Hi,
I have a question on Gas Chromatography(GC).
The following were injected into the GC system: -
1) 1% sample solution in acetone
2) a 500 times dilution of item 1)
The retention time of the main peak in the diluted sample solution 2) shifted by ~ 2min.
The expected area count of the main peak is also half of what is theoretically calculated. (i.e. I would expect the area count of the main peak in the diluted solution to be 500 times less than the sample solution.)
Can you suggest possible reasons for this difference in retention time between the sample and the diluted sample?
Does this shift in retention time happen to some samples that are too diluted?
Thank you.
The difference in retention time between the sample solution and the diluted sample can be attributed to a couple of factors in gas chromatography. Here are some possible reasons:
1) Change in sample viscosity: When the sample is diluted, there is a change in the overall viscosity of the solution. Viscosity plays a role in the interaction between the sample and the stationary phase in the chromatography column. A change in viscosity can affect the retention time of the analytes, resulting in a shift in the main peak's retention time.
2) Change in sample concentration: Dilution of the sample leads to a decrease in the concentration of the analytes. Chromatographic separation is influenced by the concentration of the analytes, and a change in concentration can affect the partitioning behavior and retention time.
3) Change in sample injection volume: When diluting the sample, the injection volume into the GC system may also change. The injection volume affects the amount of analyte introduced into the column. With a different injection volume, the sample may distribute differently in the column, leading to a shift in retention time.
Regarding the question of whether this shift in retention time occurs to samples that are too diluted, it depends on various factors such as the specific analyte and the chromatographic conditions used. In general, significant dilution can alter the retention time, but there is no specific threshold for how much dilution causes a shift. It is essential to consider the nature of the analyte, the separation conditions, and the extent of dilution.
To confirm the cause of the retention time shift, it is advisable to perform control experiments by injecting individual components in pure acetone or running known standards with varying dilutions. These experiments can help identify the specific factors contributing to the observed changes in retention time and peak area.