Quantitative determination of thiolipids in organic solution, in membranes, and on HPTLC plates

In the presence of ortho-phthalaldehyde and glucosamine, thiolipids form fluorescent isoindole derivatives. This reaction can be used to quantify single- and double-chain mercaptans in membranes (liposomes) and micellar solutions. The lower detection limit is 100 pmol. In addition, the assay allows the detection of 1.9 nmol thiolipids on HPTLC plates and the fluorescence signal is stable for days. A minor modification of the commonly used DTNB (Ellman's) assay allows the quantification of thiolipids in organic solutions at a concentration down to 3 nmol.