What Are the Effects of Column Specifications on HPLC C18 Columns?

The high performance liquid chromatography (HPLC) method has high selectivity, high sensitivity, and fast analysis speed, and most of the drugs that can be dissolved can be analyzed by this method, so this technology has become the first choice for drug analysis.

Reversed-phase chromatography HPLC column with carbooctadecane silane chemically bonded to a silica stationary phase (C18 or ODS) has accomplished the task of liquid chromatography excellently. Compared with other chromatograms, the C18 chromatography HPLC column has obvious advantages. It can be directly injected. The analysis of water-soluble samples has a wide range of applications and is known as the standard stationary phase separation model. The pharmacopeias of various countries involve the use of liquid chromatography for detection, and C18 columns are widely used as stationary phases.

C18 chromatographic columns show different selectivity due to various factors such as different bonding methods, different particle sizes, different lengths, and differences in inner diameters. In this way, hundreds of C18 columns with different separation options have appeared on the market. How to find the one that suits your analysis among the complicated C18 columns on the market is a topic worthy of in-depth discussion.

One main factor is to be considered for the selection of C18, namely the influence of column specifications on the chromatographic column.

The influence of C18 column specifications on the chromatographic column

The choice of column packing is related to the possibility of chromatographic separation, and the choice of column specifications directly affects the analysis speed, separation ability, detection ability, and solvent consumption for each analysis.

Column specifications include two aspects: column inner diameter and column length. The inner diameter of the column is generally 2-6 mm for the analytical type, 20 mm for the preparative type, and up to 80 mm for the larger one; the length of the column is 5-30 cm for the analytical type and 15-50 cm for the preparative type. Generally speaking, the column diameter does not affect the relationship between resolution and analysis time.

Today, column technology has been developed so that columns with different column inner diameters can have the same performance. Columns with different inner diameters have their own characteristics.

For the same analysis time and resolution, a column with a larger inner diameter consumes more solvent than a column with a smaller inner diameter. On the other hand, a column with a smaller inner diameter requires less sample volume for the same detection signal.

Therefore, when the sample amount is limited, a small inner diameter column can be used. Although the increase in column length can improve the separation effect, the resistance also increases, and the inlet pressure must be increased. Column pressure is the main obstacle that affects both increasing resolution and reducing analysis time. The resolution, analysis time and column pressure are mutually restricted. If two of them are selected, the third factor will be selected. Long columns can give high resolution, while short columns can provide fast separation. We can choose a suitable chromatographic column according to the sample situation.

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