Application of π acceptors to the spectrophotometric and spectrofluorimetric determination of vincamine and naftidrofuryl oxalate in their pharmaceutical preparations

Three different spectrophotometric and two spectrofluorimetric methods have been developed and validated for the determination of vincamine (VN) and naftidrofuryl oxalate (NF) in tablets. The spectrophotometric methods depend on charge transfer complex formation between each of VN and NF with 7,7,8,8‐tetracyano‐quinodimethane (TCNQ), 2,6‐dichloroquinone‐4‐chloroimide (DCQ) and 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) at 843, 580 and 588 nm, respectively. The spectrofluorimetric methods are based on the formation of charge transfer complex between each of the two drugs and TCNQ, with measurement of the fluorophore formed at 312/375 and 284/612 nm, respectively, or with DDQ at 400/475 and 284/396 nm, respectively. In the spectrophotometric measurements, Beer's law was obeyed at concentration ranges of 1.5–16, 10–180 and 12–140 μg/ml for VN with TCNQ, DCQ, and DDQ, respectively. For NF, the corresponding concentrations were 2–28, 5–75 and 25–150 μg/ml with TCNQ, DCQ, and DDQ, respectively. In the spectrofluorimetric measurements, the ranges for VN were 0.05–0.9 and 0.3–4 μg/ml with TCNQ and DDQ, respectively, whereas for NF the ranges were 0.05–0.85 and 0.5–8 μg/ml with TCNQ and DDQ, respectively. The different experimental parameters affecting the development and stability of the formed color or fluorophore were studied and optimized and the molar ratios of the complexes were calculated. The proposed methods were validated according to ICH guidelines and were successfully applied for the determination of VN and NF in their tablet dosage forms.     

Green spectrophotometric and spectrofluorimetric determination of biperiden hydrochloride using erythrosine B sensing probe

Erythrosine B (EB) is a food colorant antiviral xanthene dye that has many applications as a color additive in pharmaceuticals and cosmetics. Its use as a sensor for spectrofluorimetric and spectrophotometric analysis of amine-based pharmaceuticals renders many advantages because of its availability, low cost, rapid labeling, and high sensitivity. Herein, two fast and sensitive spectrofluorimetric and spectrophotometric methods were established for the estimation of the anti-Parkinson drug, biperiden (BIP) hydrochloride (HCl), in its raw material and tablet forms. The proposed methods depended on the interaction between the phenolic group of EB and the tertiary amino group of the studied analyte to form an ion-pair complex at pH 4 using the Britton Robinson buffer. The spectrofluorimetric method is based on the measurement of the quenching power of BIP HCl on the fluorescence intensity of EB at λ_ex/em = 527.0/550.9 nm. This method was rectilinear over the concentration range of 0.1–1.0 μg/mL with a limit of detection (LOD) = 0.017 μg/mL and a limit of quantification (LOQ) = 0.05 μg/mL. Meanwhile, the colorimetric method involved monitoring the absorbance of the formed ion-pair complex at 555 nm, showing a linearity range of 0.4–5.0 μg/mL with LOD = 0.106 μg/mL and LOQ = 0.322 μg/mL. The proposed methods were assessed for the greenness, indicating the greenness of the developed methods.     

Simultaneous determination of amlodipine and metoprolol in their combined dosage form using a synchronous fluorescence spectrofluorimetric method

Highly sensitive, rapid, accurate and precise synchronous fluorescence spectrofluorimetric method has been developed for simultaneous analysis of a mixture of amlodipine (AMD) and metoprolol (MET). The method relies on measuring the relative synchronous fluorescence intensity of both drugs at Δλ of 90 nm in acetate buffer solution at pH 5. The experimental parameters influencing the developed method were investigated and optimized. The method was linear over the ranges 0.2–2 μg/ml and 0.5–10 μg/ml for AMD and MET, respectively. The limits of detection were 50 ng/ml for AMD and 130 ng/ml for MET while the limits of quantitation were 150 ng/ml for AMD and 390 ng/ml for MET. The developed method was applied successfully for the determination of the two drugs in their co‐formulated tablet. The mean percent recoveries were found to be 100.51 and 99.57 for AMD and MET, respectively.     

Spectrofluorimetric study on fluorescence quenching of tyrosine and l‐tryptophan by the aniracetam cognition enhancer drug: quenching mechanism using Stern–Volmer and double‐log plots

A novel approach on fluorescence quenching of tyrosine and l ‐tryptophan is presented for spectrofluorimetric determination of aniracetam in drug substances and products. The quenching mechanism was investigated using Stern–Volmer plots and ultraviolet spectra figures of quencher–fluorophore mixtures. Binding constant and stoichiometry were calculated using double‐log plots. The spectrofluorimetric method was optimized for the experimental conditions affecting fluorescence quenching including fluorophore concentration, diluent, and reaction time. Moreover, the pH‐rate profile of aniracetam was studied using simple kinetics and found to be stable within the pH range 5–8. Fluorescence quenching of tyrosine and l ‐tryptophan were observed on addition of aniracetam in aqueous medium at pH 5.5–6.5. Aniracetam quenched the fluorescence of tyrosine and l ‐tryptophan in the concentration range 1–20 μg/ml and 0.3–20 μg/ml, respectively, with binomial relationships between quenching values (ΔF) and aniracetam concentration. Limits of detection were found to be 0.10 μg/ml for tyrosine–aniracetam and 0.14 μg/ml for l ‐tryptophan–aniracetam. Method validation was performed as per ICH guidelines and demonstrated that the developed spectrofluorimetric method was accurate, precise, specific, and suitable for analysis of aniracetam in routine quality control laboratories. All experimental materials and solvents used are eco‐friendly, indicating that the cited spectrofluorimetric procedure is an excellent green method.     

Micellar-emphasized simultaneous determination of ivabradine hydrochloride and felodipine using synchronous spectrofluorimetry

A sensitive and green micellar spectrofluorimetric approach was applied for the simultaneous estimation of ivabradine hydrochloride (IVB) and felodipine (FLD) in the ng/ml concentration range. The approach depended on measuring the first derivative synchronous peak amplitude (¹D) of both drugs at ∆λ = 60 nm in a Tween-80 micellar system. The method was rectilinear alongside the concentration ranges 0.02–0.4 μg/ml and 0.05–1.0 μg/ml at 269.5 nm and 378.5 nm for IVB and FLD, respectively. The proposed method was validated by following the International Council for Harmonization guidelines. The method was successfully applied without interference for laboratory-prepared synthetic mixtures, single pharmaceutical preparations, and within spiked biological fluids with acceptable percentage recoveries. A comparison of the performance of the suggested method with other methods, showed no discrepancy. The method’s ecofriendly property evaluated using three different tools, confirming an excellent green method.     

Use of eosin for green spectroscopic determination of mebendazole

New, sensitive, and reliable spectroscopic methods were constructed for the fast determination of the anthelmintic drug mebendazole. The methods depended on the reaction of the amino group in mebendazole with eosin in acidic medium forming an ion pair complex. The first method, Method I, relied on quenching of the native fluorescence of eosin after reaction with mebendazole at pH 3.7 using acetate buffer. Fluorescence quenching was measured at 538 nm after excitation at 518 nm. This method showed a linear response over the concentration range 5.0–20.0 μg/ml. The second method, Method II, was based on measuring the absorbance of the formed complex at 554 nm; the method showed good linearity from 7.0 to 22.0 μg/ml. Different parameters that influenced the formation of the reaction product were carefully investigated to reach the optimized conditions. A comparison between the proposed methods and a previous spectrophotometric method was carried out and there was no significant difference between them. The methods could be applied successfully to determine mebendazole in its tablet form. Moreover, the methods used water as diluting solvent, which made them compatible with the ‘green’ analytical chemistry principles. No organic solvents were used throughout the study.     

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 patients with COVID-19

Moxifloxacin and ofloxacin are two broad-spectrum quinolone antibiotics. They are among the most widely used antibiotics, at this time, applied to control 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 the presence of hydroxychloroquine, two co-administered mixtures used in the treatment of hospital-acquired pneumonia in patients with COVID-19. Simultaneous assay of hydroxychloroquine and moxifloxacin was carried out in methanol using a direct spectrofluorimetric method (method I) at 375 and 550 nm, respectively, after excitation at 300 nm. The direct spectrofluorimetric assay was rectilinear over concentration ranges 50.0–400.0 and 300.0–2500.0 ng/ml for hydroxychloroquine and moxifloxacin, respectively, with limits of detection (LOD) of 6.4 and 33.64 ng/ml and limits of quantitation (LOQ) of 19.4 and 102.6 ng/ml, respectively, for the two drugs. The assay for 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 Δλ = 140 nm (method II). Hydroxychloroquine was measured at 266 nm, while ofloxacin was measured at 340 nm over the concentration range 4–40 ng/ml for hydroxychloroquine and 200–2000 ng/ml for ofloxacin with LOD of 0.467 and 25.3 ng/ml and LOQ of 1.42 and 76.6 ng/ml, respectively, for the two drugs. The two methods were validated following International Conference on Harmonization guidelines and were applied to the analysis of the two drugs in plasma with good percentage recoveries (109.73–93.17%).     

Eco-friendly synchronous fluorescence spectrofluorimetric method for simultaneous determination of montelukast sodium and fexofenadine hydrochloride in their antiallergic rhinitis fixed-dose combination tablets

An innovative, simple, accurate, sensitive, and eco-friendly synchronous fluorescence spectrofluorimetric method has been developed for the simultaneous analysis of montelukast sodium (MON) and fexofenadine hydrochloride (FEX). The method relies on measuring the relative synchronous fluorescence intensity of both drugs using Δλ of 60 nm in methanol at 405 nm for MON and 288 nm for FEX. The experimental parameters influencing the developed method were investigated and optimized. The method was linear over the ranges 0.1–2.0 and 2.0–20.0 μg/ml for MON and FEX, respectively. The limits of detection were 0.018 and 0.441 μg/ml, and the limits of quantitation were 0.055 and 1.336 μg/ml for MON and FEX, respectively. The developed method was applied successfully for the determination of the two drugs in their newly released fixed-dose combination prescribed for the treatment of allergic rhinitis. The mean per cent recoveries were found to be 100.680 ± 0.890 and 100.110 ± 0.940 for MON and FEX, respectively. Furthermore, the method was found to be eco-friendly green as was evaluated according to the Green Analytical Procedure Index tool guidelines and analytical eco-scale.     

Spectroscopic determination of succinylcholine in dosage forms using eosin Y

Two simple and sensitive analytical assay methods using spectrophotometry and spectrofluorimetry techniques were developed for the estimation of succinylcholine chloride (SUC) in pharmaceutical preparations. The suggested methods are based on the formation of an ion pair complex formed between the drug and eosin Y spectrophotometrically (Method I), or the suppressive effect of succinylcholine on the native fluorescence property of eosin Y (Method II). The spectrophotometric method (Method I) involves measuring the absorbance of the complex between succinylcholine and eosin Y at 550 nm in Britton Robinson buffer of pH 3. However, the spectrofluorimetric method (Method II) involves measuring the quenching effect of the studied drug on the native fluorescence property of eosin Y at the same pH at 550 nm after excitation at 480 nm. The absorbance versus concentration of the drug is rectilinear over the range of 0.5 to 15 μg/ml. The formation constant was 3.5 × 10⁴ and the Gibb's free energy change was ?2.5 × 10⁴ J/mol. In Method II, the relative fluorescence intensity was directly proportional to SUC concentration over the range of 0.05 to 1 μg/ml. The proposed methods allowed a successful application to the estimation of succinylcholine ampoules. An explanation of the reaction pathway was postulated.     

Spectrophotometric and spectrofluorimetric determination of indacaterol maleate in pure form and pharmaceutical preparations: application to content uniformity

Two simple, rapid, sensitive and precise spectrophotometric and spectrofluorimetric methods were developed for the determination of indacaterol maleate in bulk powder and capsules. Both methods were based on the direct measurement of the drug in methanol. In the spectrophotometric merthod (Method I) the absorbance was measured at 259 nm. The absorbance‐concentration plot was rectilinear over the range 1.0–10.0 µg mL^?1 with a lower detection limit (LOD) of 0.078 µg mL^?1 and lower quantification limit (LOQ) of 0.238 µg mL^?1. Meanwhile in the spectrofluorimetric method (Method II) the native fluorescence was measured at 358 nm after excitation at 258 nm. The fluorescence‐concentration plot was rectilinear over the range of 1.0–40.0 ng mL^?1 with an LOD of 0.075 ng mL^?1and an LOQ of 0.226 ng mL^?1. The proposed methods were successfully applied to the determination of indacaterol maleate in capsules with average percent recoveries ± RSD% of 99.94 ± 0.96 for Method I and 99.97 ± 0.81 for Method II. In addition, the proposed methods were extended to a content uniformity test according to the United States Pharmacopoeia (USP) guidelines and were accurate, precise for the capsules studied with acceptance value 3.98 for Method I and 2.616 for Method II. Copyright © 2015 John Wiley & Sons, Ltd.     

Two green and sensitive spectrofluorimetric approaches for determination of Ambroxol and guaifenesin in their single and combined pharmaceutical formulations

Ambroxol hydrochloride (AMX) and guaifenesin (GFN) are approved drugs utilized to treat coughs through their potent mucolytic and expectorant properties. Due to their massive, combined administration in many illnesses, there is a persistent need for their concurrent estimation in different pharmaceutical formulations. Two sensitive, environmentally friendly spectrofluorimetric methods were developed. AMX was determined using the first method (I) without interference from GFN. This method depends on the quenching of Erythrosine B (EB) native fluorescence at 552 nm after excitation at 527 nm due to the formation of a non-fluorescent AMX-EB ion-pair complex in Britton–Robinson buffer (BRB) solution pH (3.5). The concentration plot is linear over the 0.25–5.0 μg/mL range, with a mean percent found value of 99.74%. Method (II) depends on measuring the native fluorescence of aqueous GFN solution at two analytical wavelengths, either 300 or 600 nm, after excitation at 274 nm. Relative fluorescence intensity (RFI)–concentration plots are linear over the ranges of 0.02–0.5 and 0.1–2.0 μg/ml, with mean percent found at 99.96% and 99.91% at dual wavelengths, respectively. The proposed methods were successfully applied to assay both drugs in raw materials and different single and combined pharmaceutical formulations. These methods have been thoroughly validated following International Committee on Harmonisation (ICH) guidelines. National Environmental Methods Index, Analytical Eco-Scale, and Green Analytical Procedure Index were used to prove greenness, thereby enhancing their applicability. The proposed techniques provide straightforward, precise, and cost-effective solutions for routine formulation analysis in quality control laboratories.     

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.     

Application of quinone‐based fluorophore and native fluorescence for the spectrofluorimetric determination of agomelatine in dosage form: Identification of acidic and alkaline‐ induced degradation products by LC–MS/TOF

Three spectrofluorimetric methods were developed for agomelatine (AGM) determination in commercial tablets. Method A is based on measuring the native fluorescence of AGM aqueous solution at 230/360 nm. Methods B and C are based on the formation of a charge transfer complex between AGM and 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) and 7,7,8,8‐tetracyanoquinodimethane (TCNQ) with measurement of the formed fluorophore at 365/475 nm and 250/304 nm, respectively. The relative fluorescence intensity (RFI) of AGM–DDQ complex was greatly enhanced in the presence of methyl‐β‐cyclodextrin (CD). The methods were linear over the concentration ranges of 0.015–0.5, 0.5–8.0, 0.09–6.0 and 0.05–0.2 μg/ml for AGM‐native fluorescence, AGM–DDQ, AGM–DDQ–CD and AGM–TCNQ complexes, respectively with excellent correlation coefficients (r = 0.9999). The methods were validated as per the International Conference on Harmonization (ICH) guidelines and all validation requirements were satisfied. The developed methods were extended to the analysis of AGM in commercial tablets. Furthermore, the stability of AGM was studied under different stress conditions (alkaline, acidic, oxidative and photolytic). The potential alkaline and acidic degradation products were identified by LC–MS/TOF.     

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.     

Liquid chromatographic and spectrofluorimetric assays of empagliflozin: Applied to degradation kinetic study and content uniformity testing

Stability‐indicating high‐performance liquid chromatography (HPLC) and spectrofluorimetric methods were developed for determination of empagliflozin (EGF). EGF was subjected to oxidation, wet heat, photo‐degradation, acid hydrolysis and alkali hydrolysis. The alkaline degradation pathway was subjected to a kinetics study as the major product obtained after stress conditions. Arrhenius plots were constructed and the activation energies of the degradation process were calculated. HPLC was used for the kinetic study as it enabled simultaneous determination of EGF and the degradation product while the spectrofluorimetric assay was applied to content uniformity testing due to its higher sensitivity and lower limit of detection (LOD). Isocratic chromatographic elution was attained for HPLC on a Intersil® C₁₈ column (150 mm × 4 mm, 5 μm), using a mobile phase of acetonitrile–potassium dihydrogen phosphate buffer pH 4, (50:50, v/v) at a flow rate of 1 ml/min with ultraviolet (UV) detection at 225 nm. The relative fluorescence intensity was recorded by spectrofluorimeter applying synchronous mode using ?λ = 70 nm at 297.6 nm. Linearity ranges were found to be 5–50 μg/ml and 50–1000 ng/ml for HPLC and spectrofluorimetric methods, respectively.     

Utility of a xanthene-based dye for determination of nilotinib using two spectroscopic approaches. Applications to bulk powder,capsules, and spiked human plasma

Novel, selective, facile, and precise spectroscopic approaches were validated to determine nilotinib hydrochloride, a tyrosine kinase inhibitor used to treat patients with chronic myeloid leukemia. These approaches depend on the reaction of the tertiary amine group of nilotinib with erythrosine B in the Britton–Robinson buffer at pH 4. Method I, depends on measuring the absorbance of the formed complex at 551 nm. The absorbance concentration plot showed linearity over the concentration range of 1.0 to 9.0 μg/ml. Method II, involved the measurement of the quenching of the native fluorescence of erythrosine B by adding nilotinib in an acidic medium. The fluorescence quenching of erythrosine B was measured at 549 nm after excitation at 528 nm. This approach showed excellent linearity in the concentration range of 0.04 to 0.7 μg/ml. The limit of detection values for Method I and Method II were 0.225 and 0.008 μg/ml, respectively, while the limit of quantitation values for Method I and Method II were 0.68 and 0.026 μg/ml, respectively. To get the optimal conditions, factors that may affect the formation of the ion-pairing complex were thoroughly examined. The two approaches were carefully validated following the International Conference of Harmonization (ICH Q2R1) guidelines. Statistical assessment of the results achieved using the suggested and previously published comparison approaches showed no significant difference. The approaches were successful in determining nilotinib in a pharmaceutical dosage form as well as spiked human plasma samples. The eco-friendly properties of the methods were evaluated by three different tools.     

New spectrofluorimetric and spectrophotometric methods for the determination of the analgesic drug,nalbuphine in pharmaceutical and biological fluids

We describe the first studies of a simple and sensitive spectrofluorimetric and spectrophotometric methods for the analysis of nalbuphine (NLB) in dosage form and biological fluids. The spectrofluorimetric method was based on the oxidation of NLB with Ce(IV) to produce Ce(III) and its fluorescence was monitored at 352 nm after excitation at 250 nm. The spectrophotometric method involves addition of a known excess of Ce(IV) to NLB in acid medium, followed by determination of residual Ce(IV) by reacting with a fixed amount of methyl orange and measuring absorbance at 510 nm. In both methods, the amount of Ce(IV) reacted corresponds to the amount of NLB and measured fluorescence or absorbance were found to increase linearly with the concentration of NLB, which are corroborated by correlation coefficients of 0.9997 and 0.9999 for spectrofluorimetric and spectrophotometric methods, respectively. Different variables affecting the reaction conditions such as concentrations of Ce(IV), type and concentration of acid medium, reaction time, temperature, and diluting solvents were carefully studied and optimized. The accuracy and precision of the methods were evaluated on intra‐day and inter‐day basis. The proposed methods were successfully applied for the determination of NLB in pharmaceutical formulation and biological samples with good recoveries. Copyright © 2012 John Wiley & Sons, Ltd.     

Approved spectrofluorimetric strategies for assurance of three modern antineoplastic drugs: tepotinib,sotorasib, and darolutamide in their dose forms and biological liquids utilizing mercurochrome

An approved, straightforward, fast, and delicate spectrofluorimetric strategy was developed for the estimation of tepotinib (TEPO), sotorasib (SOTO), and darolutamide (DARO) as new antineoplastic drugs. The spectrofluorimetric strategy was based on quantitative fluorescence quenching of MER at 538 nm after being excited at 350 nm by the addition of the cited drugs in the presence of acetate buffer (pH 3.5). The degree of fluorescence quenching was directly proportional to the concentrations of the cited drugs within the concentration range of 0.5–10.0, 0.2–10, and 0.4–10.0 μg ml⁻¹ for TEPO, SOTO, and DARO, respectively. Mean ± standard deviation (SD) were calculated for the studied drugs as follows; 99.9 ± 0.87, 99.72 ± 1.08, and 100.21 ± 1.44, for TEPO, SOTO, and DARO, respectively. Limit of detection (LOD) values were 0.16, 0.05, and 0.11 μg ml⁻¹, whereas limit of quantitation (LOQ) values were 0.5, 0.15, and 0.36 μg ml⁻¹ for TEPO, SOTO, and DARO, respectively. Statistical comparison through detailed strategies produced greater understanding and found that there were no noteworthy contrasts in exactness and exactness between strategies. The proposed strategy was used effectively to analyze the measurement of different forms of the examined drugs. Moreover, the recommended fluorimetric strategy was used for examination of TEPO, SOTO, and DARO in human plasma and urine tests.     

Utility of the food colorant erythrosine B as an effective green probe for quantitation of the anticancer sunitinib. Application to pharmaceutical formulations and human plasma

Sunitinib is a tyrosine kinase inhibitor used for the treatment of renal cell carcinoma and gastrointestinal stromal tumors. In this study, two spectroscopic methods, spectrofluorometric and spectrophotometric, were utilized to quantify sunitinib in different matrices. In method I, the native fluorescence of erythrosine B was quenched by forming ion-pair complex with increasing quantities of sunitinib. This approach was utilized for measuring sunitinib in its dosage forms and spiked plasma. After excitation at 528 nm, the quenching of fluorescence is linearly related to the concentration across the range of 0.05–0.5 μg mL⁻¹ at 550 nm in Britton–Robinson buffer (pH 4.0), with a correlation value of 0.9999 and a high level of sensitivity with detection limit down to 10 ng mL⁻¹. Method II relies on spectrophotometric measurements of the produced complex at 550 nm across a range of 0.5–10.0 μg mL⁻¹, with good correlation value of 0.9999. This method has a detection limit down to 0.16 μg mL⁻¹. The proposed methodologies were validated according to International Conference on Harmonization (ICH) guidelines with satisfactory results. The stoichiometry of the reaction was determined through the application of Job's method, while the mechanism of quenching was investigated by employing the Stern–Volmer plot. The designated methods were used to estimate sunitinib in its capsules and in spiked human plasma. Additionally, the statistical analysis of the data revealed no substantial differences when compared to previous reported spectroscopic method. Green assessment tools provide further details about the eco-friendly nature of the methods.     

Spectrofluorimetric determination of dipyridamole in serum — a comparison of two methods

Two spectrofluorimetric methods for the determination of dipyridamole in plasma are described. The thin-layer chromatographic—fluoridensitometric method utilizes 1 ml of plasma which is extracted at pH 10 with diethyl ether—dichloromethane (80:20). The organic phase is evaporated to dryness, reconstituted in 250 μl dichloromethane and 5 μl are spotted on a silica gel 60 plate. The plate is developed in ethyl acetate—methanol—ammonia (85:10:5), dried, dipped in a paraffin wax solution, dried, and scanned using 380 nm as excitation wavelength, a 430 nm cut-off filter, and collecting all emitted light on the photomultiplier. Quantitation was done by the external standard method, peak heights being measured and a calibration graph constructed. For the spectrofluorimetric method 1 ml of plasma is extracted at pH 10 with 8 ml of hexane—isoamyl alcohol (95:5) and the organic phase used directly for the measurement of the fluorescence intensity (excitation 405 nm, emission 495 nm). Quantitation was done by measuring the fluorescence of standards that were treated as above and constructing a calibration graph of concentration versus fluorescence intensity. Concentrations of unknowns were found by interpolation from this graph. The two methods were found to exhibit good correlation but the spectrofluorimetric method proved to be more amenable to the analysis of a large number of samples.