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Abstract. Bioaffinity analysis using a variety of biosensors has become an established tool for detection and quantification of biomolecular interactions.Biosensors, however, are generally limited by the lack of chemical structure information of affinity-bound ligands. On-line bioaffinity-mass spectrometry using a surface-acoustic wave biosensor (SAW-MS) is a new combination providing the simultaneous affinity detection, quantification, and mass spectrometric structural ({"' characterization of ligands. We describe here an on-line SAW-MS combination for direct identification and affinity determination, using a new interface for MS of the affinity-isolated ligand eluate. Key element of the SAW-MS combination is a microfluidic interface that integrates affinity-isolation on a gold chip, in-situ sample concentration, and desalting with a microcolumn forMS of the ligand eluate from the biosensor. Suitable MSacquisition software has been developed that provides coupling of the SAW-MS interface to a Bruker Daltonics ion trap-MS, FTICR-MS, and Waters Synapt-QTOF-MS systems. Applications are presented for mass spectrometric identifications and affinity (K 0 ) determinations of the neurodegenerative polypeptides, r..-amyloid (AI1), and pathophysiological and physiological synucleins (a-and r..-synucleins), two key polypeptide systems for Alzheimer's disease and Parkinson's disease, respectively. Moreover, first in vivo applications of aSyn polypeptides from brain homogenate show the feasibility of on-line affinity-MS to the direct analysis of biological material. These results demonstrate on-line SAW-bioaffinity-MS as a powerful tool for structural and quantitative analysis of biopolymer interactions.

A method for the determination of iron by differential-pulse polarography, based on the formation of a 5,5-dimethylcyclohexane-1,2,3-trione 1,2-dioxime 3-thiosemicarbazone-iron(II) complex, is proposed. The method was applied to the determination of iron in acids, waters, wines and fruit juices.