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PLC Strategies - Device selection

Glass PC 03 handling1. Selecting the separation mode of chromatography

Samples would to be treated using various analytical/separation conditions and using various columns. When more than one mode is available or suitable for the separation of samples, the following points should be considered for the selection of an appropriate mode: Resolution - selectivity of the packing phase i.e. reverese phase/normal phase/ ionic/SEC/gel filtration/chiral separation/etc. Load - capacity of the packing phase/material. Speed - separation time

2. Column characteristics

Sample load is proportional to the column cross-sectional area. It is necessary to select a column inner diameter (ID) suitable for the sample load.Longer the column length, the resolution is better. Longer column lengths allow higher sample load as well. But the column pressure becomes higher. At the same time, the duration of separation is also longer. Smaller particle sizes result in higher column efficiency as number of theoretical plates on the column (N) is depending directly on particle size. But smaller particles result in higher column pressure. Phases with smaller particle sizes are highly priced as well.Nevertheless when the target component and the nearest peak are very near and the separation demands the highest resolution, packing phases with small particle size are highly useful and recommended.

3. Pump and detector

It looks easy to select proper pump for the system, but it is necessary take in the account not only flow rate and pressure. It is optimal to use a pump which maximal flow and maximal pressure is roughly double then your needs to be sure with its long lige time.It is also important to decide if your sample will be injected trough dedicated injector (switching valve with a loop) or though the pump. Loop injector is suitable for small amount of sample (up to 20 ml) only, for bigger quantity is better to use switch valve on the pump input and deliver the sample this way. Different pumps but have different intensity of sample zone spreading.Prep chromatography has no special demands on detectors. Lower sensitivity is usually better as high concentrations are expected. One has to take care about detector cell maximal flow rate. When analytical detectors are used (usually older units) a bypass of their cells is useful. Multiwavelength photometric detectors (diode array) are a good tool for PLC as the user can identify jointed peaks and unusual impurities.

4. Performing a Preparative Separation

Decision to purchase a prep chromatograph is currently based either on existing analytical method with suitable packing phases and known analytical conditions that meets separation needs. Experience with smaller prep systems often exist beside it. One has to consider the similar packing phases for scale up. If the work demands that larger quantities of the compound need purification in future, consider scalable system better then to buy quite new one in near future. Be sure that the product of same brand manufacturer, (who assure you the same quality) is available in preparative particle sizes.