Precolumn

[Rganga]

Is it better to work with or without precolumn? I found some references that advice to use it for column protection and other which don recomand to use it for analysis quality.

thank you very much

[skunked_once]

The answer is yes I have also heard arguments both for and against using a precolumn and have come to the conclusion that both points of view are valid depending on the situation. My opinion is that the current quality of precolumns is so good that there is little or no loss in quality of analysis and I prefer to use them whenever possible. On the other hand, with good sample cleanup and with the quality and robustness of the current column technology, a precolumn may not be necessary. It's up to you and your evaluation of your samples, analysis, column/precolumn costs, etc. How's that for a definitive answer

[tom jupille]

First of all, are you referring to a "pre-column" or a "guard column". The terms are often used interchangeably, but I'll make the following distinction:
- a precolumn is located between the pump and the injector.
- a guard column is located between the injector and the analytical column.

Pre-columns are typically suggested for working at high pH; they supposedly saturate the mobile phase with silica and prolong the life of the analytical column. The couple of times I have tried it, I found no improvement ("your mileage may vary", as they say in automobile advertising). I have successfully used a pre-column to buffer the water concentration of normal-phase solvents.

As for guard columns, if you are working with clean, predictable samples and a "benign" mobile phase (e.g., no extremes of pH), then a guard cartridge provides little or no benefit.

If you are working with dirty, predictable samples, then a guard cartridge is (usually) an expensive way to protect the column; arguably a better sample cleanup might be more cost-effective.

If you are working with unpredictable samples (in terms of possible CRUD), then a guard cartridge can be cheap insurance against trashing an expensive analytical column.

[Harry Ritchie]

If you are using a guard column then there are few suggestions I would make:

(1) Always use the same packing material in the guard column as the anlytical column.
(2) Set up a very strict regime for the changing out of the guard column.
(3) Never begin a new method development using an old guard and column system. Historical contamination could significantly impact your assay. Always start fresh.