Chromatographic peak tailing and application of BDS column

Chromatographic peak tailing and application of BDS column

In high-performance liquid chromatography systems, reversed-phase C18 columns are widely used. Traditional well-tailed chromatography columns can handle most substances, as shown below:

The picture above shows the basic production process of C18 packing, in which the residual silicon hydroxyl group is mostly the main cause of the tailing of the chromatographic peak, because usually its pKa = 2-6 (depending on the silica gel raw material), it is acidic and can Electrostatic interaction with the basic group in the separated compound causes chromatographic peak tailing. The magnitude of this electrostatic interaction often determines the degree of peak tailing. The final treatment in the third step is to use small siloxanes to further react the residual silanol groups of silica gel. It is conceivable that the degree of progress of the reaction determines the degree of column tailing.

The representative products of our company, Comasil C18 and Comatex C18, achieve the above-mentioned good tail sealing. Generally, they can maintain a good peak shape for most acidic alkaline samples, as shown in the figure below. The retention of the organic base metronidazole in the column effect:

In the picture above, we will find a question. Why does metronidazole have so much electrostatic effect to achieve such a perfect peak shape? On the one hand, the superiority of chromatographic column tailing, on the other hand, I will introduce a concept of "polar distribution" here. As shown above, the hydrophobic groups and basic groups of the substance are evenly distributed on the structure of the substance. Evenly distributed substances tend to have less severe peak tailing, and a well-sealed column can guarantee its peak shape. Similar to cephalexin and so on:

There must be some basic compounds, and their hydrophobic groups and basic groups are very unevenly distributed. These substances have extremely harsh requirements on the number of residual silicon hydroxyl groups on the column, as shown in the following figure of amitriptyline structure:

The hydrophobic part and basic part of this substance are distributed at both ends, and the tailing of this substance's chromatographic peak is extremely serious, so it is often used as a pointer to check the sealing status of the chromatographic column.

This comes down to the application of the key BDS C18 in this article. The technical characteristics of this column are the second step bonding and the third step sealing and transposing step in the first picture, that is, the silicon monomer undergoes a special alkali passivation before bonding Chemical treatment to reduce residual silicon hydroxyl groups to the limit. This type of chromatographic column is far better than the traditional tailed C18 column in the separation and analysis of alkaline samples. The representative product of our company is Comasil BDS C18. The following figure shows some applications of harsh basic compounds:

Summarizing the above theory, the author personally feels that there is no one chromatographic column that can cope with all applications. The chromatographic column is not perfect and only suitable. Special samples need special analysis to select the correct chromatographic column.