Chromatography Forum

hi! I'm a high school student. I really need hlep on my chromatography lab report please. thank you very much!

1. Identify three factors that might influence where on the chromatogram the pigments end up.

2. Briefly state the specific function of each of the five pigments in the leaf extract. (carotenoids, xanthophylls, phaeophytins, chlorophyll a and chlorophyll b)

3. If you had let the chromatogram for longer, would the results have been any different? explain.

4. If you results do not appear to be quite what was expected, outline any sources of experimental error that might have influenced the results.

We won't do your homework for you. What we can do is point you in the right direction.

So, you tell us what you think the answers are, and we'll try to guide you from there.

Hi,

Tom's reply is spot on. For your first question, try looking at the Science Fair page on my website www.itsjustabox.com, which may help get you started.

Regards,

Ralph

For 2) - each of these pigments is well covered by any HS Biology text or even an online encyclopedia - Wikipedia is probably a pretty safe bet on this too (I don't normally recommend it, but it too can be a good starting point for real references & resources).

i appreciate for the info and your help cause i want to get good marks on this lab. i've come up with the following answers:

1. Identify three factors that might influence where on the chromatogram the pigments end up.
The filter paper, solvent and time is the three factors that might influence where the pigments end up on the chromatography.

2. Briefly state the specific function of each of the five pigments in the leaf extract. (carotenoids, xanthophylls, phaeophytins, chlorophyll a and chlorophyll b)
Carotenoids are secondary pigments that support the photosynthetic process by passing their absorbed light energy to chlorophyll. Another function of Carotenoids in plants is to absorb this “excess energyâ€

I think the key to 3. is the difference between actual retention and relative retention.

Regards, Pat.

You are doing well so far.

At the risk of being pedantic or sounding like a GOM

"The filter paper, solvent and time is the three factors that might influence where the pigments end up on the chromatography." should read
"The filter paper, solvent and time are the three factors that might influence where the pigments end up on the chromatogram. "

Watch out for minor errors like "Chlorophyll gives pants their green color " You'll end up in the out-takes book

For 3 and 4, follow up on Pat's suggestion and think about what would happen if you left it running for a day - would all the spots stop when the first one reached the end of the paper?
Also, how small and what shape was your separated compound? How did you measure the distances - would it make a difference if you measured to a different part of the spot? Has it started to spread out with time? Would this make it more difficult to measure. If all the peaks spread out what would be the consequences?

Regards,

Ralph

You're on the right track. As to running longer (assuming you had more/longer paper), look up the concept of throretical plates. More paper=more plates.

Or think of it in terms of two trains leaving a station at the same time but travelling at different rates. How far apart are they after 1 hour? And after 3 hours? (and you thought you'd never use algebra outside a math class).

Great analogy DR!

I meant to say in my previous post, AP, you're other answers are pretty good and pretty well written, nice work

Before I got chance to type it my LC lost pressure and started pumping mobile phase into the column compartment. C'est la vie!

Out of interest, here is a picture of a theoretical plate




Regards,

Ralph

Excellent!!

1. Identify three factors that might influence where on the chromatogram the pigments end up.
The filter paper, solvent and time is the three factors that might influence where the pigments end up on the chromatography.

If you wanted to get bonus points, you could add "relative humidity" (paper soaks up water vapor from the atmosphere, so changing the humidity indirectly affects the chemical composition of the paper) and "temperature" (your pigments will interact with the paper and the solvent in a slightly different manner as a function of temperature).

2. Briefly state the specific function of each of the five pigments in the leaf extract. (carotenoids, xanthophylls, phaeophytins, chlorophyll a and chlorophyll b) . . .

I'm not a botanist or phytochemist, so I'll pass on this one!

3. If you had let the chromatogram for longer, would the results have been any different? explain.
(i'm don't know about this one)

If you had a chance to watch the paper as the experiment was occurring, do you remember what happened at shorter time? If so, just extrapolate from there. DR's analogy is a good one, but be a bit careful about applying it. If you remember from watching the solvent move up the paper, the motion was fairly fast at the beginning, but slowed down as the "solvent front" moved further and further off the paper. At some point, the solvent is moving so slowly that it's not worth waiting any longer. For more bonus points, you might mention that most chromatography today is done under constant-flow conditions using gas pressure or a positive-displacement pump for liquids to prevent that slowdown from occurring.

4. If you results do not appear to be quite what was expected, outline any sources of experimental error that might have influenced the results.
In some cases, paper chromatography does not separate pigments completely; this occurs when two substances appear to have the same Rf values in a particular solvent.
Fingerprints on either the filter paper may have affected the experiment because the oil from hands can affect the results.

Again, excellent (and correct) answer. Additional factors might include:
- differences from one lot of paper to another (different types of paper may interact differently with the pigments)
- temperature variations (per "bonus" points on question 1)
- relative humidity variations (again, per question 1)
- variations in equilibrtion time between the paper and the solvent.

As a last comment, the "theoretical plate" joke (by the way, Ralph, I think I'll borrow it !) is chromatographer's humor. There's an explanation of what theoretical plates represent (and why they're only "theoretical" in the FAQ section here: http://www.lcresources.com/wiki/index.p ... icalPlates

Again, congratulations on an excellent job!

Well applepork, that's your homework done for you. Let us know what grade you got

Well done!

Salma