Total chorine is determined in solid materials according to ASTM International Method D6721 – Standard Test Method for the Determination of Chlorine in Coal by Oxidative Hydrolysis Microcoulometry. Samples are burned in a hydrated argon/oxygen atmosphere. The resulting chloride is led into a titration cell where it is automatically titrated by silver ions generated coulometrically. The amount of chlorine is then calculated from the quantity of electricity required for the titration.

HCl + Ag⁺ –> H⁺ + AgCl (titration)
Ag –> Ag⁺ + e^- (electrolysis)
Coal and combustion residues are the main applications for this method; however, other applicable materials include crude oil, cement, biomass, and rubber. The lower limit of quantitation for this method is 5 µg/g.