Limit of Detection (LOD) and Limit of Quantitation (LOQ)

LOD: Limit of Detection (LOD)

The Limit of Detection (LOD) is the lowest concentration of an analyte in a sample that can be reliably detected by the analytical method, but not necessarily quantified. In other words, it's the point at which the analyte's signal is distinguishable from the background noise of the measurement system. LOD is often defined as the concentration at which the signal (analyte response) is at least three times the standard deviation of the noise (background noise) or as a signal-to-noise ratio of 3:1. LOD is important when you need to detect the presence of an analyte, such as in environmental monitoring to detect pollutants or in forensic analysis to detect trace substances. LOD should be reported along with the method validation results and method detection limits should be stated in the units of the analyte (e.g., ng/mL or ppm).

LOQ: Limit of Quantitation (LOQ)

The Limit of Quantitation (LOQ) is the lowest concentration of an analyte in a sample that can be both reliably detected and quantified with acceptable accuracy and precision. LOQ represents the lowest concentration at which the method can provide quantitative results with a specified level of confidence.

LOQ ensures that not only can the analyte be detected at this concentration but also that it can be accurately and precisely quantified. The accuracy and precision at LOQ should meet predefined acceptance criteria. LOQ is often defined as the concentration at which the signal (analyte response) is at least ten times the standard deviation of the noise (background noise) or as a signal-to-noise ratio of 10:1. LOQ is crucial when you need to determine the precise concentration of an analyte, such as in pharmaceutical analysis to quantify drug levels in a formulation or in clinical laboratories to measure analytes in patient samples. LOQ should be reported along with the method validation results and is typically stated in the units of the analyte (e.g., ng/mL or ppm).

Determination of LOD and LOQ

Both LOD and LOQ are determined experimentally during method validation. Common approaches include analysing a series of diluted standard solutions with known analyte concentrations and assessing the accuracy and precision of the results at lower concentrations until the LOD and LOQ are defined.

Figure represents the basics of limit of detection and quantitation.