Direct Spectrofluorimetric Method Research Articles

Direct Spectrofluorimetric Method for the Analysis of Carbofuran and Fluometuron in Senegalese Natural Waters.

In this work, analytical study of carbofuran (CAF) and fluometuron (FLM) pesticides was carried out using direct spectrofluorimetric method in various solvents. Results showed that CAF and FLM are naturally fluorescent in all solvents under study including organic (MeOH, MeCN, DMF) and aqueous micellar one (CTAC, SDS, Brij-700). For the analysis of FLM, CTAC give the best fluorescence signal enhancement. Analytical performances, such as limit of detection (LOD) and quantification (LOQ) was evaluated after solvent optimization and were found to vary, respectively, between 0.1 and 11 ng mL- 1 and between 0.3 and 36.6 ng mL- 1. Analytical application in various environmental aqueous samples matrices (sea, tap, runoff and well waters) give satisfactory recovery rates in the limits of 73.7-113.7% for both pesticides. This method is described for its simplicity for routine analysis.

Validated spectrofluorimetric assay of two co-administered drug mixtures containing hydroxychloroquine with either moxifloxacin or ofloxacin as a drug regimen for hospital-acquired pneumonia in covid-19 patients.

Moxifloxacin and ofloxacin are two broad-spectrum quinolone antibiotics. They are among the most widely used antibiotics nowadays in controlling the covid-19 pandemic. Hydroxychloroquine is an FDA-approved drug for the treatment of covid-19. This work describes a simple, green, selective, and sensitive spectrofluorimetric method for the assay of moxifloxacin and ofloxacin in presence of hydroxychloroquine as two co-administered mixtures used in the treatment of hospital-acquired pneumonia in the covid-19 patients. Simultaneous assay of hydroxychloroquine and moxifloxacin was carried out in methanol by direct spectrofluorimetric method (method I) at 375 nm and 550 nm respectively after excitation at 300 nm. The direct spectrofluorimetric assay was rectilinear over concentration range of (50.0-400.0) and (300.0-2500.0) ng/ml for hydroxychloroquine and moxifloxacin with LOD of 6.4 and 33.64 ng/ml and LOQ of 19.4 and 102.6 ng/ml for the two drugs respectively. While the assay of hydroxychloroquine and ofloxacin was carried out by measuring the first derivative synchronous amplitude for hydroxychloroquine at the zero crossing point of ofloxacin and vice versa at Δ λ = 140 nm (method II). Hydroxychloroquine was measured at 266 nm while ofloxacin at 340 nm over concentration range of (4.0-40.0 ng/ml) for hydroxychloroquine and (200.0-2000.0 ng/ml) for ofloxacin with LOD of 0.467 ng/ml and 25.3 ng/ml and LOQ of 1.42 ng/ml and 76.6 ng/ml for the two drugs respectively. the two methods were validated following ICH guidelines and were applied to the analysis of the two drugs in plasma with good percent recoveries (109.73-93.17 %).

Utilization of a micellar matrix for simultaneous spectrofluorimetric estimation of alfuzosin hydrochloride and vardenafil hydrochloride

A sensitive and direct spectrofluorimetric method was developed for simultaneous quantitation of two co-administered drugs, namely, alfuzosin hydrochloride (AFH) and vardenafil hydrochloride (VRH). Both drugs exhibited native fluorescence properties that could be exploited to assay them in biological fluids with high sensitivity. Spectrofluorimetric analysis of AFH and VRH is based on excitation of both drugs at 265 nm where emission spectra were recorded separately for AFH and VRH at 380 and 485 nm, respectively. Micellar trends in analytical chemistry were adopted to minimize both environmental and occupational hazards, using distilled water and sodium dodecyl sulphate (serves as a micellar medium that enhanced the sensitivity of AFH and VRH) for analysis of both drugs in their raw materials, tablets, and human biological fluids (plasma and urine). Linearity ranges were 1.0–16.0 and 10.0–700.0 ng mL−1 for AFH and VRH, respectively. The proposed method was successfully assessed for analysis of AFH and VRH in spiked human plasma and urine samples over the following concentrations: 1.0–12.0 ng mL−1 and 4.0–400.0 ng mL−1 for both drugs, simultaneously with mean recoveries of 101.08 % and 102.06 % in plasma and 96.75 % and 92.8 % in urine. Statistical analysis of the practical results has proved quite good agreement and revealed there were no significant differences in the accuracy and precision with those obtained by the comparison methods. The proposed method was applied successfully to Prostetrol® and Powerecta® commercial tablets without interference with tablet additives.

Micelle-enhanced direct spectrofluorimetric method for the determination of linifanib: Application to stability studies.

A new simple stability-indicating spectrofluorimetric method has been developed and validated for the determination of the tyrosine kinase inhibitor, linifanib (LNF). The proposed method makes use of the native fluorescence characteristics of LNF in a micellar system. Compared with aqueous solutions, the fluorescence intensity of LNF was greatly enhanced upon the addition of Tween-80. The relative fluorescence intensity of LNF was measured in a diluting solvent composed of 2% Tween-80: phosphate buffer pH8.0 (20: 80, v/v) using excitation and emission wavelengths of 290 and 450nm, respectively. The proposed method was fully validated as per the ICH guidelines. The recorded fluorescence intensity of LNF was rectilinear over a concentration range of 0.3-2μg/ml with a high correlation coefficient (r=0.9990) and low limits of detection (0.091μg/ml) and quantitation (0.275μg/ml). The applicability of the method was extended to study the inherent stability of LNF under different stress degradation conditions including, alkaline, acidic, oxidative, photolytic and thermal degradation. Moreover, the method was utilized to study the kinetics of the alkaline and oxidative degradation of LNF. The pseudo-first order rate constants and half-lives were calculated.

An eco-friendly direct spectrofluorimetric method for the determination of irreversible tyrosine kinase inhibitors, neratinib and pelitinib: application to stability studies.

A new rapid and simple stability-indicating spectrofluorimetric method has been developed for the determination of two irreversible tyrosine kinase inhibitors (TKIs), neratinib (NER) and pelitinib (PEL). The method is based upon measurement of the native fluorescence intensity of both drugs at λex 270nm in aqueous borate buffer solutions (pH 10.5). The fluorescence intensity recorded at 545nm (NER) and 465nm (PEL) were rectilinear over the concentration range of 0.1-10μg/mL for both drugs with a high correlation coefficient (r>0.999). The proposed method provided low limits of detection and of quantitation of 0.07, 0.11μg/mL (NER) and 0.02, 0.05μg/mL (PEL), respectively. The method was successfully applied for the determination of NER and PEL in bulk powder. The proposed methods were fully validated as per the International Conference on Harmonisation (ICH) guidelines. The application of the method was extended to stability studies of both NER and PEL under different forced-degradation conditions (acidic-induced, base-induced, oxidative, wet heat, and photolytic degradation). Moreover, the kinetics of the base-induced and oxidative degradation of both drugs was investigated and the pseudo-first-order rate constants and half-lives were estimated at different temperatures. Also, an Arrhenius plot was applied to predict the stability behaviour of the two drugs at room temperature. Copyright © 2016 John Wiley & Sons, Ltd.

Solvolysis kinetic study and direct spectrofluorimetric analysis of the fungicide benomyl in natural waters

<p>A direct spectrofluorimetric method for the quantitative analysis of benomyl in natural waters is described. Benomyl is an instable, fluorescent fungicide that mainly decomposes into carbendazim and n-butyl-isocyanate in organic and aqueous solutions. The kinetics of benomyl solvolysis reactions were investigated in organic solvents (methanol and acetonitrile) and in aqueous solvent systems, including β–cyclodextrin (β-CD), sodium dodecyl sulfate (SDS), dodecyltrimethylammonium chloride (DTAC), cetyltrimethylammonium chloride (CTAC), cetyltrimethylammonium hydroxide (CTAOH), Brij-700, Triton X-100 and water, at different pH and/or NaOH concentrations. The benomyl fluorescence signal was found to be quasi-completely stable in 10<sup>-2</sup> M NaOH aqueous solution, various alkaline (10<sup>-2</sup> M NaOH) organized media, β-CD neutral solution and Triton X-100 aqueous solutions of different pH. Based on these results, a direct spectrofluorimetric analytical method was developed for the determination of benomyl in 10<sup>-2</sup> M NaOH aqueous solution and Triton X-100 solutions (pH7 and 10<sup>-2</sup> M NaOH), with wide linear dynamic range (LDR) values of two to three orders of magnitude, very low limit of detection (LOD) and limit of quantification (LOQ) values of, respectively, 0.002-0.5 ng/mL and 0.007-2.0 ng/mL, and small relative standard deviation (RSD) values of 0.2-1.7 %, according to the medium. This direct spectrofluorimetric method was applied to the evaluation of benomyl residues in natural waters, with satisfactory recovery values (87-94%).</p>

Direct Spectrometry: A New Alternative for Measuring the Fluorescence of Composite Resins and Dental Tissues

The aim of this study was to evaluate the fluorescence intensity of different composite resins and compare those values with the fluorescence intensity of dental tissues. Different composite resins were used to make 10 discs (2 mm in depth and 4 mm in diameter) of each brand, divided into groups: 1) Z (Filtek Z350, 3M ESPE), 2) ES (Esthet-X, Dentsply), 3) A (Amelogen Plus, Ultradent), 4) DVS (Durafill-VS, Heraeus Kulzer) with 2 mm composite resin for enamel (A2), 5) OES ([Esthet-X] opaque-OA [1 mm] + enamel-A2 [1 mm]); 6) ODVSI ([Charisma-Opal/Durafill-VSI], opaque-OM (1 mm) + translucent [1mm]), and 7) DVSI ([Durafill- VSI] translucent [2 mm]). Dental tissue specimens were obtained from human anterior teeth cut in a mesiodistal direction to obtain enamel, dentin, and enamel/dentin samples (2 mm). The fluorescence intensity of specimens was directly measured using an optic fiber associated with a spectrometer (Ocean Optics USB 4000) and recorded in graphic form (Origin 8.0 program). Data were submitted to statistical analysis using Dunnet, Tukey, and Kruskall-Wallis tests. Light absorption of the composite resins was obtained in a spectral range from 250 to 450 nm, and that of dental tissues was between 250 and 300 nm. All composite resins were excited at 398 nm and exhibited maximum emissions of around 485 nm. Fluorescence intensity values for all of the resins showed statistically significant differences (measured in arbitrary units [AUs]), with the exception of groups Z and DVS. Group DVSI had the highest fluorescence intensity values (13539 AU), followed by ODVS (10440 AU), DVS (10146 AU), ES (3946 AU), OES (3841 AU), A (3540 AU), and Z (1146 AU). The fluorescence intensity values for the composite resins differed statistically from those of dental tissues (E=1380 AU; D=6262 AU; E/D=3251 AU). The opacity interfered with fluorescence intensity, and group Z demonstrated fluorescence intensity values closest to that of tooth enamel. It is concluded that the fluorescence intensity values were significantly different among the composite resins and compared with dental tissues. The direct spectrofluorimetric method represents a tool for evaluating the fluorescence of composite resins.

Multivariate Versus Classical Univariate Calibration Methods for Spectrofluorimetric Data: Application to Simultaneous Determination of Olmesartan Medoxamil and Amlodipine Besylate in their Combined Dosage Form

Olmesartan medoxamil (OLM, an angiotensin II receptor blocker) and amlodipine besylate (AML, a dihydropyridine calcium channel blocker), are co-formulated in a single-dose combination for the treatment of hypertensive patients whose blood pressure is not adequately controlled on either component monotherapy. In this work, four multivariate and two univariate calibration methods were applied for simultaneous spectrofluorimetric determination of OLM and AML in their combined pharmaceutical tablets in all ratios approved by FDA. The four multivariate methods are partial least squares (PLS), genetic algorithm PLS (GA-PLS), principal component ANN (PC-ANN) and GA-ANN. The two proposed univariate calibration methods are, direct spectrofluorimetric method for OLM and isoabsorpitive method for determination of total concentration of OLM and AML and hence AML by subtraction. The results showed the superiority of multivariate calibration methods over univariate ones for the analysis of the binary mixture. The optimum assay conditions were established and the proposed multivariate calibration methods were successfully applied for the assay of the two drugs in validation set and combined pharmaceutical tablets with excellent recoveries. No interference was observed from common pharmaceutical additives. The results were favorably compared with those obtained by a reference spectrophotometric method.

A validated direct spectrofluorimetric method for quantification of mirtazapine in human whole blood

A spectrofluorimetric method for estimation of mirtazapine in human whole blood was developed and validated. The recovery efficiency of the processing method was 95–98%. The analytical method was linear over drug concentration of 10–200 ng/ml. The limit of quantification was 10 ng/ml. The method was precise with %RSD for intra-day and inter-day precision being <3.0 and 1.5, respectively. Excellent recoveries (97.87–99.69%) were achieved during accuracy studies. The method was robust to small changes in processing method and instrumental parameters. The present method can be employed for direct fluorimetric determination of mirtazapine in human whole blood during clinical studies.

A validated direct spectrofluorimetric method for quantification of mirtazapine in human whole blood

A spectrofluorimetric method for estimation of mirtazapine in human whole blood was developed and validated. The recovery efficiency of the processing method was 95–98%. The analytical method was linear over drug concentration of 10–200 ng/ml. The limit of quantification was 10 ng/ml. The method was precise with %RSD for intra-day and inter-day precision being &lt;3.0 and 1.5, respectively. Excellent recoveries (97.87–99.69%) were achieved during accuracy studies. The method was robust to small changes in processing method and instrumental parameters. The present method can be employed for direct fluorimetric determination of mirtazapine in human whole blood during clinical studies.

The application of glyoxal-bis-(2-hydroxyanil) to the determination of trace amounts of cadmium by spectrofluorimetry

The fluorescent reaction of the reagent glyoxal-bis-(2-hydroxyanil) (GBHA) with cadmium was studied. Based on this chelation reaction, a sensitive, rapid, direct spectrofluorimetric method for the determination of trace cadmium with GBHA has been developed. The reaction conditions for the fluorescence system of cadmium with GBHA were established. The cadmium ion can form a stable chelate with GBHA, having a ratio of 1:3 in the 12.0 -13.0 pH range. The maximum excitation and emission wavelengths are 227.4 nm and 320.0 nm for the cadmium chelate, respectively. The fluorescence intensity of the cadmium chelate remains stable from 20 to 150 min. Under the optimal experimental conditions the fluorescence intensity is a linear function of concentration in the range 1.0-10.0 ng mL-1 of cadmium and the detection limit is 0.65 ng mL-1 of cadmium. Interferences of foreign ions were studied. The method has been successfully applied to the determination of cadmium in the sewage.

The Application of Gibberellic Acid to the Determination of Trace Amounts of Lead by Spectrofluorimetry

The ionization constant of fluorescent reagent gibberellic acid (GA) was established spectrophotometrically. The fluorescent reaction of this reagent with lead was studied. Based on this chelation reaction, a sensitive, direct spectrofluorimetric method for the determination of trace lead with use of GA has been developed. The reaction conditions for the fluorescence system of lead with GA were studied. The lead ion can form a stable binary chelate with GA, having a ratio of 1:2 in the pH range 7.0-8.0. The maximum excitation and emission wavelengths are 205.0 nm and 308.8 nm for the lead chelate, respectively. The reaction is instantaneous and the fluorescence intensity of the lead chelate remains stable from 20 to 150 min. Under the optimal experimental conditions the fluorescence intensity is a linear function of concentration in the range 1.0-10.0 ng/mL of lead and the detection limit is 0.52 ng/mL of lead. Interferences of other ions were studied. The method has been successfully applied to the determination of lead in common paint.

Spectrofluorimetric Method for the Determination of Aluminum with Alizarin Red PS

A simple and direct spectrofluorimetric method has been developed for the determination of aluminum using alizarin red PS (1,2,4-trihydroxy 9,10-anthraquinone-3-sulfonic acid). The method is based on the strong fluorescence (480/564 nm) of Al3+ and alizarin red. Experimental parameters such as pH, concentration of the ligand, ionic strength of the solution, reaction time and temperature were optimized in order to maximize the analytical signal. Interferences of several ions (anions and cations) were studied and evaluated. The linear range of the method extends from 3 to 100 µg L−1. Limit of detection (3sb) was 0.9 µg L−1. The method was tested with a silicate certified reference material. Interferences were eliminated by a liquid extraction with cupferron.

The Use of Spectrofluorimetry for Monitoring the Bioaccumulation and the Biotransformation of Polycyclic Aromatic Hydrocarbons in Daphnia magna

A rapid and direct spectrofluorimetric method was tested in order to monitor the bioaccumulation of PAHs in Daphnia magna in a control media. After exposure to water containing benzo[ a ]pyrene or fluoranthene, daphnids were put in solvent, sonicated, and filtered. The fluorescence spectrum observed in the filtrate was recorded. Results were compared to HPLC measurements of the same pools of organisms. In fluoranthene experiments, the fluorescence peak of the daphnid extract spectrum was linearly related to the PAH content as measured with HPLC. In benzo[ a ]pyrene experiments, other fluorescent compounds progressively appeared in the sample. They were assumed to be metabolites. A linear regression involving fluorescence intensities at two different wavelengths was necessary for a satisfactory correlation with HPLC measurements. A water extraction was performed to isolate metabolites. None or very few fluoranthene metabolites were isolated in the aqueous phase, whereas increasing benzo[ a ]pyrene metabolites were observed while the exposure time increased.

The Use of Spectrofluorimetry for Monitoring the Bioaccumulation and the Biotransformation of Polycyclic Aromatic Hydrocarbons in Daphnia magna

A rapid and direct spectrofluorimetric method was tested in order to monitor the bioaccumulation of PAHs in Daphnia magna in a control media. After exposure to water containing benzo[ a ]pyrene or fluoranthene, daphnids were put in solvent, sonicated, and filtered. The fluorescence spectrum observed in the filtrate was recorded. Results were compared to HPLC measurements of the same pools of organisms. In fluoranthene experiments, the fluorescence peak of the daphnid extract spectrum was linearly related to the PAH content as measured with HPLC. In benzo[ a ]pyrene experiments, other fluorescent compounds progressively appeared in the sample. They were assumed to be metabolites. A linear regression involving fluorescence intensities at two different wavelengths was necessary for a satisfactory correlation with HPLC measurements. A water extraction was performed to isolate metabolites. None or very few fluoranthene metabolites were isolated in the aqueous phase, whereas increasing benzo[ a ]pyrene metabolites were observed while the exposure time increased.

The application of trimesic acid to the determination of terbium by spectrofluorimetry

A sensitive, direct spectrofluorimetric method for the trace determination of terbium with use of trimesic acid (TMA) has been developed. The reaction conditions for the fluorescence system of terbium with TMA were studied. The terbium ion can form a stable binary chelate with TMA, having a ratio of 1:1 in the pH range 3.5–6.5. The maximum excitation and emission wavelengths are 260 nm and 545 nm for the terbium chelate, respectively. The reaction is instantaneous and the fluorescence intensity of the terbium chelate remains stable from 0.25 to 4 h. Under the optimal experimental conditions the fluorescence intensity is a linear function of concentration in the range 0.0248–6.35 μg ml −1 of terbium. The relative standard deviation is still within ±4% in the presence of one-thousandfold amounts of the other lanthanide ions, and common foreign ions hardly interfere in the determination. The method can be employed for the determination of trace amounts of terbium in rare earth ores or oxides because of its high sensitivity and selectivity with good reproducibility and accuracy.

A spectrofluorimetric procedure for the determination of α-tocopherol in nutritional supplement products

A direct spectrofluorimetric method for the determination of vitamin E in nutritional supplement products is described. Samples analysed include single vitamin and multivitamin tablets and capsules as well as dietary formula preparations. The analytical procedure was carried out in a single reaction vessel and consisted of saponification of samples for 10 min in a water bath set at 85°C using absolute ethanol (5 ml) and 80% (w/v) potassium hydroxide solution (2 ml) as the saponification medium, with ascorbic acid (125 mg) as antioxidant. The analyte was extracted in situ with n-hexane (20 ml). Treatment of the n-hexane layer with 60% (v/v) sulphuric acid (2 ml) was sufficient to remove interference by retinol, and the n-hexane layer was then used for direct fluorescence measurement at 298 nm (excitation) and 330 nm (emission). The scanning of several excitation and emission spectra of sample extracts, showed no evidence of interference by any excipient matter or extraneous fluorescing lipid soluble components. Vitamin E values obtained using the described procedure showed good agreement with manufacturers' label expectations.

2-(α-Pyridyl)thioquinaldinamide: a spectrofluorimetric reagent in inorganic trace analysis. Part III. Determination of manganese in industrial and environmental samples

A highly sensitive, fairly selective, direct spectrofluorimetric method for the determination of ultratrace levels of manganese is described. The method is based on the selective oxidation of the very weakly fluorescent 2-(α-pyridyl)thioquinaldinamide by manganese(VII) to give an intensely fluorescent oxidation product (λex.= 360 nm; λem.= 500 nm). Constant and maximum fluorescence intensities were observed over a wide range of acidity, viz., 0.03–0.83 M H3PO4, for periods of between 5 min and 72 h. A linear fluorescence-concentration dependence was observed between 10–5 and 0.7 p.p.m. of manganese. More than 60 cations and anions, present in a large excess, did not interfere. The method was applied successfully to a number of standard samples (alloys, steels, sludges and sediments), environmental waters (inland and surface) and complex synthetic mixtures. The method is very simple and requires no solvent extraction or pre-concentration steps.

Fluorimetric use of morin in the ultra-trace determination of cadmium and its application to sewage sludge analyses.

A sensitive and fairly selective direct spectrofluorimetric method for the ultra-trace determination of cadmium with morin has been developed. The fluorescent chelate [λex.(max.)= 467 nm; λem.(max.)= 537 nm] shows a constant fluorescence intensity over a wide pH range (8.0–9.4). The reaction is instantaneous and the fluorescence intensity remains stable for 45 min. Beer's law is obeyed from 0.5 p.p.b. to 0.8 p.p.m. of cadmium; the stoicheiometric composition of the chelate is 1 : 2 (cadmium : morin). The method has been applied successfully to a number of synthetic mixtures of various composition and to some sewage sludge samples after a short, single clean-up step using an ion exchanger.

Determination of emetine in the presence of its decomposition products.

The study of the kinetics of the decomposition of emetine points to the importance of using a method of determination in which the decomposition products do not interfere.It is shown that the method of separation by thin-layer chromatography followed by extraction of the emetine spot and measurement of its ultraviolet absorbance provides reliable results for thermochemically as well as photochemically decomposed emetine solutions. Comparison of this method with a direct spectrofluorimetric measurement of emetine in the presence of its decomposition products shows that the latter method is also satisfactory. The BP method gives reliable results with thermochemically but not with photochemically decomposed emetine solutions. The direct spectrofluorimetric method is preferred, because of its rapidity, simplicity and sensitivity (3 × 10–6M compared with 3 × 10–2M for the ultraviolet spectrophotometric method).