Simple Linear Gradient Research Articles

Analysis of drug-impregnated paper from English prisons between 2018 and 2020

Drug misuse is a global concern that has become increasingly widespread across all levels of society. Its use in prisons contributes to greater disruption and violence, as well as having a negative influence on prisoner safety, rehabilitation, and recovery. Novel psychoactive substances (NPS) in the forms of impregnated papers posted to prisoners are of a particular concern in prison settings where they are commonly used by vaping. This study was conducted to develop a spectral database and a qualitative method to identify the variety of emerging NPS impregnated onto paper samples sent to prison inmates. The aim was to help rapid detection and identification and to demonstrate that these findings can be a good indicator of the drug prevalence and trends in prisons. In total, 1250 non-judicial paper samples seized from twelve English prisons between 2018 and 2020 were analysed to determine the NPSs circulating in the prisons. From each piece of paper, from different locations, believed to be impregnated with drugs, approximately 1 cm 2 of paper was cut. Samples were placed into separate 1.5 mL Eppendorf tubes with 1 mL of 50% (v/v) methanol in LCMS-grade water. Extracts were prepared from the samples by vortex-mixing (30 min). A mobile phase blank was injected between the analysis of each extract to check for carryover. Extracts were screened using an Agilent Technologies 1290 Infinity II - 6545 Q-TOF LC/MS instrument with electrospray ionization in positive ion mode. It uses an Agilent Eclipse Plus C18 1.8 mm 2.1 × 100 mm column, maintained at 40 °C. Drug separation was performed over a total of 13 min using a simple linear gradient of water (A), and methanol (B), both contained 0.01% (v/v) formic acid in 5 mmol/L ammonium formate, at a flow rate of 400 μL/min. Sample injection volume was 0.2 μL. The research findings showed that SCRA was the most prevalent drug group detected in drug-impregnated paper seizures in English prisons between 2018 and 2020 and followed by Class A drugs and Class B drugs. SCRAs had higher prevalence in male prisons whereas female prisons presented a higher prevalence of Class A drugs. Furthermore, male prisons with lower security level (category C) were appeared to have a higher prevalence of Class B, Class C and abused prescription drugs compared to category B prisons, which had a higher prevalence of nicotine. Associations between drug group and sex, prison category and geographical locations were statistically analysed by Pearson chi-square test using Minitab software. The outcomes of this study have provided new information regarding drug use in prison. These findings may be significant as police information and could be utilised to aid drug policymakers in prisons, particularly in the development of treatment plans addressing the most commonly misused drugs in each prison. This analysis would help in the identification of drug smuggling ways into jails, enables prison staff to pay more attention on these sites.

MODELLING THE CHLOROPHYLL-A CONCENTRATION OF LAGUNA LAKE USING HIMAWARI-8 SATELLITE IMAGERY AND MACHINE LEARNING ALGORITHMS FOR NEAR REAL TIME MONITORING

Abstract. Recent studies have investigated the use of satellite imaging combined with machine learning for modelling the Chlorophyll-a (Chl-a) concentration of bodies of water. However, most of these studies use satellite data that lack the temporal resolution needed to monitor dynamic changes in Chl-a in productive lakes like Laguna Lake. Thus, the aim of this paper is to present the methodology for modelling the Chl-a concentration of Laguna Lake in the Philippines using satellite imaging and machine learning algorithms. The methodology uses images from the Himawari-8 satellite, which have a spatial resolution of 0.5–2 km and are taken every 10 minutes. These are converted into a GeoTIFF format, where differences in spatial resolution are resolved. Additionally, radiometric correction, resampling, and filtering of the Himawari-8 bands to exclude cloud-contaminated pixels are performed. Subsequently, various regression and gradient boosting machine learning algorithms are applied onto the train dataset and evaluated, namely: Simple Linear Regression, Ridge Regression, Lasso Regression, and Light Gradient Boosting Model (LightGBM). The results of this study show that it is indeed possible to integrate algorithms in Machine Learning in modelling the near real-time variations in Chl-a content in a body of water, specifically in the case of Laguna Lake, to an acceptable margin of error. Specifically, the regression models performed similarly with a train RMSE of 1.44 and test RMSE of 2.51 for Simple Linear Regression and 2.48 for Ridge and Lasso Regression. The linear regression models exhibited a larger degree of overfitting than the LightGBM model, which had a 2.18 train RMSE.

A Simple and Efficient Two-Dimensional High-Speed Counter-Current Chromatography Linear Gradient and Isocratic Elution Modes for the Preparative Separation of Coumarins from Roots of Toddalia asiatica (Linn.) Lam.

Toddalia asiatica (L.) Lam. (Rutaceae) has shown a broad spectrum of biological properties, such as anti-inflammatory, antioxidant, antimicrobial, anti-HIV, and anticancer properties. The present study is concerned with the separation of the main components with broad partition coefficients (KD values) from T. asiatica, using linear gradient high-speed counter-current chromatography (LGCCC) combined with an off-line two-dimensional (2D) mode. Similar to the binary gradient HPLC, the LGCCC mode is operated by the adjustment of the proportion between the mobile phase of 5:5:1:9 (v/v) (pump A) and 5:5:4.5:5.5 (v/v) (pump B) in an n-hexane/ethyl acetate/methanol/water solvent system. The off-line 2D-CCC mode was used in this study for the secondary separation of two similar KD value compounds with n-hexane/ethyl acetate/methanol/water (5:5:4:6, v/v). Notably, six coumarins, namely, tomentin (1), toddalolactone (2), 5,7,8-trimethoxycoumarin (3), mexoticin (4), isopimpinellin (5), and toddanone (6), were efficiently separated. The structures of the pure compounds were elucidated by spectral techniques and compared with the literature.

A Fast and Validated HPLC Method for Simultaneous Determination of Dopamine, Dobutamine, Phentolamine, Furosemide, and Aminophylline in Infusion Samples and Injection Formulations.

A simple, fast, and validated HPLC method was developed for the simultaneous quantization of five cardiovascular agents: dopamine (DPM), dobutamine (DBM), phentolamine (PTM), furosemide (FSM), and aminophylline (APL) either in infusion samples or in an injection dosage form. The proposed method was achieved with a 150 mm × 4.6 mm, 5.0 μm C18 column, by using a simple linear gradient. Mobile phase A was buffer (50 mM KH2PO4) and mobile Phase B was acetonitrile at a flow rate of 1.0 mL/min. The column temperature was kept at 30°C, and the injection volume was 20 μL. All analytes were separated simultaneously at a retention time (tr) of 3.93, 5.84, 7.06, 8.76, and 9.67 min for DPM, DBM, PTM, FSM, and APL, respectively, with a total run time of less than 15.0 min. The proposed method was validated according to ICH guidelines with respect to accuracy, precision, linearity, limit of detection, limit of quantitation, and robustness. Linearity was obtained over a concentration range of 12.0–240.0, 12.0–240.0, 20.0–200.0, 6.0–240.0, and 10.0–200.0 μg/mL DPM, DBM, PTM, FSM, and APL, respectively. Interday and intraday accuracy and precision data were recorded in the acceptable limits. The new method has successfully been applied for quantification of all five drugs in their injection dosage form, infusion samples, and for evaluation of the stability of investigated drugs in mixtures for endovenous use. The results of the stability study showed that mixtures of DPM, DBM, PTM, FSM, and APL in 5% glucose or 0.9% sodium chloride injection were stable for 48 hours when stored in polypropylene syringes at 25°C.

A Novel Validated Eco-friendly RP-UHPLC Method for Assay and Related Substances in Meropenem

A simple, rapid, sensitive, specific, eco-friendly and stability-indicating linear gradient liquid chromatographic method (RP-UHPLC) for simultaneous estimation of assay and its related compounds in Meropenem API samples is developed and validated. Chromatographic separation was achieved on Zorbax Eclipse plus C18, (100 x 4.6) mm, 3.5 µm RRLC short column and 10 mM potassium dihydrogen orthophosphate is used as buffer, buffer solution used as eluent A and buffer and acetonitrile combination 30: 70 v/v ratio used as eluent B and Agilent RRLC (UHPLC) system is used for analysis. The mobile phase flow rate was 1.0 ml/min, and the eluted compounds were monitored at 220 nm for related substance method and 290 nm for assay method. Excellent resolution was obtained between Meropenem and its related compounds which were eluted within 10 min. The correlation co-efficient(r) is > 0.995 for both the methods from linearity data and percentage of recovery is 98.0 to 102.0 and 80.0 to 120.0 % for assay method and for related substance method respectively. Sensitivity of the method is found to be less than 0.316 µg/ml. Peak homogeneity data for Meropenem in the chromatograms from the stressed samples were obtained by using photodiode array detector demonstrated the specificity of the method for analysis of Meropenem in presence of the degradation compounds. The performance of the method was validated according to the present ICH guidelines for specificity, limit of detection, limit of quantification, linearity, accuracy, precision, and robustness.

A simple and efficient linear gradient coupled with inner-recycling high-speed counter-current chromatography mode for the preparative separation of flavonoid glycosides from leaves of custard apple

In general, the simultaneous separation and isolation of compounds with a broad polarity range from natural products is a challenge by ordinary high-speed counter-current chromatography (HSCCC). Indeed, the complex solvent system screening methods limit the broader application of HSCCC. We describe herein a rapid and efficient linear gradient CCC (LGCCC) method that enables the separation of flavonoid glycosides with a broad range of KD values from custard apple leaves. Inner-recycling CCC (IRCCC) mode has been further applied for the separation of compounds with similar KD values. Similarly to binary gradient HPLC, the LGCCC mode is achieved by adjustment of the proportion between ethyl acetate (pump A) and n-butanol (pump B) in an ethyl acetate/n-butanol/water solvent system. Various separation factors have been investigated, including separation mode, rotation speed, flow rate, and sample loading. The IRCCC mode has been used for the secondary separation of two epimers with a simple ethyl acetate/water (1:1, v/v) solvent system. Finally, five main flavonoid glycosides have been successfully separated, namely quercetin-3-O-robinobioside (1, 4.8 mg) and rutin (2, 12.1 mg), quercetin-3-O-β-d-glucoside (3, 4.2 mg), kaempferol-3-O-robinobioside (4, 9.6 mg), and kaempferol-3-O-rutinoside (5, 24.6 mg). The purities of the separated flavonoid glycosides were over 98%, as determined by HPLC. Our study indicates that a suitable combination of LGCCC and IRCCC modes is an effective strategy for separating flavonoid glycosides from custard apple leaves. The mathematical expression of the LGCCC was deduced to illuminate the separation mechanism. It may also be applied to obtain component fractions for the further screening of active compounds from complex natural products.

Functionally Graded Materials through robotics-inspired path planning

Functional grading has recently seen renewed interest with the advancement of additive manufacturing. Unfortunately, the integrity of functional gradients in alloys tends to be compromised by the presence of brittle phases. Recently, CALPHAD-based tools have been used to generate isothermal phase diagrams that are in turn utilized to plan gradient paths that avoid these phases. However, existing frameworks rely extensively on the (limited) ability of humans to visualize and navigate high-dimensional spaces. To tackle this challenge, a Machine Learning approach was used here to map out undesirable regions as ‘obstacles’, while a path-planning algorithm, commonly used in robotics community, was utilized to identify a path in a composition space that would avoid the obstacles, while simultaneously minimizing a cost function. This framework was validated by designing and 3-D printing a functional gradient in bulk samples from 316L stainless steel to pure chromium with a multi-material direct laser deposition system. Both the planned gradient and simple linear gradient samples were fabricated and characterized in as-deposited and heat-treated states to determine local compositions, microstructure and phase constituents. The planned gradient resulted in complete elimination of the detrimental σ phase after heat treatment, demonstrating the success of the methodology.

Validated liquid chromatography coupled to tandem mass spectrometry method for simultaneous quantitation of tolvaptan and its five major metabolites in human plasma.

Tolvaptan is converted to major metabolites including three monohydroxylates (DM-4110, DM-4111 and DM-4119), an oxidate (MOP-21826) and a carboxylate (DM-4103) in humans. This study developed a simultaneous quantitative method for tolvaptan and its five major metabolites in human plasma using liquid chromatography coupled to tandem mass spectrometry. Deproteinized plasma specimens using acetonitrile were separated using a 3- μm particle size octadecylsilyl column with 250 mm length and a simple linear gradient program at a flow rate of 0.3 mL/min with a total run time of 15 min. This method was applied to the determination of plasma samples collected from 20 heart failure patients treated with 3.75-15 mg tolvaptan. No interfering peak was found in drug-free plasma specimens. The calibration curves of tolvaptan, DM-4110, DM-4111, DM-4119, MOP-21826 and DM-4103 were linear over the concentration ranges of 3.125-1000, 0.3125-100, 1.25-400, 0.625-200, 0.125-40 and 31.25-10,000 ng/mL, respectively. Their pretreatment recovery rates and matrix factors were 94.1-113.9% and 86.9-108.0%, respectively. The intra- and inter-day accuracies and imprecisions were 91.6-106.5% and 0.9-10.9%, respectively, for all analytes. The plasma concentration ranges of tolvaptan, DM-4110, DM-4111, DM-4119, MOP-21826 and DM-4103 were 9.37-280, 1.91-16.3, 3.43-88.9, 1.43-10.4, 0.160-1.01 and 40.2-1471 ng/mL, respectively, in heart failure patients. This validated method with acceptable analytical performance can be utilized for evaluating the pharmacokinetics of oral tolvaptan, including the determination of its major metabolites, in heart failure patients.

Modeling of bispecific antibody elution in mixed-mode cation-exchange chromatography.

The increasing demand for cost-efficient manufacturing of biopharmaceuticals has been the main driving force for the development of novel chromatography resins, which resulted in the development of multimodal or mixed-mode chromatographic resins. Most of them combine electrostatic and hydrophobic functionalities and are designed to deliver unique selectivity and increased binding capacities also at increased ionic strength. However, the mechanism of the protein-resin interaction in mixed-mode chromatography is still not fully understood. The performance of protein separations in mixed-mode chromatography is consequently difficult to predict. In this work, we present a model combining both salt and pH dependence to characterize and to predict protein retention in mixed-mode chromatography. The model parameters are determined based on simple linear pH gradient elution experiments at different ionic strengths and they are directly transferable for the prediction of salt-induced elution at fixed pH. Validity of the model is demonstrated for a bispecific antibody and its product-related impurities.

The pentafluorophenyl stationary phase shows a unique separation efficiency for performing fast chromatography determination of highbush blueberry anthocyanins

A high-performance liquid chromatography method using an alternative pentafluorophenyl (PFP) core-shell stationary phase has been developed and used for rapid separation of 23 anthocyanins in a highbush blueberry Bluehaven cultivar. A high efficiency of separation of anthocyanins was achieved in the core-shell column Kinetex PFP, 150×4.6mm (particle size 2.6µm) with a 5×4.6mm precolumn, using a simple linear gradient elution with a mobile phase of acetonitrile and a water solution of 2% formic acid at a flow rate of 1.0ml/min and at a temperature of 50°C. The detection wavelength was set at 520nm for detection of all anthocyanins. The homogenized blueberry sample (Bluehaven cultivar) was extracted using pure methanol with 1.3% formic acid using an ultrasound bath for 20min and then filtrated. A 5-µL sample volume was directly injected into the HPLC system. The developed method showed an efficient separation of 23 anthocyanins in a total runtime of 21min. The potential of the pentafluorophenyl phase for efficient separation was demonstrated on a wide range of anthocyanins varying in glycosylation and acylation patterns found in highbush blueberries. The fluorinated stationary phase showed an alternative and complementary separation approach providing unique aromatic and polar selectivity in comparison with common C-18 phases.

A datamining approach to identifying spatial patterns of phosphorus forms in the Stormwater Treatment Areas in the Everglades, US

The Everglades ecosystem in Florida, USA, is naturally phosphorus (P) limited, and faces threats of ecosystem change and associated losses to habitat, biodiversity, and ecosystem function if subjected to high inflows of P and other nutrients. In addition to changes in historic hydropattern, upstream agriculture (sugar cane, vegetable, citrus) and urbanization has placed the Everglades at risk due to nutrient-rich runoff. In response to this threat, the Stormwater Treatment Areas (STAs) were constructed along the northern boundary of the Everglades as engineered ecological systems designed to retain P from water flowing into the Everglades. This research investigated data collected over a period from 2002 to 2014 from the interior of the STAs using data mining and analysis techniques including (a) exploratory methods such as Principal Component Analysis to test for patterns and groupings in the data, and (b) modelling approaches to test for predictive relationships between environmental variables. The purpose of this research was to reveal and compare spatial trends and relationships between environmental variables across the various treatment cells, flow-ways, and STAs. Common spatial patterns and their drivers indicated that the flow-ways do not function along simple linear gradients; instead forming zonal patterns of P distribution that may increasingly align with the predominant flow path over time. Findings also indicate that the primary drivers of the spatial distribution of P in many of these systems relate to soil characteristics. The results suggest that coupled cycles may be a key component of these systems; i.e. the movement and transformation of P is coupled to that of nitrogen (N).

Simultaneous determination and excretion study of six flavonoids in rat after oral administration ofFructus Sophoraeextract by liquid chromatography tandem mass spectrometry

A new, sensitive, and selective high-performance liquid chromatography-tandem mass spectrometric method (HPLC-MS/MS) has been developed for the quantification of six flavonoids (sophoricoside, genistin, genistein, rutin, quercetin, and kaempferol) in rat bile and urine. The sample pretreatment was simple by liquid-liquid extraction. Sulfamethalazole was used as internal standard (IS). During method development, the effect of extraction volume, mobile phase composition, column temperature, and injection volume were varied to optimize sensitivity and achieve a run time as short as possible. Chromatographic separation was accomplished on a C18 column with a simple linear gradient elution within 9 min. Full validation of the assay was in accordance with the requirement of the validation of the method in vivo and implemented including specificity, linearity, accuracy, precision, recovery, and matrix effect. This is the first report on determination of the major flavones in rat bile and urine after oral adminis...

Solvent modulated linear pH gradient elution for the purification of conventional and bispecific antibodies: Modeling and application

Classical ion-exchange chromatography using a linear salt gradient to elute the adsorbed protein at fixed pH is the most common method to separate product-related impurities during downstream processing of biopharmaceuticals. Linear pH gradient elution provides a useful alternative by separating proteins in a linear pH gradient at fixed salt concentration. Although linear pH gradient elution provides excellent selectivity, it is rarely encountered in industrial purification processes. Here, a stoichiometric displacement model is used to characterize pH gradient elution based on simple linear gradient elution experiments. Protein retention behavior is described with respect to the pH dependencies of the characteristic binding charge and the equilibrium constant of the ion exchange reaction. Furthermore, the influence of solvent composition using PEG as a mobile phase modifier is investigated. Validity and applicability of the model are demonstrated for the purification of a conventional monoclonal antibody from soluble aggregates and for a novel bispecific antibody format containing a unique product-related impurity profile. pH step elution protocols are derived from model calculations without further optimization experiments necessary.

Computer-assisted multi-segment gradient optimization in ion chromatography

This study reports simulation and optimization of ion chromatography separations using multi-segment gradient elution. First, an analytical expression for the gradient retention factor under these complex elution profiles was derived. This allows a rapid retention time prediction calculations under different gradient conditions, during computer-assisted method development. Next, these analytical expressions were implemented in an in-house written Matlab® routine that searches for the optimal (multi-segment) gradient conditions, either via a four-segment grid search or via the recently proposed one-segment-per-component search, in which the slope is adjusted after the elution of each individual component. Evaluation of the retention time simulation and optimization approaches was performed on a mixture of 18 inorganic anions and different subsets with varying number of compounds. The two considered multi-segment gradient optimization searches resulted in similar proposed gradient profiles, and corresponding chromatograms. Moreover, the resultant chromatograms were clearly superior to the chromatograms obtained from the best simple linear gradient profiles, found via a fine grid search. The proposed approach is useful for automated method development in ion chromatography in which complex elution profiles are often used to increase the separation power.

GOAT--a simple LC-MS/MS gradient optimization tool.

Modern nano-HPLC systems are capable of extremely precise control of solvent gradients, allowing high-resolution separation of peptides. Most proteomics laboratories use a simple linear analytical gradient for nano-LC-MS/MS experiments, though recent evidence indicates that optimized non-linear gradients result in increased peptide and protein identifications from cell lysates. In concurrent work, we examined non-linear gradients for the analysis of samples fractionated at the peptide level, where the distribution of peptide retention times often varies by fraction. We hypothesized that greater coverage of these samples could be achieved using per-fraction optimized gradients. We demonstrate that the optimized gradients improve the distribution of peptides throughout the analysis. Using previous generation MS instrumentation, a considerable gain in peptide and protein identifications can be realized. With current MS platforms that have faster electronics and achieve shorter duty cycle, the improvement in identifications is smaller. Our gradient optimization method has been implemented in a simple graphical tool (GOAT) that is MS-vendor independent, does not require peptide ID input, and is freely available for non-commercial use at http://proteomics.swmed.edu/goat

A Validated Specific Stability-Indicating RP-HPLC Assay Method for Ambrisentan and Its Related Substances

A validated specific stability-indicating reverse-phase liquid chromatographic method was developed for the quantitative determination of Ambrisentan as well as its related substances in bulk samples, pharmaceutical dosage forms in the presence of degradation products and its related impurities. Forced degradation studies were performed on bulk samples of Ambrisentan as per the ICH-prescribed stress conditions using acid, base, oxidative, thermal stress and photolytic degradation to show the stability-indicating power of the LC method. Significant degradation in acidic, basic stress conditions was observed and no degradation was observed in other stress conditions. The chromatographic method was optimized using the samples generated from the forced degradation studies and the impurity-spiked solution. Good resolution between the peaks corresponds to Ambrisentan-related impurities and degradation products from the analyte were achieved on a SunFire C18 column using a mobile phase consisting of a mixture of potassium dihydrogen orthophosphate at a pH adjusted to 2.5 with ortho-phosphoric acid in water and a mixture of acetonitrile:methanol using a simple linear gradient. The detection was carried out at 225 nm. The limit of detection and the limit of quantification for the Ambrisentan and its related impurities were established. The stressed test solutions were assayed against the qualified working standard of Ambrisentan and the mass balance in each case was between 98.9 and 100.3%, indicating that the developed LC method was stability indicating. Validation of the developed LC method was carried out as per the ICH requirements. The developed method was found to be suitable to check the quality of bulk samples of Ambrisentan at the time of batch release and also during its storage (long-term and accelerated stability).

Simultaneous determination and pharmacokinetic study of six flavonoids from Fructus Sophorae extract in rat plasma by LC–MS/MS

In this study, a new liquid chromatography–tandem mass spectrometry (LC–MS/MS) method has been developed and validated for the determination of six flavonoids including sophoricoside, genistin, genistein, rutin, quercetin and kaempferol in rat plasma after oral administration of Fructus Sophorae extract using sulfamethalazole as internal standard (IS). The plasma samples were pretreated and extracted by liquid–liquid extraction. Chromatographic separation was accomplished on a C18 column with a simple linear gradient elution. The detection was accomplished by multiple-reaction monitoring (MRM) scanning after electrospray ionization (ESI) source operating in the negative ionization mode. The optimized mass transition ion pairs (m/z) for quantitation were 431.1/267.9 for sophoricoside and genistin, 269.0/133.0 for genistein, 609.2/300.0 for rutin, 301.0/150.9 for quercetin, 284.9/93.0 for kaempferol and 252.0/155.9 for IS. The total run time was 8.0min. Full validation of the assay was implemented including specificity, linearity, accuracy, precision, recovery and matrix effect. This is the first report on determination of the major flavones in rat plasma after oral administration of Fructus Sophorae extract. The results provided a meaningful basis for the clinical application of this herb.

Efficient liquid chromatographic analysis of mono-, di-, and triglycerols using silver thiolate stationary phase

We show that the characterization of mono-, di- and triglycerols can be readily accomplished by high performance liquid chromatography (HPLC) with silver(I)-mercaptopropyl modified silica gel, or silver thiolate chromatographic material (AgTCM), which can be used with evaporative light scattering detection (ELSD) or atmospheric pressure chemical ionization mass spectroscopy (APCI-MS). Separation of triglycerols varying by degrees of unsaturation and cis/trans configuration in common oil samples can be achieved using a simple linear gradient of hexane and acetone. In addition to double bonds, AgTCM also displays major selectivity for compounds with different levels of polarity, allowing for efficient separation between mono-, di- and triglycerols. In comparison to conventional reversed phase columns, AgTCM produces simple chromatograms for rapid assessment of degrees of unsaturation and the amount of trans fats in triglycerides, which are central issues to food quality determination. In comparison to previous silver-ion based HPLC separations, AgTCM–HPLC based column offers greatly enhanced stability, inertness, durability, and reproducibility allowing routine coupling of the HPLC with a mass spectrometer for detection.

Dynamic response of thin strain gradient elastic beams

The governing equation of motion of thin flexural beams is studied in the context of strain gradient elasticity. Simple linear strain gradient elastic theory with surface energy is employed. The governing beam equations with its boundary conditions are derived through a variational method. It turns out that new terms are introduced, indicating the importance of the cross-section area in bending of thin beams. Those terms are due to couple stresses, and are missing from the existing strain gradient beam theories and increase highly the stiffness of the thin beam. With the full term equation of motion we will study the flexural wave propagation and free flexural vibrations of the beam. Moreover free vibrations of gradient elastic beams are also analyzed and natural frequencies and modal shapes are obtained. Furthermore, the problem of the dynamic stability of a cantilever beam compressed by a follower force (Beck’s problem) is considered. Finally there is a discussion for the results especially comparing existing theories with the present one.

A Validated Stability-Indicating RP-HPLC Assay Method for Amsacrine and its Related Substances

A validated specific stability indicating reversed-phase high-performance liquid chromatography method was developed for the quantitative determination of Amsacrine as well as its related substances determination in bulk samples, in presence of degradation products, and its process related impurities. Forced degradation studies were performed on bulk samples of Amsacrine as per International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human use (ICH) prescribed stress conditions using acid, base, oxidative, thermal stress, and photolytic degradation to show the stability indicating power of the method. Significant degradation was observed during basic hydrolysis, slight degradation was observed in oxidative and thermal stress, and no degradation was observed in other stress conditions. The chromatographic method was optimized using the samples generated from forced degradation studies and the impurity spiked solution. Good resolution between the peaks corresponds to process-related impurities and degradation products from the analyte were achieved on Inertsil ODS column using the mobile phase consists a mixture of 1.0% triethyl amine in 20 mM potassium dihydrogen orthophosphate, with pH adjusted to 6.5, with ortho phosphoric acid in water and acetonitrile using a simple linear gradient. The detection was carried out at wavelength 248 nm. The mass balance in each case was in between 99.4% to 99.9%, indicating that the developed method was stability-indicating. Validation of the developed method was carried out as per ICH requirements. The developed method was found to be suitable to check the quality of bulk samples of Amsacrine at the time of batch release and also during its stability studies.