Analysis of Polycyclic Aromatic Hydrocarbons in Water Samples Using Deep Eutectic Solvent as a Dispersant in Dispersive Liquid–Liquid Microextraction Based on the Solidification of Floating Organic Droplet

Round 1

Reviewer 1 Report

The publication is valuable and should appear in Waters, but a few changes should be made:

Lines 70-71: not true, check doi: 10.1016/j.chroma.2018.07.070 and correct this statement

Figure 3 and 4 t is the total peak area for which PAH, for which compound? What were the conditions of measurement? And what is the peak area, TIC or selected ion?

Table 2: the same questions as in the case of Figure 3 and 4. Here, the authors should provide the values of the peak area for each PAH (from Table 1), individually

Lines 235-237: I believe that the total area of all PAH peaks should not be considered, and the results should be presented individually for each compound separately in the whole paper.

Section 3.4 should be placed after the section in which the authors present their results for water samples.

To Table 5 should be added the data provided in doi: 10.1016/j.chroma.2018.07.07

Author Response

1. Lines 70-71: not true, check doi: 10.1016/j.chroma.2018.07.070 and correct this statement.

Answer 1: Thanks! The statement of line 71 has been changed. In the article “Hydrophobic deep eutectic solvents as “green” extraction media for polycyclic aromatic hydrocarbons in aqueous samples” (doi: 10.1016/j.chroma.2018.07.070, reference 20), the hydrophobic deep eutectic solvents (DESs) were used as the extractants. As far as we are acknowledged, the application of using hydrophilic DES as the dispersant in microextraction for PAHs determination has scarcely been reported. Therefore, in our paper, the synthesized DESs were of hydrophilic and their applicability using as the dispersants was studied.

2. Figure 3 and 4 is the total peak area for which PAH, for which compound? What were the conditions of measurement? And what is the peak area, TIC or selected ion?

Answer 2: Thanks! The total peak area in Figures 3 and 4 is for 16 PAHs, which is described in the first paragraph of section 3.2 (Lines 179-180), and the mixed standard solution of 16 PAHs is indicated in section 2.1. Moreover, the optimization conditions of sections 3.2.1 and 3.2.2 have been added in the captions of Figures 3 and 4, respectively. The peak area is the selected ion peak area, which is described in section 2.2 (Lines 102-103). The measurement conditions of 16 PAHs are indicated in section 2.2 (Lines 96-103).

3. Table 2: the same questions as in the case of Figure 3 and 4. Here, the authors should provide the values of the peak area for each PAH (from Table 1), individually. Lines 235-237: I believe that the total area of all PAH peaks should not be considered, and the results should be presented individually for each compound separately in the whole paper.

Answer 3: Thanks! The supplementary data of peak area values for each PAH in Figures 3 and 4 are indicated in Tables S1 and S2, respectively. When response surface methodology (RSM) is used for multi-factor optimization in microextraction, if the analytes are a multi-component mixture, the total or average of the peak area (or recovery%) of each component is commonly used to evaluate the extraction efficiency. This can be seen from the references 20-25 and 33 of our paper. Among them, this mode was also used when single factor experiment was performed (references 22, 25). There may be two reasons, one is the result (extraction efficiency) is concise and easy to describe. The second is that the result can better reflect the overall extraction efficiency of multiple components by this way. Therefore, in our paper, the total peak area was chosen to evaluate the extraction efficiency as the RSM was used.

4. Section 3.4 should be placed after the section in which the authors present their results for water samples.

Answer 5: Thanks! Section 3.4 has been placed after the results for real water samples (Section 3.5 “Analysis of real water samples”) in the article.

5. To Table 5 should be added the data provided in doi: 10.1016/j.chroma.2018.07.070.

Answer 6: Thanks! The supplementary data provided in doi: 10.1016/j.chroma.2018.07.070 (reference 20) has been added in Table 6.

Reviewer 2 Report

To,

Editor

Journal of Water

Subject:-Analysis of polycyclic aromatic hydrocarbons in water samples using deep eutectic solvent as a dispersant in dispersive liquid-liquid 

microextraction based on the solidification of floating organic droplet, water-2465896

Dear Sir,

I am submitting the following for the consideration,

1. The novelty was missing as the objectives and the works were less explained.
2. The optimization conditions as full sections were missing for volume, concentration of dispersant, extractant and solidification of organic droplet (SFOD)etc. 
3. DES I and DES III were presented in supplementary but did not well described.
4. The DLLME- SFOD and GC-MS program, if these were adopted that may also informed.
5. The %RSD 6.4 is quite high than many reported works. If any PAH member has such high RSD that may excluded.
6. It was stated the choline chloride was first used in your studies as dispersant for the determination of PAH, It may conformed please.
7. The chromatograms of the table 1 may also indicated.
8. Figures 3 and 4 histograms were unclear as computed with bars at top without numeric (range of error), or these may deleted.
9. The procedures of figure 4 may explained and instrument model, software program may explained etc.
10. The description and other physico chemical parameters of river water may also explained.
11. The %RSD was quite high, even those values with R2 (0.999) in table 4. Those values may be %RSD within decimals.

Needful of improvement 

Author Response

1. The novelty was missing as the objectives and the works were less explained.

Answer 1: Thanks! In lines 70-72, it is stated that the application of using DES as the dispersant in microextraction for PAHs determination has scarcely been reported. Therefore, the purpose of our study is to introduce a hydrophilic DES as the dispersant in DLLME-SFOD for the preconcentration of 16 PAHs from water samples (Lines 73-74). Moreover, the answer of comment 6 perhaps can further explain the novelty of the study.

2. The optimization conditions as full sections were missing for volume, concentration of dispersant, extractant and solidification of organic droplet (SFOD) etc.

Answer 2: Thanks! The optimization conditions of sections 3.2.1 and 3.2.2 have been added in the captions of Figures 3 and 4, respectively. The operation conditions of RSM have been added in the first paragraph of section 3.2.3.

3. DES I and DES III were presented in supplementary but did not well described.

Answer 3: Thanks! The descriptions of DES1 and DES2 have been added in the supplementary materials (Figures S2 and S3).

4. The DLLME-SFOD and GC-MS program, if these were adopted that may also informed.

Answer 4: Thanks! The DLLME-SFOD program is indicated in section 2.5. The GC-MS program for 16 PAHs is indicated in first paragraph of section 2.2 (Lines 96-103).

5. The %RSD 6.4 is quite high than many reported works. If any PAH member has such high RSD that may excluded.

Answer 5: Thanks! The %RSD 6.4 of component “dibenz[a,h]anthracene” is high compared to other components，perhaps this can be attributed to matrix effect of river water sample and GC-MS condition. However, in order to maintain the originality and authenticity of data, these data are preserved.

6. It was stated the choline chloride was first used in your studies as dispersant for the determination of PAH, It may conformed please.

Answer 6: Thanks! The supplementary description that DES2 synthesized by choline chloride and acetic acid was first used as the dispersant for the determination of PAH has been added in section 4 (Conclusions).

7. The chromatograms of the table 1 may also be indicated.

Answer 7: Thanks! The supplementary chromatogram of the Table 1 is indicated in supplementary materials (Figure S1).

8. Figures 3 and 4 histograms were unclear as computed with bars at top without numeric (range of error), or these may deleted.

Answer 8: Thanks! In most articles on microextraction techniques for sample preparation, the histograms as computed with bars at top without numeric (rang of error) was used. Therefore, the bars at the top of histograms were recommended to be preserved.

9. The procedures of figure 4 may explained; and instrument model, software program may explained etc.

Answer 9: Thanks! The procedures of Figure 4 are indicated in its caption and section 2.5. The instrument model is indicated in section 2.2 (Lines 109-114), and the BBD of RSM was adopted by design Expert 12.0.3.0 (Lines 213-214).

10. The description and other physico chemical parameters of river water may also explained.

Answer 10: Thanks! The description and some physic-chemical parameters of river water have been added in section 3.4 (Analysis of real water samples).

11. The %RSD was quite high, even those values with R2 (0.999) in table 4. Those values may be %RSD within decimals.

Answer 11: Thanks! In Table 4, the %RSD of 5 PAHs with R² > 0.999 is in the range of 2.8-4.8. This phenomenon also exists in some other studies including the references 8, 14, 20, 22, 24 of our paper. Therefore, we speculate that it is reasonable.

Round 2

Reviewer 1 Report

The paper was corrected and may be published.

Author Response

Thanks! We have submitted our manuscript to MDPI for English editing. Thanks for the English editors’ comments. We have carefully checked and improved the English writing in the revised manuscript, and revised portions are marked in red.

Reviewer 2 Report

.

There are possibility of improvement.

Author Response

Thanks! We have submitted our manuscript to MDPI for English editing. Thanks for the English editors’ comments. We have carefully checked and improved the English writing in the revised manuscript, and revised portions are marked in red.