ELSD (or operator) Troubles

[algae man]

Hi,
I am attempting to analyze dimethicone by HPLC-ELSD and am having some troubles. I have based my method on Shimadzu's application note (link at the bottom), with some slight modifications (I replaced the THF with ethyl acetate and am carrying out my extraction with TEA). I am having a huge problem with reproducibility. I do a test injection of a curve point at the beginning of my run to check the method and I get a great peak. It is fairly symmetrical, nice baseline, etc. This is followed by two blanks, followed by running my actual curve. At some point in these two blanks, everything goes to hell and I get nothing for the remainder of the run. The only way for me to get any usable data is to let the system re-equilibrate (usually the next day when I attempt to run again). When I do this, I can get one good inj, and it starts over again. I have carried out the baseline and solvent baseline checks. At high gain settings, my solvent baseline is high but if that were my only issue, I think that I would never get peaks. Especially since flushing with the same mobile phase clears my problem. I've never used this detector before so maybe I am not doing something right. I am going between thinking that I have a detector issue or something wrong with my chemistry. I am using a Sedex 55 detector. Any help is appreciated. Thanks!

http://www.shimadzu.com/an/hplc/support ... bgzwn.html

[Ticoscen]

A few things will affect reproducibility significantly:

[1] Internal flow cell sweep gas is blocked.
[2] Blocked exhaust causing gooseneck to percolate.
[3] Clogged up annulus for the nebulizer.

Tim Reyburn
Ticoscen
M: 301 648 4094

[Consumer Products Guy]

Ticoscen repairs and refurbishes ELSD units, a 3rd party vendor. So I'd follow his advice.