Alleviating Luminescence and Quenching toward Discrimination of Ballpoint Pen Inks Using Spectroscopy and Chromatography Techniques

1.

Reviewer:

In the chemical analysis of some selected ink samples, why was ethanol used?

Authors:

Thanks for your question. We have now added a statement to the revised version of the paper to rationalize why ethanol was used supported with a few references (Lines 116-117, Page 3).

The ethanol was used as it is sufficient for the efficient dissolving of most ballpoint pen inks in addition to being simple and greener than some other hazardous organic solvents. Also, it should be noted that ink is not soluble in water so using alcohol was a necessity. This is also in agreement with previous studies reported in the literature that have employed ethanol as a solvent for ink extraction and solvation.

Please see the references appended below.  

1.     Adam, C.D., S.L. Sherratt, and V.L. Zholobenko, Classification and individualisation of black ballpoint pen inks using principal component analysis of UV–vis absorption spectra. Forensic science international, 2008. 174(1): p. 16-25.

2.     Mekonnen, N., Examination of Different Inks Available in Ethiopia Using VSC 8000, U.V-Visible Spectrophotometer and TLC: Study of Their Discrimination Potential. International Research Journal of Science and Technology, 2019: p. 66-69.

3.     Kumar, R. and V. Sharma, A novel combined approach of diffuse reflectance UV–Vis-NIR spectroscopy and multivariate analysis for non-destructive examination of blue ballpoint pen inks in forensic application. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2017. 175: p. 67-75.

2. 

Reviewer:

UV Vis spectra of CV should be added.

Authors:

Alright, the UV-visible absorption spectrum of crystal violet dye dissolved in ethanol was added (Figure S2, supplementary materials). Thanks

3.

Reviewer:

Provide UV Vis spectra of used dye in ethanol as well as water and compare.

Authors:

We have added the absorption of the spectrum of the crystal violet dye in ethanol to the SI (Figure S2). For the sake of comparison we used only ethanol as a solvent for studied inks as inks were not soluble in water. 

4.

Reviewer:

Also provided the chemical structure of selective dyes.

Authors:

Thanks, we added that to the supplementary materials. Please see Figure S1, S3, and S5.

5.

Reviewer:

The experiment was conducted with multiple dye concentrations and should be checked in different pH levels.

Authors:

We believe that using solutions of the dye with different pH can be marginalized in this study particularly since the ink samples are not soluble in water and challenge the formation of aqueous solutions. We think identifying the dyes in the ink matrix and their percentages based on the chemical analysis using reference crystal violet dye and ink samples at a concentration of 20 ppm shall suffice and we hope you find it so as well. Thank you

6.

Reviewer:

some syntax errors and grammatical problems should be improved before publication as in 3.3. paragraph UV V is should be changed to "UV Vis".

Authors:

Thanks for this note. This was duly fixed (Line# 342, Page 12)

Also, the revised manuscript was carefully checked for errors and typos.

7.

Reviewer:

Please check and polish the paper carefully before the submission of the revised MS.

Authors:

Thanks for your advice. The revised manuscript was thoroughly checked.

1.

Reviewer:

Generally, this paper is very innovative, and current work is well carried out and well presented, the references are appropriate and the manuscript of the paper is well written. But the authors should better emphasize the novelty of current manuscript in order to attract the readership of inorganics.

Authors:

We appreciate the reviewer's comment and recognize the significance of highlighting the originality of our manuscript to touch the interest of readers in the inorganics field.

We edited the introduction section and added three paragraphs as recommended where we further emphasized the role of ink analysis in forensic inorganic and organic chemistry. We also highlighted the distinctive approach to combining spectroscopic and chromatography analysis for the forensic examination of various ink materials. Our statements were supported with proper/relevant citations.

Please see the yellow-highlighted paragraphs at the beginning, middle, and end of the introduction section (Pages 1-3, revised manuscript).

Thank you

Reviewer's Notes:

1.

Reviewer:

Page 2 lines 27,28,30 It’s not a good idea to start an article with abbreviations. It’s very confusing to the readers. Authors must provide at first appearance the full phrase followed by an abbreviation in brackets.

Authors:

Thank you for the note.

This issue was duly fixed throughout the entire manuscript. Abbreviated terms with full phrases are now mentioned together on the first appearance (in the introduction section) and afterward only abbreviation.

2. 

Reviewer:

Page 2 line 66 et seq. “video spectral comparator (VSC)” full phrase must be omitted during the rest of the manuscript. Page 3 line 102 “blue ballpoint (B.P)”; Page 3 line 111 “Thin-Layer Chromatography (TLC)”; etc. the same thing.

Authors:

Thanks. Duly fixed as required.

3.

Reviewer:

Page 2 line 167 “the initial IRL filter (400-485 nm)” The description of the experiments is vague, perhaps the phrase is unsuccessful. What does this phrase mean? In the humble opinion of the reviewer, the IR filter cannot work in the claimed region, since the IR range starts at 800 nm. Description of experiments should be revised for clarity.

Authors:

We agree. As recommended we edited that statement and other similar ones for almost all filters. We used instead the initial 400-485 nm band-pass filter and similar phrasing for all other filters. Please see the yellow-highlighted edits.

Thank you 

4.

Reviewer:

Page 9 line 260 “in case” red font.

Authors:

Duly fixed.

5.

Reviewer:

Page 11 line 293 “UV V is spectroscopy” typo

Authors:

Duly fixed throughout the entire manuscript. Thank you  

6.

Reviewer:

Fig. 1-6 Signatures in red font are difficult to distinguish. The picture quality needs to be improved. The font color and/or size may not have been chosen correctly.

Authors:

Figures 1-6 were modified and reconstructed as recommended. The pictures and fonts have been improved for better clarity. Thanks

7.

Reviewer:

Chapter 3.2, 3.3. The results of only 12 samples are presented. No mention is made of the choice of these 12 samples out of 30 and the reason for this choice.

Authors:

Thanks for this note. We have added a paragraph to explain and describe the basis for the selection of the 12 samples. Please see the yellow-highlighted paragraph at the start of Page# 7.

8.

Reviewer:

Page 11 line 300 “fature” typo? Maybe it means “feature”?

Authors:

Duly fixed.

9.

Reviewer:

Line 315,337 red dot

Authors:

Duly fixed.

10.

Reviewer:

Page 19 line 426 “their I ndividual IRL” typo

Authors:

Duly fixed.

Reviewer Questions:

1.

Reviewer:

What was the exact excitation for the IRL emission in the experiments with the Video Spectral Comparator?

Authors:

Thank you for your question. To address your concern we added a new paragraph to the experimental section 2.2. VSC explains how VSC filters and cameras work for light incidence and infrared luminescence recording. This might not be well explained before but we hope it is clearer now after that addition. Please see the yellow-highlighted paragraph on Page# 3. Also appended below:

“. The VSC 6000 features spot luminescence examination capability allowing images to be illuminated with visible light of different wavelengths, and then the luminescence is recorded in the infrared region. VSC 6000 features ten preset optical excitation filters for sample illumination allowing varying the excitation waveband over different bandwidth ranges from 400-485 nm to 645-800 nm band-pass regions in addition to the wide band-pass filter in the 300-800 nm region. The VSC then can adjust the emission filters of the camera according to the excitation waveband, and this determines the range of the infrared emitted wavelengths that will be recorded. In our experiments, the ten preset filters of VSC 600 were used to vary the excitation waveband used for sample illumination.”

2.

Reviewer:

The TLC result of crystal violet is represented by 4 chromatographic zones, while it is positioned as an individual substance. How can this phenomenon be explained? The answer to this question will decorate the article, in my opinion.

Authors:

Thanks a lot for your question.

We have added the following explanation to the discussion to address your question with supporting references. Please see the middle paragraph of Page# 9.

Here is the explanation and citations:

“It can be noted that the TLC of crystal violet displays 4 chromatographic zones, even though it is a single substance. It is worth mentioning that pristine crystal violet dye is photosensitive and it can degrade upon exposure to light. The light-exposed crystal violet can lose a methyl group and form methyl violet dye, which upon further light exposure loses another methyl group and forms tetramethyl pararosaniline. As a consequence, the TLC of the crystal violet reflects the mother dye and its light degradation products.[26-29]”

-Andrasko, J.J.J.o.F.S., HPLC analysis of ballpoint pen inks stored at different light conditions. 2001. 46(1): p. 21-30.

-Díaz-Santana, O., F. Conde-Hardisson, and D.J.M.j. Vega-Moreno, Comparison of the main dating methods for six ball-point pen inks. 2018. 138: p. 550-561.

-Ezcurra, M., et al., Analytical methods for dating modern writing instrument inks on paper. 2010. 197(1-3): p. 1-20.

-Hoang, A.D., et al., Combination of a Green and a Traditional Method for Estimating Relative and Absolute Ink Age: A Case Study of Ballpoint Pen Ink Dating in Vietnam. 2021. 2021: p. 1-10.

3.

Reviewer:

Why are only 12 samples presented by TLC when 30 ink samples appear in the article?

Authors:

We have addressed your concern and supplemented the revised paper with additional paragraph explaining the reasoning behind that selection. Please see Pages 7 and also appended below:

“Ink dissolution, IRL, and TLC were employed to further investigate the organic dye content of the ink samples which could be responsible for the different optical IRL behav-ior of the different groups. Specific samples from each of the 4 main groups were sub-selected to reduce data redundancy and at the same time assure sample diversity via the representation of the various brands in each subgroup of the solvated ink samples. The first subgroup, denoted subgroup I, comprised 4 samples, namely PE1, TO1, RX1, and RO4 which represent diverse brands of the 12 pens included in the main group I. The subsequent subgroup (subgroup II) encompassed 3 selected samples, namely PR2, RE1a, and VN1. The third sub-group (subgroup III) was represented by two samples, namely BV1, and PK1 while the last subgroup (subgroup IV) included 3 samples of distinct brands, namely SA1a, ZR1a, and TO3. The above-mentioned sub-selected ink samples were solvated and used for sample writing upon their dissolution.”

Reviewer's Conclusion:

.

Reviewer:

There are inaccuracies and sometimes unclear description of the experiments. The article mainly features data from 12 out of 30 samples, their selection is not explained. The article declares the suitability of the techniques used in the work for forensics but does not formulate their combinations to form a "fingerprint" for each ink sample. Thus, the article cannot be considered as a forensic technique for recognizing the ink of ballpoint pens. It is necessary either to remove the mention of forensics, leaving a statement of the work done, or to finalize the article and formulate a combination of the results of the methods as a "fingerprint" of each sample presented.

Authors:

Thank you for your feedback and all recommendations. We modified the whole manuscript a lot and improved clarity of the different sections according to referees’ comments. We have also presented justification for the sub-selection of the 12 samples as explained above. We moreover, further emphasized the core objective of the work at the end of the introduction and the R/D. We emphasized that the aim was to not only recognize and separate inks but was more to understand the reason behind their different optical behaviors (IRL) using spectroscopy and TLC tools.

1.

Reviewer:

as the authors mentioned in the manuscript, their aiming is to ascertain the number of dyes present in the ink specimens, as well as their photo-responsive characteristics. However, is it better to just contact the manufacturer to get information about the composition of the ink? And then study the photo-responsive characteristics of different compositions?

Authors:

Thanks for your comment. However, it is acknowledged that manufacturers in general regard their product components and production details, specifically for pen ink, as sensitive information. This makes it difficult for them to provide explicit details about the colors and chemical mix used in their ink concoctions just upon request. Accordingly, several research groups work on identifying the colors in ink samples, revealing the range of elements used in these products. Here are a few examples for your kind reference.

1.         Feraru Daniela Laura, M.M., Aurelia Meghea, Chromatic analysis of blue ballpoint pen inks and related dyes. J Color Research, 2015. 40(2): p. 169-177.

2.         Saviello, D., et al., A combined Surface Enhanced Raman Spectroscopy (SERS)/UV–vis approach for the investigation of dye content in commercial felt tip pens inks. 2018. 181: p. 448-453.

3.         Neumann, C., R. Ramotowski, and T. Genessay, Forensic examination of ink by high-performance thin layer chromatography—The United States Secret Service Digital Ink Library. Journal of Chromatography A, 2011. 1218(19): p. 2793-2811.

4.         Sun, Q., et al., Detection and identification of dyes in blue writing inks by LC-DAD-orbitrap MS. Forensic science international, 2016. 261: p. 71-81.

5.         Tsutsumi, K. and K. Ohga, Analysis of writing ink dyestuffs by TLC and FT-IR and its application to forensic science. Analytical Sciences, 1998. 14(2): p. 269-274.

2. 

Reviewer:

what are the main problems that this research is trying to solve? I cannot find this content in the current manuscript. If the purpose of the authors is to find a method to better distinguish the ballpoint pen inks, then they should establish their method based on the result in this manuscript and then compare the method with the previously reported ones, rather than just saying “The results pave the way for the development of effective approaches…”

Authors:

Thank you for this great comment and suggestion.

We modified the abstract and the introduction section in particular to address your concern. We also edited the whole manuscript and polished its clarity to reflect the aims and outcomes of the paper. Please see the last statement of the abstract and the last paragraph of the introduction (Page# 3).

3.

Reviewer:

As a science report, the use of “some triarylmethane dyes” is not acceptable, what are these triarylmethane dyes? What are their composition and structure?

Authors:

Indeed, several publications have reported that triarylmethane dyes serve as fundamental colorants in blue ballpoint pen (B.P.) ink. Among these dyes, Crystal Violet, Methyl Violet, Victoria Blue, and Acid Blue 49 are the most common. However, due to the limited reference materials for these dyes, we just presented our suggestion of possible dyes based on the existing literature.[1-3]  Our work was focused on studying the photoresponse of the ink dyes to better understand their mutual interactions and their collective impact on the overall behavior of the examined inks. Further extensive studies could help identify all the dyes utilized in ballpoint pens and various other pen types, which can be considered prospectively. Thank you

1.     Sun, Q., et al., Detection and identification of dyes in blue writing inks by LC-DAD-orbitrap MS. Forensic science international, 2016. 261: p. 71-81.

2.     Andrasko, J.J.J.o.F.S., HPLC analysis of ballpoint pen inks stored at different light conditions. 2001. 46(1): p. 21-30.

3.     Akhmerova, D., et al., Forensic identification of dyes in ballpoint pen inks using LC–ESI–MS. 2017. 80: p. 1701-1709.