# Why the obtained counts of 206Pb, 207Pb and 208Pb do not correspond natural abundance ?

Hi ,

1. we measured individual counts of 206Pb, 207Pb and 208Pb and found these counts did not correspond natural abundance. And we checked all of the previous records and found this non-correspondence always happens ( almost three years)  no matter what the concentration is.

natural abundance is 206 Pb: 207Pb: 208Pb=24.1%:22.1%: 52.4%

however, from our raw data( see the below picture), the rough abundance is : 206 Pb: 207Pb: 208Pb=13.0%:11.42%: 52.4%

the standard is named Pb, which means sum.

2. what makes this difference? is it radioactive decay or interference? 208 Pb has the interference of 207PbH, 207Pb has interference 206PbH. but we don't use hydrogen. we used He Mode and Ar2 Gas. And the diluent is 0.5% HCl and 5% HNO3. we tested Pb with other elements of V, Co, Ni, Cu, As, Cd, Hg.  Internal standards are Bi, Ge, In, Lu, Sc, and Te.

3. what should we do to solve this problem? use corrective equation if radioactive decay?

Thank you

best regards,

Di Xu

Parents
• Hi,

I have no direct answer on the difference between the theoretical abundance and counts measured. Probably due to physical differences. maybe someone els could answer this. i could not find anything in the literature.

The counts comparison between the 206/207/208 for other Agilent ICP-MS systems are the same as your example. And there is no difference seen between the no gas and He tune mode.

There is nothing wrong with your measurements and if you use the standard interference equation then there should be no error in the total of the calculated 208Pb when there is a natural abundance difference.

good luck with the measurements on the Agilent ICP-MS

• Hi Edgarvs,

Thank you for answering this question.

yes, I agree with you. initially, we did not notice there is a correction equation of Pb set in the method. we understand what is going on after you told us.

Thank you

best regards,

Di Xu

• Hi Edgarvs,

Thank you for answering this question.

yes, I agree with you. initially, we did not notice there is a correction equation of Pb set in the method. we understand what is going on after you told us.

Thank you

best regards,

Di Xu

Children
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