Many years ago, {too many to count}, I was given a method for determining type and concentrations for fluorescent whitening dyes in laundry detergent products. I used that method once. At that time, the lab where I worked had only instruments with single mobile phase, Waters pumps. Therefore, I am sure that the method employed isocratic elution. Most chromatographs in that lab used octyl columns and had UV/Vis detectors. It is most likely that was the means of separation and detection. We did have one instrument with an RID and a fast acid column, but that was most likely not the instrument used. I do not recall the mobile phase. The dyes were identified by retention time. Concentration was calculated from peak area against the response of external standards. Does anyone out there in LC land have any recent experience with this type of analysis? If so can you please provide details of an existing method or a few clues for starting some new method development? I now have access to an isocratic LC with RID, another with UV/Vis detection and another with 4 solvent gradient capability and UV/Vis detection. I have a variety of columns and am not adverse to purchasing something new. Unfortunately, I do not have access to the old original method from years back with the lab where I was then employed.

My company makes laundry detergents in U.S. For our own products' QC of fluorescent whitening agents (FWA), we mostly use UV, but we also do the fluorescent whitening agents in laundry detergents by HPLC. Dissolve 8 g ammonium phosphate dibasic in 1200 ml HPLC grade water. Add 250 ml methanol and 550 ml acetonitrile; mix thoroughly and filter through a
0.45u filter membrane. We use inexpensive RP-18 column and 365 nm mostly (but can also use fluorescence detector). Obviously, make up a similar mobile phase without ammonium phosphate to use as flush solvent to flush the salts out of the system. Peak shapes and retentions are very good.

Dear Anonymous,

Your info was much appreciated. I am sure I will be able to use it to develop a method of my own. The mobile phase sounds similar to what I recall using. Do you use standard glassware in your lab for this work or do you use Actinic, red or brown glassware?

From Anon #1: H.J., definitely use low-actinic glassware or do the aluminum foil around the volumetric flask technique, as FWA in solution is degraded by light. An extremely important issue in the assay of dry detergents is sample homogeneity. Dry detergent samples should be composite samples prepared using a sample splitter, then blended a few minutes in a laboratory blender to reduce particle size; the importance of assaying representative, pulverized samples cannot be overemphasized.