Safer Flow Cocktails

The use and detection of radiotracers in organic and biological chemistry has benefitted from advances in the efficiency and sophistication of both the chromatographic and the radioactive detection techniques. As a result, the chromatographic separation of radiolabeled compounds, sometimes referred to as “radiochromatography,” is now carried out in many laboratories throughout the world. The basic technique involves the separation of the components of a chemical mixture by High Performance Liquid Chromatography (HPLC) followed by the detection and quantitation of the radioactivity in the sample components using Flow Scintillation Analysis (FSA). Recent technological advances in HPLC have been associated with column specificity, pulseless pumping, new and improved detectors (including hybrid methods e.g., HPLC-Mass Spectroscopy) and finally, computerization for control and data handling. Likewise, the latest advances in FSA are related to cell design and type, mixing processes, scintillation measurement and detection (including TR-LSC with MCA spectral analysis), and computerization for control and data handling. The flow scintillation analyzer can be operated with two different cell types: solid scintillation cells for heterogeneous counting and liquid flow cells for homogeneous counting. Although both techniques are possible with the same instrumentation, this application note will focus on homogeneous counting using safer liquid scintillation cocktails. Until recently, FSA has been largely neglected in the changeover to safer, high flash point cocktail systems. Radiochromatographers have tried to adapt currently available safer cocktails for FSA, but have been thwarted by viscosity, as well as mixing and sample complexity problems. The only way to resolve these problems was to design and formulate high flash point, safer flow cocktails, thus offering an alternative to the classical flow cocktails that are currently in use.