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Recently I noticed that some of our glasses and cutlery had developed a blue-ish deposit as you can see for the two sets of spoons below. For each set the spoon on the left has the blue-ish deposit whereas the spoon on the right is the original.

Blue-ish deposit on spoons

I traced the cause of this blue-ish deposit to a specific effect. It only occurs when the spoon or glass has been used for a medicine called Questran-A, which is a powder that needs to be dissolved in water and then ingested. And more specifically, it only happens when these glasses/spoons are subsequently washed in our dishwasher.

This leads me to believe that some reaction occurs between the (left-overs) of the medicine and the dishwasher tablets. My question is: does anyone know what reaction between the chemicals in the medicine and those in the dishwasher tablets could cause this blue-ish deposit?

Obviously this will be impossible to say without the ingredients of both, so here is a list of the contents of the dishwasher tablets and the medicine:

Dishwasher tablets (Albert Heijn):

  • pentasodium triphosphate
  • sodium carbonate and sodium carbonate peroxide
  • taed
  • sodium silicate
  • PEG-90
  • alcohols, C16-18, ethoxylated mind 30 EO
  • acrylic copolymer
  • PEG-4
  • maleic acid/acrylic acid copolymer,sodium salt
  • alcohols, C12-18 ethoxylated propoxylated
  • zinc sulfate
  • beta-alanine, N-(2-carboxyethyl)-, N-coco alkyl derivs, disodium salt
  • mn-complex
  • benzotriazole
  • subtilisin
  • tetrasodium etidronate
  • alpha-amylase
  • benzisothiazolinone

Questran-A:

  • 4 mg colestyramine
  • 30 mg Aspartame(E 951) equal to 17 mg Phenylalanine
  • Citric acid(E 330)
  • kelcoloïd
  • Silicon dioxide(E551)
  • Orange flavoring
  • Xantham gum (E 415).
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Let's speculate a bit ;)

  • Colestyramine is a twodimensional polymer network, build from styrene and and 1,4-divinylbenzene.
  • The polymer has a lot of benzyltrimethylammonium groups. That means it can act as an anion exchanger.
  • It is used to strongly bind bile acids
  • Neither the polymer itself, nor the adduct with bile acid are supposed to degrade in the bowel. The loaded polymer is supposed to be excreted.

The dishwasher tablets, on the other hand, contain the sodium salt of a maleic acid/acrylic acid copolymer.

That means we have two polymers, one with a lot of $\ce{Ph-CH2N^+(CH3)3}$ groups and another one with lots of $\ce{-COO-}$ groups.

Sounds like a mass wedding of two chain gangs :D

Edit

It is conceivable that this deposits a thin film on the spoons and the glassware.

In order to explain the bluish colour, we have two options:

  1. The polymer aggregate absorbs in the 580 nm range - we observe the complementary colour. Due to lack of conjugation, I don't see how this could happen here.

  2. The colour results from some dispersion effect related to opalescence, as suggested in Michiel's comment.

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    $\begingroup$ Nice discussion! Small follow-up: could the mass wedding be responsible for the blue-ish deposit? Maybe just on the basis of layer thickness, or otherwise chemically? $\endgroup$ – Michiel Feb 26 '14 at 7:05

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