[Sayeh]

Hi everyone,
I am not sure if it is the right forum to post this question in. I need the measure the mass of silica (SiO2) in a solution and am wondering if anyone can suggest a reliable method.
Many thanks in advance!

[JGK]

Mass of solution  :rarrow:Filtration (on pre-wighed filter) Dry solid material on filter and reweigh


% in solution = (Mass solid on filter /mass solution) x 100

[Sayeh]

Mass of solution  :rarrow:Filtration (on pre-wighed filter) Dry solid material on filter and reweigh


% in solution = (Mass solid on filter /mass solution) x 100

Thanks for the answer. But I am dealing with very small amounts of silica nanoparticles and also I have other materials in my solution so filtration is not an option for me. Would a technique like mass spectrometry work for me?

[JGK]

Are these "other materials" Combustable ?


If so:

Mass of solution placed in a pre-weighed crucible and heated until constant weight achieved

[walterVB]

Have a spectrophotometric method available for Si:
-in boilerwater : up to 0.01 mg/l
-in any solution : up to 5 mg/l

walterVB

[Sayeh]

I would appreciate if you can provide more information. Do you think it would work for silicon dioxide (silica) as well? Although I am working with concentrations up to than 50 ug/ml.

Have a spectrophotometric method available for Si:
-in boilerwater : up to 0.01 mg/l
-in any solution : up to 5 mg/l

walterVB

[walterVB]

Photometric analysis for Si in solutions

Principle     Si-molybdate is reduced to the blue coloured complex

Reagents      * HF/HCl(1:4) : 500 ml HF + 2000 ml HCl
               * Molybdate-solution :  100 g boric acid dissolved in about 3 liter H2O
         25 g (NH4)6Mo7O24.4H2O dissolved in 200 ml H2O (heat!)
                      Transfer to a 5 liter volumetric flask; fill up to the mark
               * Reducing-solution : 100 g Na2S2O5 + 4 g Na2SO3 in 1 liter of H2O
                                            + 2 g 1.2.4.amino-naphtol-sulfonic acid; mix till clear solution
               * Standard Si-solution (100 mg/l) : 107 mg SiO2 (grinded quarts) in a 500 ml
         polyethylene flask + 100,- ml HF/HCl(1:4); shake for 4 hours, then leave for the night;                   
                       + 400,- ml H2O; mix well.

Procedure     1,- ml of sample ( max 3 mg Si) in a 100 ml polythylene pot + 5,- ml HF/HCl(1:4)
               Close and shake for at least 2 hours on a shaking table, then leave for the night
               + 20,- ml H2O (with dispensor); mix well
               1,- ml of the solution is pipetted into a 100 ml polyethylene flask
               (if Si in sample >3 mg :    or  0.5 ml + 0.5 ml of blank
                          or  0.2 ml + 1.0 ml of blank)
               + 45 ml Molybdate-solution (with dispensor)
               After 15 min : + 2 ml reducing-solution
               Colorimetry after 15 min against a blank :

                       Wavelength : 820 nm
                       Scale : 10 - 120 µg Si

Good luck,
walterVB

[Stepan]

How do we know that it is silica, and not a silicate?

[el13]

EPA Method 370.1:
Silica by Colorimetry. Official Name: Silica, Dissolved (Colorimetric)

Summary:
A well-mixed sample is filtered through a 0.45 um filter. The filtrate, upon addition of the molybdate ion in acidic solution, forms a greenish-yellow complex proportional to the dissolved silica concentration, and its absorbance is measured spectrophotometrically. If concentrations of silica are exceptionally low, the greenish-yellow complex is reduced to a more intense heteropoly blue complex using 1-amino-2-naphthol-4-sulfonic acid.

Scope:
This method determines silica in drinking, surface, and saline waters; domestic and industrial wastes.

Citation:
Methods for the Chemical Analysis of Water and Wastes (MCAWW) (EPA/600/4-79/020)

Interferences:
(A) Color/Turbidity: Correct for color or turbidity error by running blanks prepared without addition of the ammonium molybdate color reagent solution.(B) Tannin and phosphates: Interferences can be reduced or eliminated with oxalic acid.(C) Iron and sulfide: Iron and sulfide will interfere.(D) Contamination: Use silica-free reagents and minimize contact with glass. A blank also should be run.

[walterVB]

My spectrometric method for analysis of Si measures the concentration of TOTAL Si (dissolved and undissolved).
I have an other method that measures the Si dissolved in water, for lower concentration (up to 0,01 mg/l).

walterVB

[Stepan]

Mass of solution  :rarrow:Filtration (on pre-wighed filter) Dry solid material on filter and reweigh


% in solution = (Mass solid on filter /mass solution) x 100

Thanks for the answer. But I am dealing with very small amounts of silica nanoparticles and also I have other materials in my solution so filtration is not an option for me. Would a technique like mass spectrometry work for me?

What I am trying to say that if the silica particles are indeed nano-particles, they go through the 0.45um filter with no trouble at all. Also, the colorimetry test gives total Si - no matter if it is silica or silicate (let say dissolved glass from the glassware).

In results - you may have very wrong result: 100% loss if you analyse the filter (because filter does not retain anything), or 100% overestimation if you analyse filtrate (you might have no SiO2, but 100% SiO3-- and other ions).   

[Sayeh]

Photometric analysis for Si in solutions

Principle     Si-molybdate is reduced to the blue coloured complex

Reagents      * HF/HCl(1:4) : 500 ml HF + 2000 ml HCl
               * Molybdate-solution :  100 g boric acid dissolved in about 3 liter H2O
         25 g (NH4)6Mo7O24.4H2O dissolved in 200 ml H2O (heat!)
                      Transfer to a 5 liter volumetric flask; fill up to the mark
               * Reducing-solution : 100 g Na2S2O5 + 4 g Na2SO3 in 1 liter of H2O
                                            + 2 g 1.2.4.amino-naphtol-sulfonic acid; mix till clear solution
               * Standard Si-solution (100 mg/l) : 107 mg SiO2 (grinded quarts) in a 500 ml
         polyethylene flask + 100,- ml HF/HCl(1:4); shake for 4 hours, then leave for the night;                   
                       + 400,- ml H2O; mix well.

Procedure     1,- ml of sample ( max 3 mg Si) in a 100 ml polythylene pot + 5,- ml HF/HCl(1:4)
               Close and shake for at least 2 hours on a shaking table, then leave for the night
               + 20,- ml H2O (with dispensor); mix well
               1,- ml of the solution is pipetted into a 100 ml polyethylene flask
               (if Si in sample >3 mg :    or  0.5 ml + 0.5 ml of blank
                          or  0.2 ml + 1.0 ml of blank)
               + 45 ml Molybdate-solution (with dispensor)
               After 15 min : + 2 ml reducing-solution
               Colorimetry after 15 min against a blank :

                       Wavelength : 820 nm
                       Scale : 10 - 120 µg Si

Good luck,
walterVB

Thanks for your help. I am wondering if it works for both amorphous and crystalline silica. I am working with amorphous silica.