I just did an ICP measurement and been told you can go from ppm (parts per million) to the stoichiometry of your sample but I am not understanding this process how. If anyone could help out me on the right path it would be helpful. I have the mass of the powder as well if need, roughly 135 mg is what we used. The guy who did the test calculated some conversion factor of 1.574. Not sure how he got that either or what it is used for.
Trying to go from these ppm numbers to Fe_xS_y. So the subscripts (x,y) for the FeS sample I made.
Sulfur: 139,893 ppm mass: 32.06 g/mol
Iron: 572,006 ppm mass: 55.84 g/mol
Conversion Factor: 1.574
If you are sure not to have any other elements such as Oxygen you can calculate a formular of Fe and S fitting your measurements. FeS, Fe2S3....
With those ppm values I did the following:
572,006 x (1x10^-3) / 1x10^3 to get grams Fe/ grams FeS.
I didn't have 1 kg of FeS so multiplied that by the mass of FeS I put in so about .135 g.
That should give me the mass of Fe I had in the sample. I know what the mass should be if it was 1:1, and so i can find the Fe ratio which I got around .89.
Does that sound like a correct process or did I miss something?
140 ppm of 135 mg = 1.89e-5 g Sulphur
572 ppm of 135 mg = 7.72e-5 g Iron
1.89e-5 g / 32.06 g/mol = 5.90e-7 mol Sulphur in your sample
7.72e-5 g / 55.84 g/mol = 1.38e-6 mol Iron in your sample
As you see, there is much less Sulphur than Iron, so I am not sure you will get anywhere assuming you have only FeS and Fe2S3 in your sample. As mentioned above, it all depends on what exactly is your sample, and what else might be in there...
Dear colleague,
I will show the methodology for calculation of stoichiometry from ICP measurements:
The content of the major components Sr, Li and Ti, in single crystals, based on strontium–lithium–titanium oxides has been determined by inductively coupled plasma atomic emission spectrometry (ICP-AE) [1]. On the basis of the analytical information the composition of the corresponding crystallized phase was established.
I pay attention that analytical task require the determination of matrix elements (Sr, Li and Ti. In this case, after dissolution of the sample must be selected an appropriate dilution factor, which permit to measure the corresponding analytical signals of matrix constituents with desire level of precision (in this case the dilution factor = 20). The accuracy of analytical results is of prime importance. The calibration solutions for analytes were prepared from Merck Titrisols.
The content of Sr, Li and Ti (in %, w/w) obtained by ICP-AES are as follows:
Sr - 14.30 %, Li - 2.26 %, Ti - 46.88 %
The mass of the sample is 100 g. Hence in 100 g sample: Sr - 14.30 g, Li - 2.26 g, Ti - 46.88 g, O - 36.56 g.
The atomic weight (Sr) = 87.62 g / moles
The atomic weight (Li) = 6.94 g / moles
The atomic weight (Ti) = 47.87 g / moles
The atomic weight (O) = 16 g /moles
Step 1. Calculation of moleskin : Moles = Divide the mass of element by atomic weight of element Sr – 14.3 g : 87.62 g / mole = 0.1632 moles
Li - 2.26 g : 6.94 g / molse = 0.3256 moles
Ti - 46.88 g : 47.87 g / mole = 0.979 moles
O - 36.56 g :16 g/mol = 2.285 moles
Step 2. Calculation of the corresponding formula:
For this purpose the moleskins of elements have to divide by moleskins of the elements with a smallest value.
Sr = 1
Li - 0.3256 : 0.1632 = 2
Ti - 0.979: 0.1632 = 6
O - 2.285 : 0.1632=14
Therefore, the corresponding formula is: SrLi2Ti6O14
References
[1]. A. Detcheva, N. Daskalova*, S. Velichkov, I. Havezov, Analysis of single crystals based on strontium–lithium–titanium oxides by inductively
coupled plasma atomic emission spectrometry, Spectrochimica Acta Part B 58 (2003) 1481–1488
With kind regards, N.Daskalova
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