Column guard

There are quite a few techniques that can be used to extend the useful life of an HPLC column these include employing column shock method after several hundred injections, running at lower operating temperatures, not running at pH extremes, and using moderate concentrations of buffers, to name a few. However, the column should be considered as a disposable item. This might be difficult to accept, considering that the typical column costs approximately 500. However, the cost of the column should be viewed in terms of overall analysis costs. Assume that each analysis an analyst performs is on the order of 5 per sample. If the column lasts for 500 injections, this means that the column contributes to 20% of the cost. Many analysts may get 1000-2000 samples analyzed before a column dies, so the cost per sample would be even less 10% of the cost and 5% of the cost, respectively. 

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An HPLC typically includes two columns an analytical column responsible for the separation and a guard column. The guard column is placed before the analytical column, protecting it from contamination. 

A more justifiable reason for the added cost and analysis time that a guard column brings is to avoid a problem with adsorption of sample matrix components on the stationary phase of the analytical GPC columns. In many industrial laboratories, the usual GPC experiment deals with fairly well-controlled sample matrices that may not have absorbable components and therefore rarely require a guard column. In situations where slow adsorption of matrix components may occur on GPC columns, it may make better economic sense to periodically replace the first column of a set. Nevertheless, in... 

Parts that are common in SEC, but should not be used in HOPC are a sample injector (including an autosampler) and a guard column. 

Finally, the useful life of an analytical column is increased by introducing a guard column. This is a short column which is placed between the injector and the HPLC column to protect the latter from damage or loss of efficiency caused by particulate matter or strongly adsorbed substances in samples or solvents. It may also be used to saturate the eluting solvent with soluble stationary phase [see Section 8.2(2)]. Guard columns may be packed with microparticulate stationary phases or with porous-layer beads the latter are cheaper and easier to pack than the microparticulates, but have lower capacities and therefore require changing more frequently. 

Molecular weight distributions were examined by high performance size-exclusion chromatography (HPSEC) as described [22] on two serial Shodex OHpak KB-803 and KB-805 columns (0.8 x 30 cm Showa Denko, Japan) with a OHpak KB-800P guard column (0.6 x 5 cm), equilibrated at 1 mL/min in 0.1 M UNO3. The system was calibrated with a pullulan calibration kit (Showa Denko). 

Restek Rtx-IMS fused-silica open-tubular column (FSOT) with integral guard column, 30 m X 0.25-mm i.d. and 0.25-p.m film thickness Eppendorf fixed-volume pipets, 0.50-mL Eppendorf fixed-volume pipefs, 1.0-mL Eppendorf pipel lips, 1.0-mL Amber-glass boftles wifti Teflon-lined caps, 4-oz... 

Restek Rtx-IMS FSOT with integral guard column, 30 m X 0.25-mm i.d., 0.25-p.m film thickness Helium... 

Column/injector maintenance. The use of a guard column, in addition to scheduled injector maintenance, provides significantly improved GC performance. Loss of performance manifests itself in poor peak shape and reduced sensitivity. This is particularly noticeable with atrazine but also with the other analytes. Maintenance should include removal of a 30-60 cm section of the guard column and replacement of the... 

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