Hi All,

We have a mobile phase that gives a baseline which is very sensitive to laboratory temperature. We do use a column oven but we still get sinosoidal baseline fluctuations when the room A/C turn on and off.

One pecularity with this mobile phase is that it has high levels of Glacial HAc

Actual composition of the mobile phase is:
=========================================
670mL of the Ammonium Acetate buffer,
330mL of Acetonitrile,
1.35mL of fresh Triethylamine,
63mg of Octane sulphonic acid and
200mL glacial acetic acid

If any one can offer any assistance to elliminate the baselne problem it would be greatly appreciated.

Regards

Asanka.Nanayakkara@au.faulding.com

From my study of physics, this sounds like environmental noise (if you're sure it's the AC switching), in which case, you'll need to filter the electricity. I would not have expected the mobile phase to influence the base line (if you've pin-pointed the AC as the culprit). But none the less, I presume that everytime the AC is on, you're seeing the baseline fluctuations and then when the unit is off, you dont see the fluctuation ...

If this is the case, you might want to consider a more specialised electricity filter. Most uninterrupted power supply units have a reasonable filter and they're available for low cost. Alternately, talk to the manufacturer of your LC equipment. If all else fails, ONEAC is a manufacturer of these devices, but they can be expensive. I have one on our mass spec ($12k). They can be contact (in the US) on 800-327-8801 or 312-680-5999. I do not know where you would buy this equipment in Australia, despite being an Australian myself.

If the AC was not the culprit, I would start with a check for leaks at the pump and joints. I have seen this type of baseline caused by tiny air bubbles and particulates passing back and forth through the flow cell of the detector.

Good Luck !!!!

Try insulating the connecting tubing between the various HPLC components. 1/8" Tygon tubing works well. Cut the tubing to length then carefully slit it lengthwise with scissors or a razor blade. Slide the slit Tygon tubing over the connecting tubing and you're done. Let me know if this works.

I use an inexpensive Tripp Lite LC-1800 line conditioner with my HPLC detectors and pump. It has six outlets to plug in components. Before purchasing such a product, you'll need to add up the electricity demand of each component you plan to protect and buy the appropriate capacity unit. My unit is rated at 1800 watts for example. I like it because it has indicator lights to warn when the load is too much. I bought it about two years ago for less than $150 from a computer supply catalog. Search the Web for Tripp Lite and I'm sure you'll find them.

Ummm -- seems to be two interpretations of "A/C" here. Did the original post refer to "Alternating Current" or "Air Conditioning"?

Actually, though, all of the suggestions have been good ones!

I find that our mobile phase is also sensitive to laboratory environmental conditions. We are supposed to be a temperature controlled lab, but temperatures still vary up to +/- 2degC. We are looking at purchasing a column heater. This could be a relatively inexpensive fix, and could also improve your chromatography!

The right working of column thermostates depends (among other things) on the humidity of the room your working in. Turning on the AC means you change the humidity in your laboratory.
Check the manual of your column thermostate to see what the humidity specification of your column thermostate is.

M.

This sounds similar to a problem we had 20+ years ago. We were using a column oven, but our baseline (variable wavelength UV detector, probably set at 254 nm) was displaying a very nice sinusoidal curve, with a period of several minutes. We finally twigged to the fact that the HPLC was directly under an air conditioning vent, and the detector was in sync with the cycling of the air conditioner. Lagging the tubing from the oven to the detector solved our problem. I'd suggest that lagging the column and all of the solvent tubing that you can cover, especially from the column to the detector could help. If temperature is causing the fluctuation, lagging the column and tubing should have a marked effect on the sinusoidal curve.