relates to the field of geology. According to the reviewer, it is insufficiently substantiated. The comments made should be taken into account when finalizing the article.
Comments and questions on the text of the article:
1) It is not clear from the text of the article in section 2.3.1 whether the authors controlled the final volume of the solution after the sample was dissolved? Section 2.3.2 describes that 3 ml of the solution was taken, but from what volume? It should be equal for all samples.
2) The data in Figure 3 is not sufficiently explained in the text of the article. How do the 5 samples in Figure 3a differ from each other? And how can a complexing reagent affect the dissolution of quartzite? After all, hydrofluoric acid contributes to the dissolution of silicon dioxide.
3) Section 4.2 talks about 8 parallel measurements. How are these 8 measurements obtained? Are these measurements of the optical density of solutions created from a single dissolved sample by diluting it? Or is it 8 separate dissolved sample swaps?
4) Table 3 shows the verification of the analysis method by the "introduced – found" method by adding a solution with a known amount of iron. In this way, the authors do not check the extraction of iron, but the correctness of the analysis. Have the authors tested their methodology on standard samples of the chemical composition of materials close to the studied one?
5) Section 4.4 says that according to X-ray fluorescence analysis, the total iron concentration in terms of Fe2O3 ranges from 1.3-1.6%. According to Table 4, the maximum content is 2.58%.
6) In Table 5, did the authors correctly select the number of significant digits when specifying the concentrations of iron obtained by different methods? When comparing different methods, you need to specify the confidence intervals of the values obtained, for example, 0.50+/-0.03%. According to the authors' results, the number of significant digits will be 2 after the decimal point, not 4.
7) In the text before Figure 4, the authors draw conclusions about the possibility of assessing the degree of weathering by the ratio of Fe2+/Fe3+. This ratio should depend on the oxidation of Fe2+ by atmospheric oxygen. However, according to Figure 4a, we do not observe such a dependence. On the contrary, the maximum concentrations of Fe2+ are observed in the upper layers of the rock.
8) A similar question concerns the text in section 5.3 and the last two paragraphs of the conclusions at the end of the article. How well-founded is the authors' conclusion about the correlation of the Fe2+/Fe3+ ratio with the weathering indices of CIA, CIW, WPI and ICV? These indicators are mainly based on the ratios of the concentrations of the oxides of the elements forming water-soluble compounds. However, when water or air enters the upper layers of the rock, the concentration of Fe2+ should decrease, not increase.
9) The authors' conclusion about the possibility of using the Fe2+/Fe3+ ratio to assess the degree and rate of weathering is not sufficiently substantiated and contradicts practical results.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsDear Authors,
I hope this message finds you well. I've attached a PDF that includes my questions and comments regarding your work. I believe addressing these points will help enhance your manuscript.
Kind regards,
Comments for author File: Comments.pdf
Author Response
Please refer to the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe authors have submitted a revised version of the article. As a positive comment, I would like to note that the article highlights a significant advantage of the proposed method—namely, the addition of a photometric reagent to the sample digestion mixture, which should allow for the binding of Fe2+ simultaneously with its dissolution.
Regarding the reviewer's first concern, the lack of a literature review, the authors have added the necessary references 20-26 (see line 62). However, the discussion of the shortcomings of existing methods takes up only three lines of text (62-64). The reviewer believes that the novelty of the proposed method is a key issue for the entire work. This requires more attention.
Regarding the reviewer's second concern, the lack of data on CRM analysis, the authors rightly note in their cover letter that this is complex and requires finding and acquiring such a sample. It would be appreciated if the authors would add a corresponding comment in the text of the article itself.
The reviewer believes that the article can be published after minor revision.
Author Response
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Author Response File: Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors have made major changes to the article in accordance with the recommendations. The article can be accepted for publication.
Author Response
We sincerely appreciate your acceptance of our article.
