[Reeko17]

I recently measured the Manganese in steel by spectroscopy with standard addition and I'm having trouble with calculations. From the known concentration of an Mn standard, how do you calculate the concentration of added Mn into a 50-mL vol. flask containging standard addition???

[Borek]

From the mass conservation - amount of substance doesn't change during dilution, thus

C₁V₁ = C₂V₂

although if it is standard adiition, you should account for the substance already present before.

[TomOHaver]

The concentration of the sample solution is given by (Sx*Vss*Cs)/(Ss*(Vxx+Vss)-Sx*Vxx), where Cs is the concentration of the standard solution, Sx is the signal given by that sample solution by itself, and Ss is the signal given by the sample solution after the addition of standard, and Vxx and Vss are the volumes of the sample solution and added standard solution.

This will be accurate only if the signal is linearly proportional to concentration.  Also, all additive interferences (such as spectral interferences) must be corrected separately; the standard addition method corrects only for multiplicative interferences.

Tom O'Haver

[TomOHaver]

If you are interested in "playing around" with the standard addition method, as a means of learning more about its capabilities and limitations, I suggest you take a look at http://terpconnect.umd.edu/~toh/models/Bracket.html.  This is a collection of downloadable spreadsheets (in OpenOffice format) that simulate various analytical calibration methods, including the single-standard addition and multiple standard addition methods, including their error propagation properties. 

Tom O'Haver
toh@umd.edu
http://terpconnect.umd.edu/~toh/