Hi Justin_ea,
With regard to the phenomenon of volume contraction upon mixing methanol and water, I respectfully disagree:
http://www.chromatographyonline.com/how ... -degassinghttp://laserchrom.com/LaserchromHPLC-HP ... erties.htmamong other references. If you choose, you can easily verify this in the lab by mixing volumes of methanol and water. Changing the temperature of the methanol-water mobile phase is not relevant. The concentration of the formic acid is not likely to be 0.1% (v/v) during the gradient course.
I'll ask these questions. Are these two HPLC instruments both cleaned and maintained in exactly the same way? Is the comparison between the two HPLCs' behavior apt?
In any event, the larger the volume of the mixer, in general, the lesser the noise, for example: (see page 10)
https://mottcorp.com/sites/default/file ... aper_0.pdfI'm not certain that mixer volume has any impact on baseline drift during execution of gradient chromatography. In any case, the larger the mixer volume, the better the mixing of the mobile phase components.
That TFA concentration affects baseline drift during gradient chromatography is well-known:
http://www.chromatographyonline.com/gra ... &sk=&date=You're acquiring PDA data below 220 nm. As Dolan notes in the article above; "At wavelengths <220 nm, however, baseline drift caused by differential solvent absorbance can be sufficient to prevent practical use of certain solvents, such as methanol or tetrahydrofuran."
Please, see what you think, and thank you!