What causes a retention time shift?

One of the most common causes of shifts in retention time in reversed-phase LC separations is a minor change in the concentration of the organic solvent, usually methanol or acetonitrile. This can happen from a minor error in formulation or a change in the mobile-phase composition if one solvent evapo rates over time.

What causes retention time shifts in GC?

A change in the temperature program often causes a retention time shift of all the peaks. A change in the initial temperature, the initial hold time, or the ramp rate can affect all of the peaks. Retention times increase with a lower initial temperature, longer initial hold time, or a slower ramp rate.

What is retention time in gas chromatography?

Retention time (tR) is the time elapsed between sample introduction (beginning of the chromatogram) and the maximum signal of the given compound at the detector.

What causes shift in retention time HPLC?

Related to the last phenomenon are shifts in retention times that are caused by an increase of back-pressure in the column. Increasing back-pressure may indicate a contamination of the column, but even a clogged frit can affect retention times.

Why do peaks shift in HPLC?

If all of the peaks are shifted by about the same time interval, the variations are likely caused by variation in flow rate in the instrument. This can be a shift in either direction, but is often toward longer retention times/slower flow rate.

Why do peaks become broader with increased retention time?

A longer column generally improves the separation. The trade-off is that the retention time increases proportionally to the column length and a significant peak broadening will be observed as well because of increased longitudinal diffusion inside the column. This broadening is inversely proportional to the flow rate.

What factors affect retention time?

The retention time depends on many factors: analysis conditions, type of column, column dimension, degradation of column, existence of active points such as contamination. and so on. If citing a familiar example, all peaks appear at shorter times when you cut off part of column.

How do I reduce retention time?

As temperature is increased, retention will decrease. If the room experiences wide temperature fluctuations, the HPLC retention times will probably be affected. The best solution is to run analyses at a temperature that can be controlled by using an oven.

What is the formula for retention factor?

f) The retention factor (k) is the ratio of the amount of analyte in the stationary phase to the amount in the mobile phase. It is generally calculated by k’ = (tR – tM)/tM = tR’/tM.

Does retention time depend on concentration?

The magnitude and direction of the observed RT shift will depend on both the observed analyte and undetected analyte peak concentrations. As the concentration increases, the bulk of the molecules in the chromatographic peak do not interact adsorptively with these sites and the retention time becomes stable.

What is the cause of retention in HPLC?

As a rule of thumb, the retention times shift by about 1% to 2% per 1 ºC. Related to the last phenomenon are shifts in retention times that are caused by an increase of back-pressure in the column. Increasing back-pressure may indicate a contamination of the column, but even a clogged frit can affect retention times.

What causes a retention time shift in GC?

GC Troubleshooting Series Part Six: Retention Time Shifts Possible Cause: Changes in Column Dimensions vs. Previous Column If your issue occurs after changing a column, it is probably due to changes in column length. The old column may have been trimmed over time to a significantly shorter length.

What causes a change in column retention time?

Maureen Joseph is the HPLC Columns Product Manager. Some possible causes to consider for retention time changes are: • Column aging • Column contamination • A poor column/mobile phase combination for your analytes • Insufficient column re-equilibration • Changes in flow rate or column temperature

Why does my GC keep changing column length?

If your issue occurs after changing a column, it is probably due to changes in column length. The old column may have been trimmed over time to a significantly shorter length. If your GC has an electronic pneumatic control (EPC), enter the actual column dimensions in to the software.

What causes shift in peak retention times in HPLC?

Peak broadening comes from longitudinal diffusion, caused by slow flow rate, void volume within the column and tubing and excessive retention in the column. Then you have Eddy diffusion, caused most by irregular packing bed, causing some molecules use a distintive path than the “pack”.