FD&C Blue #1/Brilliant Blue FCF (Move over #2, it’s #1’s time to turn funny colors)
8th June 2006
The last, fastest spot on the chromatograph is FD&C Blue #1, or Brilliant Blue FCF:
This is the only non-azo dye of the bunch. I can’t attest to how it’s metabolized. I am willing to bet it is metabolized to something not-so-strongly colored, though. Most of these dyes are small enough that they could make it across your kidneys (kidneys filter by molecular weight, more or less).
One blue dye, methylene blue, is a perennial favorite of chemists and pranksters everywhere for its ability to make its way through the body unchanged and excreted in the urine. The dye is a very brilliant blue, with one of the higher extinction coefficients (a measure of how much light a dye absorbs at a certain concentration) among common dyes, and will often result in bright blue urine! I am told the dye is essentially harmless - in fact, it has been used in methemoglobinemia, a condition where the iron in your hemoglobin is in the wrong oxidation state. Here, the dye is actually consumed in transferring an electron to your heme iron. Some allergies have been noted, apparently, however, so perhaps it’s not best to tempt the fates. Maybe most telling is the fact that your humble, terminally curious author hasn’t tried it on himself yet, despite having ready access to very pure methylene blue for years.
Its rapid migration across the dye is puzzling. It is a tetraion, with three negative charges and one positive charge in its predominant resonance structure. If we assume ions stick better to cellulose, this is a bit confusing. This should perhaps remind you that I’m mostly speculating. However, we can rationalize its rapid migration by noting that, while it is quadruply charged, it has only two net negative charges (because one cation and one anion cancel out). Also, its substantial hydrophobic structures from the phenyl rings will probably interact strongly with the isopropanol. Any charge will also interact strongly with water; water is the best (common) liquid for solvating just about any small ion, so its four charges may help it move into the mobile phase/eluent.
Thus ends my speculation about a near-dead subset of chromatography. Night! Tomorrow we tackle the purple line at the solvent front of one of our chromatographs. There, finally, ends the madness.