Microwave-induced combustion of graphene for further determination of elemental impurities using ICP-OES and TXRF
An analytical method of microwave induced combustion (MIC) combined with ICP-OES and TXRF is proposed to determine elemental impurities in graphene. Optimized MIC conditions (e.g. sample mass up to 30 mg, microwave irradiation 900 W for 10 min, and oxygen pressure 2 MPa) can achieve the rapid and complete digestion of graphene. Analytical results show that this method can accurately determine elemental impurities such as S, Fe, Cr, Mn and Ni in graphene, and that ICP-OES and TXRF data are comparable. The validity of this method is also verified using three different CRMs for cellulose nanocrystal powder and single-wall carbon nanotubes. The limits of detection (LODs) using MIC combined with ICP-OES are 5.4, 10.6, 7.3, 0.7 and 2.7 μg kg−1 for Fe, S, Cr, Mn and Ni, respectively. The LODs using MIC coupled with TXRF are 30.2, 215, 21.3, 9.5 and 15.8 μg kg−1 for Fe, S, Cr, Mn and Ni, respectively. The experimental results are also compared with those from three other pretreatment methods including dry ashing coupled with acid digestion (DA-AD), microwave-assisted digestion (MWAD) and DA-MWAD, which shows that MIC is superior to the other procedures due to the incomplete digestion and/or escape of volatile S of the latter. The MIC digestion combined with ICP-OES or TXRF could be one of the most promising procedures for the accurate determination of some elemental impurities in carbon nanomaterials with stable structures like graphene.