In most cases with GLC the area under the peak as a % of the total area for all peaks is interpreted as representing the % mass of the compound measured in the mixture. Explain why this is only an approximation.
To understand why the area under the peak in gas chromatography (GLC) is only an approximation of the % mass of the compound in a mixture, we need to break down the process of GLC and consider its limitations.
Gas chromatography separates the components of a mixture based on their ability to partition between a stationary phase (usually a coated column) and a mobile phase (an inert gas). The separated components elute from the column at different times, forming peaks on the chromatogram.
The area under each peak corresponds to the amount of that component present in the mixture. Therefore, it is tempting to interpret the area under the peak as the percentage mass of that component since the sum of all peak areas will equal 100%. However, there are several reasons why this interpretation is only an approximation:
1. Column Efficiency: The efficiency of the column in separating the components affects the peak shape. In reality, peaks are not perfectly symmetrical, and they can be broadened or distorted due to factors like column degradation or interactions between the components and the stationary phase. Such effects can lead to errors in estimating the true area under the peak.
2. Response Factors: Different compounds exhibit different responses in the detectors used in GLC. The detectors may be more or less sensitive to certain compounds, leading to variations in the measured peak areas. This could result in the over or underestimation of the true component percentage.
3. Detector Limitations: Some detectors in GLC may not provide a full response for all compounds, especially in cases of highly volatile or poorly detectable compounds. As a result, the peak area might not accurately represent the true amount of the compound in the mixture.
4. Peak Overlaps: In complex mixtures, different compounds can co-elute, leading to overlapping peaks. It becomes challenging to accurately assign the peak area to a specific compound, making it difficult to determine the true percentage mass based solely on the peak area.
Due to these limitations and potential sources of error, it is important to calibrate and validate gas chromatography results using appropriate standards and controls. Utilizing additional analytical techniques, such as mass spectrometry, can provide more accurate quantification of compounds in a mixture rather than relying solely on the approximation from peak area under GLC chromatograms.