Determination of Rhodamine 6G with direct immersion single-drop microextraction combined with an optical probe

Arina Skok; Andriy Vishnikin; Yaroslav Bazel; Ján Toth

doi:10.1371/journal.pone.0309121

Peer Review History

Original SubmissionMay 5, 2024
27 May 2024 Decision Letter - Thanh-Danh Nguyen, Editor PONE-D-24-18021Determination of Rhodamine 6G with direct immersion single drop microextraction combined with an optical probePLOS ONE Dear Dr. Vishnikin, Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process. Please submit your revised manuscript by Jul 11 2024 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file. Please include the following items when submitting your revised manuscript: A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'. A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'. An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'. If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter. If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols. Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols. We look forward to receiving your revised manuscript. Kind regards, Thanh-Danh Nguyen, PhD Academic Editor PLOS ONE Journal Requirements: When submitting your revision, we need you to address these additional requirements. 1. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at https://journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and https://journals.plos.org/plosone/s/file?id=ba62/PLOSOne_formatting_sample_title_authors_affiliations.pdf 2. In your Methods section, please provide additional information regarding the permits you obtained for the work. Please ensure you have included the full name of the authority that approved the field site access and, if no permits were required, a brief statement explaining why. 3. Please provide a complete Data Availability Statement in the submission form, ensuring you include all necessary access information or a reason for why you are unable to make your data freely accessible. If your research concerns only data provided within your submission, please write "All data are in the manuscript and/or supporting information files" as your Data Availability Statement. [Note: HTML markup is below. Please do not edit.] Reviewers' comments: Reviewer's Responses to Questions Comments to the Author 1. Is the manuscript technically sound, and do the data support the conclusions? The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented. Reviewer #1: Partly Reviewer #2: Yes Reviewer #3: Yes ******** 2. Has the statistical analysis been performed appropriately and rigorously? Reviewer #1: No Reviewer #2: Yes Reviewer #3: N/A ****** 3. Have the authors made all data underlying the findings in their manuscript fully available? The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified. Reviewer #1: Yes Reviewer #2: Yes Reviewer #3: Yes ****** 4. Is the manuscript presented in an intelligible fashion and written in standard English? PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here. Reviewer #1: No Reviewer #2: Yes Reviewer #3: No ****** 5. Review Comments to the Author Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters) Reviewer #1: The manuscript in question is on the development of a single-drop microextraction (SDME) approach combined with the use of an optical probe to determine a single analyte, Rhodamine 6G, by spectrophotometry. The authors previously published a very similar work in Talanta ((2024) 269, 125511) (reference 18) in which the same analyte is considered, as well as identical reagents (picric acid and amyl acetate) in the SDME process. The only difference is in the detection mode (laser- and light emitting diode-based fluorescence previously). Here's the abstract from the Talanta publication: The use of an optical probe for fluorescence detection combined with direct immersion single-drop microextraction has been demonstrated as an innovative approach. The optical probe served both as a drop holder for extractant and as a measuring device which made it possible to eliminate the use of cuvettes. A laser and a light emitting diode (LED) were tested as possible light sources. Both of them showed comparable results. However, given the much smaller half-band width of the laser radiation, its use has proven to be preferable since background correction can be eliminated. Direct immersion single-drop microextraction of an ionic association complex of rhodamine 6G with picric acid with subsequent fluorescent detection (λex was 532 nm and 525 nm for laser and LED, respectively; λem was 560 nm for both laser and LED) was used a model system to evaluate the new approach. The extractant phase was a 55 μL amyl acetate microdrop fixed in the optical part of the probe. LOD, LOQ and linear calibration range were found as 0.14, 0.48 and 0.5–10 nmol L−1, and 0.15, 0.50 and 0.5–5 nmol L−1 for laser and LED light sources, respectively. The accuracy of the method was assessed by analyzing real water samples. It is felt that there is nothing novel in the latest work. It appears to be a repeat of the Talanta study, with just a different detection system. If an effort is made to expand the applicability to more analytes and differentiate from what was done before, it would make this more interesting. Reviewer #2: Authors proposed a manuscript involving the determination of Rhodamine 6G with direct immersion single drop microextraction combined with an optical probe. In general, the manuscript is well written and properly conducted. This proposal is interesting since an microextraction-based approach was succesfully developed, optimized, and applied in real samples. However, some points need to be revised before the accepance in Plos One according to the comments below: - The chemical structure and some physico-chemical properties of the analyte are important to be included at least in Supplementary Material. - A trend in sample preparation techniques is the use of metrics for the evaluation of the sustainable aspects of analytical methodologies Some recent strategies such as AGREEprep and sample preparation metrics of sustainability (SPMS) have been employed to quantify how sustainable a methodology is. It should be interesting to include one of these metrics in order to permit a more comprehensive evaluation of the environmental aspects of this methodology. - Authors have mentioned that “RSD values for different concentrations of Rh6G were ranged from 1.7 to 6.0 %”. Is intraday or interday precision? Which concentrations were examined? Please, include this information in the manuscript. Both precisions (intraday and interday) are important to be inserted. - Sample preparation time should be included in Table 3 for the comparison of analysis throughput. Reviewer #3: PONE-D-24-18021 This paper is an interesting and potentially useful application for on-site sampling and determination of dye chemicals in aqueous systems, as well as laboratory analyses of cosmetic products, using low-cost and portable UV-VIS probes and instrumentation. The authors should consider addition some relevant experimental data. In addition, while the manuscript is generally well written, there are some grammatical issues, such as sentence structure and word choices that need to be addressed. Missing data: 1. A few sentences should be added describing the procedure (chemicals, time, etc.) required for cleaning the probe during field use 2. Line 203: what is meant by “using a smaller stirrer”. Is this the magnetic stirrer or stir be. If the stir be, be specic for size and type. 3. Line 98: picric acid is ususlly used in a moist state, to avoid detonation. Describe the material and source. 4. Units: the use of units changes from µg/L to µM. If both are to be used, when doing so the other should be included in perentheses. 5. Line 333: what is meant by a data curation? Please use a more meaningful description. 6. Are the natural waters (river) filtered before analysis? 7. The authors emphasize the greenness of this procedure versus other methods. This would be be much more effectively demonstrated by adding a paragraph with comparative calculations of their procedure to 1 or 2 of the other procedures discussed using AGREEprep. Just the results can be mentioned, more detailed methodology can be placed in the electronic addendum, if desired. Grammatical issues 1. A number of sentences are too brief. These could be rewritten or combined to make a more flowing document. 2. Line 62: “such methods” is too vague”, rephrase. 3. Line 63: replace “processes” with “steps”. 4. Lines 73-78: In addition to the references, you should indicate that your research team did this, and the present work is a continuation of the previous work. 5. Lines 111-112: consider rearranging the sentence structure (buffer, pH) and use” stir bar” (consider point 2 above). 6. Line 116: Again consider rewriting. 7. Line 230: consider adding “reproducible”. 8. Line 238: Please rewrite (significant already???) 9. Line 240: “has been shown” – where, when, reference? 10. Line 267: consider rephrasing (such a toxic) 11. Line 317: consider rephrasing (not inferior not only) ****** 6. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files. If you choose “no”, your identity will remain anonymous but your review may still be made public. Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy. Reviewer #1: No Reviewer #2: No Reviewer #3: No ******** [NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.] While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step. https://doi.org/10.1371/journal.pone.0309121.r001
Revision 1
5 Jul 2024 Author Response Responses to Reviewer's questions When submitting your revision, we need you to address these additional requirements. 1. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at https://journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and https://journals.plos.org/plosone/s/file?id=ba62/PLOSOne_formatting_sample_title_authors_affiliations.pdf The manuscript has been corrected to meet PLOS ONE`s style requirements. 2. In your Methods section, please provide additional information regarding the permits you obtained for the work. Please ensure you have included the full name of the authority that approved the field site access and, if no permits were required, a brief statement explaining why. The statement has been added to Section 2.2. 3. Please provide a complete Data Availability Statement in the submission form, ensuring you include all necessary access information or a reason for why you are unable to make your data freely accessible. If your research concerns only data provided within your submission, please write "All data are in the manuscript and/or supporting information files" as your Data Availability Statement. A complete Data Availability Statement has been provided in the submission form. Comments to the Author 5. Review Comments to the Author Reviewer #1: The manuscript in question is on the development of a single-drop microextraction (SDME) approach combined with the use of an optical probe to determine a single analyte, Rhodamine 6G, by spectrophotometry. The authors previously published a very similar work in Talanta ((2024) 269, 125511) (reference 18) in which the same analyte is considered, as well as identical reagents (picric acid and amyl acetate) in the SDME process. The only difference is in the detection mode (laser- and light emitting diode-based fluorescence previously). Here's the abstract from the Talanta publication: The use of an optical probe for fluorescence detection combined with direct immersion single-drop microextraction has been demonstrated as an innovative approach. The optical probe served both as a drop holder for extractant and as a measuring device which made it possible to eliminate the use of cuvettes. A laser and a light emitting diode (LED) were tested as possible light sources. Both of them showed comparable results. However, given the much smaller half-band width of the laser radiation, its use has proven to be preferable since background correction can be eliminated. Direct immersion single-drop microextraction of an ionic association complex of rhodamine 6G with picric acid with subsequent fluorescent detection (λex was 532 nm and 525 nm for laser and LED, respectively; λem was 560 nm for both laser and LED) was used a model system to evaluate the new approach. The extractant phase was a 55 μL amyl acetate microdrop fixed in the optical part of the probe. LOD, LOQ and linear calibration range were found as 0.14, 0.48 and 0.5–10 nmol L−1, and 0.15, 0.50 and 0.5–5 nmol L−1 for laser and LED light sources, respectively. The accuracy of the method was assessed by analyzing real water samples. It is felt that there is nothing novel in the latest work. It appears to be a repeat of the Talanta study, with just a different detection system. If an effort is made to expand the applicability to more analytes and differentiate from what was done before, it would make this more interesting. Indeed, there is a certain similarity between this manuscript and a previously published article in Talanta 2024; 269: 125511. The main ideas of this manuscript are a new, original, much simpler and more efficient method for the quantitative determination of dyes, and a more detailed investigation of a number of questions of analytical importance. We believe that the proposed manuscript differs significantly from the published article in Talanta in the following criteria: 1. In the manuscript, we propose to use a much simpler detection system: instead of using a laser and then measuring the fluorescence intensity of the microextracts, the analyte is detected by UV-Vis. This method is much more convenient, simpler and can be used in conventional analytical laboratories without any problems. The use of rhodamine 6G as an analyte was due to the need to have a test system to evaluate the effectiveness of the new method, which would be more difficult to do with another dye. 2. The method of combining laser with microextraction determination of analytes, first described by us in the above-mentioned Talanta article, is quite effective, but has a number of disadvantages, such as the complexity of setting up the measurement process itself, the need to match laser parameters and analyte properties, compliance with special criteria for accurately setting the laser position relative to the extraction drop, etc. This can be a significant obstacle to the use of the proposed approach in laboratory and production environments. The use of a much simpler and easily installed optical probe-based detection has its advantages, in addition to the possibility of reproducing such a system in conventional laboratories, such as its versatility, suitability for the determination of many analytes, and quite satisfactory analytical properties, such as sensitivity, accuracy, and precision criteria. 3. The manuscript pays special attention to the selectivity of the determination. In particular, the possibility of determining rhodamine 6G in the presence of other dyes similar in structure and properties, such as fluorescein, eriochrome T and rhodamine B, is shown. 4. Another important difference is the expansion of the range of real samples in which rhodamine 6G can be determined. The effectiveness of this method for the analysis of not only water samples but also cosmetic products has been shown. 5. In contrast to the previous article, the “greenness” of the method by AGREE metric was evaluated. It is shown that the method with photometric detection is significantly superior in terms of a set of parameters to previously proposed methods with preliminary sorption or extraction preconcentration and detection by liquid chromatography, as it does not require the use of large volumes of toxic chloroform, has lower energy consumption and volume of sample and waste. Reviewer #2: Authors proposed a manuscript involving the determination of Rhodamine 6G with direct immersion single drop microextraction combined with an optical probe. In general, the manuscript is well written and properly conducted. This proposal is interesting since an microextraction-based approach was succesfully developed, optimized, and applied in real samples. However, some points need to be revised before the accepance in Plos One according to the comments below: - The chemical structure and some physico-chemical properties of the analyte are important to be included at least in Supplementary Material. The chemical structure and mentioning the high solubility of Rhodamine 6G in water have been added into the text (Fig 1, Line 42). - A trend in sample preparation techniques is the use of metrics for the evaluation of the sustainable aspects of analytical methodologies Some recent strategies such as AGREEprep and sample preparation metrics of sustainability (SPMS) have been employed to quantify how sustainable a methodology is. It should be interesting to include one of these metrics in order to permit a more comprehensive evaluation of the environmental aspects of this methodology. Analytical Greenness (AGREE) metric was used to compare the greenness of the proposed method with three other existing methods using similar sample preparation technique (solid-phase and liquid-phase microextraction) (section 3.8). - Authors have mentioned that “RSD values for different concentrations of Rh6G were ranged from 1.7 to 6.0 %”. Is intraday or interday precision? Which concentrations were examined? Please, include this information in the manuscript. Both precisions (intraday and interday) are important to be inserted. Evaluation of interday and intraday precision for the proposed method was added to the section 3.6. - Sample preparation time should be included in Table 3 for the comparison of analysis throughput. The extraction times for each method considered have been added to Table 3. Reviewer #3: PONE-D-24-18021 This paper is an interesting and potentially useful application for on-site sampling and determination of dye chemicals in aqueous systems, as well as laboratory analyses of cosmetic products, using low-cost and portable UV-VIS probes and instrumentation. The authors should consider addition some relevant experimental data. In addition, while the manuscript is generally well written, there are some grammatical issues, such as sentence structure and word choices that need to be addressed. Missing data: 1. A few sentences should be added describing the procedure (chemicals, time, etc.) required for cleaning the probe during field use Operations required for sample preparation of river water and cleaning of the optical probe between measurements were added to section 2.2. 2. Line 203: what is meant by “using a smaller stirrer”. Is this the magnetic stirrer or stir be. If the stir be, be specific for size and type. The dimensions of the magnetic stirring bar have been added. 3. Line 98: picric acid is ususlly used in a moist state, to avoid detonation. Describe the material and source. An indication of the qualification of the picric acid preparation and the method of preparing the solution has been added to section 2.1. 4. Units: the use of units changes from µg/L to µM. If both are to be used, when doing so the other should be included in perentheses. The same units for the Rh6G concentration expressed in µg L–1 were used throughout the article. 5. Line 333: what is meant by a data curation? Please use a more meaningful description. The term “data curation” was recommended by the rules of the journal. However, it was changed to a more meaningful “data evaluation”. 6. Are the natural waters (river) filtered before analysis? Yes, river water was previously filtered. Information was added to the section 2.2. 7. The authors emphasize the greenness of this procedure versus other methods. This would be be much more effectively demonstrated by adding a paragraph with comparative calculations of their procedure to 1 or 2 of the other procedures discussed using AGREEprep. Just the results can be mentioned, more detailed methodology can be placed in the electronic addendum, if desired. Analytical Greenness (AGREE) metric was used to compare the greenness of the proposed method with three other existing methods using similar sample preparation technique (solid-phase and liquid-phase microextraction). Grammatical issues 1. A number of sentences are too brief. These could be rewritten or combined to make a more flowing document. Several sentences have been merged or rewritten. 2. Line 62: “such methods” is too vague”, rephrase. The related sentence is rewritten. Lines 83-86 in a new version of Ms. 3. Line 63: replace “processes” with “steps”. Corrected. 4. Lines 73-78: In addition to the references, you should indicate that your research team did this, and the present work is a continuation of the previous work. We add an indication that our research team conducted the study described in reference [18] (lines 76, 77), as well as a mention that this paper is a continuation of a previous paper (line 117). 5. Lines 111-112: consider rearranging the sentence structure (buffer, pH) and use” stir bar” (consider point 2 above). The sentence has been rewritten (Lines 149-151). 6. Line 116: Again consider rewriting. The sentence has been rewritten (Lines 155-157). 7. Line 230: consider adding “reproducible”. The word “accurate” has been replaced by “reproducible” (Line 276). 8. Line 238: Please rewrite (significant already???) The word “significant ” has been replaced by “observed” (Line 297). 9. Line 240: “has been shown” – where, when, reference? The sentence has been rewritten (Lines 298-300). 10. Line 267: consider rephrasing (such a toxic) The sentence has been rephrased (Lines 326-328). 11. Line 317: consider rephrasing (not inferior not only) The sentence has been rephrased (Lines 395-399). In addition, the English language of the manuscript was checked by a native English speaker. Attachments Attachment Submitted filename: Response to Reviewers.docx https://doi.org/10.1371/journal.pone.0309121.r002
23 Jul 2024 Decision Letter - Thanh-Danh Nguyen, Editor PONE-D-24-18021R1Determination of Rhodamine 6G with direct immersion single-drop microextraction combined with an optical probePLOS ONE Dear Dr. Vishnikin, Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process. Please submit your revised manuscript by Sep 06 2024 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file. Please include the following items when submitting your revised manuscript: A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'. A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'. An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'. If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter. If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols. Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols. We look forward to receiving your revised manuscript. Kind regards, Thanh-Danh Nguyen, PhD Academic Editor PLOS ONE Journal Requirements: Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice. Additional Editor Comments: It should be minor revision [Note: HTML markup is below. Please do not edit.] Reviewers' comments: Reviewer's Responses to Questions Comments to the Author 1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation. Reviewer #3: (No Response) ******** 2. Is the manuscript technically sound, and do the data support the conclusions? The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented. Reviewer #3: Yes ****** 3. Has the statistical analysis been performed appropriately and rigorously? Reviewer #3: N/A ****** 4. Have the authors made all data underlying the findings in their manuscript fully available? The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified. Reviewer #3: Yes ****** 5. Is the manuscript presented in an intelligible fashion and written in standard English? PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here. Reviewer #3: Yes ****** 6. Review Comments to the Author Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters) Reviewer #3: PONE-D-24-18021R1 The authors have addressed most of the points of the reviewers of the original manuscript. However, a few important issues remain as well as a couple of suggested minor changes. Minor issues: 1. Lines 160-161: This sentence has no context? Something left out? 2. Line 203: Change to “salting out” Major issues: 1. In Table 1, the units are mM, in Table 2, nM, in Table 3 µg L-1. For readers who do not wish to look up the molar or atomic mass of something in order to convert between units, this is troublesome and irritating. It also makes it difficult to recognize the significance of 10 mM of carbonate in river water, compared to the linear range of 5-240 µg L-1 for your method without conversion to identical units. 2. In Table 3 it would be useful for comparison of methods to know, without having to go to the original publications, the volume of sample and final analytical instrumentation technique, to again accurately compare the significant differences in methodology and greenness. 3. For Figure 6, there should be a listing of the 4 methods in the footnote to identify each AGREE assessment. 4. For Figure 6, it would be helpful to the reader and context of the figure, to provide the calculations for each AGREE assessment. This would be best handled in the electronic supplemental, referenced in the Table and manuscript of course.. ****** 7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files. If you choose “no”, your identity will remain anonymous but your review may still be made public. Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy. Reviewer #3: No ******** [NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.] While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step. https://doi.org/10.1371/journal.pone.0309121.r003
Revision 2
31 Jul 2024 Author Response Responses to Reviewer's questions Minor issues: 1. Lines 160-161: This sentence has no context? Something left out? A previous review indicated that the manuscript needed to be corrected to meet PLOS ONE`s style requirements. The following was suggested. 2. In your Methods section, please provide additional information regarding the permits you obtained for the work. Please ensure you have included the full name of the authority that approved the field site access and, if no permits were required, a brief statement explaining why. The text of the manuscript has therefore been finalized to reflect this suggestion. 2. Line 203: Change to “salting out” The text has been corrected in line with this comment. Major issues: 1. In Table 1, the units are mM, in Table 2, nM, in Table 3 µg L-1. For readers who do not wish to look up the molar or atomic mass of something in order to convert between units, this is troublesome and irritating. It also makes it difficult to recognize the significance of 10 mM of carbonate in river water, compared to the linear range of 5-240 µg L-1 for your method without conversion to identical units. Concentration units in the article (Table 3, abstract and Introduction) were converted to one unit system derived from mol L–1 (nM or mM). 2. In Table 3 it would be useful for comparison of methods to know, without having to go to the original publications, the volume of sample and final analytical instrumentation technique, to again accurately compare the significant differences in methodology and greenness. The volume of sample has been added to Table 3. The caption to Table 3 indicates the final analytical instrumental methodology. In all compared methods, the analytical signal was measured by spectrophotometry. 3. For Figure 6, there should be a listing of the 4 methods in the footnote to identify each AGREE assessment. 4 methods have been listed in the caption to Fig. 6. 4. For Figure 6, it would be helpful to the reader and context of the figure, to provide the calculations for each AGREE assessment. This would be best handled in the electronic supplemental, referenced in the Table and manuscript of course. S1 Table has been added and posted as Supporting Information. It contains the data needed to assess the AGREE score for the developed and three compared methods. The AGREE scores have been refined. Attachments Attachment Submitted filename: Response to Reviewers.docx https://doi.org/10.1371/journal.pone.0309121.r004
5 Aug 2024 Decision Letter - Thanh-Danh Nguyen, Editor Determination of Rhodamine 6G with direct immersion single-drop microextraction combined with an optical probe PONE-D-24-18021R2 Dear Dr. Vishnikin, We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements. Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication. An invoice will be generated when your article is formally accepted. Please note, if your institution has a publishing partnership with PLOS and your article meets the relevant criteria, all or part of your publication costs will be covered. Please make sure your user information is up-to-date by logging into Editorial Manager at Editorial Manager® and clicking the ‘Update My Information' link at the top of the page. If you have any questions relating to publication charges, please contact our Author Billing department directly at authorbilling@plos.org. If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org. Kind regards, Thanh-Danh Nguyen, PhD Academic Editor PLOS ONE Additional Editor Comments (optional): It can be accepted in the present form. Reviewers' comments: https://doi.org/10.1371/journal.pone.0309121.r005
Formally Accepted
9 Aug 2024 Acceptance Letter - Thanh-Danh Nguyen, Editor PONE-D-24-18021R2 PLOS ONE Dear Dr. Vishnikin, I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now being handed over to our production team. At this stage, our production department will prepare your paper for publication. This includes ensuring the following: * All references, tables, and figures are properly cited * All relevant supporting information is included in the manuscript submission, * There are no issues that prevent the paper from being properly typeset If revisions are needed, the production department will contact you directly to resolve them. If no revisions are needed, you will receive an email when the publication date has been set. At this time, we do not offer pre-publication proofs to authors during production of the accepted work. Please keep in mind that we are working through a large volume of accepted articles, so please give us a few weeks to review your paper and let you know the next and final steps. Lastly, if your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org. If we can help with anything else, please email us at customercare@plos.org. Thank you for submitting your work to PLOS ONE and supporting open access. Kind regards, PLOS ONE Editorial Office Staff on behalf of Dr. Thanh-Danh Nguyen Academic Editor PLOS ONE https://doi.org/10.1371/journal.pone.0309121.r006

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