I've seen the same thing. Baking in air makes the capsules look
great--but tends to generate higher backgrounds. Baking them under
vacuum, lowers backgrounds--as long as they are allowed to cool before
venting. I've also ran a series of tarnished capsules, unbaked, and
compared them to untarnished capsules, and don't see a difference. As
Brad mentioned, it might be something other than silver oxide. Of
course, it only takes trace amounts of silver oxide or sulfide to look bad.
On a side note, I do have to remember to be clean the forceps I use to
fold capsules. Yeah, I use the ones with ridges. Not an issue for EA,
but it can cause a small but variable blank in TC/EA runs, i.e. data
noisier than I'd like.
On 12/5/2018 9:40 AM, John Howa wrote:
> Echoing part of Brad's observations, but disagreeing with the rest, I'm starting to thing the adage "thou shalt bake thy silver capsules prior to loading" is a bit of a canard. Though this is part anecdotal (gathering data is never easy), we've seen *increases* in oxygen blank after baking new-from-the-box capsules (500 ˚C muffle furnace). If the OP does do a blank study (not with peak areas, but rather with isotope dilution) I'd love to see some hard data that supports the hypothesis that baking helps in some circumstances.