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Topic: Sudden precipitation in sample solution  (Read 892 times)

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Offline Ambiiramus

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Sudden precipitation in sample solution
« on: December 21, 2021, 06:10:51 AM »
In this project I'm doing, I need to analyze the benzoic acid concentration from a meat sample. To increase the solubility of the benzoic acid, the meat was "soaked" in a solution containing a small amount of NaOH. After about half an hour, the solution was filtrated using normal gravity filtration. To remove fats and proteins, tert-buthyl methyl ether was added, mixed and separated from the aqueous layer. The slightly alkaline nature of the aqueous layer made sure that the benzoic acid should (at least for a good amount) stay in that layer. The last step was diluting the sample a bit further after which the samples were injected into the HPLC.

Now here's the problem: This sample preparation was done in duplicate. After separation of the two layers, something precipitates out of one of the two samples, but not the other. The same meat sample was taken, the same chemicals were used, the same time was spend between the steps. The only thing that differs between the two samples is the separation funnel used. When the rest of the sample preparation was done and the samples were injected into the HPLC, the peak area from the 'precipitation-sample' was way lower than the 'normal' sample.
Could this be explained by the precipitation and if so, what could it be?

Any help is appreciated!

p.s first time on this forum, feedback is always appreciated!


Offline Borek

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Re: Sudden precipitation in sample solution
« Reply #1 on: December 21, 2021, 08:38:10 AM »
The same meat sample was taken

Meat is not homogeneous so no two samples are identical.
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Offline Ambiiramus

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Re: Sudden precipitation in sample solution
« Reply #2 on: December 21, 2021, 09:34:42 AM »
Thanks for the reply!
Both samples were taken from the same piece of ground beef, wouldn't you expect to at least see a little bit of precipitation in the other sample in that case?


Offline Borek

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Re: Sudden precipitation in sample solution
« Reply #3 on: December 21, 2021, 04:11:48 PM »
Hard to say. Yes, I would expect samples to behave similarly, at the same time homogenization can be tricky so some differences are inevitable.

First thing I would do is to just repeat the experiment, to make sure every possible human error is eliminated.
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Offline billnotgatez

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Re: Sudden precipitation in sample solution
« Reply #4 on: December 22, 2021, 02:41:12 AM »
The statistician in me would suggest doing the experiment more than 7 or 8  times (actually I would do 10). Maybe with the same meat and then repeat with other meat and compare statistics. I might also try to think of a control group and possibly a blank group.
But, this is me and may not be practical.

Offline Ambiiramus

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Re: Sudden precipitation in sample solution
« Reply #5 on: December 22, 2021, 08:30:53 AM »
Thanks for all the replies.
Unfortunately due to the project coming to an end, I cannot do the experiment again. The goal of this project was to show how difficult it can be to deal with certain samples and their matrices. I certainly agree that doing more samples would give more explanations as to why this precipitation happened.

Meat is not homogeneous so no two samples are identical.
And yes, I almost overlooked that this can be a huge factor in working with these kind of samples.
Thanks for the replies!

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