On-line micro solid phase extraction of atrazine from real water samples by imprinted silica nanofibers

Sol composition and ripening condition are two important parameters in silica fibers production through the conventional sol-gel process [1]. In the current study, silica nanofibers were obtained successfully by electrospinning technique and sol-gel formation was performed during this process. Pirzada et al. have reported hybrid silica-PVA nanofibers via sol-gel electrospinning [2]. In this regards, with the aim of increasing the selectivity, we used the molecular imprinted methodology to produce the selective media via sol-gel electrospinning. In this process, sol-gel was formed during electrospinning and then the backbone polymer was removed by heating. To obtain a thin layer of silica nanofiber, the influencing parameters such as backbone polymer types, imprinting time and material ratio were explored. Then, the extraction parameters on online -solid phase extraction were optimized. First, to find the suitable backbone to produce electrospun silica nanofiber the polymer type and concentration were examined and polyamide (PA) showed the best results in electrospinning process and was easily removed by heating. So, the silica precursor was added to the solution of atrazine in acetonitrile (I), and solution of PA in formic acid (II). The ratio of these two solutions for electrospinning was explored, as well. To increase the selectivity and MIP/NIP ratio, the mixture was stored in different times and to let the atrazine template to settle in appropriate spaces. After electrospinning, the PA moiety was removed by heating. To do this, the nanofiber sheet was placed in the oven for 12 h and a control PA nanofiber mat was also fabricated under the same situation. After 2 h, the whole part of PA was quite burnt and disappeared. Finally, the thin silica nanofibers were produced. FT-IR and TGA analyses revealed that the PA is removed after heating and the SEM images indicate the geometry of the silica nanofibers. The extraction efficiency of the electrospun silica nanofibers mat was compared with the same silica precursor sol-gel by two other methods, bulk, and electrochemical synthesis by online -SPE LC-UV method. The data showed higher extraction efficiency for silica nanofibers. The linearity of the analyte was in the range of 6-400 g L-1. LOD was found to be 1.8 g L-1 and the inter- and intra-day RSD% were less than 9.6%. The method was conveniently applied to Zayanderud and tap water samples spiked with atrazine, while the relative recovery percentages for the standard samples were up to 92%.