Why Is an HPLC Column Shorter Than a GC Column?

In the chemical laboratory, two separation techniques frequently used are HPLC (high performance liquid chromatography) and GC (gas chromatography), whose purpose are to separate and quantify the organic mixtures’ components. The principle of HPLC is the same as that of GC. Both separation and analysis functions are available for online testing. Do you know why GC columns longer than HPLC columns? Before answering this question, we should understand the benefits of column length.

1. Column length

As the length of the liquid chromatography column increases, the interaction time between the eluting compound and the stationary phase also increases, resulting in improved column efficiency and separation. This leads to well separated peaks. However, the practical problems faced due to increased column head pressure and increased analysis time do not allow for an infinite increase in column length.

The size requirements of HPLC columns depend on the separation target. Typical analytical applications require a column length of 15 – 25 cm and an internal diameter of 4.6 mm. For high efficiency analysis, HAWACH offers different pore sizes and particle size packing. Also, many different stationary phases (C18, C8, phenyl, C1, cyano [CN], PFP and C30) are available, and these columns are recommended for small molecule reversed phase separations and are very durable columns for liquid phase analysis.

Preparation columns are available in wider diameters ranging from 20 – 50 mm. HAWACH preparation columns covers almost all common sizes. Even if a longer column tube is required, HAWACH can provide customization.

2. Gas chromatography column

There are two general classifications for the gas chromatography columns: capillary and packed columns. Filled columns are usually about 1.5 m or 6 ft long with an outside diameter of 1/8″ or 3.2 mm. capillary columns, on the other hand, are several meters long (10-100 m). The two are made of different materials, for the filled columns, they can be stainless steel or glass and for  capillary columns, all are made of fused silica hose. The flexible tube allows to accommodate the long column as a circular coil into the column temperature chamber. From the separation process differences, we can answer the length differences between HPLC and GC columns.

3. Mobile phase

Nature of the mobile phase – The primary reason for this is the nature of the carrier liquid called the mobile phase. For GC, the mobile phase is an inert gas. The component has no affinity to the mobile phase and only interacts with the stationary phase. The mobile phase has an affinity force between the mobile phase and the components, which adds factors to improve the selectivity of the column and improve the separation, and plays a great role in the separation.The mobile phase is more varied and has a wide choice. The choice of mobile phase polarity and pH also plays an important role in the separation. The selection of two or more liquids in different proportions as mobile phases. The separation selectivity can be increased.

HAWACH liquid chromatography columns have been developed specifically for customers requiring shorter column lengths, with small dead volumes, smooth inner walls, and uniformly rounded cross sections; ensuring high performance in the finished column.

4. Sample

Sample Volatility – The sample injected into the HPLC is a liquid, while in GC it can be either a liquid or a gas. But please note, the liquid needs to be converted to a vapor before entering the GC column, because of the high temperature in the injector module. Gases encounter less resistance in the GC column, which allows for longer column lengths to be used.