The use of fluorescent probes in pharmaceutical analysis

Three techniques for the determination of perindopril through derivatization with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole

In addition to its pure form, three accurate, rapid, and simple methods have been established for determining perindopril (PRD) in its tablet form. At pH 9.0 using a borate buffer, developing the three designated methods was successful according to the reaction between PRD and 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) and the formation of a chromogen (with a yellow color) measurable at 460 nm using the spectrophotometric method (Method I). In addition, the produced chromogen was assessed using the spectrofluorimetric method (Method II) at 535 nm following excitation at 461 nm. Afterward, the same reaction product was separated and determined using the HPLC method with fluorescence detection (Method III). A Promosil C₁₈ stainless steel column (Q7 5 mm particle size, 250-4.6 mm) has proven suitable for separation. The mobile phase adjustment was made at pH 3.0, with a 1.0 mL min ^-1 flow rate; its composition was methanol-sodium dihydrogen phosphate, 0.02 M (60: 40, v/v). Through concentration ranges of 5.0-60.0, 0.5-6.0, and 1.0-10.0 μg mL^-1, the calibration curves were rectilinear for Methods I, II, and III, respectively, with limits of quantification (LOQ) of 1.08, 0.16 and 0.19 μg mL^-1 as well as limits of detection (LOD) of 0.36, 0.05 and 0.06 μg mL^-1. The developed methods were implemented to estimate PRD in tablets, and a comparison between the obtained outcomes utilizing the developed methods as well as obtained from the official method revealed that they were comparable. The official BP method was based on dissolving PRD in anhydrous acetic acid and titrating with 0.1 M perchloric acid, then the potentiometric determination of the end-point. The designated methods were also implemented in content uniformity testing with satisfying results. The reaction pathway proposal was speculated, and according to ICH Guidelines, the statistical evaluation of the data was performed. The three proposed methods were confirmed to be green, eco-friendly and safe to environment using Green Analytical procedure index (GAPI) method.

Quantification of anthropogenic and geogenic Ce in sewage sludge based on Ce oxidation state and rare earth element patterns

Emissions of Ce from anthropogenic activities (anthropogenic Ce) into urban wastewater systems and the environment result from its widespread industrial use (abrasives, catalysts, nanotechnology). Because Ce in sewage sludge can also be of geogenic origin, the quantification of anthropogenic Ce in sewage sludge remains elusive. In this study, we evaluated the suitability of Ce oxidation state and rare earth element (REE) patterns for the quantification of anthropogenic Ce fractions in sewage sludge. A diverse set of soil samples served to gain baseline information on geogenic Ce. Geogenic Ce in the soils was characterized by high Ce(III) fractions (≥70%) and their REE patterns were comparable to the REE patterns of the upper continental crust. The sewage sludges contained on average ∼80% Ce(IV) (range 18-108%), pointing to the importance of anthropogenic inputs of Ce(IV). The quantification of the anthropogenic Ce fraction based on Ce oxidation state, however, was associated with considerable uncertainty because geogenic and anthropogenic Ce cannot exclusively be assigned to Ce(III) and Ce(IV), respectively. The REE patterns of most sewage sludges indicated a clear enrichment of Ce compared to heavier REE. Based on the assumption that the industrially used Ce is free of (most) other REE, we estimated the fraction of anthropogenic Ce in the sludges based on individual Ce/REE ratios. For the individual sludges the anthropogenic contributions were very variable (10-100%) but consistent fractions were obtained for individual sludges when calculated based on Ce/Dy (dysprosium), Ce/Er (erbium) and Ce/Eu (europium) ratios. Electron microscopy analysis of sludges dominated by anthropogenic Ce revealed that the Ce was mostly contained in nanoscale particles devoid of elements characteristic of Ce-bearing minerals. Thus, anthropogenic Ce contents derived from REE patterns may be used to validate current mass flow models for engineered CeO2 nanoparticles.

Liquid chromatography assay for 5-aminolevulinic acid: application to in vitro assessment of skin penetration via Dermaportation

The purpose of the present study was to develop a reverse-phase high performance liquid chromatographic (HPLC) assay for quantifying 5-aminolevulinic acid (ALA). The assay was applied to study the skin permeation of ALA and the influence of a novel skin penetration enhancement technology. Separation was achieved utilizing a Phenomenex Jupiter C(18) column following fluorescence derivatization with fluorescamine. The assay was linear (r(2)>0.99) with a minimum limit of quantitation of 400 ng/mL. The inter- and intraday variation was 1.6 and 0.9% at the lower end of the linear range and 1.5 and 1.9% at the upper end, respectively. The HPLC assay and fluorescence derivatization procedure is sensitive, simple, rapid, accurate and reproducible and offers advantages with regard to stability of ALA in comparison to other fluorescence derivatization methods. Results from the preliminary skin permeation study demonstrated substantial skin penetration of ALA only when applied with Dermaportation as a skin penetration enhancement device.

Environmental effects on the fluorescence behaviour of carbazole derivatization reagents

The carbazole ring is the basic structure present in the fluorescence derivatization reagents 9-chlorocarbonylcarbazole and 9-carbazolylacetic acid. The fluorescence behaviour of these carbazole derivatives was studied in solvents with different polarities (cyclohexane, ethanol, acetonitrile, water) and at different pH values (4.5 and 8.8). The influence of the low polarity environment afforded by 2-hydroxypropyl-beta-cyclodextrin (HPbeta-CD) is also described. The behaviour of the fluorescent reagents is compared to the model molecules carbazole and 9-methylcarbazole. For all derivatives studied, a bathochromic shift in the fluorescence emission maxima was observed when the solvent polarity was increased. A bathochromic shift was observed in dioxane solutions, which can be ascribed to the peculiar behaviour of this solvent. The changes in the fluorescence intensity in the case of 9-carbazolylacetic acid can be related to the ionization of the carboxylic acid group. Inclusion into the cavity of HPbeta-CD allows emission spectra to be obtained close to those obtained in ethanolic solutions with a remarkable enhancement in the fluorescence intensity, depending on the chemical structure of the carbazole derivative included.

Determination of norfloxacin by fluorescence in the presence of different antacids: quantification of analytical interferences

Norfloxacin is a fluorquinolone that can interfere with certain antacids (derivatives of Al and Mg) because its dissolution profiles are dependent on pH. Furthermore, it can form insoluble complexes that modify its absorption and bioavailability. Two sensitive and selective analytical methods using fluorescence (FL) and UV spectrophotometry (UV) have been developed to study the dissolution behaviour in gastric juice of different formulations of norfloxacin in tablets. There are no significant differences when the samples are measured by both methods and their ruggedness in the presence of some excipients is proven. From this, it is concluded that they are effective for this study. When different antacids are added to the dissolution medium, using UV and FL methods with the same samples, totally different dissolution profiles appear. Using FL, it would appear that up to 400% of the amount of norfloxacin in the tablet is released. These profiles are misleading because the uniformity of dosage units was tested before the dissolution studies. It is proven that the antacids dissolved in gastric juice do not produce fluorescence, but cause important analytical interferences with norfloxacin. This may be because their association with Al3+ or Mg2+ forms a new compound. Nevertheless, it is observed that this effect is more important in some antacids (Almagate, Magaldrate). This may be because their ability to deliver Al to the medium is greater.

High-performance liquid chromatographic determination of aliphatic thiols with aroylacrylic acids as fluorogenic precolumn derivatization reagents

The use of the methyl ester of 4-(6-methoxynaphthalen-2-yl)-4-oxo-2-butenoic acid as a fluorogenic labelling reagent for the high-performance liquid chromatography (HPLC) of biologically important thiols (glutathione, cysteine, acetylcysteine, homocysteine, cysteamine, sodium 2-mercaptoethanesulphonate and thiola) was investigated. The compound reacts selectively and rapidly (10 min at ambient temperature and pH 7.5) with the thiols to give fluorescent adducts that can be separated by reversed-phase HPLC and detected fluorimetrically (lambda em = 450 nm; lambda em = 310 nm). Applications to the determination of L-cysteine and mesna in pharmaceutical formulations are described.

Determination of thiols of biological and pharmacological interest by high-performance thin-layer chromatography and fluorescence scanning densitometry

The application of high-performance thin-layer chromatography (HPTLC) with fluorescence scanning densitometry provides a simple, rapid and reliable system for the qualitative and quantitative determination of several thiols of biological and pharmacological interest. The determination of a mixture of thiols (captopril, coenzyme A, cysteamine, cysteine and glutathione), together with their disulphides may readily be performed by pre-chromatographic derivatization with the thiol-specific fluorobenzoxadiazole reagents SBD-F and ABD-F, followed by HPTLC separation on silica gel plates using isopropyl ether-methanol-water-acetic acid (9:8:2:1, v/v/v/v) as the developing solvent, and fluorodensitometric measurement of the fluorescing derivatives. Detection limits of about 30 pg (coenzyme A) to 6 pg (cysteamine) per spot were achieved; the relative standard deviation (RSD) of the complete procedure was 1.16-3.2%.