Critical approach to synchronous spectrofluorimetry. II

Eco-friendly simultaneous estimation of atenolol and losartan potassium in spiked human plasma via synchronous fluorescence with sustainability assessment

A green, sensitive, and fast spectrofluorimetric technique for the simultaneous determination of atenolol (ATN) and losartan potassium (LSR) was developed. The proposed technique relied on the implementation of a first derivative synchronous fluorescence spectroscopy for the determination of the investigated drugs simultaneously without pretreatment procedures. The synchronous fluorescence of both drugs was measured in methanol at Δλ of 100 nm, and the first derivative peak amplitudes (1D) were measured at 321 nm for ATN and 348 nm for LSR, each at the zero-crossing point of the other. The method was rectilinear over the concentration ranges of 100-1000 ng/mL and 50-500 ng/mL for ATN and LSR, respectively. The proposed technique was successfully applied for the determination of the studied drugs in their laboratory-prepared mixture and pharmaceutical formulations, demonstrating high mean recoveries of 100.54% for ATN and 100.62% for LSR, without interference from common excipients. The results were in good agreement with those obtained by the comparison method. Three recent greenness assessment tools, the Eco-Scale tool, the Green Analytical Procedure Index (GAPI) metric, and the Analytical GREEnness metric approach, were employed to affirm the greenness of the proposed method. The developed method was proven to be eco-friendly.

An eco-friendly first and second derivative synchronous spectrofluorimetry for quantification of florfenicol in presence of its different degradation products. Application to kinetic stability study

Two rapid, simple, sensitive and selective derivative spectrofluorimetric methods (first and second derivative synchronous spectrofluorimetric (FDSFS and SDSFS) procedures) have been developed for the analysis of florfenicol in the presence of its various degradation products. FDSFS was applied to assay the drug in the presence of its alkaline, oxidative and photolytic degradation products while SDSFS was used to quantify it in the presence of its acidic degradation product. These methods permitted quantification of florfenicol at corresponding λ Em of 288, 287, 279 and 284 nm without interferences from any of its degradation products. Full validation procedures were applied to the suggested method according to International Conference of Harmonization guidelines. Moreover, different degradation kinetic parameters were calculated such as half-life (t 1/2), degradation rate constant (K) and activation energy (E a). Using the analytical eco-scale, green analytical procedure index and analytical greenness metric approach AGREE as greenness assessment tools, the proposed method was found to be environmentally friendly.

Unveiling angular sweep total fluorescence Spectroscopy:A novel multidimensional technique for analysis of complex multi-fluorophoric systems

Analyzing multi-fluorophoric real systems without pre-processing is challenging, often addressed with unconventional fluorescence techniques and chemometrics. In this context, we introduce a novel addition - 'Angular Sweep Total Fluorescence Spectroscopy (ASTFS),' to the arsenal of multidimensional steady-state fluorescence spectroscopic techniques. ASTFS utilizes a series of variable angle synchronous fluorescence spectra, strategically covering the fluorescence region between the first and second-order Rayleigh scattering ridges. The plot features a minimal data matrix size, avoids Rayleigh scattering signals, and incurs no blind regions. The study delves into the instrumental configurations for spectral acquisition, highlights the enhanced spectral resolution due to the band-narrowing effect, and discusses other notable features of the ASTFS plot. Further, this technique is reported to be effective in analyzing analytes in complex systems with strong background fluorescence, such as milk. The antibiotic- Norfloxacin is quantified via minimal pre-processing in milk samples and yields excellent analytical figures of merit.

Fast concurrent determination of guaifenesin and pholcodine in formulations and spiked plasma using first derivative synchronous spectrofluorimetric approach

Guaifenesin and pholcodine are frequently co-formulated in certain dosage forms. A new fast first derivative synchronous spectrofluorometric method has been used for their simultaneous analysis in mixtures. Here, first derivative synchronous spectrofluorometry enabled the successful simultaneous estimation of guaifenesin at 283 nm and pholcodine at 275 nm using a wavelength difference (Δλ) of 40 nm. The method was fully validated following International Council of Harmonization guidelines. For guaifenesin and pholcodine, linearity was determined within the corresponding ranges of 0.05-0.30 and 0.10-6.0 μg/ml. The two drugs were effectively analyzed using the developed approach in their respective formulations, and the results showed good agreement with those attained using reference methods. The method demonstrated excellent sensitivity, with detection limits down to 0.007 and 0.030 μg/ml and quantitation limits of 0.020 and 0.010 μg/ml for guaifenesin and pholcodine, respectively. Therefore, the procedure was successful in determining these drugs simultaneously in vitro in spiked plasma samples and syrup dosage form. The developed methodology also offered an environmentally friendly advantage by utilizing water as the optimal diluting solvent throughout the whole work. Different greenness approaches were investigated to ensure the method's ecofriendly properties.

Green Constant-wavelength Concurrent Selective Fluorescence Method for Assay of Ibuprofen and Chlorzoxazone in Presence of Chlorzoxazone Degradation Product

Lower back pain is a universal dilemma leaving a negative effect on both health and life quality. It was found that a fixed dose combination of chlorzoxazone and ibuprofen gave a higher efficiency than analgesic alone in treatment of acute lower back pain. Based on the significant benefit of that combination, a green, sensitive, rapid, direct, and cost-effective method is created for concurrent determination of ibuprofen and chlorzoxazone in presence of 2-amino para chlorophenol (a synthetic precursor and potential impurity of chlorzoxazone) adopting the synchronous spectrofluorimetric technique. Synchronous spectrofluorimetric technique is adopted to avoid the highly overlapped native spectra of both drugs. The synchronous spectrofluorometric method was applied at Δλ = 50 nm, ibuprofen was measured at 227 nm while chlorzoxazone was measured at 282 nm with no hindering from one to another. The various experimental variables affecting the performance of the suggested technique were explored and adjusted. The suggested technique showed good linearity from 0.02 to 0.6 and 0.1 to 5.0 µg/mL for ibuprofen and chlorzoxazone, respectively. The produced detection limits were 0.27 × 10^-3 and 0.03, while the quantitation limits were 0.82 × 10^-3 and 0.09 µg/mL for ibuprofen and chlorzoxazone, respectively. The suggested approach was successfully applied for the analysis of the studied drugs in the synthetic mixture, different pharmaceutical preparations, and spiked human plasma. The suggested technique was validated with respect to the International Council of Harmonization (ICH) recommendations. The suggested technique was found to be simpler and greener with lower cost compared to the earlier reported methods which required complicated techniques, longer time of analysis, and less safe solvents and reagents. Green profile assessment for the developed method compared with the reported spectrofluorometric method was performed using four assessment tools. These tools confirmed that the recommended technique attained the most possible green parameters, so it could be used as a greener option in routine quality control for analyzing the two drugs in genuine form and pharmaceutical preparations.

Green synchronous spectrofluorimetric method for the simultaneous determination of agomelatine and venlafaxine in human plasma at part per billion levels

A novel sustainable, simple, sensitive, and green spectrofluorimetric method was developed for the concurrent estimation of venlafaxine and agomelatine in pharmaceuticals and biological fluids. The method relies on synchronous fluorescence spectroscopy, where venlafaxine and agomelatine were measured at 276 and 328 nm, respectively, using Δλ of 20 nm. The potential factors affecting the fluorescence intensity were optimized by the one-factor-at-a-time (OFAT) strategy, where synchronous fluorescence intensity was significantly enhanced using a 1% w/v sodium dodecyl sulfate micellar system. The method was fully validated and exhibited excellent linearity (r² > 0.999 for both drugs) with very low limits of detection (LODs) in the range of 0.14-0.84 ng/mL. Consequently, the proposed approach was efficiently adopted to analyze the co-administered drugs in their pharmaceuticals and in spiked human plasma with excellent % recovery between 97.4 and 102.2%. Finally, the method's greenness was evaluated using different metric tools, including Green Analytical Procedure Index (GAPI) and Analytical GREEnness (AGREE), which proved its excellent greenness.

Utility of synchronous fluorimetry for the concurrent quantitation of metoprolol and ivabradine

Metoprolol combined with ivabradine have been determined up to nanogram level simultaneously relied on the synchronous fluorescence spectra. First derivative amplitudes of the synchronous spectrofluorimetric spectra are recorded at Δλ = 40 nm using ethanol as diluting solvent. Metoprolol can be measured at 286 nm which is the zero-crossing point of ivabradine, and the later can be measured at 296 nm. The calibration plots were found to be linear over the ranges of concentrations: 100.0-1000.0 ng/mL and 10.0-200.0 ng/mL for metoprolol and ivabradine, respectively. Validation of the procedure was performed using the International Council of Harmonization guidelines. Values of LODs were found to be 28.89, 2.80 ng/mL and LOQs were 87.56, 8.49 ng/mL for metoprolol and ivabradine, respectively. As the two drugs are co-administered safely and effectively to reduce heart rate, angina attacks, the current methodology is utilized for the concurrent analysis of them in their single ingredient pharmaceutical preparations, synthetic mixtures, and biological fluids. The designed method, being cost-effective and simple procedure, is the first method for metoprolol and ivabradine simultaneous analysis. The results agreed statistically with the comparison methods.

A synchronous fluorescence spectrofluorometric method for the simultaneous determination of policresulen and cinchocaine hydrochloride in ointment and suppositories

For the treatment of internal and external hemorrhoids, policresulen (POL) and cinchocaine hydrochloride (CIN) are used in combination. Using a new, simple, fast, and economical first-derivative synchronous fluorescence spectroscopic process, both drugs were simultaneously determined and validated. At Δλ60 nm and with a scanning rate of 600 nm/min, methanol was used as the solvent for both products. In the concentration ranges of 5.0-21.0 μg mL^-1 and 0.5-6.0 μg mL^-1 for POL and CIN, the amplitude-concentration plots were rectilinear. The detection limits were found to be 0.770 μg mL^-1 and 0.118 μg mL^-1 and the quantitation limits for POL and CIN were 2.541 μg mL^-1 and 0.391 μg mL^-1. To evaluate all compounds in synthetic mixtures and medicinal dosage types, the proposed method has been successfully applied. These findings were in line with the results obtained using high-performance thin layer chromatography, the comparison process.

Using constant-wavelength synchronous fluorescence spectroscopy in nanoparticle-based sensors: a minireview

This study focuses on optical nanosensors based on constant-wavelength synchronous fluorescence spectroscopy (SFS) and reviews their applications for analysis purposes in the last few decades. In comparison to conventional fluorescence, SFS shows a higher selectivity owing to the narrowing of spectral bands and the simplification of spectra. The reported SFS-based nanosensors are classified based on their mechanism for analyte detection into two types including quenching based methods and enhancement based methods. Herein, almost all studies performed in this field are reviewed and the details of each study are carefully explained. Moreover, the analytical properties of the reported nanosensors are tabulated in relevant tables. It is hoped that this study will stimulate further investigations in this field with similar nanosensors.

Excitation-Emission Synchronization-Mediated Directional Fluorescence: Insight into Plasmon-Coupled Emission at Vibrational Resolution

Light-matter interactions have always been a fundamentally significant topic that has attracted much attention. It is important to reveal a fluorophore-plasmon interaction on the nanoscale. However, as a powerful investigative tool, fluorescence spectroscopy still suffers from a limited spectral resolution and the susceptibility to interfering substances. In this work, excitation-emission synchronization-mediated surface-plasmon-coupled emission (EES-SPCE) is proposed to break the bottleneck. By actively screening the energy transitions for observation, an improved spectral resolution has been achieved, which is advantageous to the investigation of the fluorophore-plasmon interactions under different coupling modes. The spectral information related to the plasmonic interactions through tuning vibrational energy levels is clearly distinguished at directional emission angles. EES-SPCE is demonstrated to selectively and efficiently extract the coupled emission from the vibrational resolution, which would open up the opportunity to improve the capability of spectral feature identification and signal collection for practical applications of plasmonic fluorescence spectroscopy.

Analysis of various solid samples by synchronous fluorescence spectroscopy and related methods: A review

This critical Review covers the literature reports on analysis of different types of solid samples by the synchronous fluorescence spectroscopy (SFS) and its varieties, which include synchronous phosphorescence spectroscopy and synchronous luminescence spectroscopy, in the three decades (1990-2019). Both the qualitative and quantitative spectroscopic analysis is described for a wide range of specimens. Their physical forms and chemical composition include: a) organic and inorganic analytes pre-concentrated from solution on matrices (beads, membranes, filters, disks, paper), b) natural and synthetic multi-component specimens of complex composition (biological tissues, soil, polymers) and c) inorganic and coordination compounds including porous materials and particularly metal-organic frameworks (MOFs). The comparison with the data obtained by "conventional" optical emission spectroscopy and other analytical techniques (when available) is presented. The specific advantages of the high-resolution varieties of the method, the first- and second-derivative solid-state synchronous fluorescence, luminescence, and phosphorescence spectroscopy are described. An attention is also paid to practical conditions of the typical tests, and the relevant experimental setups. The impetus is on the emerging capabilities of this highly promising method e.g. in-situ monitoring of chemical reactions, in-vivo diagnostics, surface reactions, and detection of the adsorbate. The existing challenges are analyzed, and the unexplored application "niches" to further develop this and the related analytical methods are revealed. 145 references, 9 Tables, 17 Figures and 1 Scheme.

First-derivative synchronous spectrofluorimetric method for estimation of losartan potassium and atorvastatin in their pure forms and in tablets

Losartan potassium (LOS) and atorvastatin (ATR) are used in combination for long-term treatment of stroke and for treatment of hypertension with high-level cholesterol. Both drugs were simultaneously determined and validated using a novel, easy, fast, and economical first-derivative synchronous fluorescence spectroscopic method. Methanol was used as the solvent for both drugs at a Δλ 80 nm and with a scanning rate of 600 nm/min. Peaks were determined as at 288.1 nm and 263.6 nm for LOS and ATR, respectively. The proposed method was validated according to International Conference on Harmonization guidelines and, subsequently, the developed method was applicable to the analysis of the two compounds in their different formulations without interference from each other. Amplitude-concentration plots were rectilinear over the concentration ranges 1.0-10.0 μg/ml and 0.5-5.0 μg/ml for LOS and ATR, respectively. Detection limits were found to be 0.096 μg/ml and 0.030 μg/ml and quantitation limits were 0.291 μg/ml and 0.093 μg/ml for LOS and ATR, respectively. The proposed method was successfully applied to the analysis of both compounds in synthetic mixtures and in laboratory-prepared tablets. These results were in accordance with the results acquired using the comparison method, high-performance liquid chromatography.

First derivative synchronous spectrofluorimetric method for the simultaneous determination of propofol and cisatracurium besylate in biological fluids

Propofol and cisatracurium besylate have been simultaneously determined using a highly sensitive first derivative synchronous spectrofluorometric method. The method is based on measuring first derivative synchronous spectrofluorimetric amplitude at Δλ = 40 nm with a scanning rate of 600 nm/min. The different experimental parameters affecting the fluorescence intensity of the two drugs were carefully studied and optimized. The amplitude-concentration plots were rectilinear over the range 40.0-400.0 ng/mL and 20.0-280.0 ng/mL for propofol and cisatracurium, respectively with lower detection limits of 4.0 and 2.35 ng/mL and quantification limits of 12.1 and 7.1 ng/mL for propofol and cisatracurium, respectively. The proposed method was successfully applied for the determination of the two compounds in synthetic mixtures and in commercial ampoules. The high sensitivity attained using the proposed method allowed the simultaneous determination of both drugs in spiked plasma samples. The mean % recoveries in spiked human plasma (n = 3) were 96.53 ± 0.90 and 96.20 ± 1.64 for each of propofol and cisatracurium, respectively. The method was validated in compliance with International Council of Harmonization (ICH) Guidelines.

Feasibility Assessment of Synchronous Fluorescence Spectral Fusion by Application to Argan Oil for Adulteration Analysis

Synchronous fluorescence spectroscopy (SFS) is used for quantitative analysis as well as for qualitative analysis, such as with classification methods. With SFS, determination of a useful wavelength interval between the excitation and emission wavelengths (Δλ) is required. There are a multitude of Δλ intervals that can be evaluated and optimization of the best one is complex. Presented here is a fusion approach for combining Δλ intervals, thereby negating the need to perform the selection by a skilled operator. To demonstrate the feasibility of omitting selection of the best Δλ interval, adulterated argan oil samples are studied. Argan oil is made from the argan tree, endemic to southwestern Morocco, and is well-known for its cosmetic, pharmaceutical, and nutritional applications. It is considered a luxury product and exported from Morocco around the world. Consequently, detection of argan oil adulteration followed by quantitative analysis of the adulterant concentration is important. This study uses fusion of SFS spectra obtained at ten Δλ intervals to first detect adulteration of argan oil by corn oil and then determination of the corn oil content. For detection of adulteration, 15 one-class classification methods were used simultaneously over the ten Δλ sets of SFS spectra. For tuning parameter dependent classifiers such as Mahalanobis distance, non-optimized classifiers are used. Raw classification values are used, removing the need to set classifier-dependent threshold values, albeit, ultimately, a fusion decision rule is needed for classification. For quantitative analysis, two calibration approaches are evaluated with fusion of these ten Δλ SFS spectral data sets. One is multivariate calibration by partial least squares (PLS). The second approach is a univariate calibration process where the SFS spectra are summed over respective SFS spectral ranges, also known as the area under the curve (AUC). For adulteration detection and quantitation of the corn oil, prediction errors decrease with fusion compared to individually using the ten Δλ interval SFS specific data sets. For this argan oil data set, the AUC method generally provides equivalent prediction errors to PLS.

Second derivative spectrophotometric and synchronous spectrofluorometric determination of lesinurad in the presence of its oxidative degradation product

Lesinurad is a novel selective uric acid reabsorption inhibitor which has been recently approved for the treatment of chronic gout.

Water as probe molecule for midgap states in nanocrystalline strontium titanate by conventional and synchronous luminescence spectroscopy under ambient conditions

Alkaline earth metal titanates are broad bandgap semiconductors with applications in electronic devices, as catalysts, photocatalysts, sorbents, and sensors. Strontium titanate SrTiO₃ is of interest in electronic devices, sensors, in the photocatalytic hydrogen generation, as catalyst and sorbent. Both photocatalysis and operation of electronic devices rely upon the pathways of relaxation of excited charge in the semiconductor, including relaxation through the midgap states. We report characterization of nanocrystalline SrTiO₃ at room temperature by "conventional" vs. synchronous luminescence spectroscopy and complementary methods. We determined energies of radiative transitions in the visible range through the two midgap states in the nanocrystalline SrTiO₃. Further, adsorption and desorption of vapor of water as "probe molecule" for midgap states in the nanocrystalline SrTiO₃ was studied, for the first time, by luminescence spectroscopy under ambient conditions. Emission of visible light from the nanocrystalline SrTiO₃ is significantly increased upon desorption of water and decreased (quenched) upon adsorption of water vapor, due to interactions with the surface midgap states.

Determination of human albumin in serum and urine samples by constant-energy synchronous fluorescence method

A sensitive spectrofluorimetric method using constant-energy synchronous fluorescence technique is proposed for the determination of human albumin without separation. In this method, no reagent was used for enhancement of the fluorescence signal of albumin in the solution. Effects of some parameters, such as energy difference between excitation and emission monochromators (ΔE), emission and excitation slit widths and scan rate of wavelength were studied and the optimum conditions were established. For this purpose factorial design and response surface method were employed for optimization of the effective parameters on the fluorescence signal. The results showed that the scan rate of the wavelength has no significant effect on the analytical signal. The calibration curve was linear in the range 0.1-220.0 µg mL(-1) of albumin with a detection limit of 7.0 × 10(-3)  µg mL(-1). The relative standard deviations (RSD) for six replicate measurements of albumin were calculated as 2.2%, 1.7% and 1.3% for 0.5, 10.0 and 100.0 µg mL(-1) albumin, respectively. Furthermore the proposed method has been employed for the determination of albumin in human serum and urine samples.

A novel method for the rapid detection of benzo(a)pyrene in liquid milk by dimethyl sulfoxide selectively enhanced synchronous fluorescence spectrometry

Based on the high solubility efficiency and strong fluorescence response of benzo(a)pyrene (BaP) in dimethyl sulfoxide in combination with the high-performance derivative constant-energy synchronous fluorescence spectroscopic (DCESFS) technique, a simple, sensitive and economic method was developed for the determination of BaP in liquid milk. This method comprises ultrasound-assisted solvent extraction, solvent replacement and DCESFS detection. No saponification or other tedious clean-up procedures were needed. The recoveries of BaP in different milk samples were greater than 82%. Detection limits in full- and low-fat milk were 0.03 and 0.04 μg kg(-1), respectively.

A novel synchronous fluorescence spectroscopic approach for the rapid determination of three polycyclic aromatic hydrocarbons in tea with simple microwave-assisted pretreatment of sample

Many polycyclic aromatic hydrocarbons (PAHs) are carcinogenic, and some have been reported to be present in tea. People can be exposed to PAHs through tea consumption. Therefore, there is real importance for the determination of PAHs in tea. Because of the complex matrix of tea, it is hard to detect PAHs in tea without cleanup and chromatographic separation procedures. In this research, for the first time, a novel synchronous fluorescence spectroscopic approach coupling nonlinear variable-angle synchronous and matrix-isopotential synchronous scanning modes has been developed for the rapid determination of benzo(a)pyrene (BaP), benzo(k)fluoranthene (BkF), and anthracene (AN) in tea with simple microwave-assisted pretreatment of samples. This novel technique is able to resolve the spectra of the three PAHs well, even with interference from other EPA PAHs. The detection limits for BaP, BkF, and AN in tea were 0.18-0.28, 0.55-0.89, and 0.64-3.58 μg/kg, respectively, depending on various teas, with satisfactory recoveries ranging from 77.1 to 116%. The relative standard deviations achieved for BaP, BkF, and AN were 1.5, 6.6, and 8.5% for green tea; 2.9, 7.4, and 2.1% for oolong tea; and 5.6, 5.4, and 5.8% for black tea, respectively. Our results showed good correlation with those of gas chromatography-mass spectrometry. The approach developed is simple, reliable, and cost-efficient, providing an attractive alternative for the rapid selective screening of PAHs in tea.