LC/MS/MS of carbohydrates with postcolumn addition of metal chlorides using a triaxial electrospray probe

A new technique for on-line postcolumn addition (PCA) formation and tandem electrospray mass spectrometry of carbohydrate-metal complexes is presented. A metal chloride solution is added to a carbohydrate sample directly within the ion source of the mass spectrometer. Using a triaxial electrospray probe, this technique can be applied to form carbohydrate-metal complexes on-line, without the need of previously mixing the carbohydrate and metal chloride. Two basic tasks may be accomplished: structural analysis and sensitivity enhancement. The performance of this approach is demonstrated through PCA of LiCl, NaCl, KCl, RbCl, CsCl, and CoCl2, introduced via the triaxial probe after chromatographic separation of two four-component carbohydrate mixtures. Each metal-carbohydrate complex is subsequently analyzed by on-line MS and MS/MS. This technique is used to enhance sensitivity and also, in the case of cobalt coordination, to assist in carbohydrate structural elucidation. On-line LC/MS with PCA of LiCl was achieved with as little as 1.7 pmol of oligosaccharide (average consumed amount, 1.7 pmol with 1 microL of a 10 pmol/microL carbohydrate test mixture injection).