**3.2 Important and application of spectrophotometric in the pharmaceutical analysis**

The basis of spectrophotometric methods is the simple relationship between the absorption of radiation by a solution and the concentration of the colored species in the solution [48]. A molecule or ion exhibits absorption in the visible or UV region when the radiation (photons) causes an electronic transition in the molecule or ion containing one or more chromophoric groups (**Table 2**). The functional groups on drug molecules are targeted for quantitative analysis of pharmaceutical formulations using UV–visible spectrophotometry techniques. The quantitative analysis using UV– visible spectrophotometry is based mainly on the Beer-Lambert law, which explains the relationship between the absorbance of the analyte under analysis and its concentration:

$$A = \log \mathbf{I}\_0/\mathbf{I} = \epsilon \mathbf{C} \mathbf{x} \tag{8}$$

where ε is molar absorptivity, x is the path length, and C is the concentration of the analyte.

Methods usually are based on ion-pair, charge-transfer complex formation reactions, and redox-complexation reactions, which formed the backbone of


**Table 2.**

*Examples of some common chromophoric groups.*

spectrophotometric methods. The developed methods were applied to dosage forms, including tablets, injections, syrup, capsules, and also spiked human urine wherever possible [7, 14, 17, 19, 21–30, 33, 37, 44, 47]. The details of those important reactions and more examples for each application are given.
