In UV-visible spectrophotometric analysis, it is common practice to use the wavelength corresponding to the maximum absorbance (lambda max) of a particular analyte for quantitative measurements. This wavelength is chosen because it represents the region where the analyte absorbs light most strongly, resulting in a higher sensitivity and better precision.
However, there can be situations where using a wavelength other than lambda max may be acceptable or necessary. Here are a few cases:
Multicomponent analysis: If you have a sample containing multiple analytes with different absorption spectra, it may be necessary to choose different wavelengths for each component. In such cases, you would typically measure the absorbance at specific wavelengths for each analyte separately.
Specificity and selectivity: Sometimes, the analyte of interest may exhibit significant interference or overlap with other substances at its lambda max. In such cases, an alternate wavelength that minimizes interference and provides better selectivity may be used.
Absorbance range: If the analyte's absorbance is very low at its lambda max, it might be advantageous to choose a different wavelength where the absorbance is higher. This helps to improve the sensitivity and the limit of detection of the analysis.
Method development: During the development of a new analytical method, different wavelengths can be explored to determine the optimal choice for measurement. This process involves scanning a range of wavelengths to identify the most suitable one based on factors such as linearity, sensitivity, and absence of interference.
While using a wavelength other than lambda max is possible, it's important to consider the potential impact on the accuracy and precision of the analysis. The choice of wavelength should be supported by appropriate scientific justification and validation experiments to ensure reliable results.