Selective detection of azelnidipine in pharmaceuticals via carbon dot mediated spectrofluorimetric method: A green approach.

A spectrofluorimetric method using fluorescent carbon dots (CDs) was developed for the selective detection of azelnidipine (AZEL) pharmaceutical in the presence of other drugs. In this study, N-doped CDs (N-CDs) were synthesized through a single-step hydrothermal process, using citric acid and urea as precursor materials. The prepared N-CDs showed a highly intense blue fluorescence emission at 447 nm, with a photoluminescence quantum yield of ~21.15% and a fluorescence lifetime of 0.47 ns. The N-CDs showed selective fluorescence quenching in the presence of all three antihypertensive drugs, which was used as a successful detection platform for the analysis of AZEL. The photophysical properties, UV-vis light absorbance, fluorescence emission, and lifetime measurements support the interaction between N-CDs and AZEL, leading to fluorescence quenching of N-CDs as a result of ground-state complex formation followed by a static fluorescence quenching phenomenon. The detection platform showed linearity in the range 10-200 µg/ml (R2 = 0.9837). The developed method was effectively utilized for the quantitative analysis of AZEL in commercially available pharmaceutical tablets, yielding results that closely align with those obtained from the standard method (UV spectroscopy). With a score of 0.76 on the 'Analytical GREEnness (AGREE)' scale, the developed analytical method, incorporating 12 distinct green analytical chemistry components, stands out as an important technique for estimating AZEL.

An Investigative Review for Pharmaceutical Analysis of 1,4-Dihydropyridine-3,5-Dicarboxylic Acid Derivative: Cilnidipine.

Hypertension is commonly a quiet condition, and it expands the risk of heart diseases and stroke. Calcium delivers a substantial role in cardiovascular functions and hence is essential for cardiac automaticity and functioning. Calcium channel antagonists are the choice of drugs for the management of cardiovascular diseases; they precisely stop the introduction of calcium through L-type calcium channels are existing channels in the heart. Cilnidipine belongs to the class 4th generation calcium channel blockers as a foremost therapeutic agent used in the treatment of hypertension and heart diseases. This review article focuses on an inclusive account of crucial analytical methodologies used for the pharmaceutical analysis of cilnidipine in pure forms, biological samples and pharmaceuticals. According to literature reports several analytical techniques such as hyphenated techniques, high-performance thin-layer chromatography, high-performance liquid-chromatography, capillary electrophoresis, voltammetry, UV/Vis-spectrophotometry, and Fourier-transform infrared spectroscopy approaches have been used for determination of cilnidipine alone or in the combined dosage form. We have also discussed the pharmacopeial assay methods, physicochemical properties, and also depict the stacked column chart for year wise publication count for cilnidipine. From literature, concluded that the high-performance liquid-chromatography and UV/Vis-spectrophotometry methods are the most prevailing methods for the analysis of cilnidipine. The data presented in this review may provide a very significant base for further studies on cilnidipine in the area of drug analysis.

Dihydropyridine-coumarin-based fluorescent probe for imaging nitric oxide in living cells.

Nitric oxide (NO) is a messenger molecule in organisms, participating in the regulation of many biological processes. The abnormal expression of NO is often observed in a variety of diseases, including cerebral ischemia, atherosclerosis, and cancer. However, a suitable tool that can directly and sensitively detect NO in vitro and in vivo is important for understanding its various biological functions. In this report, a new fluorescent probe for nitric oxide, DHP-4, was prepared, based on dihydropyridine-coumarin. DHP-4 was able to greatly enhance the fluorescence of NO, but did not affect the fluorescence emissions of other reactive oxygen species and nitrogen species, demonstrating its highly selective and sensitive response to NO. The probe generated stable optical signals in a buffer solution at pH values ranging from 3 to 10. In addition, DHP-4 could detect NO directly, showed low cellular toxicity, and was successfully applied to determine NO in Raw 264.7 cells, indicating its great potential as a tool for investigating the biological roles of NO in vivo.

Evaluation of supercritical fluid chromatography coupled to tandem mass spectrometry for pesticide residues in food.

Supercritical fluid chromatography coupled to triple quadrupole mass spectrometry has been evaluated for pesticide residues in food. In order to check its advantages and limitations it was developed a method to identify and quantify 164 pesticides in three different matrices (tomato, orange and leek). A carbon dioxide gradient with methanol (containing 1 mM ammonium formate) was used allowing a flow rate of 1.5 mL/min that made the total run time of 12 min without any problem of overpressure. Addition of a post column flow 150 µL/min of Methanol with ammonium formate/formic acid was necessary to improve the ionization. The matrix effect study revealed that the percentages of pesticides with irrelevant matrix effect (suppression lower than 20%) was 99% in tomato, 87% in orange and 62% in leek, whereas significant suppression (higher than 50%) was not found in tomato and only 1% of the compounds in orange and 3% in leek.These results compare favorably with that typically obtained in LC-MS/MS. The absence of water in the mobile phase, also provided some important advantages regarding LC-MS/MS as (i) higher retention of polar compounds in the column, which elute with high sensitivity and good peak shape and (ii) a general increase of the sensitivity of the analysis, consequence of the high ionization and ion extraction efficiency. Pesticides evaluated were identified following the SANTE/11813/2017. At the spiking concentration of 5 µg/kg, 98% of the pesticides were identified in tomato, 98% in orange and 94% in leek, whereas for the concentration of 10 µg/kg all the compounds were identified in tomato and only spiromesifen was not identified in orange and leek. At the concentration of 20 µg/kg, spiromesifen was also identified in these two matrices. The linearity and reproducibility of the method were evaluated with results which guarantee high quality in the analytical measurements. Even though only 2 µL of final extract were injected, the sensitivity of the SFC method was enough to achieve stringent LOQs.Real samples, including 6 different fruits and vegetables, were analyzed by the SFC-MS/MS proposed method, the results being similar to those obtained by LC-MS/MS. The method was also applied to a proficiency test of fipronil in eggs with good results in all the cases. Carbon dioxide as mobile phase with methanol as modifier can represent a good alternative to LC-MS/MS with reduction of matrix effects and shorter run times.

Microwave Mediated Synthesis and Analytical Method Development for the Estimation of Novel 1,4-Dihydropyridines in Bulk by RP-HPLC.

The present work describes a rapid and green microwave mediated method for the synthesis and a simple and precise isocratic reverse phase HPLC method for the estimation of the biologically significant dihydropyridines. The conventional synthesis of these dihydropyridines has been previously reported from our lab. The analysis of a standard solution (1 mg/ml) was accomplished on a symmetry (4.6 mm I.D x 250 mm) C-18 column using mobile phase acetonitrile:water:triethylamine (TEA) (70:30:0.1 v/v/v) at a flow rate of 0.7 ml/min. Detection was monitored at 354 nm. The retention time for all the compounds was accomplished as less than 10 min. The compounds showed the linear response over the concentration range 10-100 µg/ml. The study is aimed to develop a rapid method for the quantification of these potent molecules. Various parameters like linearity (10-100 µg/ml), USP tailing and plate count were found to be satisfactory. The investigated parameters were studied with the freshly prepared solutions.

Pharmacokinetics and tissue distribution study of clevidipine and its primary metabolite H152/81 in rats.

This present study was designed to investigate the pharmacokinetic profiles and tissue distribution characteristics of clevidipine and its primary metabolite H152/81 in rats following a single intravenous administration of clevidipine butyrate injectable emulsion. For this study, a sensitive and selective liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was established and validated for the simultaneous quantitation of clevidipine and H152/81 in rat whole blood and various tissues. A Hedera ODS-2 column with two gradient elution programs was employed for the troubleshooting of matrix effect on the detection of analytes among different biological samples. The experimental data showed that clevidipine represented quick elimination from blood with a half-life of about 4.3 min and rapid distribution in all of the investigated tissues after administration; the highest concentration of clevidipine was found in the heart whereas the lowest concentration was detected in the liver. In addition, clevidipine was almost undetectable in most tissues except for heart and brain at 90 min post-dosing, suggesting that there was no apparent long-term accumulation in rat tissues. For H152/81, the peak concentration of 3714 ± 319 ng/mL occurred at 0.129 ± 0.048 h, the half-life was 10.08 ± 1.45 h and area under the concentration-time curve was 42091 ± 3812 ng h/mL after drug administration. In addition, H152/81 was found at significant concentration levels in all tissues, in descending order of lung, kidney, heart, liver, spleen and brain at each time point. The results of current study offer useful clues for better understanding the distribution and metabolism of clevidipine butyrate injectable emulsion in vivo.

Enantioselective behaviour of the herbicide fluazifop-butyl in vegetables and soil.

The enantioselective dissipation of the enantiomers of fluazifop-butyl in tomato, cucumber, pakchoi, rape and soil under field condition was investigated to elucidate the enantioselective environmental behaviours and chiral stability of the optical pure product. Fluazifop, the major chiral metabolite of fluazifop-butyl, was also detected. Fluazifop-butyl dissipated rapidly in the vegetables and soil with the half-lives of the enantiomers ranging from 1.62 to 2.84days. Enantioselective degradations of fluazifop-butyl were found. In tomato and cucumber, S-fluazifop-butyl dissipated faster than R-enantiomer, while R-fluazifop-butyl showed a faster degradation in pakchoi, rape and soil. Fluazifop was found almost immediately after the application of fluazifop-butyl and had relatively longer persistent time. When the optical pure product fluazifop-P-butyl was applied, rapid degradation to R-fluazifop was found with half-lives from 1.24 to 2.28days, and no S-fluazifop-butyl or S-fluazifop was detected showing the herbicidally active fluazifop-P-butyl and R-fluazifop were configurationally stable.

Comparison and evaluation of pesticide monitoring programs using a process-based mixture model.

A number of European countries run large-scale pesticide monitoring schemes in watersheds aimed at identifying and evaluating the presence of pesticide residues in the environment. These schemes provide national and regional scale assessments of pesticide concentrations within the context of environmental quality assessment, aiming to ensure some degree of ecological protection. The present study is aimed at evaluating the joint effects of the pesticide mixtures detected in monitoring programs, using a process-based mixture model that was parameterized for Daphnia magna. In total, over 15 000 samples containing over 1 million individual measurements were evaluated for effects. It was found that there are only a small number of places where one can expect to have effects on daphnids, based on measured concentrations. The most polluted samples would cause extinction of a daphnid population within only 30 h. The results show that effects are mostly triggered by a limited number of pesticide residues at locations with high emissions. It was also shown that the analytical detection limits are basically too high to exclude mixture effects. So, despite all the effort that is put into chemical monitoring programs, it remains a challenge to make statements on whether or not the environment is protected. Recommendations are offered for a different setup of monitoring programs to improve this situation. Environ Toxicol Chem 2016;35:3113-3123. © 2016 SETAC.

Micelle-enhanced spectrofluorimetric method for determination of lacidipine in tablet form; application to content uniformity testing.

A highly sensitive, simple and rapid spectrofluorimetric method was developed for the determination of lacidipine (LCP) in tablets. The proposed method is based on the investigation of the fluorescence spectral behavior of LCP in both sodium dodecyl sulphate (SDS) and the tween-80 micellar system. In aqueous solutions of acetate buffer (pH 4.5), the fluorescence intensities of LCP were greatly enhanced (ca. 2.4 and 4.3 folds) in the presence of either SDS or tween-80, respectively. The fluorescence intensity was measured at 444 nm after excitation at 277 nm using either SDS or tween-80 as a surfactant. The fluorescence-concentration plots were rectilinear over the ranges of 50.0-500.0 ng/ml and 5.0-200.0 ng/ml with lower detection limits of 5.11 and 2.06 ng/ml and lower quantification limits of 17 and 6.87 ng/ml using SDS and tween-80, respectively. The method was successfully applied to the analysis of LCP in commercial tablets and the results were in good agreement with those obtained with the comparison method. Furthermore, content uniformity testing of pharmaceutical tablets was also conducted.

Determination of the purity of pharmaceutical reference materials by 1H NMR using the standardless PULCON methodology.

A fast and reliable nuclear magnetic resonance spectroscopic method for quantitative determination (qNMR) of targeted molecules in reference materials has been established using the ERETIC2 methodology (electronic reference to access in vivo concentrations) based on the PULCON principle (pulse length based concentration determination). The developed approach was validated for the analysis of pharmaceutical samples in the context of official medicines control, including ibandronic acid, amantadine, ambroxol and lercanidipine. The PULCON recoveries were above 94.3% and coefficients of variation (CVs) obtained by quantification of different targeted resonances ranged between 0.7% and 2.8%, demonstrating that the qNMR method is a precise tool for rapid quantification (approximately 15min) of reference materials and medicinal products. Generally, the values were within specification (certified values) provided by the manufactures. The results were in agreement with NMR quantification using an internal standard and validated reference HPLC analysis. The PULCON method was found to be a practical alternative with competitive precision and accuracy to the classical internal reference method and it proved to be applicable to different solvent conditions. The method can be recommended for routine use in medicines control laboratories, especially when the availability and costs of reference compounds are problematic.

Malondialdehyde-derived epitopes in human skin result from acute exposure to solar UV and occur in nonmelanoma skin cancer tissue.

Cutaneous exposure to solar ultraviolet radiation (UVR) is a causative factor in photoaging and photocarcinogenesis. In human skin, oxidative stress is widely considered a key mechanism underlying the detrimental effects of acute and chronic UVR exposure. The lipid peroxidation product malondialdehyde (MDA) accumulates in tissue under conditions of increased oxidative stress, and the occurrence of MDA-derived protein epitopes, including dihydropyridine-lysine (DHP), has recently been substantiated in human skin. Here we demonstrate for the first time that acute exposure to sub-apoptogenic doses of solar simulated UV light (SSL) causes the formation of free MDA and protein-bound MDA-derived epitopes in cultured human HaCaT keratinocytes and healthy human skin. Immunohistochemical staining revealed that acute exposure to SSL is sufficient to cause an almost twenty-fold increase in general MDA- and specific DHP-epitope content in human skin. When compared to dose-matched solar simulated UVA, complete SSL was more efficient generating both free MDA and MDA-derived epitopes. Subsequent tissue microarray (TMA) analysis revealed the prevalence of MDA- and DHP-epitopes in nonmelanoma skin cancer (NMSC). In squamous cell carcinoma tissue, both MDA- and DHP-epitopes were increased more than threefold as compared to adjacent normal tissue. Taken together, these date demonstrate the occurrence of MDA-derived epitopes in both solar UVR-exposed healthy human skin and NMSC TMA tissue; however, the potential utility of these epitopes as novel biomarkers of cutaneous photodamage and a functional role in the process of skin photocarcinogenesis remain to be explored.

Flow injection chemiluminescence determination of lercanidipine based on N-chlorosuccinimide-eosin Y post-chemiluminescence reaction.

A novel post-chemiluminescence (PCL) reaction was discovered when lercanidipine was injected into the CL reaction mixture of N-chlorosuccinimide with alkaline eosin Y in the presence of cetyltrimethylammonium bromide (CTAB), where eosin Y was used as the CL reagent and CTAB as the surfactant. Based on this observation, a simple and highly sensitive PCL method combined with a flow injection (FI) technique was developed for the assay of lercanidipine. Under optimum conditions, the CL signal was linearly related to the concentration of lercanidipine in the range 7.0 × 10(-10) to 3.0 × 10(-6) g/mL with a detection limit of 2.3 × 10(-10) g/mL (3σ). The relative standard deviation (RSD) was 2.1% for 1.0 × 10(-8) g/mL lercanidipine (n = 13). The proposed method had been applied to the estimation of lercanidipine in tablets and human serum samples with satisfactory results. The possible CL mechanism is also discussed briefly.

Estimation of the validation parameters for a fast analysis of herbicide residues by LC-MS/MS.

Due to strict regulatory requirements for pesticide residue analysis, only the results of residue analysis with acceptable quality should be reported. As a consequence proper validation of the measurement method is required. In this context, accuracy, precision, specificity, limit of determination (LOQ), matrix effect, linearity, uncertainty calculation and ruggedness become increasingly important. This paper reports a description of the validation parameters of a fast method for the determination of five phenoxy acid herbicides (2,4-D, MCPA, MCPP, haloxyfop and fluazifop) in food crops. The recoveries were performed in the concentration range from 0.05 to 0.5 mg kg⁻¹ for apples, pears, carrots and celeriac with five replicates at each level. The mean recoveries ranged from 70% to 95% for all crops. The precision of the method expressed as a relative standard deviation (RSD%) was found to be in the range 3-14%. For all herbicides, the linearity response of the detector was tested by correlation coefficients (r² > 0.99) in the concentration range from 0.05 to 0.5 mg kg⁻¹. The LOQ was determined as the lowest spiked level meeting the requirement of accuracy (70-120%) and precision (RSD% < 20% according to European Union guidelines. The uncertainty and robustness were calculated. On the basis of the results, the method can be considered fast, simple and robust and is suitable to be applied to the analysis of studied herbicides in routine testing laboratories.

First-order derivative UV spectrophotometric method for simultaneous measurement of delapril and manidipine in tablets.

A first-order derivative spectrophotometric (1D-UV) method was developed and validated for simultaneous determination of delapril (DEL) and manidipine (MAN) in tablets. The 1D-UV spectra were obtained using change lambda = 4.0 nm and wavelength set at 228 nm for DEL and 246 nm for MAN. The method was validated in accordance with the ICH requirements, involving the specificity, linearity, precision, accuracy, robustness and limits of detection and quantitation. The method showed high specificity in the presence of two drugs and formulation excipients and was linear over the concentration range of 18-54 microg mL(-1) (r2 = 0.9994) for DEL and 6-18 microg mL(-1) (r2 = 0.9981) for MAN with adequate results for the precision (< or = 1.47%) and accuracy (98.98% for DEL and 100.50% for MAN). Moreover, the method proved to be robust by a Plackett-Burman experimental design evaluation. The proposed 'D-UV method was successfully applied for simultaneous analysis of DEL and MAN in tablets and can be used as alternative green method to separation techniques. The results were compared with the validated liquid chromatography, capillary electrophoresis and liquid chromatography-tandem mass spectrometry methods, showing non-significant difference.

Voltammetric and RP-LC assay for determination of benidipine HCl.

The detailed electrooxidative behavior of benidipine (BEN) has been studied by using glassy carbon (GC) and boron-doped diamond (BDD) electrodes. Using cyclic voltammetry, depending on the pH values and the working electrodes, BEN showed one or two sharp and irreversible oxidation responses. The voltammetric experiments on some model compounds allowed elucidation of the oxidation mechanism of BEN. Highly sensitive, selective, rapid, and fully validated voltammetric methods for the determination of BEN in tablet dosage form were also presented. Under optimized conditions, the peak current showed a linear dependence with concentration in the range between 3.25 µg mL(-1) and 54.20 µg mL(-1) for GC and 1.08 µg mL(-1) and 54.20 µg mL(-1) for BDD electrodes by using differential pulse (DPV) and square wave (SWV) voltammetric techniques. In this study, acid dissociation constant (pK(a)) value of BEN was determined by using the dependence of the retention factor on the pH of the mobile phase using reverse phase-liquid chromatographic (RP-LC) method. The effect of the composition of the mobile phase on the ionization constant was studied by measuring the pK(a) at different acetonitrile-water mixtures, ranging between 50 and 65% (v/v). Also simple, accurate, precise and fully validated RP-LC method for the assay of BEN in dosage form has been developed. XTerra RP-18 column at 25 °C with the mobile phase of acetonitrile:water 55:45 (v/v) adjusted to pH 3.0 with 15 mM o-phosphoric acid was used. Isocratic elution was performed in less than 5.0 min with a flow rate of 1.0 mL min(-1). The RP-LC method allowed quantitation over the 0.25-15.00 µg mL(-1) range for BEN. The proposed voltammetric and RP-LC methods allow a number of cost and time saving benefits. BEN was also exposed to thermal, photolytic, oxidative stress, acid-base catalyzed hydrolyses, and the stressed samples were detected by the proposed RP-LC method.

Mechanistic study on degradation of azelnidipine solution under radical initiator-based oxidative conditions.

We identified four degradants (Dg-A, Dg-B, Dg-C, Dg-D) of azelnidipine to be generated under radical initiator-based oxidative conditions and proposed the mechanistic pathway for their formation. 2,2'-Azobisisobutyronitrile was used as a radical initiator. There appeared to be two major pathways in the oxidation of the 1,4-dihydropyridine moiety. One was initiated by hydrogen abstraction from the C-4 position of the dihydropyridine ring, followed by hydrogen abstraction from the N-1 position, leading to aromatization of the dihydropyridine ring and Dg-A generation. The other was initiated by hydrogen abstraction from the N-1 position of the dihydropyridine ring followed by oxidation and hydrolysis to yield Dg-B. Furthermore, Dg-B was subjected to hydrolysis to generate Dg-C and Dg-D. It has been revealed that the rate of the Dg-B degradation was predominantly governed by the water content of the solvent used. Water participation in Dg-B degradation was proved by monitoring the incorporation of heavy oxygen atom ((18)O) into the structure with LC-MS, in which the experiment was carried out in a medium prepared with heavy oxygen water to label (18)O during the hydrolysis.

Automatized flow-batch method for fluorescent determination of free glycerol in biodiesel samples using on-line extraction.

An automatic method, based on flow-batch (FB), for determining glycerol in biodiesel was developed. The FB systems draw upon the useful features of flow, batch and multi-commutation approaches. The standards and samples preparation, as well as, derivatization and analysis were fully automated. For that purpose, a homemade chamber was built. The proposed method is based on liquid-liquid extraction of glycerol and simultaneous oxidation with periodate, generating formaldehyde that reacts with acetylacetone. A fluorescent product of 3,5-diacetyl-1,4-dihydrolutidine was obtained. The fluorescence signal was recorded at λ(ex) =417 nm and λ(em) = 514 nm. A linear response was observed from 0.10 to 5.00 mg L(-1) glycerol, variation coefficient 1.5%, sampling rate 14 h(-1) and detection limit 0.036 mg L(-1) glycerol. The procedure was successfully applied to the analysis of biodiesel samples, and the results agreed with the reference method (ASTM D6584-07) at 95% confidence level.

Development and validation of a reversed-phase ultra-performance liquid chromatographic method for assay of lacidipine and related substances.

A simple isocratic, RP-ultra-performance LC method was developed and validated for the determination of lacidipine, three process impurities formed during synthesis, and three degradation products present in drug substance and the drug product. An efficient chromatographic separation was achieved on an Acquity BEH C18 column using pH 4.5 ammonium acetate-acetic acid buffer-methanol (70 + 30, v/v) mobile phase. The monitoring wavelength was 240 nm, and the flow rate 0.25 mL/min. Forced degradation studies using acid, alkali, peroxide, water, heat, and light were conducted, and all impurities were separated. The method was validated successfully for specificity, precision, linearity, accuracy, LOD, LOQ, and robustness, according to International Conference on Harmonization guidelines. The linearity of the calibration curve for lacidipine and each impurity was found to be very good (r2 > 0.999). This method is shown to be suitable for analysis of lacidipine to evaluate the quality of drug substance and a drug product.

Determination of pK(a) values of some antihypertensive drugs by liquid chromatography and simultaneous assay of lercanidipine and enalapril in their binary mixtures.

In this study, pK(a) values were determined using the dependence of the retention factor on the pH of the mobile phase for three ionizable substances, namely, enalapril, lercanidipine and ramipril (IS). The effect of the mobile phase composition on the ionization constant was studied by measuring the pK(a) at different methanol-water mixtures, ranging between 50 and 65% (v/v), using LC-DAD method. Two simple, accurate, precise and fully validated analytical methods for the simultaneous determination of enalapril and lercanidipine in combined dosage forms have been developed. Separation was performed on an X-Terra RP-18 column (250 mm x 4.60mm ID x 5 microm) at 40 degrees C with the mobile phase of methanol-water 55:45 (v/v) adjusted to pH 2.7 with 15 mM orthophosphoric acid. Isocratic elution was performed in less than 12 min with a flow rate of 1.2 mL min(-1). Good sensitivity for the analytes was observed with DAD detection. The LC method allowed quantitation over the 0.50-20.00 microg mL(-1) range for enalapril and lercanidipine. The second method depends on first derivative of the ratio-spectra by measurements of the amplitudes at 219.7 nm for enalapril and 233.0 nm for lercanidipine. Calibration graphs were established for 1-20 microg mL(-1) for enalapril and 1-16 microg mL(-1) lercanidipine, using first derivative of the ratio spectrophotometric method. Both methods have been extensively validated. These methods allow a number of cost and time saving benefits. The described methods can be readily utilized for analysis of pharmaceutical formulations. The methods have been applied, without any interference from excipients, for the simultaneous determination of these compounds in tablets. There was no significant difference between the performance of the proposed methods regarding the mean values and standard deviations.