Looking for guidance.. newbie with no idea!

hi all.. i have just signed up... sorry for not being a regular, however science has never been my strong point!

bare with me as what i'm trying to make probably wont make any sense and weeks of google searching is driving me crazy!

Im trying to move liquid along a strip (picture a immunoassay strip/lateral flow).. that is the simple bit!

however i'm trying to add a area that changes colour once the liquid has reached it ( abit like litmus paper..however this isnt working!) a ph strip wont work as it offers too many colour changes.. i need 2! this isnt the simple bit... and where i need assistance...

i want a one colour change for acidic and one colour for alkaline environments.. i know.. this domain is usually ph strip territory.. however that entails in having a static colour as a display until the liquid is reached! this is the issue im stuck with! i need a white display and then 2 colour changes... is it even possible??

i have attached an image..albeit it could be useless but it gives an insight of what im trying to achieve in terms of the liquid flow and colour change.. *** it wont allow me to attach or add image** sorry

can anyone recommend something?

thank you

Natalie

At what pH levels do you want the two colour changes to occur?

4-6 and 7-9

Off the top of my head the best indicator would be phenol red. It changes from very pale yellow to very pale salmon pink at around pH 6.8 and then to a very dark pink at pH 8.4. I think bromothymol blue and methyl red also have 2 colour changes but I can't remember the pH ranges. One of these may be suitable, if not let me know and I'll have a think (and check the data books) for other options tomorrow.

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Originally Posted by PhDemon

Off the top of my head the best indicator would be phenol red. It changes from very pale yellow to very pale salmon pink at around pH 6.8 and then to a very dark pink at pH 8.4. I think bromothymol blue and methyl red also have 2 colour changes but I can't remember the pH ranges. One of these may be suitable, if not let me know and I'll have a think (and check the data books) for other options tomorrow.

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the issue i have with them all are they are a colour to begin with. it wont allow me to attach the image but that looks like some sort of gel or shiny clear top layer i wasnt sure if that helped it or just helped the liquid change the colour faster.

i did consider the bromothymol blue, however that is green colour no where near the neutral white/grey/ light shade im after.

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Originally Posted by newbienat

i did consider the bromothymol blue, however that is green colour no where near the neutral white/grey/ light shade im after.

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Presumably the paper will have a PH reading before it gets wet. Sounds like you want to avoid that happening?

Could you perhaps use some sort of micro encapsulation, holding the color-changing element at bay until the paper is exposed? Either a dissolving encapsulation or something activated by pressure like normal encapsulation uses?

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Originally Posted by NoCoPilot

Quote:

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Originally Posted by newbienat

i did consider the bromothymol blue, however that is green colour no where near the neutral white/grey/ light shade im after.

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Presumably the paper will have a PH reading before it gets wet. Sounds like you want to avoid that happening?

Could you perhaps use some sort of micro encapsulation, holding the color-changing element at bay until the paper is exposed? Either a dissolving encapsulation or something activated by pressure like normal encapsulation uses?

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hi yes ideally.

i will look into the latter now. i have never heard of it. it wont allow me to upload the image..maybe because im a newbie, so its hard to explain what im after. :bh

the actually colour metric im trying to work with will be placed in a housing. so the display window will show the colour change of the liquid that has been absorbed at the tip. the other issue with ph paper is the standard colour it comes in. i want the actual display window to stay white until the liquid environment has been identified ( acid/base) so ideally some other mechanism to either produce a dye or something.. this is soooo hard! so sorry if i cant explain it correctly.