Tham khảo tài liệu 'microengineering mems and interfacing - danny banks part 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Micro Total Analysis Systems 181 TABLE HPLC Capillary Electrophoresis and Microstructure Separations Compared HPLC Capillary Electrophoresis Microstructure Cycle time 90 50 1 Fluid consumption 680 000 90 1 the column more slowly because the packing material slows them down more than it does the smaller molecules. By passing a calibration solution through it one can find out how long it takes for a particular molecule to pass through the column and with this knowledge determine if that molecule was present in the sample. When identifying active chemicals in a mixture . identifying drug candidates from plant extracts each different band from the column can be analyzed to see if it has the same effect as the mixture and if so further work can be carried out to discover exactly what the chemical is. Additionally the packing material may be treated to slow down a particular molecule. For instance if one wishes to find out what proteins bind to a particular DNA sequence then the inside of the column may be coated with DNA and proteins that bind to it will be delayed more than others. The principal advantage of miniaturization is that of speed. High-pressure liquid chromatography HPLC requires considerable time to run a single cycle whereas microstructure separations take seconds or minutes. HPLC also consumes considerable volumes of fluid which may be especially significant in biological circumstances in which the compound of interest is a relatively rare one within the cell. Table compares HPLC capillary and microstructure separations normalized to typical values found for microstructures 3 . Electrophoresis Electrophoresis extends chromatography it separates not only by size of the molecule but also by electrical charge Figure . In solution polar elements of macromolecules such as hydroxide and carboxyl groups dissociate so that the molecule itself is left with an overall charge. When placed in an electric field the molecule will migrate toward
