Raman Spectroscopy of Glass Beads in Ammonium Nitrate Solution and Compensation of Signal Losses

Round 1

Reviewer 1 Report

Manuscript ID: sensors-2772569

Type of manuscript: Article

Title: Raman spectroscopy of glass beads in ammonium nitrate solution and compensation of signal losses

1. Recommendation:

Reconsider after major revisions

 2. Comments to the authors:

2.1 Overview and general recommendation

The paper "Raman spectroscopy of glass beads in ammonium nitrate solution and compensation of signal losses" presents the experimental setup of a mathematical correction for signal loss when measuring in-depth liquid phases in suspensions. The experiment presented in this work is well designed, yet the way it is presented in the text requires editing to be clearer. Moreover, a better contextualization of the possible application of this correction in real situations could help to highlight the impact this work can have. For this reason, I recommend reconsidering it after major revisions. My concerns are explained in detail below.

2.2 Major comments

In my opinion, the work could benefit from a more structured revision of the state-of-art in the introduction, to show non-especialized readers the impact that the results of this study can have. The possible applications of the suspension or emulsion investigation in industrial applications (eg. polymer production, etc.) should be broadened and explain what problems can be avoided/solved by monitoring the process with Raman spectroscopy. 

In the same area, you can remove or reduce the explanation of the Raman effect to concentrate more on the description of the problem. You could also add further information regarding other Raman modalities (eg. Spatially resolved Raman spectroscopy) that have been used for similar analysis. 

2.3 Minor comments

- Page 1. Line 25. There is a double citation. Revise.

- Page 1. Line 31. The term "spectroscopies" might be better than "spectroscopy" since you are referring to more than one technique.

- Page 2. Line 57. "[...] from 100 to 500 mW and still [...]" these values are quite high, today there are commercially available instruments that use lasers with lower powers. Indeed the reference cited is relatively old. Please revise. 

- Page 3. Section 2. Materials and Methods. Please indicate the characteristics of the objective (numerical aperture) and spot size. Also in this section, please indicate how you managed to move the focal point inside the cuvette if both the probe and the cuvette are fixed. Is there any stage with a precision displacement? 

- Figure 2. The decimals should be separated by a point instead of a comma. A space between the units and the number is needed.

- Page 5. Line 169. Please indicate the correspondence in the text with the variables in the formula. For example, "[...] The peak heights of ammonium nitrate (I_AN) read form [...]".

- Figure 6. The color code is not clear. it is hard to differentiate clearly between 0.00 and 0.05 for example. Also, I suggest you present the labels in ascendent order in 1 column to make it easier to read.

- Page 7. Line 188. There is a problem with the automatic figure references in the text. Please revise the text.

- Page 7. Lines 206-231. This paragraph is very difficult to read, please revise it.

- Page 8. Line 239. There is a double reference to Figure 8. 

- Page 8. Formula 2. Please explain in the text the variables in the formula. For example, what do c and d stand for? something similar should be done for formulas 4 and 5 with E variable

- Page 8. Line 244. There are no square data points. Diamonds is the most adequate word. I also suggest to indicate better the color instead of the shape to make it easier to identify the information. Also, you should cite as "(green curve in Figure 8)". This should be corrected also on page 10. line 271.

- Figure 9 and Figure 10. You could add in the Y-axis "arb. units" instead of "-".

The text requires moderate editing.

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 2 Report

The present study aims to develop a universal correction method for signal losses in diverse systems, irrespective of specific characteristics. The focus is on a suspension with a consistent particle size distribution, ensuring easily reproducible measurements. By utilizing a fluid system without inherent Raman bands, the authors concentrate on measuring the continuous fluid phase and identifying correlations and changes during dispersed phases.

The paper presents a straightforward solution based on fundamental principles in spectroscopy. It is written in proper language, with a few linguistic errors, repetitions, and inconsistencies identified in the text. I recommend including a greater number of measurement examples in the paper.

Major Comments

Could you describe the normalization process of Raman spectra? Have you attempted to calculate the relative standard deviation (RSD) (as demonstrated in the referenced paper https://doi.org/10.1016/j.saa.2020.118204).

Minor comments

Line 177, punctuation correction

Line 188 – there is a fragment in German, punctuation correction

Consider adjusting the colors of lines on Figures 6, as there appears to be no noticeable difference between concentrations.

Author Response

Please see the attachment

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

I would like to thank the authors for considering some of the previous comments and for integrating the text accordingly. The paper has increased its readability and the authors added useful information to contextualize the problem and highlight the contribution of their work.

Therefore, I recommend accepting this work for publication after some minor corrections and editing. 

Minor comments:

- Some issues can be solved in the editing phase, for example, in line 46, the citations are misplaced and they should be all inside the brackets before the period.

- Consider including more recent references in the paragraph that discusses the use of NIR spectroscopy and chemometric techniques and the limitations when studying multicomponent systems, for example, 10.1140/epjp/s13360-021-02267-1

Author Response

Thank you very much for the feedback. I have corrected the problem with the misplaced citations and changed a few other similar problems.
Also I have added more recent sources from recent years to the paragraph on NIR spectroscopy, as well as the source you recommended.

Reviewer 2 Report

Thank you for the corrections made. I accept the work in its current form.

Author Response

Thank you very much for your feedback and for accepting my work.