Qualitative analysis: identification - Chemistry LibreTexts
in boiling points! Lower b.p. Higher b.p 50 oC greater than least volatile ( highest boiling point compound). So high boiling point means a long retention time. Oct 23, Since the retention time is a specific property of a component, it may be used Relation Between Retention, Boiling Point and Carbon Number. The column is typically made of stainless steel and is between 1 and 4 metres long with an internal diameter So high boiling point means a long retention time.
A high value of K means the compound is more soluble in the liquid phase than in the gas phase. K is temperature dependent. Polar or Non-Polar Stationary Phase One of the key factors when setting up a GC method is to choose the polarity of the stationary phase. The polarity is chosen using knowledge of the sample matrix and what separation is required.
If the polarity of the target compound and the stationary phase are similar, then there is likely to be a greater interaction between the two. Consequently, the retention time will be longer for polar compounds on polar stationary phases and shorter on non-polar stationary phases. Boiling point If a component has a low boiling point, then it is likely to spend more time in the gas phase.
How does the boiling point affect gas chromatography?
Therefore its retention time will be lower than a compound with a higher boiling point. Column temperature A high column temperature will give shorter retention times, as more components stay in the gas phase but this can result in poor separation.
For better separation, the components have to interact with the stationary phase.
Carrier gas flow-rate A high flow rate lowers retention times but also yields a poor separation. Column length A longer column will produce longer retention times but better separation.
analytical chemistry- factors that influence retention time.
For instance, shortening the column length say to one half will half the retention times. Overview of parameters in a chromatographic process which determine the analysis time: Volatility of the component Volatile components travel through a column faster than non-volatile components. The volatility is related to the boiling point and to the size of the molecules. This means that the smaller molecules within a homologous series have shorter retention times than the larger molecules Stationary phase Not the stationary phase itself, but the affinity of the sample component for the stationary phase is important.
The stronger this affinity, the stronger is the interaction, and therefore the longer the retention time. Amount of stationary phase The k-values of sample components are related to the amount of stationary phase.
The more stationary phase is present, the larger the k-values and thus the longer the retention time. Column diameter In a narrow bore column the optimum gas velocity is much higher than in a wide bore column.
This has immediate effect on the analysis time.
A narrow bore column is a 'fast' column; a wide bore column is a 'slower' column. Column length The length of a column affects the retention time proportionally. Thus halving the column length yields a considerable profit: Evidently, the quality of the separation is reduced as well.
Type of carrier gas and linear gas velocity In the previous section we have discussed the effect of the type of carrier gas.