Choosing Your LC Column Dimensions
There are so many options when choosing a column for liquid chromatography. Here, we focus on the physical dimensions of the column—length and internal diameter. How do they impact our chromatography? What analytical requirements might impact our selection? By understanding these factors, we can always make an informed LC column selection.
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50 by 2.1, 100 by 3, 150 by 4.6—which column is best for your application? HPLC column dimensions are an important selection during method development as they impact the efficiency, sensitivity, and speed of your analysis. You want to be sure that your choice in column dimension can accomplish both your chromatography and any additional application objectives, such as sensitivity, reduced solvent consumption, or instrument compatibility. It is important to consider both column length and inner diameter (ID) when choosing your column dimension. When considering your column’s length, ask yourself how much resolution is actually needed. A longer column is not always better. Remember that efficiency is directly proportional to column length. This approach has its limitations as doubling column length increases resolution, but only by a factor of 1.4 while also significantly increasing back pressure.
Short column lengths, such as 50 mm, will give short run times and are ideal for gradient analysis. Long column lengths, such as 250 mm, have more resolving power, but come with the cost of longer analysis time and increased back pressure. When considering your column’s inner diameter, it is important to keep your mode of detection in mind. RI, fluorescence, or UV detectors can handle much higher flow rates than LC-MS. Conventional LC-MS flow rates are in the range of 0.3-0.6 mL/min. These flow rates pair well with 2.1 mm and 3.0 mm ID columns. Additionally, as column diameter is reduced, sensitivity can be improved several fold, assuming mass on column is kept constant and your instrument is optimized for low-volume columns.
Before choosing the dimension of your next analytical column, consider these tips in order to effectively pair your column with your analysis. If you enjoy these videos, please like, share, and subscribe. You can post your ideas for a future tech tip in the comments below. Thanks for watching and we’ll see you next time.