Peak problems
Nico Vonk, Avans+, Breda, The NetherlandsLevelBasic
Symptoms:
- No peaks
- Very small peaks
- Back tailing peaks
- Front tailing peaks
- Split / double peaks
- Round peaks
- Negative peaks
- Ghost peaks
No peaks
| Possible causes | Solution |
| Detector lamp is defect. | Replace the lamp. |
| No mobile phase flow to the column. | Check the pump pressure and eluent flow. Check for leaks. |
| Detector or data system settings fault. | Apply correct values. |
| No sample injected. | Check the injector valve or when an autosampler is used, see whether the vials contain sufficient liquid. |
| Compounds too strongly retained. | Try a higher eluent strength. |
| Zero level of detector cannot be reached. | This can have several causes: Air bubble in the measuring cell Contaminated measuring or reference cell Leaking flow cell Impure eluent Eluent not compatible at chosen wavelength Wrong UV wavelength No column equilibrium Detector sensitivities too high |
Very small peaks.
| Possible causes | Solution | |
| Sample deterioration | Prepare fresh samples or check stockage conditions | |
| Insufficient mobile phase flow to the detector. | Check for leaks. | |
| Detector or recorder settings too high. | Check all values in the data system. | |
| Not sufficient sample injected. | Check the injector valve or when an autosampler is used, see whether the vials contain sufficient liquid. | |
| Pollution of the detector cell. | Rinse the detector cell with clean solvents. |
Back tailing peaks.
| Possible causes | Solution | |
| Extra column back broadening. | Make sure the tubing length and tubing id are kept to a minimum.
| |
| Interferences in the sample. | Use clean standards to see whether this is a column problem. | |
| Mobile phase pH not correct or optimal. | Check and change | |
| Dirty or old column. | Basic compounds show tailing peaks if the (pre) column has trapped parts from previous samples. | |
| Column overloading. | Try injecting less sample or a lower concentration. | |
| Solvent of sample has too high elution strength. | Try to dissolve the sample in the mobile phase, or in a weaker solvent. | |
| Basic analytes with active residual silanols. | Use another stationary phase with higher surface coverage or try adding triethylamine to the eluent (usually < 1 ml/l). | |
| Guard or analytical column dirty or saturated. | Replace guard column, followed by regeneration of the analytical column. |
Front tailing peaks.
| Possible causes | Solution | |
| Column overloaded. | Try injecting less sample or a lower concentration. | |
| Sample solvent not compatible with eluent. | Try to dissolve the sample in mobile phase. |
Split peaks.
| Possible causes | Solution | |
| Contamination of guard or analytical column. | Replace the guard column. Regenerate the analytical column. | |
| Channelling in the analytical column. | Replace the column and/or wash the analytical column in back flush. Try to avoid high salt concentrations in sample or eluent. | |
| Sample solvent not compatible with eluent. | Try to dissolve the sample in mobile phase. |
Round (double) peaks.
| Possible causes | Solution | |
| Sample concentration higher than linear detector range. | Dilute the sample. | |
| Column overloaded. | Dilute the sample. | |
| Co-elution of 2 components. | Improve separation. Change conditions? | |
| Poor column bed stability | Backflush or replace the column. |
Negative peaks.
| Possible causes: | Solution | |
| Refractive index of analytes less than that of the eluent (with RI detection). | Flush reference detector cell with mobile phase. | |
| Large difference in composition of eluent and sample solvent. | Dissolve samples in mobile phase. | |
| Eluent absorbs more uv than the analytes (indirect uv detection). | Try another UV wavelength. |
Ghost peaks.
| Possible causes | Solution | |
| Contamination in injector from previous sample (cross contamination). | Flush more with stronger solvents between injections. Reduce sample concentration, if possible. | |
| Contaminants in mobile phase, when using gradient elution. | Prepare new mobile phase in clean glassware. | |
| When continuous degassing with helium is applied: contaminants from the helium coming our of the helium itself or out of the gas tubing.
| Use a gas clean filter in the helium line. |
