Protein quantitation at the picomole level: an O-phthaldialdehyde-preTSK column-derivatization assay.

A fluorescent protein assay was described wherein an isocratic high-performance liquid chromatography system was used to separate the o-phthaldialdehyde-derivatized proteins from interfering components. Using a small TSK guard column equilibrated in 0.1% sodium dodecyl sulfate, it was demonstrated that all proteins and peptides examined, containing more than 22 residues, coelute in the excluded volume and were resolved from fluorescent signals contributed by commonly used reagents. The assay was linear over a useful range of 3 ng to 1 microgram of protein and required less than 15 microliter of sample.