106.3.2.56 TM-56, Determination of Sodium Metasilicate (Na2SiO3)

This method determines the percent of anhydrous sodium metasilicate (Na₂SiO₃) in automotive antifreeze by Atomic Absorption Spectrophotometry.

106.3.2.56.1 Reagents and Apparatus

1) An Atomic Absorption Spectrophotometer.

2) Potassium Chloride (KCl), Reagent Grade.

3) Ethylene Glycol, Reagent Grade.

4) Silicon Standard Solution, 1000 ppm. This solution can be purchased from a number of sources.

106.3.2.56.2 Preparation of Standard Solutions

0,000 ppm Potassium Stock Solution: Weigh 19.068 g of dried, reagent grade KCl into a 1000-mL volumetric flask, dissolve, and dilute to volume with distilled water.

152% Na₂SiO₃ Standard: Pipette a 20-mL aliquot of 10,000 ppm K stock solution and a 7-mL aliquot of 1000 ppm Si standard solution into a 200-mL volumetric flask. Add 20.00 g of reagent grade ethylene glycol and dilute to volume with distilled water.

0.109% Na₂SiO₃ Standard: Pipette a 20-mL aliquot of 10,000 ppm K stock solution and a 5-mL aliquot of 1000 ppm Si standard solution into a 200-mL volumetric flask. Add 20.00 g of reagent grade ethylene glycol and dilute to volume with distilled water.

Blank Solution: Pipette a 10-mL aliquot of 10,000 ppm K stock solution into a 100-mL volumetric flask. Add 10.00 g of reagent grade ethylene glycol and dilute to volume with distilled water.

106.3.2.56.3 Procedure

Weigh, to the nearest 0.1 mg, 10 ± 0.05 g antifreeze into a 100-mL volumetric flask. Pipette a 10-mL aliquot of 10,000 ppm K stock solution into the volumetric flask and dilute to volume with distilled water.

Calibrate the instrument with the blank solution, the 0.109% Na₂SiO₃ solution and the 0.152% Na₂SiO₃ solution, then determine the concentration of the sample solution.

106.3.2.56.4 Calculation and Report

The method of calculating the % sodium metasilicate will vary according to the make and model of instrument used.

Report the results to the nearest 0.01% Na₂SiO₃ as follows:

% Sodium Metasilicate (Na₂SiO₃), anhydrous