Removing Chloride Interference in Total Carbon Analysis

Chloride ions in water samples (e.g., seawater, brines, or industrial effluents) can severely interfere with total carbon (TC) determination by high-temperature combustion methods. 

During oxidation at 680–1200 °C, chloride may react to form chlorine or hydrogen chloride, which corrodes the catalyst and detector, while also causing positive or negative spikes in the non‑dispersive infrared (NDIR) signal. To obtain accurate TC results, several effective elimination strategies have been developed.

The most common approach is chemical masking using silver nitrate or mercuric salts. Adding AgNO₃ to the sample precipitates chloride as insoluble AgCl, which is removed by filtration or centrifugation before combustion. This method works well for chloride concentrations up to 20 g/L but introduces extra handling steps and potential silver residues. Alternatively, a pre‑oxidation purge with acidified persulfate can strip out volatile chloride species, though this may also remove some volatile organic carbon. 

For online or routine analysis, ion‑exchange cartridges (silver‑form or hydrogen‑form resins) placed upstream of the combustion tube offer a clean, automated solution. Another advanced technique is using a high‑temperature ceramic reactor with a platinum catalyst that tolerates moderate chloride levels (<5 g/L) without pretreatment.

In practice, the choice depends on sample matrix and required precision. For most environmental waters (chloride <2 g/L), a silver‑resin guard column is sufficient. For high‑chloride industrial samples, chemical precipitation followed by dilution is recommended. 

Regardless of the method, a matrix‑matched calibration and regular validation with spiked samples are essential to confirm interference removal. With proper chloride elimination, reliable total carbon determination can be achieved even in challenging saline waters.