Chloride
Definitive Method: Isotope Dilution Mass Spectrometry
Reference Method: Coulometric Titration.
Common Method:
Ion Selective Electrode (ISE); Example Shown Component of Bayer 800 series Blood gas Analyser.

Derivitized Quaternary Ammonium compound in a polymer matrix

~2% CV.

Other Methods:

Mercuric/Ferric thiocyanate Quantitative endpoint Good accuracy and precision
Coulometric Titration Quantitative Titration, Endpoint Reference Method
Highly Accurate
Ion selective electrode Silver Chloride /Silver Sulphide sensing element More common now
Good accuracy and precision.
Isotope Dilution Mass Spectrometer
Dilution of common isotopes with 37Cl 		Definitive method





Mercuric/Ferric thiocyanate

Formerly a common method:

Quantitative displacement of thiocyanate by chloride from mercuric thiocyanate and subsequent formation of red ferric thiocyanate, complex which is measured colorimetrically at 525nm

2Cl- + Hg(SCN)2 ==> HgCl2 + 2(SCN)-

3 (SCN)- + Fe 3+ ==> Fe(SCN)3 (red) -Amax 525nm





Coulometric Titration:

Reference method. Quite commonly used. Retired from RPH in 1995.

Cl- ions in the reaction chamber precipitate the Ag+ ion being produced by the silver anode. The current runs through the main circuit whilst the Ag+ continue to be precipated. Free Ag+ ions are detected by another circuit which can turn the other circuit on (when Ag+ disappears) or off (when Ag+ is detected) The time taken to precipitate the available Ag+ with Cl- is measured and compared to a calibration.