How do I determine the best column I.D. to maximize separation performance of my LC system? - WKB121874

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Article number: 121874

ENVIRONMENT

LC systems
Column performance
Bandspread
Dispersion
Resolution
Peak width

ANSWER

Match the column I.D. on the basis of the measured system dispersion volume.

ADDITIONAL INFORMATION

Bandspread (dispersion), inherent within all LC systems, is directly related to the volume in the system flow path between an injector and a detector (no column installed), which contributes to a loss in efficiency or chromatographic performance/resolution.

To achieve maximum efficiency, column I.D.s should be selected based on your instrument’s specific bandspread value (system dispersion), as columns that have larger volumes (larger column I.D.s) are less susceptible to negative impact of the system volume (dispersion).

Here are some general guidelines on how to determine which column I.D. is most appropriate for you, based on your system bandspread (dispersion) measurement values:

If your system bandspread (dispersion) value is greater than 120µL:
- You may need to reduce your system bandspread (dispersion) by using tubing with smaller I.D., such as 0.010" or 0.009", in order to run a 4.6mm I.D. column successfully.
- You can also try to increase retention time (tR) of the analyte(s) of interest.
  - Peaks that retain longer will elute in more volume and are less susceptible to system bandspread (dispersion) effects.
  - A capacity factor of >2.0 is preferred.
    - See: What is the role and importance of determining the capacity factor of a peak in chromatography?

If your system bandspread value is 80µL-120µL, you should be able to run 3.9mm, 4.6mm and 7.8mm ID columns without worrying about system bandspread (dispersion) effects.
- You can also try to increase retention time (tR) of the analyte(s) of interest.
  - A capacity factor of >2.0 is preferred.
  - Peaks that retain longer will elute in more volume and are less susceptible to system bandspread (dispersion) effects.
  - See: What is the role and importance of determining the capacity factor of a peak in chromatography?

If your system bandspread value is 26µL-80µL, you should be able to run a 3.0mm I.D. (or 4.6mm I.D.) column without worrying about peak broadening due to your system volume.
- The smaller 3.0mm I.D. will help to save solvent.
- A 4.6mm ID column would still be a great option, because the wider I.D. will still be less susceptible to system bandspread (dispersion) effects.

If your system bandspread value is 25µL or less, you should be able to run a 2.1mm I.D. (or 3.0mm I.D. or 4.6mm I.D) column without worrying about peak broadening due to your system’s bandspread (dispersion) volume.
- A tubing I.D. of 0.005" is usually used to obtain <25µL system bandspread (dispersion) volumes.
- 2.1mm I.D. columns are preferred to mass spectrometry due to the lower flow rates used in MS methods.
- 25µL is the highest bandspread value in which a 2.1mm I.D. column should be used, in terms of how bandspread will negatively affect peak width.
- You can also try to increase retention time (tR) of the analyte(s) of interest.
  - A capacity factor of >2.0 is preferred.
  - Peaks that retain longer will elute in more volume and are less susceptible to system bandspread (dispersion) effects.
    - See: What is the role and importance of determining the capacity factor of a peak in chromatography?
- If optical detection is being used, a 3.0mm I.D. column is recommended if it is packed in particle sizes of less than 2.0 μm.
  - Larger column I.D.s are not as susceptible to system bandspread effects.

See Bandspread (System Dispersion) Test Instructions.pdf

See Bandspread Test Result - Calculated Manually - 68 uL - HPLC.pdf