Trace-Level Determination of Polycyclic Aromatic Hydrocarbons in Dairy Products Available in Spanish Supermarkets by Semi-Automated Solid-Phase Extraction and Gas Chromatography–Mass Spectrometry Detection

Round 1

Reviewer 1 Report

this is an interesting article about the investigation of PAHs using GC-MS analyses in commercial foods.

The manuscript and the data presented are clear and consistent. 

The overall language is good.

Most sections are well prepared.

I would be grateful if the authors may improve the manuscript according to the following suggestions:

 

•  I would suggest the authors modify ‘yoghourt’ with the most used ‘yoghurt’ through the manuscript;
• Page 3, line 33 please modify ‘CG’ in ‘GC’;
• The material and Method section could be improved. I would suggest the authors reorganize the paragraph according to the following order: 2.1 Chemicals and solvents; 2.2 Diary samples, 2.3 Extraction of PAHs; GC-MS analysis 2.4 Method validation (in this last section please, explain the analyses performed, in the results and discussion section comment the results obtained only);
• In the 2.2 Equipment section, I would be grateful if the authors may report the number of analyses per sample and per STDs (duplicate, triplicate etc.);
• In 2.1 and 2.2, if you followed some procedures to achieve yours, cite them also in these sections; 
• Precision data are intra-day and Inter-day or both? I would suggest specifying it;
• In Table 2, I would be grateful if the authors may improve the title and if they could add LOQ, slope and intercept values of the reference standards;
• In Table 3, I would be grateful if the authors may add the total amount of PAHs per diary product with SD.

Author Response

 

 

 

Author Response File: Author Response.docx

Reviewer 2 Report

this study presents and interesting investigation of Polycyclic Aromatic
Hydrocarbons in Dairy Products, however, a full review is not possible due to the following:

• P5  under table 1, as if the explanation overlap with last rows or LOD, RSD values are out of place. The text under the table should be smaller font and below the whole table
• Figure 1: too small text font, same comment for Figs 2, and 3, where can not be read the legend as well
• Fig 4 also too small
• P12. It seams that the text is out of the range of the page 
• Table 3: remove "+" sign from the Matrix effekt which is positive. No sign before the number is equivalent to positive 
• Table 4. the title of the table "..found in various types of milk samples .." and first three skimmed milk samples have the same % fat content/ protein content. So what is different? For such samples is expected to present the average with SD (same comment for Butter, Milkshake, Yoghurt 1 and 3, Whole cow milk...)
• Check where you have mentioned references - I can not see where is cited reference [36]

Sincerely

Author Response

First of all, the authors would like to thank the Reviewer for his/her apt comments on their manuscript. An itemized reply to the points raised in his/her report follows:

Point 1: P5 under table 1, as if the explanation overlap with last rows or LOD, RSD values are out of place. The text under the table should be smaller font and below the whole table

Response 1: Thanks for your suggestion. The text under the Table 1 is now smaller and below the whole table.

Point 2: Figure 1: too small text font, same comment for Figs 2, and 3, where can not be read the legends well

Response 2: Thanks. Legends of Figures 1-3 have been enlarged.

Point 3: Fig 4 also too small

Response 3: Thanks. The editorial will be asked to increase the size of Figure 4.

 

Point 4. P12. It seams that the text is out of the range of the page

Response 4: Thanks. The editorial will be asked to include all text on several pages within the established margins.

 

Point 5. Table 3: remove "+" sign from the Matrix effect which is positive. No sign before the number is equivalent to positive

 

Response 5: Thanks. The "+" have been removed from Table 3 in the matrix effect columns.

 

Point 6. Table 4. the title of the table "..found in various types of milk samples .." and first three skimmed milk samples have the same % fat content/ protein content. So what is different? For such samples is expected to present the average with SD (same comment for Butter, Milkshake, Yoghurt 1 and 3, Whole cow milk...)

Response 6: Thanks. Milk samples from different origin (whole cow's milk and semi-skimmed cow's milk) were analysed although they have the same % fat content/ protein content. Therefore, we cannot make the average as they are different milk brands.

 

Point 7.  Check where you have mentioned references - I can not see where is cited reference [36]

Response 7: Thanks for your suggestion. The reference [36] was included in the original text in the Analytical performance Section when the formula for calculating the matrix effect is given. 

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Supplementary: Table 1S:  unknowns are usually represented by lowercase letters (rather than combining lowercase and uppercase letters as in the regression equations "y" and "X", or both uppercase letters or both lowercase- these are unknowns)

Related to the "Response 6: Thanks. Milk samples from different origin (whole cow's milk and semi-skimmed cow's milk) were analysed although they have the same % fat content/ protein content. Therefore, we cannot make the average as they are different milk brands."

If those samples are different brands - this must be emphasized (either below the table or in the discussion)