Internal standard

Definition

An internal standard is a known quantity of a substance added to a sample to improve the accuracy and precision of analytical measurements. It helps to compensate for variations in sample preparation, instrument response, and other factors that can affect the results of chromatographic and spectroscopic analyses. By comparing the response of the analyte to that of the internal standard, analysts can obtain more reliable quantitative data.

5 Must Know Facts For Your Next Test

1. Using an internal standard helps correct for variations in instrument performance and sample matrix effects that can influence measurement accuracy.
2. The choice of an appropriate internal standard is critical; it should have similar chemical properties to the analyte but should not be present in the sample naturally.
3. Internal standards are particularly useful in methods such as gas chromatography (GC) and liquid chromatography (LC), where variations can arise from sample introduction or ionization efficiency.
4. The ratio of the analyte's response to the internal standard's response is used for quantification, providing a more stable reference point for analysis.
5. In environmental analysis, internal standards can enhance data reliability when assessing complex matrices containing multiple interfering substances.

Review Questions

• How does the use of an internal standard improve the accuracy of analytical measurements?
  • The use of an internal standard improves accuracy by compensating for variations that may occur during sample preparation and analysis. For instance, if an instrument's sensitivity changes between runs or if different sample matrices affect the detection of an analyte, the internal standard serves as a reference. By comparing the response of the analyte to that of the internal standard, analysts can correct for these discrepancies, leading to more precise quantification.
• Discuss the factors involved in selecting an appropriate internal standard for a specific analytical method.
  • Choosing an appropriate internal standard involves considering its chemical properties and behavior relative to the analyte. It should ideally have similar characteristics, such as retention time in chromatography or ionization efficiency in mass spectrometry. Additionally, it must not be present in the sample being analyzed to avoid interference. The selected internal standard should also produce a strong and consistent signal across varying concentrations to ensure accurate comparisons.
• Evaluate the impact of using an internal standard on the overall reliability and validity of quantitative environmental analyses.
  • Using an internal standard significantly enhances the reliability and validity of quantitative environmental analyses by providing a built-in mechanism to account for errors and variabilities inherent in analytical procedures. This method ensures that fluctuations due to instrument variability or sample complexity are systematically corrected. As a result, environmental scientists can confidently interpret their findings regarding contaminant levels or other chemical species in complex environmental samples, thus supporting informed decision-making about pollution control and regulatory compliance.

Related terms

Calibration curve: A graph that relates the concentration of an analyte to its response in an analytical method, used to determine the concentration of unknown samples.

Method validation: The process of confirming that an analytical method is suitable for its intended purpose, including aspects like accuracy, precision, specificity, and linearity.

Quantitative analysis: The determination of the amount or concentration of a substance in a sample, often involving various analytical techniques.