What affects peak shape in gc? I know peak area is proportional to the amount of a species and tailing occurs due to adsorption of polar species. Also fronting can occur if too much sample is added but these are the only things i can think of that would affect peak shape.
i was asked if i would expect peak shapes to be the same for all standards on a non-polar column. the standards to be tested are pentane, hexane, heptane, octane, decane, cyclohexane, toluene, acetone, and 1- and 2-propanol
In gas chromatography (GC), several factors influence the peak shape. While peak area represents the amount of a specific species in the sample, peak shape provides additional information about the separation efficiency and resolving power of the chromatographic system. Let's discuss the factors that affect peak shape in GC:
1. Injection volume: The volume of sample injected can affect peak shape. If too much sample is injected, it can cause fronting, where the peak becomes broader and asymmetrical. On the other hand, injecting too little sample can result in narrower and taller peaks.
2. Column efficiency: The efficiency of the GC column affects peak shape. Higher column efficiency leads to sharper, more symmetrical peaks with better resolution. Factors like column length, inner diameter, and film thickness can influence column efficiency.
3. Stationary phase polarity: In GC, the stationary phase can be non-polar or polar. Non-polar columns are more suited for the separation of non-polar compounds, while polar columns are better for polar compounds. Using a non-polar column for polar compounds or vice versa can result in peak broadening or tailing.
4. Sample matrix: The composition of the sample matrix can impact peak shape. For instance, impurities or high levels of solvent can cause peak distortion or tailing. It is essential to clean up or remove impurities to achieve better peak shape.
5. Temperature: The temperature at which the analysis is performed can affect peak shape. Keeping the temperature too high or too low can lead to peak distortion and tailing. Optimizing the temperature conditions for the specific sample and column is critical.
Now, let's address your specific question about whether you would expect peak shapes to be the same for all standards on a non-polar column. In general, on a non-polar column, non-polar compounds tend to elute faster and with better peak shapes compared to polar compounds.
Based on the standards you mentioned (pentane, hexane, heptane, octane, decane, cyclohexane, toluene, acetone, 1- and 2-propanol), most of them are non-polar compounds. Therefore, you can expect relatively good peak shapes for these compounds on a non-polar column. However, polar compounds like acetone and 1- and 2-propanol might exhibit some degree of tailing due to their polarity. It is important to optimize the GC conditions, such as temperature and column selection, to improve the peak shape for polar compounds on a non-polar column.