Pengaruh Anion, Asam Humat dan Fosfat organik terhadap pengikatan Ortofosfat oleh binding gel perangkat DGT (Diffusive Gradient in Thin Film) dengan TiO2 = The effect of Anion, Humic Acid and Organic Phosphorus on the adsorption of Orthophosphate on Titanium Dioxide based DGT (Diffusive Gradient in Thin Film) technique for Phosphate measurement