Solution (Standard)
5 mL standard NaCl
0.4 mL s-diphenylcarbazone
Color of undeteriorated s-diphenylcarbazone
Reddish-orange
Prepared by adding 0.5 mL 2/3 N sulfuric acid and 0.5 mL 10% sodium tungstate to 1 mL serum and 8 mL distilled water
Folin-Wu protein-free filtrate
Forms a lavender-colored complex
Excess of mercuric ions
Reagents
1 Mercuric nitrate solution 2 2 N HNO3 3 S-diphenylcarbazone indicator, 0.1% 4 NaCl standard 5 H2SO4, 2/3 N 6 10% sodium tungstate
Orange precipitate formed upon dilution
Mercuric oxide
Reference range for 24 hour urine
11-250 mmol/day
Titrant
Standard mercuric nitrate solution
Procedure
1 Prepare a Folin-Wu protein-free filtrate 2 Label (2) Erlenmeyer flasks U and S and add solution 3 Using a 2 mL serological pipette, titrate both U and S to the lavender end point with mercuric nitrate solution and record the mL required to obtain the end point for each specimen
Indicator
s-diphenylcarbazone
Stability of indicator if stored in a brown bottle
Approx. 3-4 weeks
Product of reaction of chloride with mercuric ions
Soluble but undissociated mercuric chloride
Method
Schales and Schales Method
Solution (Unknown)
5 mL PFF
0.4 mL s-diphenylcarbazone
Principle
The sample is titrated with standard mercuric nitrate solution at the proper pH, in the presence of an indicator (s-diphenylcarbazone). The chloride present reacts with the mercuric ions in the mercuric nitrate solution to form soluble but undissociated mercuric chloride. When an excess of mercuric ions has been added a lavender-colored complex is formed. This is a mercurimetric procedure utilizing a direct titration.
Calculations
- (mL Hg(NO3)2 required to titrate unknown/mL Hg(NO3)2 required to titrate standard) x 5 mg/mL x 100/0.5 = mg Cl as NaCl/100 mL
- Serum Cl = (mg % Cl x 10)/58.5
- mg % Cl as NaCl x 10 = mEq/L
Reference range for serum, plasma
98-107 mmol/L