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HPLC A Praactical User'S Guide Part 8

Tham khảo tài liệu 'hplc a praactical user's guide part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 134 TROUBLESHOOTING AND OPTIMIZATION Commercial mobile phase recyclers use peak detection from either a computer or an integrator to signal baseline acquisition. A waste recycle valve is triggered by this signal to discard peak containing mobile phase and recycle the baseline. There is little solvent recovery for chromatograms containing many closely spaced peaks but for normal chromatography or in cases where the HPLC is always left running this might represent 40-50 solvent recovery. Estimates have appeared in the literature that claim that for a quality control instrument run on a single shift this would mean a savings of about 60L per year at a savings of about 3 000 yr in solvent man power and environmental impact. Obviously the savings would be higher in stat instruments running in clinical laboratories and in quality control laboratories that operate on a three-shift schedule. III HPLC UTILIZATION 11 PREPARATIVE CHROMATOGRAPHY The preparative use of HPLC is often overlooked in the rush to analyze. There are two outputs. The detector s electrical signal to the strip chart or computer and the liquid output normally sent to waste. Most columns and detectors are nondestructive aqueous samples can be run without derivatization. The same system used for analysis can be used for all but the largest preparative runs. Usually all that is required is a change of columns and a slight modification of the running conditions to accommodate the increased sample concentration and load Table 11.1 . Speed load and resolution are the three trade-off considerations that must be balanced to optimize the three levels of preparative runs Fig. 11.1 . Analytical preparative is concerned with isolation of up to microgram quantities of material and with obtaining enough material for spectrometric analysis the most important factors are speed and resolution. As we move to semipreparative separation in the milligram range we are usually purifying analytical standards of recovering .