I recommend a dynamically stirred, two-pump, high-pressure mixing system. If, on the other hand, you’ll mainly be doing scouting gradients, dial-a-mix isocratics, and the occasional uncomplicated gradient, the low-pressure mixing system would be excellent and save you about $4,000. This system has the advantage of giving you three- or four-solvent capability, which would be of advantage in scouting and automated wash-out, but it requires continuous, inert gas solvent degassing. I generally find low-pressure mixing gradient reproducibility performance to be about 95% that of the high-pressure mixing system. Gradients from 0 to 5% and 95 to 100% B may be worse. | 20 SELECTING AN HPLC SYSTEM I recommend a dynamically stirred two-pump high-pressure mixing system. If on the other hand you ll mainly be doing scouting gradients dial-a-mix isocratics and the occasional uncomplicated gradient the low-pressure mixing system would be excellent and save you about 4 000. This system has the advantage of giving you three- or four-solvent capability which would be of advantage in scouting and automated wash-out but it requires continuous inert gas solvent degassing. I generally find low-pressure mixing gradient reproducibility performance to be about 95 that of the high-pressure mixing system. Gradients from 0 to 5 and 95 to 100 B may be worse than 95 and should be checked before buying see Chapter 9 . You can replace an integrator-based data acquisition system with a computer-based system but let the buyer beware. I am not impressed with most of the control data acquisition add-on systems I ve seen. The system made by Axxion runs on most systems is competitively priced and is reasonably friendly. For maximum control and processing benefit the computer and software have to be carefully matched to the HPLC hardware. If I was going to buy anything I d get data acquisition processing only. My operating rule is to try it before you buy it and think again. I ve been using personal computers for 25 years I m a fan but I m still not convinced that most people can upgrade to a useful component system. Manufacturers carefully match computer and HPLC hardware with optimized software and even then many control pro-cessing systems leave much to be desired. If you do buy a computer to acquire data keep your integrator or strip chart recorder. You will thank me. Type III System Automated Clinical Cost 25-35 000 The most common job for these systems is the fast-running isocratic separation. They could be built up from the QC isocratic but dial-a-mix isocratic is faster and more convenient since they switch easily from job to job. These systems .
