francis
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Analysing water in paint
I'm trying to test the water content of a sample of paint waste. The paint is solvent + binder with some (4.09%) water.
Typically the solvent is mixed with heptane and decanted. This gives a cloudy-white emulsion.
The emulsion is dried over MgSO4 or Na2SO4 and becomes clear.
How can I analyse the water content of this sample?
I can think of only one way:
(1) Distill the paint + solvent directly. The lowest BP of the solvent is 150 deg C. So the water can be collected as the first fraction, then the
solvent collected as the second.
Dissolved substances in the water won't be found in the water distillate, so we'd then wash the binder/resin in the distillation flask with water, and
test that.
How else can we test the water? I'm concerned about water-soluble metal contaminants and also about residual hydrocarbon contaminaton of the water.
The sample must be disposed of and so these are concerns.
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blogfast25
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Sounds like job for Karl-Fisher:
http://en.wikipedia.org/wiki/Karl_Fischer_titration
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francis
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Yep, but the problem is the Karl Fisher will tell us how much water, rather than what's in the water.
I'm thinking, the likely contaminants in the water are soluble ionic compounds, possibly metals introduced by corrosion of the storage environment.
The only two methods I can think of are:
(1) distill off the water, then extract the undistilled sludge with a water wash and test that by IC and AAS
(2) If we dried the paint over Na2SO4 and digested the hydrated drying agent in strong acid, then tested that by AAS...
The problem with (1) is: the paint sludge will be very hard, and viscous, and a water extraction may not dissolve all, or any ionic contaminants
The problem with (2) is: the drying agent will introduce sulphate contaminants, it may be hard to digest to release the water, there's the likelihood
of error by the drying agent drawing water from the atmosphere.
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fledarmus
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I'm a little confused. You are adding water to the paint mixture, and then trying to test what impurities were present in the water? Wouldn't it be
easier to test the water beforehand?
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francis
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The paint mixture has water in it...the problem is, how can we separate that water from the paint, and test it?
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watson.fawkes
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Quote: Originally posted by francis  | | The problem with (1) is: the paint sludge will be very hard, and viscous, and a water extraction may not dissolve all, or any ionic contaminants
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There are plenty of mechanical means to reduce your sample: blender, (meat) grinder, ball mill. Also, if you
dry your sample so that it's more line-shaped than plane-shaped, it will be easier to get into the machine. Using a squeeze bottle on polyethylene
sheet should be adequate.
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