# Applications of Graphene-Based Nanomaterials in Environmental Analysis
## 3 Analytical Applications in Environmental Samples
### Applications of GO-Fe\({}_{3}\)O\({}_{4}\)
The pH was adjusted to 9-10 and kept in a water bath for 90 min at 80 \({}^{\circ}\)C. The black precipitate was rinsed with CH\({}_{3}\)OH and deionized water, until the pH attained the value of 7 and then dried in an oven at 50 \({}^{\circ}\)C. Afterwards, for the surface modification of GO-MC with 3-mercaptoppropyl trimethoxysilane (MTPS), 100 mg of the GO-MC was added in 100 mL distilled water with simultaneous sonication for 5 min. The MTPS was added drop by drop under continuous stirring for 6 h under nitrogen, at 60 \({}^{\circ}\)C. The new material was magnetically separated and washed two times with 40 mL of double distilled water and 40 mL of ethanol. Lastly, the GO-MC-MTPS was dried in an oven at 40 \({}^{\circ}\)C. The prepared nanocomposite material was characterized by SEM, FT-IR and energy dispersive X-ray spectroscopy (ED-X), to confirm the presence of -NHCO-, -CHO, -COOH, epoxy and -SH groups, to carry out morphology studies of the nanocomposite and verify the attachment of -SH groups onto GO-MC. The LODs achieved were 0.06 ng/mL and the recoveries varied from 95%-100% from the water samples. [PERSON] et al. [81] utilized a diethylenetriamine-functionalized mGO (mGO-DETA) for the extraction and determination of lead and cadmium (Pb(II) and Cd(II)) from water samples prior to FAAS analysis. The LOD of lead was 0.38 \(\upmu\)g/L and of cadmium was 0.40 \(\upmu\)g/L. The maximum adsorption capacity of the two metal ions was calculated as 172.41 and 59.88 mg/g sorbent, respectively and the recoveries were 99.2 and 103.9% for sea water samples, 98.0% and 94.4% for river water samples and 95.4 and 100.8% for well water samples. [PERSON] et al. [82; 83] used d-\(\upmu\)SPE as the extraction technique of gold and chromium (Cr(III) and Cr(VI)) ions for two different methods. For both methods, mGO was used as the sorbent and they were determined by FAAS. In the first method, under the optimum conditions, the LOD of gold ions from water and wastewater samples reached the level of 4 ng/L, with a preconcentration factor of 500. The recoveries ranged between 98.3%-102.1% for the four different water samples. In the second method, the LOD was found to be 0.1 \(\upmu\)g/L, with an preconcentration factor of 200 and the recoveries were 98.5%-102.0% for Cr(III) ions and 97.0%-102.5% for Cr(VI) ions in drinking water, river water, spring water and sea water samples. [PERSON] et al. [84] exhibited the quantitative analysis of gold from environmental water samples by using mGO in dSPE, determined via microwave plasma-atomic emission spectrometry (MP-AES). Recoveries of analytes ranged from 97%-101% and LOD was calculated to be 5 ng/L. [PERSON] et al. [85] prepared a novel triethylenetramine-functionalized mGO (TETA-mGO) composite used as a MSPE adsorbent for the swift detection of 10 trace amounts of phenolic environmental estrogens in water samples (tap water, river water, well water). Its synthesis was done in three steps: first the magnetic Fe\({}_{3}\)O\({}_{4}\) nanoparticles were prepared by a solvothermal method, then they were dispersed in acetonitrile (ACN), with the usage of an ultrasonicator. In the dispersion solutions of 10 mmol of glycidylmethacrylate and 20 mmol of divinylbenzene were added, along with a certain quantity of 2,2-azobis(2-methylpropionitrile) as the initiator. The new solution was stirred at 500 rpm under nitrogen atmosphere and heated to 70 \({}^{\circ}\)C for 3 h. Lastly, 1% of mGO in methanol solution was prepared and TETA was dissolved and stirred for 3 h at 80 \({}^{\circ}\)C. The obtained material was washed three times with methanol and vacuum dried in an oven at 25 \({}^{\circ}\)C overnight. The determination of the above analytes was done by ultra-fast liquid chromatography coupled to MS tandem MS (UFLC-MS/MS). The proposed method exhibited LODs in the range of 0.15-1.5 ng/L, which was lower than the ones reported in other studies regarding phenolic environmental estrogens, and the recoveries ranged between 88.5% to 105.6%. [PERSON] et al.