Hello,
We are using a test tube from our school with a half inch diameter, and we are planning on testing it tomorrow. We want to make sure it will be sensitive enough to the amount dog less we're using- in order to reflect realistic pollution levels, we wanted to stick to a concentration of 500 ppm, but we are starting to wonder if the spectrometer will be sensitive enough to test the differences between what we start with and what we end with, (if the Azolla can absorb some lead.)
The thing is, I’ve searched all over the internet but I can’t seem to figure out what wavelength I need to set the spec 20 at in order to detect lead. Perhaps I’m not looking for it the right way? A few experiments mentioned wavelengths around 250 nm, and that’s all I could find about it. If that’s accurate, it’ll be tricky because our Spec 20 only goes as low as 340. Would this mean we just set it as low as we can and hope it can detect the wavelengths emitted by the lead?
Thank you,
Sirenity
Phytoremediation Science Project: The Effect of Mustard Plants on Lead Concentration in Water
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Re: Phytoremediation Science Project: The Effect of Mustard Plants on Lead Concentration in Water
Hi Sirenity,
I'm happy to hear from you again and glad that you are making progress on the lead experiment. If you remember, I talked about detecting lead salts in water in one of my previous posts:
"I did a search for color reaction for lead testing and discovered a chemical called sodium rhodizonate that reacts with Pb2+ to give a purple color. The test is used in forensics to identify lead from gunshot residue: https://dps.mn.gov/divisions/bca/bca-di ... onate.aspx
https://pubs.acs.org/doi/abs/10.1021/i560110a034
Here's a source for sodium rhodizonate: https://www.flinnsci.com/sodium-rhodizonate-1-g/s0448/
I tried finding a procedure for using a spectrophotometer to measure lead concentration after reaction with rhodizonate, but the paper I found was from 1986 and our library did not have access to it. I will do some more searching and see if I can find a detailed, doable method for you.
Basically, the technique would be to make a solution of sodium rhodizonate and add a small, measured amount of a solution of lead nitrate (or whatever lead compound you have) to it. This should produce a purple color and you can put the solution into the test tube, put the test tube into the Spec20 and measure the absorbance at a wavelength of 565 to 590 nm. Remember, if a solution appears purple when you hold it up to light, it means that the solution is absorbing the complementary color which for purple is yellow and that is the color wavelength that you have to set on the spec--between 565 and 590 nm.
What I will need to find out for you is the concentration of rhodizonate to use and the pH of the solution. Once I have found that, then you can have your school order the rhodizonate and you will be able to test it with your lead solution.
Once you have all your chemicals and the method, you will have to make what is called a standard curve of absorbance vs concentration. This is simply a series of dilutions of your lead solution that you make, measure the A565 and plot on a graph on the y-axis with the concentration of the lead on the x-axis. Then later, when you measure the A565 of an unknown solution that contains lead, you simply look up the A565 on your standard curve and read off the concentration on the x-axis.
Here are some references about standard curves:
https://en.wikipedia.org/wiki/Standard_curve
https://www.youtube.com/watch?v=R6WiXa8R73c
I'm sure you will have lots more questions. Do as much reading on this as you can so you understand better what you are doing to measure lead. Try explaining it to a friend and see if they understand. That is one of the best ways to make sure that YOU understand a concept.
Good luck!
Sybee
I'm happy to hear from you again and glad that you are making progress on the lead experiment. If you remember, I talked about detecting lead salts in water in one of my previous posts:
"I did a search for color reaction for lead testing and discovered a chemical called sodium rhodizonate that reacts with Pb2+ to give a purple color. The test is used in forensics to identify lead from gunshot residue: https://dps.mn.gov/divisions/bca/bca-di ... onate.aspx
https://pubs.acs.org/doi/abs/10.1021/i560110a034
Here's a source for sodium rhodizonate: https://www.flinnsci.com/sodium-rhodizonate-1-g/s0448/
I tried finding a procedure for using a spectrophotometer to measure lead concentration after reaction with rhodizonate, but the paper I found was from 1986 and our library did not have access to it. I will do some more searching and see if I can find a detailed, doable method for you.
Basically, the technique would be to make a solution of sodium rhodizonate and add a small, measured amount of a solution of lead nitrate (or whatever lead compound you have) to it. This should produce a purple color and you can put the solution into the test tube, put the test tube into the Spec20 and measure the absorbance at a wavelength of 565 to 590 nm. Remember, if a solution appears purple when you hold it up to light, it means that the solution is absorbing the complementary color which for purple is yellow and that is the color wavelength that you have to set on the spec--between 565 and 590 nm.
What I will need to find out for you is the concentration of rhodizonate to use and the pH of the solution. Once I have found that, then you can have your school order the rhodizonate and you will be able to test it with your lead solution.
Once you have all your chemicals and the method, you will have to make what is called a standard curve of absorbance vs concentration. This is simply a series of dilutions of your lead solution that you make, measure the A565 and plot on a graph on the y-axis with the concentration of the lead on the x-axis. Then later, when you measure the A565 of an unknown solution that contains lead, you simply look up the A565 on your standard curve and read off the concentration on the x-axis.
Here are some references about standard curves:
https://en.wikipedia.org/wiki/Standard_curve
https://www.youtube.com/watch?v=R6WiXa8R73c
I'm sure you will have lots more questions. Do as much reading on this as you can so you understand better what you are doing to measure lead. Try explaining it to a friend and see if they understand. That is one of the best ways to make sure that YOU understand a concept.
Good luck!
Sybee