The problem is that it is not reliable. I continue to get variable results from the MOSS. Even with flows optimized, no leaks, good reagents and columns (Applied Biosystems), my yields will suddenly drop to between 1/4 and 1/8 of the theoretical OD. On top of that, I've had several unexplained total trityl failures. Without the MOSS attached, it is more reliable. There is a lot of extra tubing involved, and the Expedite does not use the excess of reagents the 394 does. My ABI 394 is still cranking 'em out, and with higher yields than the expedite.
The MOSS, by the way, must be disconnected, (let me emphasize: the MOSS must be disconnected) and the instrument thoroughly, thoroughly flushed before doing a PNA synthesis. Then you will have to do all that flushing again to rid the machine of the PNA chemicals before doing a DNA synthesis, and then reconnect the MOSS, if you have one. My understanding is that some large facilities use multiple Expedite units, rather than use the MOSS option. Also, it is recommended you use UHP helium for the Expedite, rather than argon. I've just switched to helium, so I can't say how much affect it has yet.
Terry Mulcahy
>>> "Richard F. Cook" <cook@MIT.EDU> 3/16/01 >>>
Dear ABRFers,
Someone on my campus is considering the following instrument to do PNA and
DNA synthesis.
If anyone has any opinions, I'd appreciate them.
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".... trying to find someone familiar with the Applied Biosystems Expedite
8909 Nucleic Acid Synthesizer. The
Expedite with the PNA option can execute the PNA protocol as well as
existing DNA/RNA protocols. The MOSS option that we are interested in
expands the column capacity from two to sixteen. We are interested in
purchasing this instrument but were a little suprised when the vendor told
us the MOSS option, although still supported, was no longer being made.
There are a few MOSS options left and if we decide we want one we will
purchase one.
I am primarily interested in its reliabilty and any insight as to why ABI
stopped its production."
-----------------------------------------------------------
Thanks in advance.
Dick
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