This Small Business Innovation Research Phase I project will adapt the proprietary Multi Photon Detection (MPD) technology to high performance liquid chromatography (HPLC) techniques, thereby significantly improving the detection limits of HPLC. Current HPLC sensitivity is limited by the performance of the detectors used, and is typically in the range of 10-12 g/ml. Preliminary experimental results suggest the possibility of achieving detection limits of better than 10-15 g/ml. The proposed research focuses on the development of derivatizing agents and techniques to introduce MPD-compatible labels to analytes which are present at subattomole/ml concentrations. If successful, this R&D effort will yield an ultra-high sensitivity detector and reagents for research and analysis using HPLC. The resulting HPLC/MPD system will enable researchers to isolate, detect and measure substances at levels which were previously unattainable. Ultra-sensitive HPLC/MPD instrumentation will significantly facilitate the study of the role and function of biologically important substances such as neurotransmitters, steroidal hormones, angiotensins, and others. It will also greatly facilitate pharmaco-kinetic studies leading to a better understanding of drug interactions and the safety and effectiveness of new pharmaceuticals. Thus HPLC/MPD instrumentation should find application in both academic and industrial laboratories.