Phenolphthalein Agar

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remlap12
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Re: Phenolphthalein Agar

Post by remlap12 »

So, I have an order for Phenophthalein Agar for Thursday, only to realise I don't have any Agar......so I am experimenting with gelatin.
Has anyone tried this?
I'll let you know if:
1. it sets and
2.it works (or not).......................
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Labbie
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Re: Phenolphthalein Agar

Post by Labbie »

Or ask a local high if they can help??
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Merilyn1
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Re: Phenolphthalein Agar

Post by Merilyn1 »

I agree with Labbie - go on the bludge. The time you mess about with it could be time spent "networking". I have never tried or heard of anyone using gelatine.
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Lyn
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Re: Phenolphthalein Agar

Post by Lyn »

I think you are pushing your luck with the gelatine. If you give the teacher something that doesn't work there will be no end to the complaints. Labbie's advice is good or just tell them that when the agar is ordered in then they can have their prac.
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remlap12
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Re: Phenolphthalein Agar

Post by remlap12 »

I did try the bludge option but agar is pretty expensive......so wasn't successful there.
I have made the teacher fully aware of the problem, I'm lucky my teachers are pretty relaxed, so she said if it doesn't work then she will just reschedule the prac when I have some :-)
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ELIZABETH
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Re: Phenolphthalein Agar

Post by ELIZABETH »

Any health food shop should stock it, and it's pretty cheap.
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Re: Phenolphthalein Agar

Post by bigmack »

Woolies have 64 g pack for $4.00
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remlap12
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Re: Phenolphthalein Agar

Post by remlap12 »

Gee, thanks people! I didn't think to check woollies!!!! or health food shops!!
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Re: Phenolphthalein Agar

Post by remlap12 »

bigmack wrote:Woolies have 64 g pack for $4.00
Bigmack, sorry to be a pain, but do you know what product name it sells under?? I just rang my local woollies and they said they don't stock agar....
thanks!
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Re: Phenolphthalein Agar

Post by bigmack »

remlap , it was this one but I'm not sure now if it truly is Agar :blush2:
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Re: Phenolphthalein Agar

Post by linotas »

Health food shops or catering suppliers generally have plain agar
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remlap12
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Re: Phenolphthalein Agar

Post by remlap12 »

Thanks Bigmack, I'll get some and try it considering the price!
I found some agar agar at a health food shop nearby, $20 for 75g.
Thanks all for your input!
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Re: Phenolphthalein Agar

Post by Lyn »

$20 for 75g is pretty much on the money for the agar agar. ChemSupply has agar agar at $122 for 500g. So the price is reasonable from the health food store.
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remlap12
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Re: Phenolphthalein Agar

Post by remlap12 »

Lyn wrote:$20 for 75g is pretty much on the money for the agar agar. ChemSupply has agar agar at $122 for 500g. So the price is reasonable from the health food store.

Yea, I thought so too!
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Re: Phenolphthalein Agar

Post by Lyn »

For the first time ever my phenolphthalein agar blocks have been an absolute disaster. Cooked it last Friday according to my tarted up recipe in The Laboratory. Put it in the fridge while it was still warm. Checked it today and it is looking and behaving like jam. Only one tray appears to have set and the rest - well!!! I boiled it - did I boil it long enough - I don't know. Did I add too much phenolphthalein to the mix - I don't know. I put it into the fridge while it was still warm - (it was past going home time) - should it have been absolutely cool before being refrigerated. I have been back through this thread looking for answers. Is adding powdered phenolphthalein better than adding the liquid which also has ethanol added to it? Can the agar be too old to do its job? I used 20g agar per litre and it should have worked. I mixed 4g NaOH with 100 ml of distilled water - should I have just added the NaOH solid to the agar once the agar cooled down. Anyhow round two tomorrow. Fresh batch or rework what was made last Friday. Big decision! All suggestions welcome. It is very disappointing when you find that your never fail recipe has let you down. I have talked the teacher into doing the prac on Thursday instead. So I have two days to come up with something decent.
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Re: Phenolphthalein Agar

Post by Labbie »

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?
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Re: Phenolphthalein Agar

Post by nickykinz »

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.
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emma.hunt
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Re: Phenolphthalein Agar

Post by emma.hunt »

Heya.
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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Re: Phenolphthalein Agar

Post by Merilyn1 »

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.
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Re: Phenolphthalein Agar

Post by KylaW »

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?
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