Ghorbani, Azam, et al. “Determination of Some Trace Elements in Natural Waters by Atomic Absorption Spectroscopy After Preconcentration by XAD-4 GBHA System”. Asian Journal of Chemistry, vol. 23, no. 9, June 2011, pp. 4202-4, https://asianpubs.org/index.php/ajchem/article/view/10819.