This technique consists in sampling at the source of emissions and transferring the samples to the laboratory for processing and analysis. The group has two laboratories equipped with advanced analytical techniques that give it a wide analytical capacity. Among the techniques available are the following: Flame Atomic Absorption Spectrophotometer to analyse heavy metals (Cu, Ni, Zn, Cd, Cr, Pb, Co, Mn, Fe, etc); Ion Chromatograph for analysis of anions (Cl-, NO3-, SO42-, PO42-, etc), and cations (NH4+, K+, Na+, Ca2+, Mg2+, etc. ); UV-Visible Spectrophotometry to determine organic matter (COD), nitrogen (NT), total phosphorus (TP), sulphide (S2-), sulphite (SO3-), etc. Total organic carbon (TOC) and inorganic carbon (IC) analyser; automatic titrator to analyse volatile acids and alkalinity; instruments to determine the concentration of solids (total, suspended, volatile); portable pH, conductivity and dissolved oxygen meters.