Bead not complete digested.

[ap83]

Hello everyone if any of you have any clue.
Lately when I do the digestion for gold bead (aqua regia) some of the beads do not digest complete.( it also hapen with CRM,s and Blanks).
The water bath temp. is at 35 degres C.
We add 0.5 ml mixture of nitric and de-onized water to each tube and the rack is place in the water bath for 15-20 min.
We remove the rack from water bath and add 1.5 ml of concentrate Hydrochloric acid to each sample and let it sit for 10-15 min then return to the water for 30 min.
After the 30 min. in aqua regia we check the samples to see if the dore bead are dissolved, if not totally digested we keep it in the water until bead is totally digested.(It ussualy take about 30 min. to complete digest the bead).
Once the samples are complete digested we remove it from the water bath and allow to cool for 10-15 min. then diluting with to 5 ml usin de-onized water and vortex.

* We already try by encresaing the water temp.
* I dont tink is the sample because we re-run the same sample a second time and it complete digested.

 

[Yggdrasil]

Hello everyone if any of you have any clue.
Lately when I do the digestion for gold bead (aqua regia) some of the beads do not digest complete.( it also hapen with CRM,s and Blanks).
The water bath temp. is at 35 degres C.
We add 0.5 ml mixture of nitric and de-onized water to each tube and the rack is place in the water bath for 15-20 min.
We remove the rack from water bath and add 1.5 ml of concentrate Hydrochloric acid to each sample and let it sit for 10-15 min then return to the water for 30 min.
After the 30 min. in aqua regia we check the samples to see if the dore bead are dissolved, if not totally digested we keep it in the water until bead is totally digested.(It ussualy take about 30 min. to complete digest the bead).
Once the samples are complete digested we remove it from the water bath and allow to cool for 10-15 min. then diluting with to 5 ml usin de-onized water and vortex.

* We already try by encresaing the water temp.
* I dont tink is the sample because we re-run the same sample a second time and it complete digested.

Welcome to us.
The Dore might not be completely homogenous, some beads might have enough Silver so the digestion is stopped by Silver Chloride.
Ideally the digestion should be done around 70 centigrade.

 

[ap83]

Welcome to us.
The Dore might not be completely homogenous, some beads might have enough Silver so the digestion is stopped by Silver Chloride.
Ideally the digestion should be done around 70 centigrade.

Hello, and thank you for your answer.
What is strange, is that it also happen with CRM and BLANK samples. We also retest the same sample (same sample that did not digested the first time) without doing anything different and completed digested.

 

[tmj883]

Two suggestions: one, I was taught when making aqua regia to always add the nitric acid to the hydrochloric acid, not the other way around, and two: I would not add the bead to be digested until the aqua regia was well formed, not in the tube with nitric acid alone.

 

[Yggdrasil]

Two suggestions: one, I was taught when making aqua regia to always add the nitric acid to the hydrochloric acid, not the other way around, and two: I would not add the bead to be digested until the aqua regia was well formed, not in the tube with nitric acid alone.

Any would do, unless you have some very strange alloy.
HCl først or Nitric first do not matter.