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Abstract The current study developed a method for quantifying four drugs—Sulfamethoxazole, Trimethoprim, Isoniazid, and Pyridoxine—in rabbit plasma. The method uses gradient liquid chromatography based on analytical quality by design. To achieve separation, a Eclip Plus C18 (250 mm × 5 mm, 4.6 µm) column with L1 packing was used, and analytes were detected at 254 nm at ambient temperature. The optimized mobile phase consisted of 50 mM potassium dihydrogen phosphate buffer (pH 6.5) and Methanol. The concentration of Methanol was 3% (0–5 min), 15% (5–15 min), 55% (15–27 min), and 3% Methanol until the end of the 30-min runtime, and the flow rate was set at 0.95 mL/min. Control Noise Experimentation was used to screen studies, revealing that flow rate, pH, and Methanol concentration significantly affected the analytical attributes. The study identified critical attributes (resolution and asymmetric factor) and developed a quality target method profile. A central composition design was used to optimize the essential parameters. The method developed for the drugs showed peaks at retention times of 6.990 min for Isoniazid, 7.880 min for Pyridoxine, 15.530 min for Sulfamethoxazole, and 26.890 min for Trimethoprim, respectively. The method was validated with linearity in the range of 10–640 ng ml−1, with R2 of 0.9993, 0.9987, 0.9993, and 0.9992 for Sulfamethoxazole, Trimethoprim, Isoniazid, and Pyridoxine, respectively.

In this study, a discontinuous Galerkin (DG) finite element method is employed to solve the nonlinear equilibrium dispersive (ED) model, for the simulation of multi-component gradient elution chromatography using a liquid mobile phase in fixed-bed columns. The ED model comprises a set of coupled nonlinear convection-dominated partial differential equations integrated with nonlinear Langmuir type adsorption isotherms. Gradient elution, characterized by the gradual increase in eluent strength through variations in the chemical composition of the mobile phase, is analyzed. An investigation into the advantages of gradient elution chromatography in comparison to isocratic elution is conducted via a sequence of numerical test experiments that assess the influence of solvent strength, modulator concentration, gradient start and end times, and gradient slope on the elution profiles and temporal moments. It has been observed that gradient elution chromatography influences the behavior, shape, and propagation speed of elution profiles, which subsequently affect the cycle time and column efficiency. The results of this study provide significant insights that are critical for understanding, optimizing, and enhancing gradient elution chromatography. [ABSTRACT FROM AUTHOR]

Abstract Background In the dapagliflozin (DPF) synthesis, 5-Bromo-2-chlorobenzoic acid (5-BC impurity) and 4-Bromo-1-chloro-2-(4-ethoxybenzyl) benzene (4-BC impurity) are used as starting and reagent sources, respectively. The presence of 5-BC and 4-BC impurities in DPF could potentially affect the effectiveness of the final DPF product. The purpose of this investigation was to develop a stability indicating HPLC methodology for the separation of DPF, its process-related impurities and degradants. The method of analysis was developed on Xbridge Phenyl C18 column of dimensions, 250 × 4.6 mm, 5 μm with gradient elution using mobile phase made up of 0.05% aqueous trifluoroacetic acid and acetonitrile (AcN). Results The method proposed indicates a good linearity (R 2 = 0.9996 and 0.9993), good system precision (RSD ≤ 2%), good method precision (RSD ≤ 2%), accuracy (50–150%), LOD (0.000053 ppm and 0.0000165 ppm) and LOQ (0.00016 ppm and 0.00005 ppm) for 4-BC impurity and 5-BC impurity, respectively. LC–MS was used to detect and characterise degradants that were obtained in acid and base condition were identified and characterised. A comparison of the fragmentation pattern of the [M + H] + ions of DPF and its degradation products revealed the most likely processes for the generation of degradation products. Conclusion DPF sample quality can be evaluated using the suggested method for the presence of 4-BC impurity, 5-BC impurity and 2-(3-(4-ethoxy benzyl)-4-chloro phenyl)-tetrahydro-6-(hydroxy methyl)-2H-pyran-3,4,5-triol.

Vilanterol (VT) and fluticasone furoate (FF) are components recently used in dry powder inhaler (DPI) to be administrated for patients with respiratory diseases, such as asthma or chronic obstructive pulmonary disease (COPD). In the present study, an approach to an analytical procedure development and validation is presented. Next generation impactor (NGI) and high performance liquid chromatography (HPLC) with UV detector were applied to determine two compounds and fine particle dose (FPD) of each active ingredients in DPI. The most satisfying chromatographic separation was obtained on Poroshell SB C18 (100 mm × 4.6 mm, 2.7 µm) column applying gradient elution by phosphonate buffer and acetonitrile. VT and FF were detected on a UV detector at wavelength of 210 nm and 245 nm, respectively. Among various coating agents, 4% polyethylene glycol PEG 200 in acetone (w/v) was selected as the most effective. Although various physicochemical properties of VT and FF, the analytical procedure allows simultaneously determine two compounds at different wavelengths. Limit of quantitative (LOQ) of vilanterol and fluticasone furoate were determined as 0.049 µg/ml and 0.032 µg/ml, respectively, what is desirable to determine of FPD of active ingredients in microdoses in DPI. The analytical procedure was determined as linear and accurate in the range of LOQ – 2.5 µg/ml and LOQ – 10.0 µg/ml of VT and FF, respectively. The coefficient of determination (R2) was found to be 0.9999 and 1.000 for VT and FF, respectively.

In this paper, the fingerprints of 10 batches of Angelica sinensis herbs and 5 batches of commercially available Angelica sinensis preparations originating from different parts of China were determined by high-performance liquid chromatography (HPLC) fingerprinting using a methanol-acetonitrile solution system with linear gradient elution, and the similarity analyses were applied for the classification. Derringer’s satisfaction function evaluated the acceptable limit values for processing multiple characteristic peaks of Angelica sinensis herbs. The results showed that under selected chromatographic conditions, HPLC fingerprints of Angelica sinensis were obtained, and four characteristic peaks were calibrated. The similarities of 10 batches of Angelica sinensis herbs ranged from 0.953 to 0.998, and those of 5 batches of Angelica sinensis preparations ranged from 0.969 to 0.999. The method established in this paper is stable, reliable and reproducible, and it can be used to provide a reference for quality control of the herbs of Angelica sinensis and the drinkable tablets of Angelica sinensis body and to provide a reference for quality control of the classic prescriptions containing Angelica sinensis or the It can provide a reference for the quality control of Angelica sinensis herb and Angelica sinensis body tablets, and provide a basis for the development and research of classical prescriptions containing Angelica sinensis or Angelica sinensis.

Background: In the dapagliflozin (DPF) synthesis, 5-Bromo-2-chlorobenzoic acid (5-BC impurity) and 4-Bromo-1-chloro-2-(4-ethoxybenzyl) benzene (4-BC impurity) are used as starting and reagent sources, respectively. The presence of 5-BC and 4-BC impurities in DPF could potentially affect the effectiveness of the final DPF product. The purpose of this investigation was to develop a stability indicating HPLC methodology for the separation of DPF, its process-related impurities and degradants. The method of analysis was developed on Xbridge Phenyl C18 column of dimensions, 250 × 4.6 mm, 5 μm with gradient elution using mobile phase made up of 0.05% aqueous trifluoroacetic acid and acetonitrile (AcN). Results: The method proposed indicates a good linearity (R2 = 0.9996 and 0.9993), good system precision (RSD ≤ 2%), good method precision (RSD ≤ 2%), accuracy (50–150%), LOD (0.000053 ppm and 0.0000165 ppm) and LOQ (0.00016 ppm and 0.00005 ppm) for 4-BC impurity and 5-BC impurity, respectively. LC–MS was used to detect and characterise degradants that were obtained in acid and base condition were identified and characterised. A comparison of the fragmentation pattern of the [M + H] + ions of DPF and its degradation products revealed the most likely processes for the generation of degradation products. Conclusion: DPF sample quality can be evaluated using the suggested method for the presence of 4-BC impurity, 5-BC impurity and 2-(3-(4-ethoxy benzyl)-4-chloro phenyl)-tetrahydro-6-(hydroxy methyl)-2H-pyran-3,4,5-triol. [ABSTRACT FROM AUTHOR]

Vilanterol (VT) and fluticasone furoate (FF) are components recently used in dry powder inhaler (DPI) to be administered to patients with respiratory diseases, such as asthma or chronic obstructive pulmonary disease (COPD). In the present study, an approach to the analytical procedure development and validation is presented. Next generation impactor (NGI) and high performance liquid chromatography (HPLC) with UV detector were applied to determine the two compounds and the fine particle dose (FPD) of each active ingredient in DPI. The most satisfying chromatographic separation was obtained on Poroshell SB C8 (100 mm × 4.6 mm, 2.7 µm) column applying gradient elution by phosphonate buffer and acetonitrile. VT and FF were detected on a UV detector at wavelengths of 210 nm and 245 nm, respectively. Among the various coating agents, 4% polyethylene glycol PEG 200 in acetone (w/v) was selected as the most effective. Despite the various physicochemical properties of VT and FF, the analytical procedure allows to simultaneously determine two compounds at different wavelengths. The limit of quantitative (LOQ) of vilanterol and fluticasone furoate were determined as 0.049 µg/mL and 0.032 µg/mL, respectively, which is desirable to determine the FPD of active ingredients in microdoses in DPI. The analytical procedure was determined as linear and accurate in the range of LOQ - 2.5 µg/mL and LOQ - 10.0 µg/mL of VT and FF, respectively. The coefficient of determination (R2) was found to be 0.9999 and 1.000 for VT and FF, respectively. [ABSTRACT FROM AUTHOR]

A new optimization strategy based on the mixed quantitative structure– retention relationship (QSRR) model is proposed for improving the RPHPLC separation of aripiprazole and its impurities (IMP A-E). Firstly, experimental parameters (EPs), namely mobile phase composition and flow rate, were varied according to Box–Behnken design and thereafter, an artificial neural network (ANN) as a QSRR model was built correlating EPs and selected molecular descriptors (ovality, torsion energy and non-1,4-van der Waals energy) with the log-transformed retention times of the analytes. Values of the root mean square error (RMSE) were used for an estimation of the quality of the ANNs (0.0227, 0.0191 and 0.0230 for the training, verification and test set, respectively). The separations of critical peak pairs on chromatogram (IMP AB and IMP D-C) were optimized using ANNs for which the EPs served as inputs and the log-transformed separation criteria s as the outputs. They were validated by application of leave-one-out cross-validation (RMSE values 0.065 and 0.056, respectively). The obtained ANNs were used for plotting response surfaces upon which the analyses chromatographic conditions resulting in optimal analytes retention behaviour and the optimal values of the separation criteria s were defined. The optimal conditions were 54 % of methanol at the beginning and 79 % of methanol at the end of gradient elution programme with a mobile phase flow rate of 460 μL min-1.

A method is proposed for the HPLC separation of a mixture of carboxylic acids on a porous graphitized Hypercarb adsorbent under the conditions of gradient elution with formic acid solutions. The analytes were detected using a single quadrupole mass spectrometer. The stepwise gradient of formic acid without an addition of an organic solvent made it possible to achieve good resolution of the analyte peaks and decrease the limits of detection by a factor of 4.4–17.8 compared to their separation with 0.1% formic acid under isocratic conditions. The effect of methanol on the separation of analytes is less pronounced. [ABSTRACT FROM AUTHOR]

Gradient and isocratic liquid chromatography were applied for the simultaneous determination of three preservatives, namely; benzyl alcohol (BA), methyl paraben (MP) and propyl paraben (PP). Separation for both elution modes was carried out using a C18 column kept at 60°C throughout the analysis, accompanied with a flow rate of 2 mL/min and UV detection at 254 nm. Gradient liquid chromatography used a time programme with two solvents (0.1% formic acid and acetonitril), while isocratic elution was performed with 0.1% formic acid: 2-propanol in a ratio of 70:30, v/v. Full validation study was conducted for both separation modes, where both of them were linear over the concentration ranges of 100.0–2000.0, 2.5–100.0, and 2.0–200.0 µg/mL for BA, MP and PP respectively. Using gradient elution, the detection limits for BA, MP, and PP were found to be 50.0, 1.8, and 1.5 µg/mL respectively. The corresponding values in isocratic elution were 60.0, 1.5, and 1.3 µg/mL. On the other hand, the limit of quantification for BA, MP, and PP using gradient mode are 70.0, 2.0, and 1.8 µg/mL respectively. While isocratic elution resulted in corresponding values of: 80.0, 2.3, and 1.7 µg/mL. The accuracy of the proposed method was illustrated from the high percentage recoveries values which were 99.67%, 100.42%, and 99.85% for BA, MP, and PP respectively using gradient mode, with corresponding values of 99.79%, 100.39%, and 99.87% for the isocratic elution mode. In addition, gradient elution was further applied to detect and assay the selected preservatives in different pharmaceutical formulations demonstrating that their quantities are within the stated ranges, and eventually, a comparative overview was introduced.

There are several different approaches for LC method development; beside traditional, different software programs for method development and optimization are available. The solvatic retention model of reversed-phase LC was applied for prediction of retention in the gradient elution mode for aripiprazole and its related substances described in European Pharmacopoeia. As some of these compounds have very similar and others quite different chemical structure, their separation is challenge. Prediction was suitable on examined stationary phases (C18, C8 and phenyl-hexyl) with 0.1% phosphoric acid as aqueous mobile phase and acetonitrile or methanol as organic modifier. Predicted retention times take into account structural formulae of compounds and properties of stationary and mobile phases result in average difference of 14-17% compared to experimental ones on phenyl-hexyl stationary phase, where the highest matching was obtained. After utilisation of the retention models with data from one experimental run, the average difference decrease to maximal 7% and after contribution of data from two experimental runs, to maximal 2%. For majority of studied compounds difference between predicted and experimental values on all examined stationary phases is lower than 3%.

Abstract Background A novel phosphatidyl nanoprodrug system can be selectively released parent drugs in cancer cells, triggered by the local overexpression of phospholipase D (PLD). This system significantly reduces the intrinsic disadvantages of conventional chemotherapeutic drugs. However, the separation and purification processes of phosphatidyl prodrug, the precursor of phosphatidyl nanoprodrug, have not been established, and the preparation of nanocrystals with good stability and tumor-targeting capability is still challenging. Results In this study, we established a successive elution procedure for the phosphatidyl prodrug—phosphatidyl mitoxantrone (PMA), using an initial ten-bed volume of chloroform/methanol/glacial acetic acid/water (26/10/0.8/0.7) (v/v/v/v) followed by a five-bed volume (26/10/0.8/3), with which purity rates of 96.93% and overall yields of 50.35% of PMA were obtained. Moreover, to reduce the intrinsic disadvantages of conventional chemotherapeutic drugs, phosphatidyl nanoprodrug—PMA nanoprodrug (NP@PMA)—was prepared. To enhance their stability, nanoparticles were modified with polyethylene glycol (PEG). We found that nanoprodrugs modified by PEG (NP@PEG–PMA) were stably present in RPMI-1640 medium containing 10% FBS, compared with unmodified nanoprodrug (NP@PMA). To enhance active tumor-targeting efficiency, we modified nanoparticles with an arginine-glycine-aspartic acid (RGD) peptide (NP@RGD–PEG–PMA). In vitro cytotoxicity assays showed that, compared with the cytotoxicity of NP@PEG–PMA against tumor cells, that of NP@RGD–PEG–PMA was enhanced. Thus, RGD modification may serve to enhance the active tumor-targeting efficiency of a nanoprodrug, thereby increasing its cytotoxicity. Conclusions A process for the preparation and purification of novel phosphatidyl prodrugs was successfully established, and the nanoprodrug was modified using PEG for enhanced nanoparticle stability, and using RGD peptide for enhanced active tumor-targeting efficiency. These procedures offer considerable potential in the development of functional antitumor prodrugs.

Gradient and isocratic liquid chromatography were applied for the simultaneous determination of three preservatives, namely; benzyl alcohol (BA), methyl paraben (MP) and propyl paraben (PP). Separation for both elution modes was carried out using a C18 column kept at 60°C throughout the analysis, accompanied with a flow rate of 2 mL/min and UV detection at 254 nm. Gradient liquid chromatography used a time programme with two solvents (0.1% formic acid and acetonitril), while isocratic elution was performed with 0.1% formic acid: 2-propanol in a ratio of 70:30, v/v. Full validation study was conducted for both separation modes, where both of them were linear over the concentration ranges of 100.0–2000.0, 2.5–100.0, and 2.0–200.0 µg/mL for BA, MP and PP respectively. Using gradient elution, the detection limits for BA, MP, and PP were found to be 50.0, 1.8, and 1.5 µg/mL respectively. The corresponding values in isocratic elution were 60.0, 1.5, and 1.3 µg/mL. On the other hand, the limit of quantification for BA, MP, and PP using gradient mode are 70.0, 2.0, and 1.8 µg/mL respectively. While isocratic elution resulted in corresponding values of: 80.0, 2.3, and 1.7 µg/mL. The accuracy of the proposed method was illustrated from the high percentage recoveries values which were 99.67%, 100.42%, and 99.85% for BA, MP, and PP respectively using gradient mode, with corresponding values of 99.79%, 100.39%, and 99.87% for the isocratic elution mode. In addition, gradient elution was further applied to detect and assay the selected preservatives in different pharmaceutical formulations demonstrating that their quantities are within the stated ranges, and eventually, a comparative overview was introduced. [ABSTRACT FROM AUTHOR]

There are several different approaches for LC method development; beside traditional, different software programs for method development and optimization are available. The solvatic retention model of reversed-phase LC was applied for prediction of retention in the gradient elution mode for aripiprazole and its related substances described in European Pharmacopoeia. As some of these compounds have very similar and others quite different chemical structure, their separation is challenge. Prediction was suitable on examined stationary phases (C18, C8 and phenyl-hexyl) with 0.1% phosphoric acid as aqueous mobile phase and acetonitrile or methanol as organic modifier. Predicted retention times take into account structural formulae of compounds and properties of stationary and mobile phases result in average difference of 14-17% compared to experimental ones on phenyl-hexyl stationary phase, where the highest matching was obtained. After utilisation of the retention models with data from one experimental run, the average difference decrease to maximal 7% and after contribution of data from two experimental runs, to maximal 2%. For majority of studied compounds difference between predicted and experimental values on all examined stationary phases is lower than 3%. [ABSTRACT FROM AUTHOR]

A validated high-performance liquid chromatography (HPLC) method has been developed to analyze the (±)-gossypol in the selection of strains of Candida tropicalis culture. Since gossypol was easily degraded and oxidized, the addition of antioxidant NADPH-Na4 and acetone extraction was chosen to prevent gossypol degradation and gradient elution assay was applied to obtain gossypol resolution. Concentrations of gossypol in C. tropicalis ZD-3 culture 20 µg/mL were determined, and concentration-time profiles were observed. Linearity of the gossypol standard curve by HPLC area method was ranged from 0.1 to 20 µg/mL with Y = 26.954 x X - 29.547, R² = 0.9991, and n = 3, with limit of detection (LOD) of 50 ng/mL and lower limit of quantification (LLOQ) of 500 ng/mL. The recovery rate is dose-dependent and ranged from 85.3% to 103.5%. It is a rapid and reliable HPLC method for gossypol quantization in microorganism culture which could be applied in solid fermentation in the feed industry. [ABSTRACT FROM AUTHOR]

This paper aims to establish a detection method for simultaneous determining four additives in flour products: one simultaneously determines the acesulfame, sodium cyclamate, bromate, and calcium propionate through the selection of ion chromatography pump flow rate, injection volume, eluent concentration, optimization of sample pretreatment and the influence of interfering ions. When using the pump flow rate of 0.8 ml/min, 200 µL large volume injection, 0-14 min, 14-25 min eluent concentration 30 mmol/L gradient elution, 25-26 min eluent concentration 6 mmol/L, flour product is pulverized after addition of water vortex ultrasonic extraction, the supernatant by C18 solid phase extraction (SPE) columns and silver filter, 0.22μm water phase porous membrane testing on the machine, the detection limits of the four kinds of targets are 0.16 μg/ml, 0.19 μg/ml, 0.24 μg/ml, and 0.38 μg/ml, respectively; The standard deviations of retention time and peak area are calcium propionate, respectively 0.13~0.42%, 2.14~4.25% ; bromate 0.20~0.67%, 1.33~4.52% ; sodium cyclamate 0.14~0.53%, 3.57~5.62% ; acesulfame potassium 0.64~0.93%, 0.42~5.81%. This method uses water as the sole extraction solvent and can detect four additives in flour products in a single test. And the pretreatment process is also very simple. When it is applied to other food tests, some compounds may cause interference, which can be assisted by other testing methods.

Phenoxy acid herbicides are used worldwide and are potential contaminants of drinking water. Reversed phase high-performance liquid chromatography (RP-HPLC) is commonly used to monitor phenoxy acid herbicides in water samples. RP-HPLC retention of phenoxy acids is affected by both mobile phase composition and pH, but the synergic effect of these two factors, which is also dependent on the structure and pKa of solutes, cannot be easily predicted. In this paper, to support the setup of RP-HPLC analysis of phenoxy acids under application of linear mobile phase gradients we modelled the simultaneous effect of the molecular structure and the elution conditions (pH, initial acetonitrile content in the eluent and gradient slope) on the retention of the solutes. In particular, the chromatographic conditions and the molecular descriptors collected on the analyzed compounds were used to estimate the retention factor k by Partial Least Squares (PLS) regression. Eventually, a variable selection approach, Genetic Algorithms, was used to reduce the model complexity and allow an easier interpretation. The PLS model calibrated on the retention data of 15 solutes and successively tested on three external analytes provided satisfying and reliable results.

The semi preparative HPLC method with PDA Detector was proposed for the determination of one phenolic acid, three flavonoids and one polyalcohol from Butea monosperma and Hedychium coronarium in gradient elution system. The influence of composition of the mobile phase concentration of the mix modifier and temperature on the separation of gallic acid, quercetin, iso-butrin, butrin and eugenol for 90 min was studied. Two different gradient programmes were used to separate these components. The lower limit of quantification of phenolic acid, flavonoids and eugenol is 0.050–0.150 μg/mL and was determined by the least square method and a good correlation was obtained for all separated components.

Recycled Nd and Dy from the end-of-life NdFeB permanent magnet is an important supplement for the increasing demand of rare-earth elements. Thus, there is an urgent need to develop an environmentally friendly recycling method. Amorphous zirconium phosphate exhibits selective separation properties towards the ternary Co-Nd-Dy system, however, its powdery form limits development of scaled-up applications. We present an efficient amorphous ZrP/Polyacrylonitrile (am-ZrP/PAN) composite ion exchanger for uptake and separation of Nd, Dy and Co. The am-ZrP/PAN composite was synthesized and its structural, morphologic and acidic properties were investigated by various methods. X-ray tomography revealed rather evenly distributed am-ZrP in the PAN polymer matrix. The selectivity and ion-exchange kinetics of the am-ZrP/PAN composite were determined in relation to the individual elements. Due to dimethylformide (DMF) intercalation into the interlayer of ZrP, the uptake of Co, Nd and Dy increased 50% compared with that of the pristine am-ZrP. Column separation of Co, Nd and Dy from the Co-Nd-Dy ternary system was assessed by varying the feed concentration, loading degree, temperature, running speed and elution agent (HNO 3 ) concentration. Finally, gradient elution was employed for Co, Nd and Dy separation from a simulated ternary leachate. Fractions with 87.9% pure Co, 96.4% pure Nd and 40% pure Dy were collected through a single-column operation. [ABSTRACT FROM AUTHOR]

A procedure is proposed for the determination of succinic acid, riboxin, nicotinamide, and riboflavin by ion-pair HPLC with UV detection. Owing to the addition of an ion-pair modifier to the mobile phase and the selection of gradient elution conditions, the optimal retention and resolution of peaks of the components to be determined are achieved. Specificity, linearity, accuracy, and precision of the developed procedure are proved on an example of the determination of active substances in the Cerebronorm® preparation. [ABSTRACT FROM AUTHOR]

Context: Monochoria vaginalis and Monochoria hastata belonging to Pontederiaceae are edible aquatic herbs commonly used by ethnic communities of India for treating various afflictions. Objective: The main objective of the study is to propose a simple and a rapid bioautographic fingerprinting profile using high-performance thin-layer chromatography (HPTLC) with gradient elution for screening the phytochemicals for the antioxidant property. Quantification of stigmasterol is carried in selected parts of Monochoria genus. Materials and Methods: Stigmasterol content of the three different parts of the species were quantified and validated by HPLTC. Fingerprint analysis was carried out using HPTLC-automated multiple development 2 (HPTLC-AMD2)-based gradient elution technique. Bioautography was done using 1-diphenyl-2-picrylhydrazyl (DPPH) solution to check the antioxidant property. Phytochemicals such as phenols, flavonoids, sterols, and saponins were estimated using 96-well plate and antioxidant potential were confirmed by DPPH, hydroxyl and nitric oxide scavenging activity. Results: The developed HPTLC-AMD2 method showed clear separations resulting in sharp, intense peaks. Phytoconstituents were determined for the first time in the Monochoria species. The results indicate that both species are rich in various bioactive contents with potent antioxidant potential. Stigmasterol was found to be present in all the selected parts with varying concentration. Conclusion: This study reveals that Monochoria species are rich in phytoconstituents with potent antioxidant activity and the developed method is efficient, simple, rapid, and reliable for separating the phytoconstituents of Monochoria providing a passport data of extracts. A positive, significant linear relationship between antioxidant activity and total phenol content and total flavonoid content showed that phenolic compounds and flavonoids were the dominant antioxidant components present in the extracts. [ABSTRACT FROM AUTHOR]

A simple and rapid ultra - high performance liquid chromatographic (UHPLC) method for the separation and determination of oxcarbazepine and its related substances in tablets, was developed. Chromatographic separation of oxcarbazepine from its related substances (degradation and by-products) was achieved on a reversed phase C18 column (Pinnacle DB C18, RESTEK, 100 x 2.1 mm, 1.9 μm particle size) using gradient program with water (as mobile phase A) and acetonitrile (as mobile phase B), at a flow rate 0.5 mL min-1 and UV detection at 254 nm. The column temperature was 30°C.The method has good selectivity towards oxcarbazepine and its related substances. The accuracy of the method for oxcarbazepine assay, expressed as mean recovery was 101.8 %, and of the method for quantification of degradation products was 95.9 % - 103.3 %. Limit of quantification for oxcarbazepine and its degradation products ranged from 0.60 μg mL-1 to 1.30 μg mL-1. The linearity range for oxcarbazepine assay was from 2.4 to 3.60 mg mL-1 (R2=0.999). Mean value for oxcarbazepine assay from the tablets was 299.92 mg (label claim 300 mg). The method can be used for routine analysis and the quality control of oxcarbazepine drug substance and its formulated products.

Objective: The aim of the present study is to develop a simple and precise HPLC method for simultaneous determination of thiocolchicoside, aceclofenac and related impurities in a tablet formulation and validate as per ICH guidelines. The aim of study extends to perform forced degradation study to trace the degradation pathways of potential degradant impurities. Materials and Methods: The separation was achieved on a 4.6 mm × 100 mm, 3 μm C 18 column at 40°C with the mobile phase containing 0.1 M ammonium acetate buffer and methanol in a gradient mode at a flow rate of 1.0 mL min−1 . The UV detection was carried out at 257 nm. Results: Acelofenac, thiocolchicoside and their related compounds were well separated from each other with good resolution and symmetry factor without interference of excipients. The method for assay was linear in the range of 10-200 μg mL−1 for aceclofenac and 0.4 to 8 μg mL−1 for thiocolchicoside. Conclusion: The method was validated according to ICH guidelines and the acceptance criteria for accuracy, precision, linearity, specificity, robustness, ruggedness and system suitability were met in all cases. The method was highly specific, as two related compounds of thiocolchicoside and nine related compounds of aceclofenac were well separated from each other. Stress study ensured the specificity of the method as the unknown degradation products formed during stress studies did not interfere with the determination of thiocolchicoside and aceclofenac, thus proving the stability indicating capacity of the method.

A methodology was implemented for purifying peptides in one chromatographic run via solid-phase extraction (SPE), reverse phase mode (RP), and gradient elution, obtaining high-purity products with good yields. Crude peptides were analyzed by reverse phase high performance liquid chromatography and a new mathematical model based on its retention time was developed in order to predict the percentage of organic modifier in which the peptide will elute in RP-SPE. This information was used for designing the elution program of each molecule. It was possible to purify peptides with different physicochemical properties, showing that this method is versatile and requires low solvent consumption, making it the least polluting one. Reverse phase-SPE can easily be routinely implemented. It is an alternative to enrich and purified synthetic or natural molecules.

A multi-layer artificial neural network (ANN) was used to model the retention behavior of 16 o-phthalaldehyde derivatives of amino acids in reversed-phase liquid chromatography under application of various gradient elution modes. The retention data, taken from literature, were collected in acetonitrile⁻water eluents under application of linear organic modifier gradients ( gradients), pH gradients, or double pH/ gradients. At first, retention data collected in  gradients and pH gradients were modeled separately, while these were successively combined in one dataset and fitted simultaneously. Specific ANN-based models were generated by combining the descriptors of the gradient profiles with 16 inputs representing the amino acids and providing the retention time of these solutes as the response. Categorical “bit-string„ descriptors were adopted to identify the solutes, which allowed simultaneously modeling the retention times of all 16 target amino acids. The ANN-based models tested on external gradients provided mean errors for the predicted retention times of 1.1% ( gradients), 1.4% (pH gradients), 2.5% (combined  and pH gradients), and 2.5% (double pH/ gradients). The accuracy of ANN prediction was better than that previously obtained by fitting of the same data with retention models based on the solution of the fundamental equation of gradient elution.