The purity of fluorescent dyes: a report delivered to the scientific session of the annual meeting of the Biological Stain Commission.

The Biological Stain Commission occasionally has been requested to certify fluorochromes as biological stains. Although formal certification is unlikely in the near future, the Commission is nevertheless concerned with the quality of these reagents. Commercial samples of fourteen fluorochromes were investigated for the presence of fluorescent organic impurities using reverse phase thin layer chromatography. Our findings suggest that some fluorochrome dyes are pure, but most are impure. Most fluorochromes vary in purity among vendors and among batches sold by single vendors. Impurities may be present at such high concentration that little of the presumed compound is present. Some impurities behave quite differently from the nominal dye. This may either create confusion or it might be useful. In the latter case, however, the impurity may occur only in a single batch. Impurities result from problems related to organic syntheses, separations, and economics. Solving those problems is often expensive, and what is expensive may not be performed. Fortunately, knowledge of synthetic chemistry often permits identification of fluorochromes likely to be impure. Moreover, predictions of likely staining effects of particular impurities can be made if appropriate structure-activity models are available. Possible actions by the Commission aimed at limiting the problems resulting from impurities of fluorescent dyes are noted.