External Standard vs. Internal Standard

Attribute	External Standard	Internal Standard
Definition	Standard substance added to the sample before analysis	Standard substance added to all samples before analysis
Usage	Used for calibration and quantification	Used for normalization and correction of variations
Stability	May be less stable due to external factors	More stable as it is added to all samples
Cost	May be more expensive due to separate standards	May be more cost-effective as one standard is used for all samples

Introduction

External standard and internal standard are two common methods used in analytical chemistry to quantify the amount of a particular analyte in a sample. Both methods have their own advantages and disadvantages, and choosing between them depends on the specific requirements of the analysis. In this article, we will compare the attributes of external standard and internal standard to help you understand the differences between the two approaches.

External Standard

External standard is a method where a series of known concentrations of the analyte are prepared separately from the sample. These standards are then analyzed using the same method as the sample, and a calibration curve is constructed by plotting the response (e.g., peak area) against the concentration of the standards. The concentration of the analyte in the sample is then determined by comparing its response to the calibration curve.

• Advantages of External Standard:
• Simple and straightforward method
• Does not require additional sample preparation
• Useful for samples with low analyte concentrations
• Can be used for a wide range of analytes

Internal Standard

Internal standard is a method where a known amount of a compound not present in the sample (internal standard) is added to both the standards and the sample. The internal standard is used to correct for variations in sample preparation, injection volume, and instrument response. The ratio of the analyte peak area to the internal standard peak area is then used to quantify the analyte in the sample.

• Advantages of Internal Standard:
• Corrects for errors in sample preparation and analysis
• Improves accuracy and precision of the analysis
• Useful for complex samples with matrix effects
• Reduces variability between samples

Comparison

When comparing external standard and internal standard methods, several factors need to be considered. One of the main differences between the two methods is the way in which the calibration is performed. External standard requires the preparation of a series of standards with known concentrations, while internal standard involves the addition of a known amount of a compound to the sample.

Another key difference is the ability of internal standard to correct for errors in sample preparation and analysis. This makes internal standard more suitable for complex samples with matrix effects, where external standard may not provide accurate results due to variations in the sample matrix.

On the other hand, external standard is a simpler and more straightforward method that does not require additional sample preparation. It is also useful for samples with low analyte concentrations, where internal standard may not be necessary. External standard can be used for a wide range of analytes, making it a versatile choice for many analytical applications.

Conclusion

In conclusion, both external standard and internal standard methods have their own advantages and disadvantages. The choice between the two methods depends on the specific requirements of the analysis, including the complexity of the sample, the accuracy and precision needed, and the range of analytes being measured. By understanding the attributes of external standard and internal standard, analysts can make an informed decision on which method to use for their analytical needs.