All Solvents are NOT Created Equal

If you look through a solvent vendor's catalog, you'll see quite a list of different versions of methanol (MeOH) or acetonitrile (ACN) - the most common solvents used in reversed-phase HPLC.

In a manufacturer's listing you will see HPLC-grade, GC-grade, MS-grade, and so forth. Solvents are manufactured for specific applications. These solvents are selected and purified for each specific application. For example, HPLC-grade solvents focus on UV absorbing impurities, whereas GC-grade ones look for compounds that interfere with some of the element-selective detectors, such as chlorinated compounds. MS-grade ones have another specification, and so forth.

For HPLC, the most common detector is UV absorbance, so the solvent specifications for HPLC-grade solvents focus on UV absorbance. When I looked up specifications for products from a couple different suppliers, I noticed that one included a fluorescence test (response ≤1 ppb equivalent of quinine at 254 nm and 365 nm), whereas a second supplier did not list this (it may have been tested, but it was not listed in the specifications). So, whereas I would expect the two brands of MeOH to be comparable for UV work, it doesn't surprise me that there may be differences in the fluorescent impurities present. Also, you are derivatizing, so there may be non-UV and non-fluorescent impurities in the solvent that are of no consequence in normal use, but they may be reactive with the derivatizing agents and create background signal.

One final thought: I believe that nearly all solvent manufacturers use the same specifications for a particular type of solvent, such as HPLC-grade MeOH. How close they come to those specifications may differ from one vendor to another. I have heard through the rumor mill that with the decreased availability of ACN some vendors are releasing product that is closer to the specification than in past years. This allows for reduced waste in manufacturing, but it may mean that the solvent isn't quite as pure as you have been used to. Will it make any difference? If you are running a content assay with high concentrations of analyte with an isocratic method, I doubt if you will notice the difference. However, if you use gradient elution for trace analysis, the level of background interferences may be higher today than it was a year or two ago.