I saw an announcement for a seminar in my area next week that is called something like "Take Your Mass Spectrometry to the Ultimate Dimension of Supreme Amazingness with MICROFLOW." I may have exaggerated the title...a little... Then that got me to thinking that maybe everybody doesn't know about microflow?
What is microflow? That is the grey area between what is clearly nanoflow (nanoliters/minute) and what I've always called analytical flow (the flow level that HPLCs have been able to stably handle since before I was born)..say...50uL/min. Microflow is generally considered a few microliters per minute (1uL - 10uL/min)
I've always been a big fan of microflow rates and not only because I hate nanoLC
Best part. Every Thermo mass spec I've ever used has been compatible with microflow LC. You may need to make a source adjustment, but you can go two ways with it.
Option 1: Smaller gauge ESI or HESI needle. If you want to use your orthogonal source (the old ESI or the newer HESI and HESI 2 sources) you can flow 1uL/min or whatever, but the stock needle is a little wide and it is hard to get great spray stability out of it at <10uL/min (proof? calibration! try getting that sucker to tune/calibrate at 1uL/min with the stock needle. You can probably eventually do it in positive mode, but it isn't easy).
The stock needle is 32 gauge. The low flow is 34 gauge
If you have a Fusion/Lumos/Endura or Quantiva, the low flow needle insert is Thermo part number: OPTON-30136
If you have a HESI for any other instrument the low flow needle is. As far as I can tell, this is the same exact needle used in the older ESI source as well: OPTON-53011
In both cases, these needles will set you back less than $500. And they're steel so they last a good long time.
Pop in the smaller needle (there are instructions here: PDF), make sure your LC can do that flow rate (or borrow one that can) and you're microflowing!
Option 2: Convert your nanosource to microflow!
This is easiest with the EasySpray (coincidence?) this set microspray emitter is part number ES792. You can find it online here. Just put on your column and pop it in. Did you know that your EasyNLC 1000 can do microflow rates? Sure can. But you have to use short gradients cause each pump is only 50uL. I'm pretty sure, don't quote me, that you can do up to 12uL/min. At 50/50 -- that is only an 8 minute run.
For the old nanospray source or the flex you'll have to do a little more work. New Objective, for example has steel emitters that go up to 50um at the tip. Since that page says "microflow workhorse" on it, that seems like the product to use these days from them. There used to be a cool worksheet on their page for plumbing things up, but I'd just get mixed up and call them and they'd walk me through any weird setup I was doing -- I bet that hasn't changed.
This link is to the PDF of a poster from Thermo people on doing microflow that shows some of the advantages.
Disclaimer: Ben doesn't really hate nanoLC, but he does dream of the day when sensitivity is high enough that we don't need to use it anymore. With each new generation of instrument he wonders if we've finally made it over that hump...and maybe we have?