Phenolphthalein Agar
- Labbie
- Posts: 3237
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Re: Phenolphthalein Agar
I always found Agar 1000 was just awful, it just never never set. I like agar 750 but find it so hard to purchase. There never use to be different agar's around, so perhaps there is another one?
Regards Labbie
Lab Manager/Lab Tech, mind reading etc etc
Now retired
Lab Manager/Lab Tech, mind reading etc etc
Now retired
- nickykinz
- Posts: 271
- Joined: 02 Feb 2009, 12:53
- Job Title: Lab Assistant
- School: St Augustine's College
- Suburb: Augustine Heights
- State/Location: QLD
Re: Phenolphthalein Agar
I usually use 25g per L but just because it gives a firmer agar, not because it didn't set. I do also use powdered phenolphthalein as it seems to give a better colour. I do 1g per litre. It sounds like you did everything else right though. I make sure it boils but not for a particular amount of time and I add the NaOH as a solution once it has cooled to 60. I don't see why putting it in the fridge would stop it from setting. It should have just speeded it up. I wouldn't have been surprised if you got some cracking or something from cooling it quickly but not stopping it set at all.
I would suggest increasing the amount of agar in case it is old, maybe boiling it for an extra 30 seconds, using powdered phenolphthalein and crossing your fingers.
If you have time though you could boil it up again and see if it sets. You should be able to do that quite quickly and may save you redoing the whole lot. I've reused ones when they haven't set properly, but I think they were from not being brought to boil properly in the first place.
I would suggest increasing the amount of agar in case it is old, maybe boiling it for an extra 30 seconds, using powdered phenolphthalein and crossing your fingers.
If you have time though you could boil it up again and see if it sets. You should be able to do that quite quickly and may save you redoing the whole lot. I've reused ones when they haven't set properly, but I think they were from not being brought to boil properly in the first place.
Nicky
St Augustine's College
Augustine Heights, QLD 4300
St Augustine's College
Augustine Heights, QLD 4300
Re: Phenolphthalein Agar
Heya.
If using the dropper trays (or any trays), does the agar come out easily enough or does it stick to the edges?
Thanks
If using the dropper trays (or any trays), does the agar come out easily enough or does it stick to the edges?
Thanks
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- Joined: 12 Mar 2013, 08:10
- Job Title: Labbie
- School: Wollondilly Anglican College
- Suburb: Tahmoor
- State/Location: NSW
Re: Phenolphthalein Agar
Comes out fine. It's been ages since I made it, but I don't ever remember a problem. Might have to run a blade around the edge but can't remember doing that.
Re: Phenolphthalein Agar
Hi Lyn, my phenolpthalein agar didn't work this year either. Two failed batches. The third time I boiled it for a few minutes (I've always just added boiling water), and used bromothymol blue instead. It set great, plus the agar turns from blue to yellow (rather than clear) which makes the diffusion easier for the students to see. The teacher asked to stick to this recipe in future years.
Still not sure what went wrong, perhaps the age of my agar meant it needed the extra boiling?
Still not sure what went wrong, perhaps the age of my agar meant it needed the extra boiling?
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- Posts: 216
- Joined: 01 Aug 2017, 12:19
- Job Title: Laboratory technician
- School: College
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Re: Phenolphthalein Agar
People have been wondering how long the phenolphthalein agar lasts for - I had some in the fridge when I started at this school in 2016 and didn't have to make more until this year. It worked perfectly and the only reason I had to make more was because it went mouldy.
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- Posts: 816
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- Job Title: Lab Technician
- School: FCAC
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Re: Phenolphthalein Agar
That's funny Marama , I just ditched a couple of icecream containers full of moldy stuff myself a few days ago . It sure does last a long time in the fridge but yup....it goes moldy after a whileMarama T wrote: ↑27 Aug 2019, 08:17 People have been wondering how long the phenolphthalein agar lasts for - I had some in the fridge when I started at this school in 2016 and didn't have to make more until this year. It worked perfectly and the only reason I had to make more was because it went mouldy.
- kimmy
- Posts: 418
- Joined: 01 Jun 2006, 10:00
- Job Title: School Lab Assistant
- School: Quirindi High School
- Suburb: Quirindi
- State/Location: NSW
Re: Phenolphthalein Agar
i know this is a old old post but i have just came across a great idea of how to prepare the squares for the diffusion experiment.
K mart have silicone ice-cube molds that are perfect for the 3cm square cubes then students can cut another one down to get a 2cm square and 1cm square.
K mart have silicone ice-cube molds that are perfect for the 3cm square cubes then students can cut another one down to get a 2cm square and 1cm square.
- Labbie
- Posts: 3237
- Joined: 28 Nov 2006, 10:00
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Re: Phenolphthalein Agar
That's a great idea Kimmy
Regards Labbie
Lab Manager/Lab Tech, mind reading etc etc
Now retired
Lab Manager/Lab Tech, mind reading etc etc
Now retired
Re: Phenolphthalein Agar
There are also silicon ice cube trays perfect for 2cm cubes and 1 cm cubes - so much less waste!
Re: Phenolphthalein Agar
It's my time of year to do this again. Last year I saved the leftovers for the first time, and it seems to have kept well in the fridge. For any others that do this, what method do you use to re-melt the agar for pouring? I'm reluctant to use the microwave method since we don't have our own science microwave; I would have to use the staff room ones people use for their lunch, and I have concerns about using science equipment in there, spillage, etc.
- Labbie
- Posts: 3237
- Joined: 28 Nov 2006, 10:00
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Re: Phenolphthalein Agar
Good point Milo, we got a new one for the staff room, so I was able to take the old one just for the prep room. One of the best things we ever did.
Regards Labbie
Lab Manager/Lab Tech, mind reading etc etc
Now retired
Lab Manager/Lab Tech, mind reading etc etc
Now retired
Re: Phenolphthalein Agar
Short of using the microwave, perhaps heating in a water bath?
I couldn't manage without my cranky old microwave
I couldn't manage without my cranky old microwave
Re: Phenolphthalein Agar
It takes an age without a microwave......just sayin'!!
Regards
remlap12
science support and problem solver
remlap12
science support and problem solver
Re: Phenolphthalein Agar
Indeed it does. I ended up buying a new microwave for us last week! Now I just need to make sure nobody uses it for their lunch...
- Labbie
- Posts: 3237
- Joined: 28 Nov 2006, 10:00
- Job Title: Retired
- Suburb: At Home
- State/Location: NSW
Re: Phenolphthalein Agar
Good one Milo, is it in the prep room? We had a sign on the door of microwave, Needs deep cleaning if used for food.
Regards Labbie
Lab Manager/Lab Tech, mind reading etc etc
Now retired
Lab Manager/Lab Tech, mind reading etc etc
Now retired
Re: Phenolphthalein Agar
Yes it's in the prep room, which directly adjoins the Science office. For now I've just written on it in texta, need to get around to making a sign.
Re: Phenolphthalein Agar
Hey,
So I've got this agar from 3-4 weeks ago. It's been stored in the fridge uncovered and has cracked and come away from the edges as you can see.
How do you all store yours for the next time someone wants to do this?
Is it past saving now?
Thanks
So I've got this agar from 3-4 weeks ago. It's been stored in the fridge uncovered and has cracked and come away from the edges as you can see.
How do you all store yours for the next time someone wants to do this?
Is it past saving now?
Thanks
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- Posts: 1477
- Joined: 12 Mar 2013, 08:10
- Job Title: Labbie
- School: Wollondilly Anglican College
- Suburb: Tahmoor
- State/Location: NSW
Re: Phenolphthalein Agar
Wrap it up in a few layers of cling wrap. This will help although I've never had to keep it longer than a few weeks.