External Standard vs. Internal Standard in Gas Chromatography

Attribute	External Standard	Internal Standard in Gas Chromatography
Definition	Standard substance added to the sample before analysis	Standard substance added to the sample before analysis
Role	Used for calibration and quantification	Used for calibration and quantification
Stability	May be less stable due to external factors	More stable as it is added to the sample
Cost	May be more cost-effective	May be more expensive due to purity requirements

Introduction

Gas chromatography is a widely used analytical technique that separates and analyzes compounds in a mixture. Two common methods for quantifying analytes in gas chromatography are external standard and internal standard. Both methods have their own advantages and disadvantages, and choosing the right method depends on the specific requirements of the analysis.

External Standard

External standard is a method where a known concentration of a standard compound is injected into the gas chromatograph alongside the sample. The peak area of the standard compound is compared to the peak area of the analyte in the sample to determine the concentration of the analyte. One of the main advantages of external standard is its simplicity and ease of use. It is a straightforward method that does not require additional steps or calculations.

However, external standard does have some limitations. One major drawback is that it is sensitive to variations in injection volume and instrument conditions. Any changes in these parameters can affect the accuracy of the results. Additionally, external standard does not account for losses of analyte during sample preparation or injection, which can lead to inaccuracies in the quantification.

Internal Standard

Internal standard is a method where a known concentration of a standard compound is added to the sample before injection into the gas chromatograph. The peak area ratio of the analyte to the internal standard is used to calculate the concentration of the analyte. One of the main advantages of internal standard is its ability to correct for variations in injection volume and instrument conditions.

Internal standard also accounts for losses of analyte during sample preparation and injection, leading to more accurate quantification. However, internal standard does require additional steps in sample preparation, as the internal standard must be added to the sample in a precise manner. This can make the method more time-consuming and complex compared to external standard.

Comparison

• External standard is simpler and easier to use compared to internal standard.
• Internal standard provides more accurate results by correcting for variations in injection volume and instrument conditions.
• External standard is more sensitive to changes in experimental conditions, leading to potential inaccuracies in quantification.
• Internal standard accounts for losses of analyte during sample preparation and injection, improving the accuracy of the results.
• Internal standard requires additional steps in sample preparation, making it more time-consuming and complex.

Conclusion

Both external standard and internal standard are commonly used methods for quantifying analytes in gas chromatography. While external standard is simpler and easier to use, internal standard provides more accurate results by correcting for variations in experimental conditions. The choice between the two methods depends on the specific requirements of the analysis and the level of accuracy needed for the results.