Detection of nonderivatized peptides in capillary electrophoresis using quenched phosphorescence

A capillary electrophoresis detection technique for (small) peptides is pre sented, i.e. quenched phosphorescence, a method that is generally applicabl e and does not require chemical derivatization. For this purpose, a novel p hosphorophore, 1-bromo-4-naphthalenesuffonic acid (BrNS), was synthesized. BrNS has sufficient water solubility and provides strong phosphorescence at room temperature over a wide pH range. the detection is based on the dynam ic quenching of the BrNS phosphorescence background signal by electron tran sfer from the amino group of the peptides at pH 9.5-10. For the di- and tri peptides Val-Tyr-Val, Val-Gly-Gly, Ala-Ser, Gly-Asn, Gly-Ala, and Gly-Tyr, detection limits in the range of 5-20 mug/L were obtained. The novel techni que is even a good alternative for the (limited) group of peptides containi ng tyrosine and, thus, exhibiting native fluorescence as well as strong UV absorption: using Gly-Tyr, Val-Tyr-Val, methionine enkephalin, and human an giotensin II as test compounds, quenched phosphorescence detection was foun d to compare favorably with absorption detection at 190- and 266-nm laser-i nduced fluorescence detection, as performed with a recently developed, smal l-size, quadrupled Nd-YAG laser.