The Green chromatographer, part II - Narrow bore columns

The biggest enviromental concern about liquid chromatography is the waste. The widely used reversed-phase mode uses organic solventsto modify an aquous mobile-phase (MP) and elute the analytes.

The most used solvents, Methanol and Acetonitrle are toxic to environment, and shoud be, "in theory", incinerated.

Much better than giving a proper destiny to you waste, decrease its amount is a much better approach.

The Narrow bore (>4mm id)  and Microcolumn (>1mm id) LC rely on the smaller internal diameter columns, that work with a lower flow.

Narrow bore columns can work on normal HPLC equipments while Microcolumn LC need special low volume conections.

Running samples from a 4.6mm id column to a 2mm will decrease you flow 5 times! from 1ml/min to 0.2 ml/min!

The flow is proportional to the are from column, if you decrease the internal diameter to half, the cross sectional area will decrease about four times.

Just take a look at most common column diameters and the cross sectional area:

While the 4 mm id column have an area of 12.5  mm² uses 1 ml/min of  MP, the 2 mm id column has 3,1 mm² of area and requires 0.25 ml/min of MP.

The very economic 1 mm id column with 0.78 mm² only need 0,062ml/min to run in the same linear velocity.

NOTE: I 'm considering that packing is the same as the instrumental.

Example:
Fatty acids analysis on HPLC with 2.1 mm id C18 column, 85% MeOH at 0.2 ml/min.

F.O. Silva, V. Ferraz / Talanta 68 (2006) 643–645

Good luck!!

Peaks are: 1, linoleic + myristic; 2, linoleic; 3, palmitic; 4, oleic; 5, elaidic; 6, margaric (internal standard); 7, stearic phenacyl ester.