Defines a method for the determination of the mass concentration of water soluble NO[3][-] (nitrate), SO[4][2-], (sulphate), Cl[-], (chloride), NH[4][+], (ammonium), Na[+], (sodium), K[+], (potassium), Mg[2+], (magnesium), Ca[2+] (calcium) in PM[2,5] as deposited on filters.