# Applications of Graphene-Based Nanomaterials in Environmental Analysis
## 3 Analytical Applications in Environmental Samples
### Applications of \(G\) and \(G\)
[63] covalently bonded GO nanosheets to spherical silica via the coupling of the -NH\({}_{2}\) groups of the spherical amino-silica with the -COOH groups of GO (GO@SiO\({}_{2}\)),which was validated by electron microscopy and X-ray photoelectron spectroscopy, for its usage in SPE to determine Pb(II) and Cu(II) by FAAS from water samples. The water samples were filtered through a 0.45 mm cellulose acetate membrane and put in storage at 4 \({}^{\circ}\)C. Before each extraction, the cartridge was rinsed with an acetate buffer solution to pH 5.5, as well as the analyzed solution with the addition of 0.1 mol/L HNO\({}_{3}\) and NH\({}_{3}\). The two metal ions were eluted from the cartridge with the addition of 2 mL of 1 mol/L HNO\({}_{3}\). The recoveries of Cu(II) and Pb(II) were 98.7 \(\pm\) 0.9% and 95.2 \(\pm\) 1.0% respectively, while the LODs were 0.084 and 0.27 ng/mL. [PERSON] et al. [64] used an ethylenediamine-modified GO (GO-EDA) for the preconcentration of Cu(II), Zn(II), Fe(III), Ni(II), Co(II) and Pb(II) in water samples. The target metal ions were adsorbed onto GO-EDA by d-\(\upmu\)SPE, then the solution was filtered and the filter paper was exposed directly to energy dispersive X-ray fluorescence spectrometry (ED-XRF). The limits of detection of the six metals were calculated as 0.08, 0.06, 0.07, 0.07, 0.10 and 0.10 ng/mL, respectively and their recoveries from the analyses from real samples were in the range of 92-110%. In a different study, [PERSON] et al. [65] proposed a new and green method of sample preparation by using GO in dispersive micro-solid phase extraction (d-\(\upmu\)SPE) for the preconcentration of trace amounts of Co(II), Ni(II), Zn(II), Cu(II) and Pb(II) of water samples determined by energy dispersive X-ray fluorescence spectrometry (ED-XRF). The GO was dispersed in aqueous samples containing the above-mentioned elements and during stirring, metal ions were sorbed onto GO. Later, the solution was filtered under vacuum and the sorbent with the adsorbed metal ions was collected onto a membrane filter. Finally, the obtained samples were analyzed directly by ED-XRF. This procedure demonstrates low LODs, 0.5, 0.7, 1.8, 1.5 and 1.4 ng/mL, respectively for each metal ion and the recoveries ranged between 94-106%. [PERSON] et al. [66] studied the preconcentration and determination of trace amounts of Ni(II) and Co(II) ions by FAAS, after their extraction with GO on column SPE in water samples. The adsorption on GO was achieved at pH 6.0 and then the target compounds were eluted with 3 mol/L nitric acid. Experimental conditions for the optimal separation of the analyte ions such as concentration of eluent, sample volume, pH, flow rate and interference ions were investigated. An enrichment factor of 250 was achieved, whilst the LODs of Ni(II) and Co(II) were found to be 0.18 and 0.25 ng/mL, respectively. [PERSON] [67] utilized GO nanoparticles for the d-\(\upmu\)SPE of heavy metals as their complexes with 2-(5-bromo-2-pyridyllazo)-5-diethylaminophenol (5-Br-PADAP) in water samples. The heavy metals examined in this study were Cr(III), Co(II), Ni(II), Cu(II), Zn(II) and Pb(II) ions and their determination was achieved by ED-XRF. Under optimum conditions, the LODs ranged from 0.07 to 0.25 ng/mL and the recoveries of the ions in water and spiked water samples were 94.4-103.5%. In an additional study, [PERSON] et al. used glycine modified GO (GO-Gly) as a new sorbent for the preconcentration of chromium, zinc and copper ions from water samples, prior to ED-XRF determination. 500 mg/mL GO-Gly mixture were added to an aqueous sample and the pH of the sample was modified to 6 by adding 0.1 mol/L NH\({}_{3}\)-H\({}_{2}\)O and the solution was agitated for 10 min. The analyzed sample was put through a membrane filter with the use of vacuum. This filter containing GO-Gly and the adsorbed ions was air-dried and then immediately measured using the ED-XRF [68]. Furthermore, in a third study, [PERSON] et al.