Spectophotometer and Lead Reactions help please

[x3kristiemarie]

I want to do a spectrophotometric analysis of the amount of lead in dried apricots for a my science project this year but i have no idea how to extract the lead or put it in solution and then cause a color change to analyze it using absorption vs. concentration.

[agm]

Hi x3kristiemarie,

What kind of spectrophotometry are you thinking of using? An overview of different kinds is here:

http://en.wikipedia.org/wiki/Spectrophotometry

A quick search of scholar.google.com indicates that atomic absorption spectrophotometry has been used for measurement of lead in fruits/vegetables before, but other kinds could be useful as well -- I don't have much experience in this area.

If the equipment you plan to use is at your school, and teachers, etc, have only operated it with liquid samples -- if nothing else, you could try apricot juice.

If the equipment is located at a local university, there is almost certainly a technician in charge of the equipment. I would ask this person how samples are prepared or if there's a grad student or professor who has measured similar things before that you could contact. Even if you aren't planning to use their equipment, these people would probably be happy to help you via email and maybe give you a tour of their lab or send you articles that you'd otherwise have to pay for (I'm a grad student, and I'm here!). If you have no idea where you're getting the equipment, a professor who does vaguely related research or has the equipment in his/her lab would be the person to contact to ask if you could use an instrument. I would check the chemistry, materials science, and biology departments for lists of equipment. There may also be some research centers with fancy names that have separate collections of equipment.

My intuition says that you could do pretty much whatever you needed to make your sample liquid enough -- microwaving, boiling, etc. I'd be wary of cooking it in a pot or other container that might contain lead itself (it could leach into your sample), and you'd want to keep track of the mass of apricot initially added (and maybe whether it was a whole or half fruit, etc) and the mass of liquid you end up with if you add water -- otherwise you won't be able to figure out the concentration in the fruit. However, depending on the type of spectrophotometry, you might have to do something called "ashing" the sample -- if this is necessary, there is almost certainly someone in charge of the machine who can explain.

Some links that might help:
http://www.uga.edu/~sisbl/aaplant.html
http://www.rsc.org/publishing/journals/ ... 9739800596

Also, when you talk about "caus[ing] a color change" -- this isn't something that you do, it's something that the lead (or whatever you're looking for) does. Light of a certain wavelength (color) shines on the samples, and if lead is there it absorbs it and emits it at a slightly different wavelength (color). The exact wavelengths you shine on the sample and look for in the detector depend on the element you're testing for.

Let us know more about what you're planning and other questions you have, and we'll be happy to help!

Amanda

[barretttomlinson]

Hi,

There seem to be at least two reasonable approaches to analysis of lead in foods. The most common approach seems to be the use of atomic absorption spectroscopy(AA). Here is an application note written by a manufacturer of AA equipment about analyzing lead in food:

https://www.varianinc.com/media/sci/apps/aa052.pdf

The other approach of which I am aware is electrochemical - polarography. Here is an introduction to that technique:

http://www.rsc.org/delivery/_ArticleLin ... nalCode=SA

And a short article on analysis of lead in food by polarography:
http://www.rsc.org/delivery/_ArticleLin ... nalCode=SA

I have seen some passing references to lead analysis by colorometric or spectrophotometric analysis but don’t have specific references.

If you have access to a college chemistry library you should consult Chemical Abstracts, the comprehensive index to the chemical literature, which is available in almost all college and university libraries. It would give you extensive references to the analysis of lead, including how to do it and what problems you will encounter. Chemical Abstracts( a service of the American Chemical Society) is also available online, though there is a significant charge to access it. If you can find a mentor at a college or university I suspect that they can enable access.for free, as well as being a source of comprehensive support.

This sounds like an excellent project that could be both fun and very instructive.

I wish you the best of luck with it!

Barrett Tomlinson

[barretttomlinson]

Hi,

Sorry, the link to the primer on polarography was incorrect. The correct link is:


http://www.amelchem.com/download/items/ ... al_eng.pdf


Hope this helps.

Barrett Tomlinson

[barretttomlinson]

Hi,

I found a few references to colorimetric determination of lead which sound more like what you were asking about. Here is the paper:

http://www.jstage.jst.go.jp/article/ana ... /1227/_pdf


Here is a very old paper describing a slightly different method:

http://www.biochemj.org/bj/033/1231/0331231.pdf

Here is an abstract of another spectrophotometric method.
http://iospress.metapress.com/content/1b8ye9bcubdqtk06/

Here is a reference for some ASTM methods for lead analysis. You can often find good collections of ASTM methods in university or college libraries, or get them through interlibrary loan:

http://www.astm.org/Standards/E1775.htm

I hope this gives you enough to get started on reasonable colorimetric analytical methods.

Good luck! This sounds like a very excellent project,

Best Regards,

Barrett Tomlinson