Determination of Lead Elemental Concentration and Isotopic Ratios in Coal Ash and Coal Fly Ash Reference Materials Using Isotope Dilution Thermal Ionization Mass Spectrometry
Round 1
Reviewer 1 Report
Dear authors as you are not native English speakers I noted that you need to thoroughly check your manuscript for the use of English. I have gone through the text and made all the possible correction. I also found few discrepancies in the reference list, as some references in the list are not cited in the text, which I have underlined in the text. However I did not cross check all the references.
The scientific points of the paper are well presented and I think the paper contains new and useful data that deserve to be published.
Comments for author File: 
Comments.pdf
Author Response
Dear reviewer,
Thank you very much for your English polishing. We revised this ms following your comments and made response about your comment.This ms has been further polishing by a senior professor Simon.A.Wilde from Curtin University.
Best regards
Chaofeng Li
Author Response File: Author Response.pdf
Reviewer 2 Report
The paper presents detailed measurements of the Pb content and Pb isotopic composition of 4 reference materials of coal fly ash and coal ash. The study is methodologically sound and there is no reason to believe that the results are not accurate and very precise. The paper also presents a short discussion on why measuring Pb isotopes in coal fly ash is of increasing interest. What the paper lacks is a discussion of why is is advantageous to use coal fly ash reference materials. There is no reason that one cannot obtain good data on coal fly ash samples using rock standards for example. The four selected reference materials come from China (3) and Japan (1), I was not able to find a website for for the Chinese agency to check the availability of the three reference materials, and my Japanese is too limited to readily check if the standard from Japan is still available. The paper is irrelevant if people cannot obtain these reference materials for themselves and hopefully use them in many laboratories across the world. Information on how to obtain the CRMs should be included in the paper.
Other points:
Define TIMS the first time it is mentioned.
You state the acids used in the study are purified by distillation, but what are the starting acids? Commercial grade, research grade, or what?
The sample digestion is described for rock samples. Is the same procedure used for the coal samples?
The column chemistry presented here is similar to many other studies, yet no references are given for the column chemistry procedure.
The sample sizes of around 50 milligram used for the CRMs seems large compared to real samples obtained from air filters. How low can one expect to go in sample size?
Are there any studies comparing Pb concentrations in coal fly ash across the globe?
The sample loading technique is not new, more appropriate references than 29, and 30 could be chosen.
Likewise in the discussion on the use of single-spike ID measurements it is stated that this has been used for more than 50 years, yet the four references given are all quite new and perhaps not the best to use for this argument.
For the Pb concentration of BCR-2, Stracke et al. 2012 (Refractory element fractionation in the Allende meteorite: Implications for solar nebula condensation and the chondritic composition of planetary bodies, GCA) presents a vlaue of 10.9 ppm using isotope dilution. It seems a more appropriate comparison.
For the Pb concnetration and isotopic composition of JB-3 Kuritani et al. 2006 (Accurate Isotopic and Concentration Analyses of Small Amounts of Pb Using Isotope Dilution Coupled with the Double Spike Technique, GS & GAR) reported data using double spike, yet this paper is not even referenced. This is a grave oversight.
Author Response
Dear reviewer,
Thank you very much for your constructive and valuable suggestions. we have made substantial modifications according your comment. The quality of English is further polished by a senior professor from Curtin University. Please, check the attachment that shows detail response.
Best regards
Chaofeng Li
Author Response File: 
Author Response.docx
Round 2
Reviewer 2 Report
This revised version of the manuscript presents a much improved text. The added information on how to procure these reference materials will be very useful for readers who want to analyse the Pb composition of coal samples.
I feel that the authors are still overselling the importance using these reference materials compared to other well-characterized reference materials, but it may be a matter of personal taste.
