Guard columns pressure

An online filter was also used to protect the analytical column. A guard column was used before the T to prevent breakthrough. A restrictor was used to balance the pressure before, during, and after the valve switches. After sample transfer, the valve was switched back. With this method, both water-insoluble retinoids and water-soluble retinoic acid were extracted simultaneously. Because of the minimal light exposure of these light-sensitive analytes during the procedure, an extraction recovery of 97 to 100% was achieved with a quantitation range of 100 fmol to 3 nmol. 

Analysis of biological samples requires an inline precolumn or guard column installed before the analytical column, to protect against the gradual accumulation of particulates or contaminants originating from the sample. They should be packed with a similar material as the analytical column and should be disposed of on the first indication of contamination (i.e., high back pressure or loss of resolution). 

A guard columns is a mini analytical column pressure packed with the same type of material used in the analytical column. It is connected in the path from the injector and collects anything that normally would be deposited on the main column. It must be cleaned or replaced periodically because contamination will eventually bleed through. Since guard columns usually are only about... 

The column length varies from 3 to 30 cm, the inner diameter from 1 to 10 mm. Columns are made of very resistant materials to withstand high pressures (<40 MPa) Most commonly, a stainless steel or heavy-walled glass tube is inserted into a metal tube. Columns are packed with a solid material of particle size <10 pm (spherical and nonporous microglass beads or polymer particles). A guard column is usually placed before the column to remove suspended particles from solvents, as well as certain sample constituents that could irreversibly bind to the stationary phase. 

Because HPLC columns have a limited lifetime, care must be taken in their use. It is important to read the manufacturer s recommendations regarding eluents, flow rates, mobile phase pH, maximum pressure, organic modifier content, and storage procedures in order to prevent destruction of the column. Only HPLC-grade reagents, or better, should be used, and the eluent should be filtered prior to introduction into the chromatographic system. Guard columns should be used wherever possible to prevent con-... 

Usually, a short guard column is introduced before the analytical column to increase the life of the analytical column by removing not only particulate matter and contaminants from the solvents but also sample components that bind irreversibly to the stationary phase. The composition of the guard-column packing should be similar to that of the analytical column the particle size is usually larger, however, to minimize pressure drop. When the guard column has become contaminated. it is repacked or discarded and replaced with a new one of the same type. Thus, the guard column is sacrificed to protect the more expensive analytical column. 

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