Self-Assembled Three-Dimensional Microporous rGO/PNT/Fe₃O₄ Hydrogel Sorbent for Magnetic Preconcentration of Multi-Residue Insecticides

Round 1

Reviewer 1 Report

The manuscript entitled: „Self-assembled three-dimensional microporous rGO/PNT/Fe3O4 hydrogel sorbent for magnetic preconcentration of multi-residue insecticides” describes a very interesting study on the development of a new method for insecticides detection. The optimized method is characterized by good sensitivity, linearity and precision. The manuscript contains some language mistakes, but in general, is well-written and my only comments are more editorial. Please use the journal template file, the manuscript is not formatted according to journal requirements. Please, be sure that all the abbreviations are explained in the first use. The discussion of “optimization of extraction condition” would be recommended. Why do the authors think, these parameters had or had no influence on the efficiency of extraction.

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Reviewer 2 Report

The manuscript is very well put together with all the necessary experiments. I 

Author Response

Thank you very much for your hard work. 

Reviewer 3 Report

The article is clearly and well written.

I would give following comments to authors:

1. The aim should be clearly defined in the abstract.
2. Page 3, lines 1-3. The following reference can be added about the use of graphene oxide:Jamróz, E., Kopel, P., Tkaczewska, J., Dordevic, D., Jancikova, S., Kulawik, P., Milosavljevic, V., Dolezelikova, K., Smerkova, K., Svec, P. and Adam, V., 2019. Nanocomposite Furcellaran Films—the Influence of Nanofillers on Functional Properties of Furcellaran Films and Effect on Linseed Oil Preservation. Polymers, 11(12), p.2046.
3. Page 4, line 9, the synthesis of Fe₃O₄ should be described in detail.
4. Statistical methods are not described in the method part.
5. Figure 3, some satistical analysis can be done, such as ANOVA, maybe principal component analysis.
6. Table 1, the regression was not described in the method part.
7. Table 2. standard deviation can be included? 

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Reviewer 4 Report

Authors proposed a three-dimensional microporous reduced graphene oxide / polypyrrole nanotube / magnetite hydrogel (3D-rGOPFH) composite for the magnetic solid-phase extraction (MSPE) of insecticides from vegetables. The extracts were analysed by gas chromatography-tandem mass spectrometry. 3D-rGOPFH was characterized by means microscopic and spectroscopic techniques. The extraction was optimized in terms of several parameters, such as desorption solvent, desorption time, extraction time, and sorbent amount. The method was also submitted to a validation and some performance parameters were evaluated. The method potential was assessed by the analysis of vegetable samples.

 

Despite of the very good limits of detection and quantitation as well as recoveries and precision obtained by the proposed approach, the following important limitations are present, and they must be improved before publication.

• 3D-rGOPFH were already synthesized and proposed as extraction-cleanup systems in previous papers (see paragraph 2.2 and refs. 26, 27). Authors should clearly indicate along the manuscript, and in particular, in the abstract and in the introduction section, that 3D-rGOPFH preparation was carried out by a previous published procedure. Moreover, Authors should remark that graphene-based magnetic composites were already proposed as extraction-clean-up systems for pesticides in previous papers (see refs. 26, 27 and in particular the review of ref. 7 with several papers quoted therein). The Authors should also evidence the improvement of the proposed approach, in particular with respect to refs. 26 and 27 that were not mentioned in table 3 and discussed in the paragraph 3.5, as well as with respect to papers quoted in ref. 7, such as Wang et al., J. Sep. Sci. 35 (2012) 2266 and Wang et al. Anal. Methods 6 (2014) 253.

 

• Some claims even those about the possible drawbacks of conventional extraction clean-up systems (e.g. QUECHERS) in comparison with the proposed method are not supported by experimental data or papers from the literature. For instance at lines 20 -22 of pag. 2, Authors assert that conventional “methods often require excessive organic solvents, a time-consuming operational process, or limited clean-up ability with restrictions in no concentration factors.” On the contrary, several conventional methods including those based on QUECHERS did not show the above mentioned disadvantages (see e.g. Analytical Chemistry Volume 80, Issue 24, 15 December 2008, Pages 9450-9459; Analytical Chemistry Volume 97, Issue 11, 2 September 2017, Pages 1003-1023), and the method used by the Authors is not as fast as claimed (40 min necessary only for the steps of adsorption and desorption) and requires the use of organic solvents in the order of millilitres.“Comparison of the developed method with others reported in the literature” should be improved by mentioning and discussing the reasons for using 3D-rGOPFH in place of conventional method such as QUECHERS based methods that show similar or better performances. Lines 15 -19 at pag. 3 - The most part of phenols, esters, acids, and alcohols, as potential interferences in vegetable matrices, are monomers with molecular weights and then sizes lower than pesticides. Moreover, the references 19, 20 and 21 quoted by the authors, to support the idea of using proper pore size structured materials to reduce the matrix effects, are not pertinent.

 

• In the method validation, the evaluation of some performance parameters was carried out in an incorrect manner. As it is well documented in important regulation about validation of analytical methods for the analysis pesticides (see for instance EC 657/2002 and SANCO 2013 quoted as ref. 28), spiking levels for precision, and recoveries determination should be as low as possible and around (1, 1.5 and 2 times) the method performance level (LOQ, i.e. 0.02-0.1 ng/g). The use of levels of about 50 - 250 times higher (i.e. 5, 25 and 50 ng/g) certainly allow very better precision (repeatability and reproducibility) and recoveries performance parameters. Therefore, the determination the above mentioned performance parameters at spiking levels around LOQ are compulsory.

 

Minor remarks

 

• Class of pesticides used in the present study should be reported in the abstract.

Author Response

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Round 2

Reviewer 3 Report

In the method part regresion should be mentioned in the part where statistical analysis are described.

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