The Power of 4. It can determine which Rheodyne LC valve you need. Operating within the flow passages of every LC valve is a powerful exponential term, D4, passage diameter raised to the power of 4. A little knowledge of D4can help you choose the best valve for your application. Sample dispersion is proportional to D4 So a small diameter provides high resolution. Good. FU But loss of pressure due to flow resistance is inversely 4 proportional to D So a small diameter causes a large pressure drop. Not good. In analytical LC small diameter passages cause only insignificant pressure drops, because flow rates are low. But in preparative LC, small passages can cause
excessive pressure drops. So for preparative work at flow rates above 100 mL/min, Rheodyne now manufactures a line of valves with larger passages. They cause only a tenth as much pressure drop as analytical valves. Literature on the prep valves is available-along with a relevant and helpful technical note. Our Tech Note 7 100 / RATE (mL/min) explains the practical effect of passage diameter in injectors, valves, and connecting tubes-with the aid of graphs like the one above. For literature, tech note, and an up-to-date catalog, phone your Rheodyne dealer. Or contact Rheodyne, Inc., PQ Box 996, Cotati, California 94928, U.S.A. Phone (707) 664-9050.
RHEODYNE T H E LC C O N N E C T I O N C O M P A N Y CIRCLE 182 ON READER SERVICE CARD
