Hexavalent
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Determination of the Concentration of Vitamin C in Urine
Please have a look at this paper and tell me what you genuinely think of it. I am very welcome to suggestions for improvements, I am here to learn
after all and the more seasoned chemists here can certainly help with that by offering their views.
Thanks,
Hexavalent
Attachment: ascorbic paper pdf.pdf (173kB)
This file has been downloaded 996 times
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kavu
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One general remark on references. You should number them and use these numbers in the text as you go along. If you have a statement based on a
reference, end that sentence in the corresponding number. This is the standard method used in publishing. With books and everything a publication year
and publisher should be shown.
Another thing that has to do with analytical stuff. You state no errors in your measurements. "As seen on the previous page, the concentration of
Vitamin C in the urine sample was found to be 339.28mg/L". This assumes that your result is EXACTLY 339.28 mg/L. It should contain a margin of error.
Error can be estimated by working out how accurate your titration procedure is (at least +- 1 drop it seems).
Also l-Ascorbic acid should be L-Ascorbic acid. The L should not be in caps, but in small-caps. Also the experimental section is a bit too broadly
described (to my taste at least). Your preparation of Gram's iodine is a bit vague, it has percentages whereas I would prefer grams and moles. What
you are describing is an analytical method after all.
The graphics are OK, but you should really consider learning to use a drawing program. It's easier as you can draw exactly what you want. Figure 1
title is not centered and text would look a bit tidier if justified. Now it's just flushed to the left.
Otherwise it's a really good article and a lot of work and thought has gone into it!
[Edited on 24-8-2012 by kavu]
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Hexavalent
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Thanks a lot for those pointers, they are very helpful indeed.
I'll wait to see what others think so that I can edit it all at once and produce Version 2.
P.S. I don't quite get what you mean by 'small-caps', could you clarify?
Thanks
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kavu
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This wikipedia article covers the typographic thingamabob: http://en.wikipedia.org/wiki/Small_caps
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Hexavalent
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Ah, thanks. I'll change them now, as well as the references and the other things you picked up on.
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Hexavalent
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Here is the edited version, with all the suggestions you made, kavu;
Attachment: ascorbic paper3.pdf (176kB)
This file has been downloaded 811 times
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Wizzard
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Page 2:
stains *literally* almost everything. - This word seems too casual.
"Take care when using heat sources or any sharp objects used to cut and deliver samples (e.g. scalpels and hypodermic needles)..."- Run on sentence,
shorten it 
Page 3:
"...such as *millilitres* can be determined." Spelling counts!
Cite "eBay", I would provide a link. Looks professional.
Page 5:
"specifically termed *flavanoids*, flavan..." - Is the "a" bolded in flavanoids, or is it just me?
I also noticed many times you capitalize "Vitamin C", and other times it's just "vitamin C". I'd pick one, and stick with it.
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Hexavalent
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Page 2: Ok, thanks. I have a habit of making sentences too long
Page 3: Will provide a link, and fix the spelling.
Page 5: Yes, the 'a' is bolded to show the difference between flavonoid and flavAnoid.
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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Hexavalent
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Version 4, with Wizzard's corrections.
Attachment: ascorbic paper4.pdf (178kB)
This file has been downloaded 1194 times
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Nicodem
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First the scientific stuff...
You should correct the wrongly cited references. You cited articles as if they were books (the location is not given! The location is way more
important than the tittle). Take some casual scientific article as the basis for the citation format to use, but generally it goes like this: N.
Surname, Journal, year, volume, firstpage-lastpage.
You list among the references also sources where you took the schemes (ref. 5). The list of references is reserved for scientific reasons only. You
can not use it for listing media sources from which you borrowed material just because you didn't feel like drawing schemes by yourself. The
information on sources should be given near the material borrowed and not in the references.
In the introduction and elsewhere you mention lots of factual data, but there are no pointers to the references where you found them. You should make
sure to point to references whenever giving discovered facts (numerical values based on experimental measurements and discoveries). This is a general
advice. The scientific method demands the traceability of all experimental data. If you are uncertain of when a reference is needed, you can help
yourself by questioning: "Will the reader be able to trace the experimental evidence supporting the given fact in a humanly tolerable period of time?"
For this reason, references to primary literature should preferably be used for specific facts, and reviews or other secondary literature for a
collection of facts and theory.
Correct representation of values is extremely important in science, because the reader evaluates how trustworthy a report is, not only based on the
correct use of references, but also on the correct representation of data:
You were already advised to correct the values in accordance to the known measurement error - you still didn't. The "339.29mg/L (7.14% potential
error)" sounds oxymoronic - should be made rational, e.g. "340 mg/L (+- 35 mg/L)" or similar.
Units should be separated from the value by a blank. For example "100mg/L" should be "100 mg/L". Also, don't exaggerate with units: it is pointless to
use cm3 and mL units in the same report, and two symbols for the same unit (l and L for liter). Sensible use of prefixes is also advised
("0.00028 moles" -> "0.28 mmol"). About the "339.28mg/L, or 0.33929g/L" - more decision needed?
Compounds names start with low case, for example, "Ascorbic acid" -> "ascorbic acid".
... then the content
You did a nice job, but there is much place for improvement. You improved greatly since the beginning, but it will take years more and quite some
patience.
The focus on certain topics in the introduction is in contrast with the complete lack of focus on the topics directly pertaining to the experimental
work.
Specifically, you don't review the analytical methods for ascorbic acid determinations in urine. After all, your report is about measuring ascorbic
acid in urine, but you totally avoid this topic.
You also do not describe how this method that you used was developed. I'm unable to figure out from which of the references it originates, which means
that I cannot check for issues that I'm interested in and you don't discuss. Specifically and most importantly, you do not discuss the effect of the
matrix on the validity of the analytical method, which is obviously of extreme importance given that your matrix is full of potentially oxidizable
compounds.
Your discussion on the calibration of the iodine solution is a bit hard to understand - it could be written a bit more concisely. I must admit that,
from that paragraph, I can not figure out how you validated the analytical method. You must present the scientific arguments on which you based the
validation, as well as all the arguments against it.
What is Figure 3 supposed to represent? It is completely obsolete and thus attacks your credibility.
In some points you go blatantly against yourself, for example, you write: "... was found to be 339.28mg/L, or 0.33929g/L. This value is expected to be
relatively accurate and reliable, as steps were taken to prevent both oxygen-caused and photo-degradation of the Vitamin C, when in the form of the
standard solution and when handling the urine specimen."
The number is obviously not accurate as you already acknowledged in the experimental. You also do not demonstrate it is anything close to reliable.
Your validation was apparently done in water rather than in the matrix. So, we know absolutely nothing about its reliability. You should strictly
avoid claiming conclusions that are contrary to your own findings, because this seriously affects the credibility of a researcher.
This same approach of strict consistency should be maintained also for referenced discussions. One example is where you go counter your claim in the
same sentence: "The reaction that takes place between the iodine and the ascorbic acid (more specifically, the ascorbate anion) is somewhat complex
but is shown to be that one mole of ascorbic acid reacts with one mole of iodine, producing two moles of iodide ions and one mole of dehydroascorbic
acid."
First you say the reaction is complex, then you imply it was shown to be totally simple. You say there is a fixed stoichiometry and a single product,
which is furthermore apparently produced by a single and expected addition/elimination pathway, so how can it be considered complex? When you are
uncertain on the possible oxymoron deviations in your statements, read them carefully by considering them factual rather than literary works. I know
this is difficult to do at a young age (I certainly was not able to do this as a teenager), but you seem quite intelligent for your age, so perhaps
you will learn fast.
Conclusions would be most valuable. You should give a summary of all the contributions you reports give.
Now you have a taste of how the peer-review system works. It is always painful, even when publishing articles becomes a routine, but at the end you
feel like you accomplished something and learned something important.
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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Hexavalent
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That's a huge help, Nicodem - thank you. I am not at my own computer at present but as soon as I get access again I will sit down and review what you
have mentioned in my paper. Your knowledge and experience is invaluable and I genuinely appreciate your comments, alongside kavu's and Wizzard's, for
improvements.
Many thanks,
Hexavalent
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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Hexavalent
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Updated to incorporate Nicodem's comments;
Attachment: Version 5 (Ascorbic Paper).pdf (286kB)
This file has been downloaded 1860 times
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woelen
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I had a look at the final paper and given your age, available equipment and experience, I think you did a very good job. As others already noted,
there still is a lot to learn, but you have a whole life in front of you where you can learn things, so expect things to become better in the (near)
future.
Of course, I still have some remarks, most of them in the field of numerics. If you write 50 mg, or 1 ml, you should specify accuracy, instead of
writing 1 ml you should write 1.00 ml, indicating that you could determine the volume up to 0.01 ml accuracy. Even better (but more laborious) is to
specify intervals, e.g. 1.00 ml +/- 0.02 ml, which indicates that your volume most likely is 1.00 ml, but it could be as low as 0.98 ml or as high as
1.02 ml.
In another place you write 339.29 mg/L +/- 35.7 mg/L. I would write 340 +/- 35. Accuracy of numbers and how you represent that accuracy is an
important aspect of science and it is also of very high importance when doing calculations.
Another totally different issue is that the iodine-starch method determines amount of reducing species in a solution. You touch this aspect briefly,
where you mention the possible presence of other potentially oxidizable compounds, but could you find information on this and use this information to
obtain more insight in the correctness of the number you found?
There also still are some typos: Vitamin C must be written as vitamin C (or simply use the term ascorbic acid all over the place. There is a typo at
the start of the introduction: excpetions.
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Hexavalent
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Thanks for that woelen, it is of great help. I'll correct it when I have a chance and will re-publish when that is complete. By the way, do you prefer
the text as it is, in one column, or do you prefer multiple columns?
Thank you for taking the time to read the article and offering your views,
Hex
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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bigmol
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VitaminC
Vitamin C is usually considered to be equivalent to ascorbic acid. This is not strictly true as the first oxidation stage dehydroascorbic acid
nutritionally still has vitamin c activity. From a legal stand point in the food industry vitamin c equals the sum ascorbic acid plus dehydroascorbic
acid. Ascorbic acid is is used in the food and beverage industry as as oxygen absorbing component. From this viewpoint only ascorbic acid is
considered to be the active component. The second oxidation stage from dehydroascorbic to threonic and oxalic requires a much more oxidising redox
potential and hence is not considered an antioxidant. For my ascorbic acid determinations in my commercial lab I use either silico molybdate
colourimetry or oxidative voltammetry on a carbon electrode. Both of these are much more selective than iodometry or the indophenol titration.
Iodometry the method you are using is quite convenient but is reliable only when other reducing materials are absent.
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