FI-chemiluminometric study of thiazides by on-line photochemical reaction

• Published in: Journal of pharmaceutical and biomedical analysis 2004-11, Vol.36 (4), p.693-700
• Main Authors: Ciborowski, M., Icardo, M. Catalá, Mateo, J.V. García, Martínez Calatayud, J.
• Format: Article
• Language: English
• Subjects: Analysis; Analytical, structural and metabolic biochemistry; Biological and medical sciences; Chemiluminescence; FIA; Flow Injection Analysis - instrumentation; Flow Injection Analysis - methods; Fundamental and applied biological sciences. Psychology; General pharmacology; Hydrochlorothiazide; Luminescent Measurements - instrumentation; Luminescent Measurements - methods; Medical sciences; Pharmaceuticals; Pharmacology. Drug treatments; Photochemical reaction; Photochemistry - methods; Thiadiazines - analysis; Thiadiazines - chemistry; Thiadiazines - radiation effects; Thiazides
• ISSN: 0731-7085; 1873-264X
• DOI: 10.1016/j.jpba.2004.08.020

The present manuscript deals with a simple and sensitive flow-injection method for the chemiluminescent determination of thiazides. The method is based on the on-line photodegradation and chemiluminescent determination of the resulting photo-fragments. The on-line photodegradation is performed in basic medium by using a photoreactor consisting of a 550 cm long × 0.8 mm ID piece of PTFE tubing helically coiled around an 8 W low-pressure mercury lamp. The determination of the photo-irradiated thiazides is performed by a chemiluminescent oxidative reaction with Ce(IV) in sulphuric acid medium. A heterogeneous group of thiazides (indapamide, metolazone, hydroflumethiazide, chlorthalidone and bendroflumethiazide) has been studied. Hydrochlorothiazide was selected as a test substance. The “on-line” photochemical reaction approach allows the sensitive chemiluminescent determination of thiazides which do not present native chemiluminescence in the absence of sensitizers such as Rhodamine 6G. Linear calibration graphs were typically over the range 0.5–12 μg ml −1 (indapamide, metolazone, hydroflumethiazide and chlorthalidone); and over the range 0.5–5 μg ml −1 (hydrochlorothiazide). Limits of detection ranged between 0.005 μg ml −1 (hydrochlorothiazide) and 0.06 μg ml −1 (bendroflumethiazide). The relative standard deviation for the test substance was 2.0% for 2 μg l −1 of the drug ( n = 11) and the throughput was 65 h −1 in all cases. The assessment of the photodegradation step on the molecular structure of thiazides was established by recording UV and fluorimetric spectra. The viability of the on-line photoinduced fluorescent determination of hydroflumethiazide and bendroflumethiazide was confirmed. The method was also applied to the determination of hydrochlorothiazide in commercially available formulation.