Chromatography Forum

when I used 5% formic acid in water as A and pure methanol as B, it always gave me spiked baseline. I degased the two solvents well. What are other possible reasons? please suggest!

we never mix 100% organic with 100% water; try to put 5% to 10% of A in B and visa versa. Good luck!

Bert - here we almost always mix a 100% aqueous from one reservoir with a 100% organic from another, been doing that 25 years. I don't claim expertise in the mixing dynamics, maybe I can learn something here.

Just curious, what type of detection are you using?

Rick

Bert - here we almost always mix a 100% aqueous from one reservoir with a 100% organic from another, been doing that 25 years. I don't claim expertise in the mixing dynamics, maybe I can learn something here.

Never change a winning team! But, if you experience problems, I think it is worth to try and expand your mixing expertise. Mixing of alcohols and water may release air as a consequence of mixing heat.

when I used 5% formic acid in water as A and pure methanol as B, it always gave me spiked baseline. I degased the two solvents well. What are other possible reasons? please suggest!

Hi Zhi,

There might be the following reasons
1. Usually (majority) peoples are not using the 100% organic solvent as a solvent B, some of reasons are there.
2. Especially Methanol, you know, bubble forms when you mix the MeOH with water or any aqueous phase (exothermic reaction), the temperature of the phase increases and causes bubble formation (bcoz low solubility dissolved air as higher temperature).
3. If you are using integrator, some times due to lose wire connections to integrator or detector also found as a cause of spike
4. Some time power fluctaution also causes a spike.
5. As Rick asked, What type of detection you r using, that is also important.

water mixing with methanol produces air bubble and then spike in baseline. My back pressure regulator was broken and let air bubble pass flow cell, whcih gave spike. Now I solved problem.

My detector is beckman 166 with UV light at 280 nm. Previously, I run vis at 480nm, everything is ok when using organic solvents.

Thank you all for good suggestion!