Melting Phenolphthalein Agar

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remlap12
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Melting Phenolphthalein Agar

Post by remlap12 » 16 Jun 2020, 14:15

Hi all,

Has anyone melted their already set / pre used phenolphthalein agar and then reset it?

I did, for the first time today.................I did learn a lesson!
I thought slow heat on the hot plate would be the best option.....WRONG!! :redcard:
After a long time, with not much happening, I then decided to try some in the microwave..............BINGO!
Two minutes in the microwave, totally melted!! :clap3: \:D/ and an hour and a half of my life I'll never get back... :cheesy: :whistling2:
Regards
remlap12
science support and problem solver :mail:

mtg
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Re: Melting Phenolphthalein Agar

Post by mtg » 21 Jul 2020, 11:32

Good to know. What strength Phenolphthalein did you use and how much? I find it's so hard to get the right colour so it doesn't fade. usually make it too pink.

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remlap12
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Re: Melting Phenolphthalein Agar

Post by remlap12 » 21 Jul 2020, 12:53

mtg wrote:
21 Jul 2020, 11:32
Good to know. What strength Phenolphthalein did you use and how much? I find it's so hard to get the right colour so it doesn't fade. usually make it too pink.
I actually can't tell you the strength, the bottle I have here was made up prior to me being here! It's almost gone now......time to make up a new batch. The agar did fade after a day or so, but it served the purpose, no complaints! My recipe is : 14.4g agar, 480ml water, 24ml Na OH, 4.8ml Phenophthalein. =D> :clap3:
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remlap12
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shellythenewlabby
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Re: Melting Phenolphthalein Agar

Post by shellythenewlabby » 21 Jul 2020, 12:57

mtg wrote:
21 Jul 2020, 11:32
Good to know. What strength Phenolphthalein did you use and how much? I find it's so hard to get the right colour so it doesn't fade. usually make it too pink.
I usually use the crystals and it works well

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remlap12
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Re: Melting Phenolphthalein Agar

Post by remlap12 » 21 Jul 2020, 13:10

shellythenewlabby wrote:
21 Jul 2020, 12:57
mtg wrote:
21 Jul 2020, 11:32
Good to know. What strength Phenolphthalein did you use and how much? I find it's so hard to get the right colour so it doesn't fade. usually make it too pink.
I usually use the crystals and it works well
I'll try that next time! 8-)
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remlap12
science support and problem solver :mail:

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kimmy
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Re: Melting Phenolphthalein Agar

Post by kimmy » 28 Jul 2020, 08:49

This is also a way that you can do the diffusion Agar

1. Measure out 1.6 g of agar-agar and 200 ml water. Mix them together with a whisk or fork in a large microwave-safe bowl.
2. Heat the solution in the microwave on high for 30 seconds. Remove to a heat-safe surface using a hot pad or oven mitts, stir, and return to the microwave for 30 seconds. Repeat this process until the mixture boils. (Keep your eye on it as it can boil over very easily.)
3. Choose ONE pH indicator to work with (either bromothymol blue or phenolphthalein) and add a few drops of it to the agar solution. If you’re using bromothymol blue, add enough indicator so that the mixture turns blue. If it has a greenish hue, add ammonia a drop at a time until it is blue (see photo below). If you're using phenolphthalein, add enough indicator so that the mixture turns pale pink. Add ammonia drop by drop until the mixture turns (and remains) a bright pink color (see photo below).
4. Carefully pour the agar solution into silicone ice-cube molds or a small glass baking pan. Make sure the agar block(s) will be at least 3 cm deep when they solidify. If you don’t have enough solution, make more using the ratio of 0.8 g agar-agar powder to 100 ml water.
5. Let the agar cool until it solidifies (an hour is usually sufficient). Remove the agar blocks from the molds or cut in the pan with a sharp knife to obtain two sets of cubes of three sizes: 1 x 1 x 1 cm, 2 x 2 x 2 cm, and 3 x 3 x 3 cm. If you're using bromothymol blue, you should have two sets of blue cubes. If you're using phenolphthalein, you should have two sets of pink cubes. The sets need to match in order to compare the color change later on in the Snack.

mtg
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Re: Melting Phenolphthalein Agar

Post by mtg » 28 Jul 2020, 14:00

Great ideas, thank you. Kimmy I never thought to add a base to the phenolphthalein gel.

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remlap12
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Re: Melting Phenolphthalein Agar

Post by remlap12 » 30 Jul 2020, 12:32

thanks kimmy, that one has gone into my recipe book too!!
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remlap12
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