DISCRETE ANALYZER CHEMISTRY Chloride (Cl - ) Method
Methods Referenced • Standard Methods 4500-Cl - E — Automated Ferricyanide Method • EPA Method 325.2 — Chloride by Automated Colorimetry AKA Colorimetric, Automated Ferricyanide AAII Method Range 2.0 – 100 mg Cl/L Reagent Composition Final reagent is made from the following sub-solutions: 1. Ferric nitrate, Fe(NO 3 ) 3 2. Mercuric thiocyanate, Hg(SCN) 2 Sub-solutions are combined to create the only reagent used for the Cl - method.
Final concentrations are as follows: SEALAnalyticalAQ Chloride Rgt • 0.6255 g/L Mercury (II) thiocyanate • 30.3 g/L Iron (III) nitrate nonahydrate Or • 1.974 mmol Hg +2 • 3.943 mmol (SCN) - • 75 mmol Fe+3 Chemical Reactions Fe +3 + Hg(SCN)
Note: We recommend using ICCL1 to make your standards check solutions for this method.
2 + Free Cl- HgCl 2 + Fe
+3 + 2SCN- HgCl
2 + Fe(SCN) 3
The thiocyanate ion (SCN - ) is liberated from mercuric thiocyanate through sequestration of mercury by chloride ion to form un-ionized mercuric chloride in the presence of ferric ion, the liberated SCN - forms highly colored ferric thiocyanate in concentration proportional to the original chloride concentration. Balanced Reaction 12Cl- + 6Hg(SCN) 2 + 4Fe +3 6HgCl 2 + 4Fe(SCN) 3 Note: Calculations using the limiting factor of Hg +2 (by moles) show that this reagent can react with a maximum of ~140 mg/L free chloride.
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