[Organoid]

Hello,

This week I ran an AA Spectroscopy experiemnt in my university, in which we had to analyze the percentage of Copper in a metal coin, and the containment of Iron in morning cereal.

We used 2 standard solutions of 1 and 10 ppm (containing both Copper and Iron), and exprimented a few diluted solutions of the extracted Copper and Iron from the substances.

The results we received were an average conc. in mg/L and standard deviation of the 3 tests run by the machine.

My question is: what do the concentration results that the machine provides us with mean? i.e. if 1 and 10 ppm standards had an average of 0.525 and 1.426 mg/L respectively, and the diluted solutions (x10, x100, x1000) had an average of 10.72, 4.094 and 2.644 mg/L respectively, how can I analyze these results to calculate the original conc. in the original substance?

I tried to search the net for answers, but only things it provides me with are theoretical articles about AA, with no actual lab reports to assist me.

I'd appreciate your help, thank you.

[Arkcon]

What you need is a standard curve, your class notes and text books should have the information for you, giving you the steps the instructor expects you to know.

Now.  To help you visualize.  If the 10 ppm solution gave you a reading of 1, and you could have crunched up some cereal  into the instrument and get a reading of 2, you'd know exactly how many ppm.  But you couldn't do that, and you didn't get obvious results like that.  But after you generate a standard curve, you will essentially be able to convert your unknown reading into amount, which you will correct for any dilutions that you've made along the way.

Give it a try.  We're here to help you along the way.

[Organoid]

What you need is a standard curve, your class notes and text books should have the information for you, giving you the steps the instructor expects you to know.

Now.  To help you visualize.  If the 10 ppm solution gave you a reading of 1, and you could have crunched up some cereal  into the instrument and get a reading of 2, you'd know exactly how many ppm.  But you couldn't do that, and you didn't get obvious results like that.  But after you generate a standard curve, you will essentially be able to convert your unknown reading into amount, which you will correct for any dilutions that you've made along the way.

Give it a try.  We're here to help you along the way.

Ok, so I've generated a standard curve, although it has only 2 points due to only 2 standards. I hope the results will be reliable enough.
I added a linear trend line, and now I have the linear equation.

Since it's y = ax + b, how can I use this equation to calculate the unknown samples' concentrations?
I tried relating to the equation as AA = a x C (AA=absorbance, a is the trend line's slope and C is the variable) but my results don't make sense. Is it the wrong way?

I'd appretiate anyone to contribute to my understanding of this process.

[marquis]

Hopefully, you have the weights of the samples you analyzed.

Usually, liquid samples are calculated in micrograms per ml(an equivalent
unit is milligrams per liter).  This is usually called ppm.

Calculate the total amount of copper and iron is the samples that you have (on
a weight /volume basis).

This involves the concentration, dilution factors, and total volume.  The answer
should be in milligrams or micrograms (depending on units used).  Then divide
the weight of copper or iron(in micrograms) by the weight of the sample (in grams).

This gives the amount of copper or iron on a weight/weight basis, but still in ppm.

Good luck.

[Corribus]

Ok, so I've generated a standard curve, although it has only 2 points due to only 2 standards. I hope the results will be reliable enough.

For practice, it's fine I guess, but for any serious application you'd want at least, probably more like 4 or 5. You can always draw a perfect line between two points, so the degree of error can be quite large. Aside from the usual averaging out of noise, having several points allows you to determine if you're in a linear concentration region.

Also, your analyte concentrations should not be larger than your most concentrated standard or less than your least concentrated standard. Basically, you want to be interpolating rather than extrapolating your unknown concentrations. Most instrument software packages will automatically notify you of this if your unknowns are outside your standard range, but it's good to be aware of it before you get started.