# Applications of Graphene-Based Nanomaterials in Environmental Analysis
## 3 Analytical Applications in Environmental Samples
### Applications of GO-Fe\({}_{3}\)O\({}_{4}\)
The preparation of the material consisted of the following steps: firstly, 0.1% of GO aqueous dispersion was prepared, under ultrasonication for 3 h. A certain amount of (NH4)2 Fe(SO4)2-6H2O and FeCl3 was added to the dispersion under a stream of nitrogen. To dissolve the salts, 8 mol/L NH4 OH was added dropwise under sonication for 10 min and the reaction was carried out at 50 \({}^{\circ}\)C for 30 min. The mGO was separated by using a strong magnet and it was rinsed with deionized water and ethanol. The obtained material was suspended in an aqueous solution that also contained ethanol and NH4 OH. Then, tetraethyl orthosilicate was put into the suspension under continuous agitation for 12 h at 40 degrees Celsius. After separating it with a magnet and rinsing it, the new material (GO@Fe3O4@SiO2) was dispersed in a certain volume of dried C6H5 CH3 and (3-chloropropyl)-triethoxysilane (CPTS) was put into the mixture under reflux for 24 h. Meanwhile, a solution of thiocarbamate imidazole was synthesized by combining 1-(3-aminopropyl)imidazole and carbon disulfide and agitating it for 3 h at room temperature. A fixed mass of GO@Fe3O4@SiO2@CPTS was dispersed in a solution of methanol:triethylamine (volume ratio 1:1) and a certain amount of the other compound was added under reflux for another 24 h. Separated by a magnet, rinsed with methanol and ethanol and dried at 50 \({}^{\circ}\)C, the material was lastly mixed with \(n\)-bromobutane under stirring and a nitrogen atmosphere for 24 h at 80 \({}^{\circ}\)C. Finally, the adsorbent was once again separated with a strong magnet and rinsed with tetrahydrofuran and vacuum dried. The LODs of the two Cr ions altogether were 1.9 ng/L, the sorption capacity of the sorbent was 304 mg/g and the preconcentration factor was 357. [PERSON] et al. [95] presented a method for the determination of di-2-ethylhexyl phthalate (DEHP) by HPLC-DAD in different environmental water samples, using MSPE as an extraction technique and mGO as the sorbent. The process of the extraction is as follows: 0.05 g of mGO were added to 200 mL of the water sample that contained the analyte and the solution pH was modified to the value of 7. After shaking for 25 min, the mGO was separated from the mixture with the use of a strong magnet. The adsorbed analyte was eluted with 2 mL of CH3 OH. The obtained recovery rates were 91.6%-106.5% and the LOD of DEHP was 0.35 \(\mu\)g/L. Most applications on magnetic graphene-based nanomaterials are on tap, river, sea and wastewater samples, examining either the trace amounts of certain metal ions or the concentration of organic pollutants. These materials, also, demonstrate pretty high enrichment factors and very low LODs, in the range of a few ng/L-ug/L. A summary of the above works and methods can be found in Table 2. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**adsorbent** & **Analyte(s)** & **Applications** & **Sample Preparation** & **Analytical Technique** & **LODs** & **EF** & **Reference** \\ \hline mGO & PAHs & Tap, river, sea & MSPE & HPLC-UV & 0.09-0.19 \(\mu\)g/L & 25 & [76] \\ mGO & PCB 28 & School sewage, & MSPE & GC-MS & 0.027–0.059 \(\mu\)g/L & 200 & [77] \\ mGO & Sulfonamides & Tap, river water & MSPE & HPLC-DAD & 0.05–0.10 mg/L & N/R & [78] \\ mGO-porphyrin & Sulfonamides & Tap, river water & MSPE & HPLC-DAD & 0.2 mg/L & N/R & [79] \\ GO-MC-MTPS & Hg(II) & Tap, sea water & MSPE & CV-AAS 1 & 0.06 \(\mu\)g/L & 80 & [80] \\ mGO-DETA & Cd(II), Pb(II) & Sea, river, wall & MSPE & FAAS & 0.40, 0.38 \(\mu\)g/L & 150, 167 & [81] \\  & Cr(III), Cr(VI), & Drinking, river, & & & & 0.1, 0.1, & 200, 200, & [82; 83] \\ mGO & Au(III) & supra & & & & 0.004 \(\mu\)g/L & 500 & [84] \\ mGO & Au(III) & Tap, lake, sea water & dSPE & MP-AES & 5 ng/L & 60 & [84] \\ TETA-mGO & Phenolic estrogens & Tap, river, wall & MSPE & UFLC-MS/MS & 0.15–1.5 ng/L & 10,000 & [85] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Main applications of magnetic graphene-based nanomaterials in environmental samples analysis.