NIOSH 7300 - ICP OES calculation

need some help with NIOSH 7300 method <https://www.cdc.gov/niosh/docs/2003-154/pdfs/7300.pdf>


I have two 37mm cellulose filter paper, one is my filter blank while other is sample. The sample has 80L of natural gas passed through and I plan to test for Mg , final concentration in mg/kg.


Both are digested and top up to 10 ml with dilution acid. 


ICP OES Result:


Filter Blank : Mg = 0.022 mg/L , Pb = 0.002 mg/L 


Sample : Mg = 0.038 mg/L , Pb = 0.006 mg/L 




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(From Method) 
Given the formula is


Solution concentrations for the sample, Cs(µg/mL), 


Filter blank , Cb(µg/mL)


Volumes of sample, Vs(mL), and Filter blank , Vb(mL), 


calculate the concentration,C (mg/m3), of each element in the air volume sampled, V (L):


C= (CsVs - CbVb)/V = mg/m3


NOTE: µg/L / mg/m3




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My calculation,


[(0.038 mg/L x 0.01 L) - (0.022 mg/L X 0.01 L)]/ 80L 


= 0.00016 mg/ 80L 


Edit:


According to the composition result, density is = 17 gmol-1 , 
and I calculate this under STP. 


= 0.00016 mg / [(80/22.4)mol \* (0.017kg/mol)] 


= 0.00263 mg/Kg 


is this correct?


