Dear Andrea Santa

Actually I do not know what the purpose you digesting the sediment by using the Pb210, it is for studying geochronology , sedimentation or accumulation rate. and what type of the sediment it is in sediment cores profiling, surface sediment and what the sediment condition in clay, soil,sand or silt nature. And if running the sample before you platting the radionuclide you are using the leaching or total digestion. But anyway, those will help the public to try figure out your research..

thank's

Best regards

Zolhizir bin Daud

You are right! I’m going to determinate Pb210 for geochronology and sedimentation rates.

Before I use to do a total digestion in the microwave using HCl, HNO3 and HF, but right now since my microwave is broken I need to find another way to do the total digestion. The only methodology I have, uses HClO4 but I don’t have the right fume hood to work with it.

Do you have any suggestions? 

Thank you for your help

I think it's can work because you can digesting it in open system because the heat is low about 90-200C . But beware of contamination and unpleasant or bad air flow during  the sample dried that might be affecting your yield or recovery .  If you do not have the right of fume hood you can modified the fan  absorber in your lab as far  as can move out the smoke from your lab. But sorry this is not the right and practical but anyway just a basic problems. Or other alternative uses the leaching method.

Zolhizir, 

Thank you for your time and ideas, I will try your idea of the fume hood and the leaching method. Right now my recovery is very low 60%, I tried a total digestion in an open system using HCl, HNO3 and HF. 

Thank you again for your time! 

Andrea

Dear Andrea Santa

You welcome

Regards

Zolhizir bin Daud

We use open digestion in our lab. Briefly, about 2 to 3 g of powdered material in the presence of 208Po tracer are brought into complete dissolution by treating sequentially with HF, HClO4, HNO3 and HCl in a teflon vessel. The solution is finally made in 60-70 ml of 0.5 to 0.6 M HCl, ascorbic acid is added to mask the Fe+3 ion in solution. The Polonium isotopes (210Po and 208Po) are then auto plated onto a 1.5 cm diameter silver disc. Standard methods are available in the literature.

Thank you for your advise. Right now I have the problem with using the HClO4 since I don’t have the right fume hood. I try the open digestion with HCl, HNO3 and HF but I didn’t get the best results.

Dear Andrea

What do you mean have gotten bad result. It's  do not appear  yellow or red pastel precipitate digestion or still having remains look likes black dot when ending the total digestion. The appropriate or suitable  samples amount  for digestion is around 0.5-1g. and from my experience you need first, digesting the sample with HNO3 + HClO4 ( evaporated 2 hours ) + HF dryness until well mix in 2-3hour. Then with HCl and (H2O2 if having) and dried up. You have to try 3-6 times for testing or running samples before you digesting the actual sample for precise and accuracy result.

All the best Andrea.

Regards

Zolhizir bin Daud

Dear Zolhizir

The problem I had is that my total digestion didn’t look like it. The final digestion was very dark (I attached a picture).

I will try the digestion as you told me, Im sorry I ask you so many questions, but what temperatures do you use during the digestion?

Thank you

And happy 2015

While this is a bit off topic, you probably know that Pb-210 is a low energy beta emitter. At ELI, we measure it directly by LSC (after a leaching digestion &) then chemical separation/purification. It's granddaughter, Po-210, is measured using Alpha spec; we prepare to do that (after a leaching digestion) by lanthanide micro co-preciptation.

WE often do both measurements because these two radionuclides are not always in equilibrium in the samples that we receive.

As a radiochemist without specific expertise in geochronology/sedimentation rate measurement, maybe I am missing something basic. However, I would be concerned about the need to demonstrate that Pb-210 & Po-210 are in secular equilibrium for your specific sample matrix (sediment).

Maybe this equilibrium is already well established for this matrix when used for  geochronology and sedimentation rate measurements. 

I do find a reference from 1975 that makes this assumption, (http://www.epa.gov/glnpo/lmmb/methods/lead-210.pdf) says, "Po-210 is the alpha emitting granddaughter of Pb-210, and can be used to represent the actual Pb-210 concentration in each sample because the two isotopes are assumed to be in secular equilibrium."

With Po-210's half-life of 138 days, I think that the sediment would have to be undisturbed for at least ~2 years & that Pb-210, Bi-210 & Po-210 were all ~insoluble for the assumption to be valid. Can you address my concern? 

I wish you the best in your work!

Dear Andrea

The black end might be interfered of MnO or Carbon. Try add more H2O2 and HCl and dry up again also if those prolong repeat again with chemical mixture as usual until the black precipitate is digested properly or shall be reduced to yellow, white or red pastel. some time it's take much or long  time. try also maintain the temperature at 100-200C. and you can adjust and play around it. And before you digest the sample did you homogenize and sieve the sample first?. using what size of sieve 63um or 125um?. What type of your sample e.g. clay. silt, soil, or mangrove mud?. try use the amount of sample about 0.5-1g.

Regard's

Zolhizir bin Daud

Thank you Zolhir and Jack!

Jack we do assume that the Pb-210 & Po-210 are in secular equilibrium, and before we do any type of digestion we leave the sample undisturbed for at least 1 year.

Zolhir we do homogenize the sample but we don’t sieve it! I will try that before the digestion

Thank you for all your help

If you don'l care  Po-210 (initial), then frist, you can try using furnace (note the volatile of Pb-210) to remove some organic materials or destroy some things else, then try "digesting the sample with HNO3 + HClO4 ( evaporated 2 hours ) + HF dryness until well mix in 2-3hour. Then with HCl and (H2O2 if having) and dried up.." according to Zolhizir bin Daud's suggestion. Finally, waiting for around 6 months---> Po-210 determination by alpha spectroscopy.

LSC is best choice for Pb-210 if you don't want to wait for 6 months.