Automated Derivatization of Pharmaceutically Active Thiols Under Flow Conditions Using an o-Phthalaldehyde/Glycine Fluorogenic System and Sequential Injection Analysis

Abstract

The present study reports a new automated, generic analytical method for the determination of the pharmaceutically active thiols captopril (CAP), N-acetylcysteine (NAC), and D-Penicillamine (PEN). The proposed sequential injection (SI) method is based on the on-line reaction of the selected thiols with o-phthalaldehyde/glycine in alkaline medium (pH = 9.5) to form highly fluorescent iso -indole derivatives. The effect of all major flow and reaction variables was investigated, while validation was carried out in terms of linearity/range (2.5–7.5 mg L⁻¹), limits of detection (1.6–2.3 µ g L⁻¹), quantification (5.3–7.7 µ g L⁻¹), precision (0.9–1.2% for repeatability and 3.5–4.9% for intermediate precision), selectivity, and accuracy (98.3–102.8%). The developed method was applied to the assay and dosage uniformity tests of various pharmaceutical formulations at a sampling rate of 73 h⁻¹.

Keywords:

• Derivatization
• Fluorimetry
• o-phthalaldehyde
• Sequential injection
• Thiols

Notes

^a Upper limit of the linear regression line.

^b Maximum placebo concentration tested.

F: Fluorescence intensity (mV).

γ: Analyte mass concentration in mg L⁻¹.

^a Standard deviation of the recoveries.