A Simple and Fast Method for the Determination of Lead(II) Ions in Some Cosmetic Products Through Spectrophotometric Technique by Using Thiosemicarbazone-Linked Substituted Indole-2-one

We aimed to develop a simple, fast, and inexpensive colorimetric approach for detecting lead(II) ions in solution by forming a complex with 1-(1-benzyl-2-oxoindolin-3-ylidene)thiosemicarbazide. A detailed description of spectrophotometric lead(II) determination is provided. When combined with the N-benzyl-isatin-thiosemicarbazone ligand (L) in a slightly acidic solution (pH 12), lead(II) produces a yellow chelate. The molar absorptivity of the complex at 253 nm (λmax) is 1.9 × 103 L mol−1 cm−1, and the quantification limit is 2.28 µg mL−1 (11 µM), whereas the detection limit is 0.73 µg mL−1 (3.5 µM). The concentration range when Beer's law is observed is from 9.7 × 10−6 to 1.9 × 10−4 M. We studied the structure and stoichiometry of the Pb(II) and L complex in solution through the synthesis of the solid complex (PbL) and proved using the analytical techniques such as FTIR, NMR, UV-vis spectroscopy, SEM, and thermal analysis. Lead(II) recovery percentages in lipstick samples were determined using the developed method, with results ranging from 88.1 ± 1.9 to 117.3 ± 1.1%. The high lead(II) recovery rate from the samples indicates the effectiveness of the developed method and its potential use for accurate measurement and quality assessment of lead(II) in various samples.