Fluoride

FLUORIDE
Method - SPANDS

Principle

The SPANDS Colourimetric method is based on the reaction between Fluoride and a
Zirconium dye lake. Fluoride reacts with the dye lake dissociating a portion of it into a
colourless complex anion (ZrF6-) and the dye.

Reagents

Spand Solution: - Dissolve 968 mg SPANDS i.e Sodium 2 –parasulfophenylazo 1, 8
Dihydroxy – 3, 6 Naphthalene Disulfonate to 500 ml distilled water. This solution is stable
for at least 1 year if protected from direct sunlight.

Ziroconyl-Acid Reagent: - Dissolve 133 mg Zirconnyl chloride octahydrate, ZrOCl2, 8H2O, in
about 25 ml distilled water. Add 350-ml concentrate HCI and dilute to 500 ml with distilled
water.

Acid Ziroconyl-SPANDS Reagent: - Mix equalvolumes of SPANDS solution and Ziroconyl
reagent. The combined reagent is stable for at least 2 years.

Standard Sodium Fluoride: - Dissolve 0.221 gm of dry sodium fluoride in distilled water and
make up to 1000 ml. Dilute 100 ml. Of solution to 1000 ml one millimeter of this diluted
solution contains 0.01 mg of fluoride. This solution shall be kept in Polyethylene or wax-lined
glass bottles.

Procedure
1. Take 50 ml sample or a portion diluted to 50 ml with distilled water
2. Add 5 ml each of spands solution and Ziroconyl-acid reagent or 10.0 ml acid Zirconyl
spands reagent.
3. Mix well and read absorbance at 570 nm.

Calculation
Mg F-/L = A/ml sample x B/C

Where,
A = g – determined from plotted curve
B = Final volume of diluted sample ml.
C = Volume of diluted sample ml.