testing for flavonoids in tea with milk. oh dear, help.
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deleted-71588
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http://www.safety.duke.edu/msds/ProdPharmacy/AlCl3.pdf
Here is a Duke Medical Center Material Safety Data Sheet for a 30% aqueous solution of AlCl3 for reference.
This stuff is VERY corrosive! It is used in etching and plating processes and in a paste form for some exotic soldering processes. You defininately want to stay away from the anhydrous (powdered) forms because it is hard to contain while mixing and not end up everwhere!
Here is a Duke Medical Center Material Safety Data Sheet for a 30% aqueous solution of AlCl3 for reference.
This stuff is VERY corrosive! It is used in etching and plating processes and in a paste form for some exotic soldering processes. You defininately want to stay away from the anhydrous (powdered) forms because it is hard to contain while mixing and not end up everwhere!
-Craig
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Louise
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The anhydrous form is also potentially explosive when in contact with water. It appears to be sold as anhydrous (solid), hexahydrous (solid), and as prepared solutions in benzonitrile and ethanol. I did not find a 10% solution in water that was availible. It would be best if you did not have to make the solution, since the solid form (esp. anhydrous) is much more dangerous. If you did, you would definitely use the hexahydrate form, which already has some (six) waters.Craig_Bridge wrote:http://www.safety.duke.edu/msds/ProdPharmacy/AlCl3.pdf
Here is a Duke Medical Center Material Safety Data Sheet for a 30% aqueous solution of AlCl3 for reference.
This stuff is VERY corrosive! It is used in etching and plating processes and in a paste form for some exotic soldering processes. You defininately want to stay away from the anhydrous (powdered) forms because it is hard to contain while mixing and not end up everwhere!
Some people I work with might use this stuff, so I want to ask around at work tomorrow. The MSDS is not too bad- this stuff isn't toxic or carcingenic, but this stuff is a strong base, and consequently, as Craig said, very corrosive.
Louise
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vanillabean16
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so i was able to talk with my teacher today...
the spectrophotometer works! it did exactly what you said it should do. phew.
we have NaOH, but my teacher is going to order the AlCl3 and NaNO2. I mentioned to her what you said about the AlCl3 and we looked in the chemical book of the company from which the school orders, and it didn't mention any hazards.. so perhaps whatever they send out isn't as corrosive? But anyways, when i actually do the experiment she will be supervising.
she also mentioned that it would be a good idea to find a substance (such as HCl) that would be able to really clean the test tubes so that nothing interferes with the reading. I'm going to see what i can find out...
the spectrophotometer works! it did exactly what you said it should do. phew.
we have NaOH, but my teacher is going to order the AlCl3 and NaNO2. I mentioned to her what you said about the AlCl3 and we looked in the chemical book of the company from which the school orders, and it didn't mention any hazards.. so perhaps whatever they send out isn't as corrosive? But anyways, when i actually do the experiment she will be supervising.
she also mentioned that it would be a good idea to find a substance (such as HCl) that would be able to really clean the test tubes so that nothing interferes with the reading. I'm going to see what i can find out...
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Louise
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Okay, I meant to say "acid" above (it is a lewis acid), not "base". I found one person who worked with the anhydourus stuff, which you definitely don't want to do.Louise wrote:The anhydrous form is also potentially explosive when in contact with water. It appears to be sold as anhydrous (solid), hexahydrous (solid), and as prepared solutions in benzonitrile and ethanol. I did not find a 10% solution in water that was availible. It would be best if you did not have to make the solution, since the solid form (esp. anhydrous) is much more dangerous. If you did, you would definitely use the hexahydrate form, which already has some (six) waters.Craig_Bridge wrote:http://www.safety.duke.edu/msds/ProdPharmacy/AlCl3.pdf
Here is a Duke Medical Center Material Safety Data Sheet for a 30% aqueous solution of AlCl3 for reference.
This stuff is VERY corrosive! It is used in etching and plating processes and in a paste form for some exotic soldering processes. You defininately want to stay away from the anhydrous (powdered) forms because it is hard to contain while mixing and not end up everwhere!
Some people I work with might use this stuff, so I want to ask around at work tomorrow. The MSDS is not too bad- this stuff isn't toxic or carcingenic, but this stuff is a strong base, and consequently, as Craig said, very corrosive.
Louise
NaOH is a strong base (this time, I really do mean base). You need gloves, long sleeves, googles and preferably a hood to to these reactions. You need to follow the procedures very carefully (the full procedure, not the brief version) and you should have a mentor assisting you.
I don't think this is beyong your level. I did my 11th grade science fair project on a similar level of chemical difficulty (and danger- using strong acids and bases), and my chemistry teacher let me work in the lab on Saturday's while he was there. He also approved my procedure so everything was safe.
Louise
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deleted-71588
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I suspect that Louise meant for you to find the "full" text of the experimental write up that describes the experimental proceedure fully and not just an abstract that glosses over the details (the things that people who have done it before might understand, but somebody new to the process has no clue that there is more to it).
-Craig
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Louise
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Your paper says something like "We followed the procedure of these other authors (references 8,9). In brief, this is what we did..."Craig_Bridge wrote:I suspect that Louise meant for you to find the "full" text of the experimental write up that describes the experimental proceedure fully and not just an abstract that glosses over the details (the things that people who have done it before might understand, but somebody new to the process has no clue that there is more to it).
So, the "in full" part, should be in the references 8 and 9. It is like me saying, "I made a pound cake, using lemon extract and whole wheat flour". A cook who knew the recipe for pound cake could make my cake (and would know how I modified the procedure). But, if you've never made a pound cake, or seen a recipe for one, you'd be lost. Since we've never seen the full "recipe" for this procedure, we have no idea how much detail is omitted. Additionally, good papers provide information about the dangers and things that can go wrong, which is very useful.
Louise
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vanillabean16
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Well, i sent the reference to the hospital library with my father to get the full text that's not available online... and somehow he managed to get completely different articles...
is there any other way to get ahold of that article? I would ask him to look for it again but he's actually leaving the country for the next 10 days so he won't be able to help me.
Thanks again.

is there any other way to get ahold of that article? I would ask him to look for it again but he's actually leaving the country for the next 10 days so he won't be able to help me.
Thanks again.
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Louise
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Please post the references here and I will look for them.vanillabean16 wrote:Well, i sent the reference to the hospital library with my father to get the full text that's not available online... and somehow he managed to get completely different articles...
is there any other way to get ahold of that article? I would ask him to look for it again but he's actually leaving the country for the next 10 days so he won't be able to help me.
Thanks again.
Louise
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vanillabean16
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i actually found it. the procedure is pretty much the same.. except there is one problem! The replicated procedure calls for 0.3 mL NaNO2 and 0.3 mL of AlCl3. The original calls for the same of NaNO2, but for 3 mL AlCl3. and everything else is absolutely the same.
Which volume should i go with?!
and now for some questions..
what does 2 mL of 1 M NaOH (also written 2 mL 1 mol liter^-1 NaOH) mean?
Also, how much milk should be added to each tea sample? The tea is brewed in 200 mL distilled water (about 3/4 cup), so i was thinking a tablespoon or two? That seems to be about average..
thank you, as always.
Which volume should i go with?!
and now for some questions..
what does 2 mL of 1 M NaOH (also written 2 mL 1 mol liter^-1 NaOH) mean?
Also, how much milk should be added to each tea sample? The tea is brewed in 200 mL distilled water (about 3/4 cup), so i was thinking a tablespoon or two? That seems to be about average..
thank you, as always.
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vanillabean16
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i just thought to mention that in the original procedure they are not testing tea, they are testing dried mulberry leaves.. i don't know if that makes any difference.
also, the procedure says "AlCl3 was added 5 mins later. After 6 mins, NaOH was added.." so does this mean that 1 minute after the AlCl3, the NaOH was added, or 6 minutes after?
i'm sorry to ask so many questions! but you guys are very helpful.
also, the procedure says "AlCl3 was added 5 mins later. After 6 mins, NaOH was added.." so does this mean that 1 minute after the AlCl3, the NaOH was added, or 6 minutes after?
i'm sorry to ask so many questions! but you guys are very helpful.
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Louise
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vanillabean16 wrote:i actually found it. the procedure is pretty much the same.. except there is one problem! The replicated procedure calls for 0.3 mL NaNO2 and 0.3 mL of AlCl3. The original calls for the same of NaNO2, but for 3 mL AlCl3. and everything else is absolutely the same.
Which volume should i go with?!
and now for some questions..
what does 2 mL of 1 M NaOH (also written 2 mL 1 mol liter^-1 NaOH) mean?
Also, how much milk should be added to each tea sample? The tea is brewed in 200 mL distilled water (about 3/4 cup), so i was thinking a tablespoon or two? That seems to be about average..
thank you, as always.
Give me the other reference, and I'll see if I can find out what the reaction is and why NaNO2 is important. Then I will see why there is such a large difference in volume. (Sounds like someone made a typo to me)
molar is a method of specifying concentration. It is number of moles/volume, where moles is mass used/ molecular weight. What form is your NaOH in? If you have a solid, we can make some 1 M NaOH. I will show you how to do the math. If you have a solution of NaOH already, it will either be labeled in Molar Units (1 M, 10 M, whatever) or in Normal units which is abbreviated as N. In this case, they are the same. So, 1 N sodium hydroxide (NaOH) is the same as 1 M NaOH.
Louise
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vanillabean16
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the other reference is not available online.. i had to have it printed from the hospital library, and i only have a text copy of it. it doesnt mention the chemicals that were used anywhere else in the lab other than the methods..the only thing it talks about is the OH and O2 scavenging properties of flavonoids. It says..
"It is suggested that the overall antioxidant effect of flavonoids on lipid peroxidation may be related to their OH and O2 scavenging properties and their reaction with peroxy radicals. Thus, O2 may play an important role during the perodixation of unsaturated fatty acids and possibly other susceptible substances. Therefore, the study of the scavenging effects of antioxidants on O2 is one of the most important ways of making clear the mechanism of antioxidant activity and has therefore caused growing interest among researchers. Flavonoids can be used directly to scavenge O2 and OH by single electron transfer. The scavenging process can generally be followed by means of electron spin resonance... The photochemical reduction of riboflavin was first used to determine the dismutation of O2 by superoxide dismutase (SOD) and has been adapted for analysis of the dismutation of O2 by a model compound of superoxide dismutase and other natural compounds."
and thats it for useful information! The rest is just background... rather useless, actually.
So maybe that is where the NaOH and NaNO2 come in, to be targets for OH and O2 "scavenging", and the AlCl3 causes color to appear?
and i do believe that the NaOH we have is in solid tablets.. i certainly hope my teacher will know how to concentrate it correctly.. but it wouldn't hurt for me to know as well!
i hope that exerpt from the lab helped maybe a little.. thats really all there is about flavonoids, as the rest of the lab tested the scavenging of superoxide radicals and used an HPLC.
:)thanks[/img]
"It is suggested that the overall antioxidant effect of flavonoids on lipid peroxidation may be related to their OH and O2 scavenging properties and their reaction with peroxy radicals. Thus, O2 may play an important role during the perodixation of unsaturated fatty acids and possibly other susceptible substances. Therefore, the study of the scavenging effects of antioxidants on O2 is one of the most important ways of making clear the mechanism of antioxidant activity and has therefore caused growing interest among researchers. Flavonoids can be used directly to scavenge O2 and OH by single electron transfer. The scavenging process can generally be followed by means of electron spin resonance... The photochemical reduction of riboflavin was first used to determine the dismutation of O2 by superoxide dismutase (SOD) and has been adapted for analysis of the dismutation of O2 by a model compound of superoxide dismutase and other natural compounds."
and thats it for useful information! The rest is just background... rather useless, actually.
So maybe that is where the NaOH and NaNO2 come in, to be targets for OH and O2 "scavenging", and the AlCl3 causes color to appear?
and i do believe that the NaOH we have is in solid tablets.. i certainly hope my teacher will know how to concentrate it correctly.. but it wouldn't hurt for me to know as well!
i hope that exerpt from the lab helped maybe a little.. thats really all there is about flavonoids, as the rest of the lab tested the scavenging of superoxide radicals and used an HPLC.
:)thanks[/img]
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Louise
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Just give me the citation for the paper. I work at a University, so I can get it online.vanillabean16 wrote:the other reference is not available online.. i had to have it printed from the hospital library, and i only have a text copy of it. it doesnt mention the chemicals that were used anywhere else in the lab other than the methods..the only thing it talks about is the OH and O2 scavenging properties of flavonoids. It says..
"It is suggested that the overall antioxidant effect of flavonoids on lipid peroxidation may be related to their OH and O2 scavenging properties and their reaction with peroxy radicals. Thus, O2 may play an important role during the perodixation of unsaturated fatty acids and possibly other susceptible substances. Therefore, the study of the scavenging effects of antioxidants on O2 is one of the most important ways of making clear the mechanism of antioxidant activity and has therefore caused growing interest among researchers. Flavonoids can be used directly to scavenge O2 and OH by single electron transfer. The scavenging process can generally be followed by means of electron spin resonance... The photochemical reduction of riboflavin was first used to determine the dismutation of O2 by superoxide dismutase (SOD) and has been adapted for analysis of the dismutation of O2 by a model compound of superoxide dismutase and other natural compounds."
and thats it for useful information! The rest is just background... rather useless, actually.
So maybe that is where the NaOH and NaNO2 come in, to be targets for OH and O2 "scavenging", and the AlCl3 causes color to appear?
and i do believe that the NaOH we have is in solid tablets.. i certainly hope my teacher will know how to concentrate it correctly.. but it wouldn't hurt for me to know as well!
i hope that exerpt from the lab helped maybe a little.. thats really all there is about flavonoids, as the rest of the lab tested the scavenging of superoxide radicals and used an HPLC.
:)thanks[/img]
Oh, and I think 1-2 T of milk is fine. If I put milk in my tea (black, not green), I usually put in 2 T.
Louise
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Louise
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I don't think it matters. I've found looked at 4 more papers (in addition to the two you have) and half use the 0.3 mL amount, and half use 3 mL amount. I don't really understand the chemistry of this reaction yet, and nothing I am reading helps, but I guess the amount of this chemical doesn't matter. I would use the value in the tea, cocoa, wine paper, since it is the closest to what you want to do.vanillabean16 wrote:Here's the reference:
Zhishen, J.; Mengcheng, T.; Jianming, W. The determination of flavonoid contents in mulberry and their scavenging effects on superoxide radicals. Food Chem. 1999, 64, 555-559.
thanks!
Louise
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vanillabean16
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well i'm doing the experiment in about a week. my biggest issue has been how many samples to do, and of what. This is my preliminary plan, with questions:
1. 3 types of teas, each brewed in 200mL distilled water, to test for the original levels of flavonoids before adding milk. Im thinking 4 samples of each type of tea, each from a different brew. Or 3 samples, or 5 samples?
2. each type of tea with each type of added milk (3 types; whole, skim and 2%) again, probably 4 samples of each. (I'm assuming that i can't take these tea samples from the previously brewed teas; because with an extracted sample (which is 1mL from each) it would be adding milk to 199 mL instead of 200.. not sure if it will really matter? it would certainly save on time..)
3. i was originally planning on testing the milk, but then i realized that we can't test it, because, silly me, milk doesn't have flavonoids in it! and i'm not doing a separate casein-test. So i'm just assuming they're in there.. maybe i'll correlate it to the amount of protein on the labeled package or something.
so total, if each type of tea is individually tested 4 times, and each type of tea is tested with each type of milk 4 times, then thats about 60 samples, 48 of them just testing flavonoid content with added milk. Sufficient?
thanks
1. 3 types of teas, each brewed in 200mL distilled water, to test for the original levels of flavonoids before adding milk. Im thinking 4 samples of each type of tea, each from a different brew. Or 3 samples, or 5 samples?
2. each type of tea with each type of added milk (3 types; whole, skim and 2%) again, probably 4 samples of each. (I'm assuming that i can't take these tea samples from the previously brewed teas; because with an extracted sample (which is 1mL from each) it would be adding milk to 199 mL instead of 200.. not sure if it will really matter? it would certainly save on time..)
3. i was originally planning on testing the milk, but then i realized that we can't test it, because, silly me, milk doesn't have flavonoids in it! and i'm not doing a separate casein-test. So i'm just assuming they're in there.. maybe i'll correlate it to the amount of protein on the labeled package or something.
so total, if each type of tea is individually tested 4 times, and each type of tea is tested with each type of milk 4 times, then thats about 60 samples, 48 of them just testing flavonoid content with added milk. Sufficient?
thanks
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Louise
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I'd test milk anyway, just to make sure you get what you expect.vanillabean16 wrote:well i'm doing the experiment in about a week. my biggest issue has been how many samples to do, and of what. This is my preliminary plan, with questions:
1. 3 types of teas, each brewed in 200mL distilled water, to test for the original levels of flavonoids before adding milk. Im thinking 4 samples of each type of tea, each from a different brew. Or 3 samples, or 5 samples?
2. each type of tea with each type of added milk (3 types; whole, skim and 2%) again, probably 4 samples of each. (I'm assuming that i can't take these tea samples from the previously brewed teas; because with an extracted sample (which is 1mL from each) it would be adding milk to 199 mL instead of 200.. not sure if it will really matter? it would certainly save on time..)
3. i was originally planning on testing the milk, but then i realized that we can't test it, because, silly me, milk doesn't have flavonoids in it! and i'm not doing a separate casein-test. So i'm just assuming they're in there.. maybe i'll correlate it to the amount of protein on the labeled package or something.
so total, if each type of tea is individually tested 4 times, and each type of tea is tested with each type of milk 4 times, then thats about 60 samples, 48 of them just testing flavonoid content with added milk. Sufficient?
thanks
I'd actually ditch the three types of tea, and do more samples of each type. I have _no_ idea how much variation you are going to get, and having 12 data points to average vs. 4 data points can make a significant difference! For milk, I'm not sure I'd do three types. Maybe whole and skim, and leave out the two percent. Again, I'd do more trials rather than more variables. If your teacher is requiring a certain number of IVs then obviously you have to do that. But, it is better to have a lot of high quality data for a few variables than poor quality data on a lot of variables.
It does matter- so testing fresh samples is best. It may be that the effect is so large that the 1 mL difference wouldn't be super important, but if your flavanoid change is really small, then this difference could make your experiment show the incorrect result.(I'm assuming that i can't take these tea samples from the previously brewed teas; because with an extracted sample (which is 1mL from each) it would be adding milk to 199 mL instead of 200.. not sure if it will really matter?
Here is another thought. You could brew tea in 200 mL. Then divide it in to 2x 100 mL. Test one with and one without milk. Or even divide in to 3 or 4. There is no reason not to do this, as long as you can divide consistently and you always add your milk at the same time (or temperature) of tea.
Louise
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vanillabean16
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im not sure how i would test the milk though.. because the chemicals are for flavonoid testing..and if the milk did for some strange reason turn pink as indicated that would bring about a whole nother area to factor into the results. so what would be the point? again, i'm just trying to concentrate my samples to just tea, and tea with milk.
and i could divide the tea into 100mL samples, and then just add 1 tablespoon of milk to that 100mL instead of 2 tablespoons to 200mL?
then i also was thinking about this: "Absorbances of the mixtures upon the development of pink color were determined at 510 nm relative to a prepared blank." Would the blank just be a plain tea sample, without milk? since i am comparing with milk to without milk? Or should i just use water to be the blank and the zero? since distilled water won't have flavonoids....
and i could divide the tea into 100mL samples, and then just add 1 tablespoon of milk to that 100mL instead of 2 tablespoons to 200mL?
then i also was thinking about this: "Absorbances of the mixtures upon the development of pink color were determined at 510 nm relative to a prepared blank." Would the blank just be a plain tea sample, without milk? since i am comparing with milk to without milk? Or should i just use water to be the blank and the zero? since distilled water won't have flavonoids....
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Louise
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Because if milk turns the solution pink then you aren't measuring flavanoids. This is a very important control. This test is key to tell if you experiment has any meaning.vanillabean16 wrote:im not sure how i would test the milk though.. because the chemicals are for flavonoid testing..and if the milk did for some strange reason turn pink as indicated that would bring about a whole nother area to factor into the results. so what would be the point.
Yes.again, i'm just trying to concentrate my samples to just tea, and tea with milk.
and i could divide the tea into 100mL samples, and then just add 1 tablespoon of milk to that 100mL instead of 2 tablespoons to 200mL?
The blank should be all the chemicals but what you are testing.then i also was thinking about this: "Absorbances of the mixtures upon the development of pink color were determined at 510 nm relative to a prepared blank."
Louise
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vanillabean16
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ok, here is what i plan to be my final procedure.
the tea will be prepared according to instructions, 200mL ddH at 100`C for each 2g tea bag. I decided that splitting them into 100mLs may cause the results to be a little skewed seeing as a lot of the samples would come from the same exact brew of tea. the samples will be centrifuged, and 1mL samples will be taken from the supernatants.
I figured out that the AlCl3 issue i brought up earlier (3mL versus .3mL) was a typo on the original document's part.. it was supposed to add up to 10mL but with 3mL of AlCl3 it added up to be more like 12mL.
The zero will be just ddH, and the blank will be ddH with all the chemicals added.
As far as samples go; I'll prepare 12 samples of each plain tea (hoping to test 10 of them) and a little less of each plain milk (since i should be able to tell pretty quickly whether or not the solution turns pink!).
I'm going to prepare 15 samples of each type of tea with each type of milk (green tea, black tea, skim and whole) in the hopes of doing about 12.. assuming i'll probably mess a couple of them up or run out of time.
Total, about 84 prepared tea samples, although not all of them will actually be tested. I really hope this won't take hours and hours! its worrying me! because i only have day to do it that my teacher is available before break ends.
please tell me how this looks.. and thank you so so so much for helping me get to this point; i honestly could not have done it without your advice!
:)thanks
the tea will be prepared according to instructions, 200mL ddH at 100`C for each 2g tea bag. I decided that splitting them into 100mLs may cause the results to be a little skewed seeing as a lot of the samples would come from the same exact brew of tea. the samples will be centrifuged, and 1mL samples will be taken from the supernatants.
I figured out that the AlCl3 issue i brought up earlier (3mL versus .3mL) was a typo on the original document's part.. it was supposed to add up to 10mL but with 3mL of AlCl3 it added up to be more like 12mL.
The zero will be just ddH, and the blank will be ddH with all the chemicals added.
As far as samples go; I'll prepare 12 samples of each plain tea (hoping to test 10 of them) and a little less of each plain milk (since i should be able to tell pretty quickly whether or not the solution turns pink!).
I'm going to prepare 15 samples of each type of tea with each type of milk (green tea, black tea, skim and whole) in the hopes of doing about 12.. assuming i'll probably mess a couple of them up or run out of time.
Total, about 84 prepared tea samples, although not all of them will actually be tested. I really hope this won't take hours and hours! its worrying me! because i only have day to do it that my teacher is available before break ends.
please tell me how this looks.. and thank you so so so much for helping me get to this point; i honestly could not have done it without your advice!
:)thanks
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Louise
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I think this is fine. I agree you don't have to test a lot of milk samples, just a few to get an idea if milk gives a reading in the spectrometer.vanillabean16 wrote:ok, here is what i plan to be my final procedure.
the tea will be prepared according to instructions, 200mL ddH at 100`C for each 2g tea bag. I decided that splitting them into 100mLs may cause the results to be a little skewed seeing as a lot of the samples would come from the same exact brew of tea. the samples will be centrifuged, and 1mL samples will be taken from the supernatants.
I figured out that the AlCl3 issue i brought up earlier (3mL versus .3mL) was a typo on the original document's part.. it was supposed to add up to 10mL but with 3mL of AlCl3 it added up to be more like 12mL.
The zero will be just ddH, and the blank will be ddH with all the chemicals added.
As far as samples go; I'll prepare 12 samples of each plain tea (hoping to test 10 of them) and a little less of each plain milk (since i should be able to tell pretty quickly whether or not the solution turns pink!).
I'm going to prepare 15 samples of each type of tea with each type of milk (green tea, black tea, skim and whole) in the hopes of doing about 12.. assuming i'll probably mess a couple of them up or run out of time.
Total, about 84 prepared tea samples, although not all of them will actually be tested. I really hope this won't take hours and hours! its worrying me! because i only have day to do it that my teacher is available before break ends.
please tell me how this looks.. and thank you so so so much for helping me get to this point; i honestly could not have done it without your advice!
:)thanks
I think that you can get all this done, but don't rush... you are more likely to make mistakes if you rush through this. It probably will be take a while. I wouldn't do all the samples at once, in case you run out of time. So, I would do maybe:
Half of the controls and half of the experimental groups.
Then, if you still have time, do the other half. This way, if you don't have time to complete everything, you can still have a full data set.
The originial procedure had pretty specific timing requirements, so again, doing all at once will be difficult.
Louise
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vanillabean16
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i will most likely split the samples into 2 parts. thats a good idea.
i also just found this:
http://209.85.165.104/search?q=cache:w0 ... cd=5&gl=us
an experiment in which the concentration of catechins in black tea with and without milk were determined with an HPLC. These samples were centrifuged for 20 mins instead of 5 mins. I'm wondering if maybe longer would be better, since this experiment uses milk, whereas my procedure does not?
i also just found this:
http://209.85.165.104/search?q=cache:w0 ... cd=5&gl=us
an experiment in which the concentration of catechins in black tea with and without milk were determined with an HPLC. These samples were centrifuged for 20 mins instead of 5 mins. I'm wondering if maybe longer would be better, since this experiment uses milk, whereas my procedure does not?
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Louise
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I think the first procedure was at 20000g, this one is at 13000g. This is how "fast" the centrifuge spins. Longer cannot hurt, but I don't know how many samples you can run at one time, so you may have to do shorter than 20 min just to get them all spun.vanillabean16 wrote:i will most likely split the samples into 2 parts. thats a good idea.
i also just found this:
http://209.85.165.104/search?q=cache:w0 ... cd=5&gl=us
an experiment in which the concentration of catechins in black tea with and without milk were determined with an HPLC. These samples were centrifuged for 20 mins instead of 5 mins. I'm wondering if maybe longer would be better, since this experiment uses milk, whereas my procedure does not?
Louise
Louise
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vanillabean16
- Posts: 31
- Joined: Sun Mar 11, 2007 3:18 pm
hello again!
i was wondering if anybody could explain to me or suggest a website or something that could help me understand what exactly is going on in my experiment when the NaOH, NaNO2, and AlCl3 are added to the tea and tea with milk to form a pink color.
I've heard that AlCl3 can turn pink when exposed to other metal ions (like Na?) to form color, i've heard that NaNO2 is used to manufacture dyes and colored things.. there are so many reactions that could be taking place between these chemicals and the stuff in the tea that i just don't know which one is happening!
and ofcourse the introduction to the procedure i'm following and its major reference doesn't help me out at all. i'd just like to know exactly what i'm doing...
thanks!
i was wondering if anybody could explain to me or suggest a website or something that could help me understand what exactly is going on in my experiment when the NaOH, NaNO2, and AlCl3 are added to the tea and tea with milk to form a pink color.
I've heard that AlCl3 can turn pink when exposed to other metal ions (like Na?) to form color, i've heard that NaNO2 is used to manufacture dyes and colored things.. there are so many reactions that could be taking place between these chemicals and the stuff in the tea that i just don't know which one is happening!
and ofcourse the introduction to the procedure i'm following and its major reference doesn't help me out at all. i'd just like to know exactly what i'm doing...
thanks!
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Louise
- Former Expert
- Posts: 921
- Joined: Mon Jan 16, 2006 2:17 pm
I'm not exactly sure what the chemistry is either... I read a bunch of the papers and didn't find anything useful. I'll look around some more.vanillabean16 wrote:hello again!
i was wondering if anybody could explain to me or suggest a website or something that could help me understand what exactly is going on in my experiment when the NaOH, NaNO2, and AlCl3 are added to the tea and tea with milk to form a pink color.
I've heard that AlCl3 can turn pink when exposed to other metal ions (like Na?) to form color, i've heard that NaNO2 is used to manufacture dyes and colored things.. there are so many reactions that could be taking place between these chemicals and the stuff in the tea that i just don't know which one is happening!
and ofcourse the introduction to the procedure i'm following and its major reference doesn't help me out at all. i'd just like to know exactly what i'm doing...
thanks!
Louise
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vanillabean16
- Posts: 31
- Joined: Sun Mar 11, 2007 3:18 pm
and here comes yet ANOTHER dilemma! what a surprise 
well everything was going quite smoothly. we mixed the solutions, and even tried one of the samples to see if it actually turned pink, which it did. And then.............. the spectrophotometer DIED. Literally minutes before we were going to take the first reading.
We had let it warm up for about 2 hours.. we had it on while we were making the solutions.. i don't know if thats why it wasn't working, because when we first turned it on it was working just fine! but after 2 hrs it didn't produce those green and red lights when a white piece of paper was put inside when it was set at 532 and 640 nm. When we put the blank into it, it didn't read 100% transmittance like it had before, it read like 5, and the needle wouldn't move above about 10 no matter what knobs we turned.
Now that i have EVERYTHING ready to go, and if the spec 20 doesn't recover overnight, is there a qualititative way that i can measure this? Technically i could line all the samples up next to one another and say hmm, this one looks more pink than this other one.. which i may have to do, because i really don't want to just throw all of my work out the window.
This is very discouraging.
well everything was going quite smoothly. we mixed the solutions, and even tried one of the samples to see if it actually turned pink, which it did. And then.............. the spectrophotometer DIED. Literally minutes before we were going to take the first reading.
We had let it warm up for about 2 hours.. we had it on while we were making the solutions.. i don't know if thats why it wasn't working, because when we first turned it on it was working just fine! but after 2 hrs it didn't produce those green and red lights when a white piece of paper was put inside when it was set at 532 and 640 nm. When we put the blank into it, it didn't read 100% transmittance like it had before, it read like 5, and the needle wouldn't move above about 10 no matter what knobs we turned.
Now that i have EVERYTHING ready to go, and if the spec 20 doesn't recover overnight, is there a qualititative way that i can measure this? Technically i could line all the samples up next to one another and say hmm, this one looks more pink than this other one.. which i may have to do, because i really don't want to just throw all of my work out the window.
This is very discouraging.
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Louise
- Former Expert
- Posts: 921
- Joined: Mon Jan 16, 2006 2:17 pm
The lamp is probably burned out if there is no red and green and the transmittance is low. Can you turn the wavelength to 0? This should produce white light (if you can do this, do not let the white light go to the detector. Keep the paper in, change the wavelength to 530 or something, and then take the paper out. If there is no light at 0, it is dead for sure. Also, this will be very bright, so be careful looking at it. If there is light, but it is very dim, then the lamp is dying... You can try to open the slits all the way open.vanillabean16 wrote:and here comes yet ANOTHER dilemma! what a surprise
well everything was going quite smoothly. we mixed the solutions, and even tried one of the samples to see if it actually turned pink, which it did. And then.............. the spectrophotometer DIED. Literally minutes before we were going to take the first reading.
We had let it warm up for about 2 hours.. we had it on while we were making the solutions.. i don't know if thats why it wasn't working, because when we first turned it on it was working just fine! but after 2 hrs it didn't produce those green and red lights when a white piece of paper was put inside when it was set at 532 and 640 nm. When we put the blank into it, it didn't read 100% transmittance like it had before, it read like 5, and the needle wouldn't move above about 10 no matter what knobs we turned.
Now that i have EVERYTHING ready to go, and if the spec 20 doesn't recover overnight, is there a qualititative way that i can measure this? Technically i could line all the samples up next to one another and say hmm, this one looks more pink than this other one.. which i may have to do, because i really don't want to just throw all of my work out the window.
This is very discouraging.
You can rank the samples if that is all you can do. Here are some other ideas:
1) see if they have one at the hospital you could use. It might be called a "UV-VIS" and common brands are Cary, Varian, and Shimadzu.
2) Try to fix the spec 20 with your teacher. See if there is a replacement lamp. The lamp is a fancy light bulb, so you cannot just run out and buy them. There might be one lying around. I couldn't find instructions. But, I can tell you this-
Wear gloves and goggles.
Turn off the system. Unplug it. Wait 10 minutes before starting. Make sure the old lamp is cold before you take it out.
Don't touch anything with your bare hands. Wear gloves. Oil from your hands can cause the lamp to explode when you turn the system on.
Wipe off the new lamp with a chimwipe or optical paper to remove any finger prints before you put it in. Be careful with the lamp. The inside is under vacuum, if you break it, it implodes and glass goes every where.
Close the system. Then turn everything back on. Don't turn the system on with it open, because if something goes wrong (lamp exploding) you want that contained inside the case.
If you don't have the replacement lamp, you can still open it up and see if any connections are loose. You can take out the lamp and put it back in. Follow the safety precaustions above.
3) You had mentioned a colorimeter... will that not work?
4) If the lamp is dead, and you have a very small very bright flashlight, you can try to put it in. You don't want to take the lamp out, because when you turn the power on it wil be dangerous not to have a part there, but try to fit the flashlight in. I have no idea how much space there is inside. Follow all the safety instructions from part 2. (Gloves, goggles, no power)
Here is a diagram:

You will want to point the flashlight toward the slits. Turn it on, and check for light at 530, 640. If you have light, and it is the right color, try your blank. Obviously, the lamp knobs will do nothing with this setup, so you should turn them to the lowest setting.
Louise

