Synthesis and application of microporous carbon spheres for solid phase membrane tip extraction of nitrosamines from water samples

Abstract

Microporous carbon spheres possess outstanding adsorptive properties and thus are advantageous in the development of solid phase microextraction sample preparation techniques. In this study, the feasibility of using microporous carbon spheres for the extraction of selected nitrosamines from water samples using solid phase membrane tip extraction (SPMTE) technique was investigated. Two types of adsorbents namely non-activated carbon spheres (NCS) and chemically activated microporous carbon spheres (MCS) were hydrothermally synthesized from sucrose. The prepared adsorbents were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), nitrogen adsorption analysis, transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). Both adsorbents were spherical in shape as indicated by SEM. The FTIR spectra showed that the NCS and MCS have various surface functional groups such as OH, C=C and C-H which act as active sites. The surface areas of NCS and MCS are 7.88 and 308.10 m2/g, respectively as obtained from nitrogen adsorption analysis. The two prepared materials and a commercial activated carbon (granular activated carbon, GAC) were used in SPMTE to extract the selected nitrosamines namely Nnitrosodiethylamine (NDEA), N-nitosodipropylamine (NDPA), N-nitrosopiperidine (NPIP) and N-nitrosodiphenylamine (NDPhA) from tap water and lake water matrices. Gas chromatography-mass spectrometry (GCMS) was used for quantitative analysis of the target analytes in the extracts. The optimized SPMTE conditions were conditioning solvent, extraction time, salt addition, pH, desorption solvent, desorption time and sample volume. Under the optimized conditions, the method showed good linearity in the range of 10 - 100 µg/L, good coefficients of determination (r2 = 0.9984 - 0.9994), good precision (relative standard deviations, RSD < 9%, n = 3) and low limits of detection (LOD = 3.2 - 4.8 µg/L) for all the adsorbents. The extraction performance of each adsorbent was evaluated and compared in terms of percent recovery. The results showed that MCS gave better percent recovery in the range of 83.2 - 107.5% than both NCS (65.5 - 100.3%) and GAC (69.7 - 100.9%). This infers that MCS offered improved extraction efficiency and higher recovery of the tested nitrosamines compared to conventional activated carbon.