Analyte Peak Research Articles

Some Aspects of the Use of Carbon Dioxide as a Carrier and Makeup Gas in GC–FID Analysis

The paper presents the possibility of using carbon dioxide as a carrier gas in capillary gas chromatography (with a stationary liquid phase) to analyze semi-volatile compounds (boiling points of up to 400 °C). Based on the experiments carried out for compounds from the group of organochlorine pesticides (OCPs), organophosphate pesticides (OPPs), polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), the maximum volumetric flow rate (2.4 mL/min for CO2) was determined, enabling the correct separation of the tested standard mixtures (except for two compounds from the OCP group: 4,4′-DDD and Endrin aldehyde and two other pairs of compounds with Rs slightly less than 1.5). Compared to using helium as a carrier gas (and makeup), carbon dioxide produces wider (about 1.6 times) and lower (about 1.8 times) peaks of analytes; these values can vary depending on the separation efficiency of the column. Carbon dioxide can also be effectively used as a makeup gas for the FID detector. The signal increase is comparable to that obtained with helium used as makeup (on average 40–50% depending on the carrier gas). When high sensitivity and high resolution are not required, CO2 can be an alternative carrier and makeup gas to helium under the same flow conditions. The paper also describes practical aspects related to the implementation of CO2 as a carrier and makeup gas in GC.

Liquid Chromatography Column Screening for the Analysis of Corrosion Inhibitor Molecules Using Derringer Desirability Functions.

Corrosion inhibitors (CIs) are extensively employed in the oil and gas industry, yet their analysis remains a challenge. To develop a suitable liquid chromatography method for a wide array of CIs, a column screening was conducted. Nine different chromatographic conditions were tested across eight RPLC and mixed-mode columns (Accucore C18, CORTECS Shield RP18, Acquity HSS T3, Acquity Premier HSS T3, Accucore 150-C4, Accucore PFP, Synergi Polar RP, and Acclaim WCX-1). Seven model mixtures representative of CIs, which included quaternary ammoniums, imidazolines, and phosphoric esters, were considered to probe the columns. Each column exhibited unique analytical performances, peak shape, and separation profiles. To find a compromise to analyze all the mixtures with one method, Derringer desirability functions were used. Shielding of residual silanols proved to be a critical factor. The trifunctional grafting of the Acquity HSS T3 columns appeared to be a promising strategy to minimize residual silanol effects. However, it was the Premier technology, which protects the column's inner walls and frits against parasitic adsorption, which delivered the best overall results. Based on the desirability study, the Acquity Premier HSS T3 column was selected and the gradient was optimized, which enabled the separation of the molecules present in the model mixtures.

Concurrent estimation of Pregabalin and Etoricoxib by new stability indicating RP-UPLC approach: application in assay of commercial tablets

The present research aims to establish new stability indicating RP-UPLC method for concurrently estimating Pregabalin and Etoricoxib in blended powder and their combined tablet formulation. The effective separation of Pregabalin and Etoricoxib achieved with HSS column C18 (150 × 2.1 mm, 1.8 µm), 0.1% orthophosphoric acid: acetonitrile in 65:35 v/v) at a flow rate of 0.3 mL/min, and isocratic elution at 228 nm. The elution of PRB and ETB was noticed at 1.56 and 2.01 min, with good resolution and system suitability with the developed approach. PRB and ETB have shown linear responses from 18.75 to 112.5 µg/mL and 15 to 90 µg/mL, respectively. The range of the % RSD for intraday and inter-day precision was 0.33 to 0.81. The LOD and LOQ of Pregabalin and Etoricoxib were computed to be 0.07 µg/mL, 0.21 µg/mL, and 0.01 µg/mL, 0.04 µg/mL, respectively, by standard deviation method. The validation method was carried out using ICH standards. The stability- indicating the feature of the method was confirmed by the forced degradation studies where degradants generated by stress testing were clearly distinguished from the peaks of analytes. The shorter elution period and superior sensitivity of both analytes with this method are appropriate for regular analysis of Pregabalin and Etoricoxib.Graphical

An AI-assisted microfluidic paper-based multiplexed surface-enhanced raman scattering (SERS) biosensor with electrophoretic removal and electrical modulation for accurate acute myocardial infarction (AMI) diagnosis and prognosis

SERS detects single molecules with exceptional sensitivity. To counter the issue of selectivity faced by point-of-care, herein, an externally applied electric field that allows electrical modulation and electromigrates unbound SERS tags without multiple washing steps is successfully developed and demonstrated to improve the biosensor's selectivity and sensitivity in multiplexed detection of cTnI, HDL, and LDL in human serum at a low LoD. Ultra-sensitive detectors can detect signals from non-specifically absorbed species, and these species can cover up overlapping analyte peaks, amplifying the effect of non-specific binding. Even though antifouling molecules can prevent non-specific adsorption at the sensor interface, this approach does not completely eliminate it. Our significant findings show that an electrically regulated device can electromigrate non-specifically bound species without cross-reacting with endogenous albumin proteins. Stability, repeatability, and reproducibility were good, with an RSD of 10%. Artificial intelligence was employed to interpret and analyze high-dimensional fingerprint SERS spectra using feature selection and dimensionality reduction for accurate acute myocardial infarction diagnosis and prognosis. These machine learning methods allow quantification of cTnI, HDL, and LDL biomarkers with low RMSE. Machine learning classifiers showed strong AUROC values of 0.950 ± 0.111 and 0.884 ± 0.139 for early and recurrent AMI detection, respectively. A high negative predictive value (NPV) of ≥99% indicates an effective early AMI rule-out. In short, this work demonstrated that a simple, low-cost, electrophoretic modulated biosensor with machine learning can diagnose, rule out, and predict recurring AMI.

Concurrent Estimation of Pregabalin and Etoricoxib by New Stability-Indicating RP-UPLC Approach - Application in Assay of Commercial Tablets

Background: The study emphasizes establishing a stability-indicating RP-UPLC method for concurrent estimation of pregabalin and etoricoxib in combined pharmaceutical formulations, confirming effective separation, sensitivity, and repeatability, validated according to ICH guidelines. Objective: The present research study aims to establish a new stability-indicating RP-UPLC method for concurrently estimating pregabalin and etoricoxib in blended powder and their combined tablet formulation with less run time, high sensitivity, and specificity. Methods: The effective separation of pregabalin and etoricoxib was achieved with HSS column C18 (150x2.1mm,1.8μm), 0.1% orthophosphoric acid:acetonitrile (65:35 v/v) at a flow rate of 0.3mL/min, and isocratic elution at 228nm. The elution of PRB and ETB was noticed at 1.56 and 2.01 minutes, with good resolution and system suitability with the developed approach. Results: Pregabalin and etoricoxib have shown linear responses from 18.75 to 112.5μg/mL and 15 to 90μg/mL, respectively. The range of the % RSD for intraday and inter-day precision was 0.33 to 0.81. The LOD and LOQ of pregabalin and etoricoxib were computed to be 0.07 μg/mL and 0.21 μg/mL, and 0.01μg/mL and 0.04 μg/mL, respectively, by standard deviation method. The validation method was carried out using ICH standards. The stability-indicating feature of the method was confirmed by the forced degradation studies where degradants generated by stress testing were clearly distinguished from the peaks of analytes. Conclusion: The shorter elution period and superior sensitivity of both analytes with this method have been found to be appropriate for regular analysis of pregabalin and etoricoxib.

Flow injection analysis of hydroquinone using amperometric sensor modified with nanomaterials

Modified carbon paste electrodes (CPE) have been widely used in diverse applications, such as environmental, food, and pharmaceutical analysis, among other applications. In this work, the development of an amperometric sensor modified with functionalized multi-walled carbon nanotubes (CNT) and HY-type zeolite (ZEO) is reported for the analysis of hydroquinone (HQ) in pharmaceuticals. Practical and theoretical studies were carried out regarding the modifiers used. No chemical bond was observed between the modifiers and the analyte, such as HQ and CNT. It is likely that dynamic interactions governed by surface adsorption phenomena, rather than covalent bonding, are occurring. Furthermore, the contribution of modifiers to the improvement of the analytical peak current was elucidated through characterization studies, such as electrochemical impedance spectroscopy. These experiments revealed a 147-fold decrease in charge transfer resistance when CPE was modified with ZEO and CNT, which is likely due to an enhancement in electron transfer. A sample rate of 100 injections per hour, and the limit of quantification (LQ) of 8.99 x 10-7 mol/L were achieved during the oxidation of HQ using amperometry in association with flow injection analysis (FIA). The sensitivity of the proposed sensor was of 0.0186 mol/L cm−2. Determinations of pharmaceutical samples were in good agreement with results obtained by High Performance Liquid Chromatography.

Temperature dependent stochastic dynamics mass spectrometric analysis of configurationally locked polyenes

This paper derived relation between mass spectrometric variable intensity of analyte peaks and three-dimensional molecular structures of ions toward temperature utilising innovative stochastic dynamics equations, which provide exact analyte quantification and 3D structural analysis and are attractive formulas for modelling of mass spectrometric phenomena. The same equations are opened to develop new relations accounting for temperature; thus, providing argumentation about temperature dependent variables. High-temperature measurement of vapours are important tool, amongst others and use the Arrhenius’s plot. However, there is a variation between experimental and theoretical linear correlation toward temperature; thus, highlighting soft ionisation methods showing significant standard deviations. It could be explained with temperature perturbation of charge values. Descriptive models, so far, provide semi-quantification. This study, first shows validity of new functional model. Straightforwardly, its empirical proof is obtained determining 3D structurally protomers and isotopomers of configurationally locked polyenes via ultra-high resolution electrospray ionization and atmospheric pressure chemical ionization mass spectrometry within the temperature range T=300-450°C. There are used high accuracy quantum chemical static methods, molecular dynamics and chemometrics. There are excellent method performances (|r|=0.99978). The tool could be regarded as an actually honest alternative of available theoretical models.

Systematic Method Development and Validation of Paclitaxel and Tamoxifen by RP-HPLC for Simultaneous Estimation in Nanoformulations

Background: Paclitaxel (PTX) is well known anticancer drug used for treatment of a wide range of cancers. Tamoxifen (TMX) is a gold-standard drug for the treatment of breast cancer. They show synergistic action against breast cancer. Quantitative analytical methods are still not available for simultaneous quantification of these drugs. So for the first time, we developed and validated a new systematic analytical technique for simultaneous estimation of PTX and TMX in nanoformulations. Objective: Systematic method development and validation of Paclitaxel and Tamoxifen by RP-HPLC for simultaneous estimation in nanoformulations. Methods: PTX and TMX were successfully separated and quantified using RP-HPLC. The detection was done based on the isobastic point of both drugs. Thermo Scientific Company's C18 column, measuring 2.5 cm × 4.5 cm x 5 µm, was utilized for separation. A 50:50 (vol/vol) ratio of ACN: Phosphate buffer solution (pH 3.0) was employed as the mobile phase, with a flow rate of 1 mL/minute. The detection was done at 235nm. The method was developed and validated as per the criteria. The developed method was then evaluated for applicability by detecting both analytes in prepared SLN and LPHNPs. Results: The well-resolved separate peaks of both analytes were found and distinct RT for PTX and TMX. The linear relationship of both the analytes against concentration was found over the concentration range of 0.25-9 µg/mL. The PTX RT was 10.358 minutes and that of TMX was 12.57 minutes. Every criterion for method validation fell within the acceptable range. The method is precise with inter-day and intra-day precision and shows a %RSD of < 2%.

Electrochemical sensing platform for anticonvulsant drug carbamazepine detection based on graphitic carbon nitride and tetrabutylammonium chloride ionic liquid

The development of a rapid and straightforward electrochemical approach for the quantification of the anticonvulsant drug carbamazepine (CBZ) is herein presented. Carbon paste electrode (CPE) was bulk modified with a type of two-dimensional conjugated polymer, i.e., graphitic carbon nitride (g-C3N4), and additionally with an ionic liquid tetrabutylammonium chloride (TBACl) to obtain advanced electrochemical sensor for CBZ. Synthesized g-C3N4 material was structurally and morphologically characterized by Raman spectroscopic, FTIR, and SEM/EDX methods. CV experiments showed that the resulting electrode (TBACl-g-C3N4-CPE) has an improved electrochemical response compared to unmodified CPE and g-C3N4-CPE due to the synergistic effect of electrode modifiers, as well as that the CBZ oxidation process is irreversible and diffusion-controlled. After optimization steps concerning the amount of electrode modifiers and the selection of pH of the supporting electrolyte, the analytical performance of TBACl-g-C3N4-CPE was investigated by direct anodic square-wave voltammetry (SWV). The most intensive peak of the target analyte was obtained in Britton-Robinson buffer solution at pH 7.0, whereby the developed SWV method was characterized by a linear concentration range of CBZ from 0.42 to 9.31 µmoL L−1, limit of detection (LOD) of 0.13 µmoL L−1, and relative standard deviation lower than 3 %. The interference study showed that TBACl-g-C3N4-CPE exhibits adequate selectivity for CBZ in the presence of ions/compounds commonly present in the urine matrix. The developed sensor was utilized to determine CBZ in pharmaceuticals and spiked human urine sample with excellent recovery and reproducibility, indicating a good application capability of TBACl-g-C3N4-CPE for monitoring CBZ in different matrices.

A Quality by Design (QbD) driven gradient high performance liquid chromatography method development for the simultaneous estimation of dasatinib and nilotinib in lipid nanocarriers

Tyrosine kinase inhibitors (TKIs) are effective as a targeted treatment for chronic myeloid leukemia (CML), which can selectively suppress BCR-ABL1 kinase activity. CML therapy with TKIs combination has been supported by in-vitro, in-vivo, and patient-based data where the nilotinib-dasatinib co-administration has exerted superior anticancer efficacy with greater cellular uptake, less resistance to chemotherapy, and no additive adverse events encountered. Therefore, it is essential to develop a suitable analytical method for the simultaneous estimation of these drugs in the developed novel lipid nanocarriers like liposomes. Design of Experiment (DoE) has been implemented as a tool of QbD to systematically investigate the relation between the HPLC method attributes and analytical responses, i.e., chromatographic detection, quantification, and peak properties for dasatinib and nilotinib. An Ishikawa diagram is constructed to delineate possible influencing variables to the analytical performances. Afterward, 4 factors 2 level full factorial design (FFD) was employed to model and identify the main effects and interaction effects between the factors selected after the initial risk assessment. The suggested design space for optimized chromatographic conditions by QbD analysis is linear within the selected range of drug concentrations, accurate and precise, sensitive, and robust according to the ICH guidelines. The optimal method is comprised of a 1 mL/min flow rate of mobile phase (ACN and 20 mM KH2PO4 of pH 7.00) in gradient mode at 25 °C column temperature for 20 μL sample injection volume and detection wavelength fixed at 297 nm. Most importantly, this novel HPLC method is simple and selective enough to evaluate dasatinib and nilotinib content in the lipid nanocarriers.

Pillar Array Mixer for Postcolumn Derivatization Integrated into Liquid Chromatography-Based Microfluidic Device.

The chemical derivatization of target analytes can enhance the sensitivity and selectivity of separation-based methods for metabolite analysis using microfluidic devices. However, the development of chromatography-based microfluidic devices with integrated derivatization units is challenging. In this study, a novel derivatization unit with a pillar array (PA)-based mixing channel was developed for postcolumn derivatization during on-chip liquid chromatography (LC). The PA mixer enhanced mixing between the derivatization reagents and analytes in the transverse direction, while preventing analyte dispersion in the flow direction. After the concept was confirmed using computational fluid dynamics analysis, microfluidic devices with a LC column and PA mixer were fabricated on a 20 × 20 mm silicon plate. Fluid experiments were performed using a PA mixer with a pillar size of 5 or 10 μm or a hollow-channel mixer, which revealed that the PA mixer enhanced transverse mixing without increasing the width of the analyte peak. Moreover, the developed device enabled the analysis of three amino acids within 40 s by separation via hydrophilic interaction chromatography followed by postcolumn fluorogenic derivatization with naphthalene-2,3-dicarboxaldehyde and fluorescence detection. Our results demonstrate the potential of integrated derivatization units for the development of micrototal analysis systems for use in bioanalysis.

Trace level Quantification of N-Nitroso Safinamide: A Genotoxic Impurity in Safinamide Mesylate Using ESI-MS/MS

This study presents a novel, sensitive and highly reliable liquid chromatography-tandem mass spectrometry (LC-MS/MS) methodology for the determination of N-Nitroso Safinamide, a genotoxic impurity in Safinamide mesylate. The optimized chromatographic conditions utilized Poroshell HPH-C18 (150 x 4.6 mm, 2.7 µm) and Ghost Buster columns with a flow rate of 0.8 ml/min and a column temperature of 40 °C. The mobile phase consisted of formic acid and methanol. Mass spectrophotometric analysis employed the Agilent Jet Stream Electrospray Ionization (AJS ESI) mode with a capillary voltage of 3500 V and a nitrogen gas flow rate of 12 L/min at 350 °C, while Multiple Reaction Monitoring (MRM) mode was used for scanning. Rigorous validation demonstrated the method's reliability and robustness. Linearity experiments showed a strong correlation coefficient of 0.999 between analyte concentration and peak area response. The method exhibited low limits of detection (LOD) and quantification (LOQ) of 0.00593 ppm and 0.01797 ppm, respectively, enabling accurate detection and quantification of N-Nitroso Safinamide at low concentrations. Precision studies demonstrated good repeatability and reproducibility, with % RSD values falling within acceptable limits. Specificity evaluations confirmed the absence of interferences in blank, standard, sample, and spiked sample solutions. The method's accuracy was established through satisfactory recovery values, ranging between 70 % and 130 % in spiked samples. The developed LC-MS/MS methodology offers a highly reliable and precise approach for quantifying N-Nitroso Safinamide in Safinamide mesylate.

Stability Indicating Assay of Empaglifozin and Metformin

The newly developed stability‐indicating RP-HPLC method is simple, robust and validated on the basis of ICH guidelines for the simultaneous determination of Empaglifozin and Metformin hydrochloride in the tablet. Retention times under the optimized condition were 2.104 and 4.0822min for Metformin and Empaglifozin respectively. This research article indicates best separation of Empaglifozin and Metformin from their degradation products. Separation was achieved on a Sunniest ECO C18, 250mm x 4.6mm, 5µm analytical column at wavelength of 225nm, using a mobile buffer (pH-1.8): acetonitrile (50:50) in an isocratic elution mode at a flow rate of 1.2ml/min, Injection volume: 10µl and run time 6mins. The %RSDs for the precision studies was less than 1.5% for both drugs. The %RSD was less than 1.5% in all the parameters of robustness. The forced degradation studies were carried by using 0.1N HCl, 0.1 N NaOH and % 3 H2O2 and there is only % 7.2 degradation in an acidic medium for emplaglifozin and 11.63% for Meformin where as there was nothing degradation in basic and oxidative method. The analyte peaks were clearly separated from the degradant peaks in forced degradation studies. So this method is a fast, sensitive, robust and efficient high performance liquid chromatographic method for the concurrent determination of Metformin and Empaglifozin in their combination, and thus this method can be effectively employed for routine quality control works.

VOC-based detection of prostate cancer using an electronic nose and ion mobility spectrometry: A novel urine-based approach.

Many diseases leave behind specific metabolites which can be detected from breath and urine as volatile organic compounds (VOC). Our group previously described VOC-based methods for the detection of bladder cancer and urinary tract infections. This study investigated whether prostate cancer can be diagnosed from VOCs in urine headspace. For this pilot study, mid-stream urine samples were collected from 56 patients with histologically confirmed prostate cancer. A control group was formed with 53 healthy male volunteers matched for age who had recently undergone a negative screening by prostate-specific antigen (PSA) and digital rectal exam. Headspace measurements were performed with the electronic nose Cyranose 320TM. Statistical comparison was performed using principal component analysis, calculating Mahalanobis distance, and linear discriminant analysis. Further measurements were carried out with ion mobility spectrometry (IMS) to compare detection accuracy and to identify potential individual analytes. Bonferroni correction was applied for multiple testing. The electronic nose yielded a sensitivity of 77% and specificity of 62%. Mahalanobis distance was 0.964, which is indicative of limited group separation. IMS identified a total of 38 individual analytical peaks, two of which showed significant differences between groups (p < 0.05). To discriminate between tumor and controls, a decision tree with nine steps was generated. This model led to a sensitivity of 98% and specificity of 100%. VOC-based detection of prostate cancer seems feasible in principle. While the first results with an electronic nose show some limitations, the approach can compete with other urine-based marker systems. However, it seems less reliable than PSA testing. IMS is more accurate than the electronic nose with promising sensitivity and specificity, which warrants further research. The individual relevant metabolites identified by IMS should further be characterized using gas chromatography/mass spectrometry to facilitate potential targeted rapid testing.

Voltammetric behavior of solifenacin succinate on gold, glassy carbon and boron-doped diamond electrodes: Stability testing and determination

The anticholinergic drug, solifenacin, is frequently used for the treatment of the urological tract for urinary incontinence, and urinary frequency. The development of reliable and effective solifenacin electrochemical sensors is of great importance for the pharmaceutical industry and clinical practice. In this work, the electrochemical behavior of solifenacin succinate (SOL) was studied using three different working electrodes: gold (Au), glassy carbon (GCE) and boron-doped diamond electrode (BDDE). The cyclic voltammetric (CV) measurements performed in 0.05 M NaHCO3 indicated that the SOL oxidation process is irreversible and diffusion-controlled at all investigated working electrodes. Afterwards, the testing of SOL electrochemical stability and the possibility of its electrochemical degradation was performed at the Au electrode by the cycling of the potential during 3 h and continuously to 6 h. It was shown that the SOL was electrochemically transformed into another electroactive species and its degradation was excluded. For electroanalytical application, the anodically pretreated BDDE (+2.0 V; 30 s) was selected. Various experimental parameters were optimized, including the pH of the aqueous Britton-Robinson (B-R) buffer as a supporting electrolyte (from pH 2.0 to 11.98) and the most intensive peak of the target analyte was at pH 11.0, so this pH value was chosen as the optimum for further measurements. Based on the correlation of the SOL peak intensity and different concentrations, the developed differential pulse voltammetric (DPV) method was characterized by a linear concentration range from 0.041 to 2.50 µM, with a correlation coefficient of 0.999, and a relative standard deviation of 0.3 %. Taking into account the sensitivity of the developed DPV method towards the electrochemical oxidation of SOL, a very low detection limit of 0.012 µM in the model system was achieved. The BDDE showed adequate selectivity for SOL in the presence of the investigated interferents. The obtained results indicate that the BDDE with an optimized DPV method could be applied for the trace-level electroanalytical determination of SOL in human urine sample with excellent recovery and reproducibility.

SSSMuG: Same Sample Sequential Multi-Glycomics.

The mammalian glycome is structurally complex and diverse, composed of many glycan classes such as N- and O-linked glycans, glycosaminoglycans (GAGs), glycosphingolipids (GSLs), and other distinct glycan features such as polysialic acids (PolySia), sulfation, and proteoglycan attachment stubs. Various methods are used to analyze these different components of the glycome, but they require prefractionated/partitioned samples to target each glycan class individually. To address this need for a knowledge of the relationship between the different glycan components of a biological system, we developed a sequential release workflow for analysis of multiple conjugated glycan classes (PolySia, GAGs, GSL glycans, N-glycans, and O-glycans) from the same tissue lysate, termed SSSMuG─Same Sample Sequential Multi-Glycomics. With this sequential glycan release approach, five glycan classes were characterized (or four glycan classes plus proteomics) using enzymatic or chemical release from a single sample immobilized on a polyvinylidene difluoride membrane. The various released glycan classes were then analyzed by HPLC and MS techniques using commonly available analytical setups. Compared to single glycan class release approaches, SSSMuG was able to identify more glycans and more proteins with higher-intensity analytical peaks and provide a better comparative normalization of the different glycan classes of the complex glycome. To this end, the SSSMuG technology workflow will be a foundation for a paradigm shift in the field, transforming glycoanalytics and facilitating the push toward multiglycomics and systems glycobiology.

Electric field-enhanced backscatter interferometry detection for capillary electrophoresis

Backscatter interferometry (BSI) is a refractive index (RI) detection method that is easily integrated with capillary electrophoresis (CE) and is capable of detecting species ranging from inorganic ions to proteins without additional labels or contrast agents. The BSI signal changes linearly with the square of the separation voltage which has been used to quantify sample injection, but has not been explored as a potential signal enhancement mechanism in CE. Here we develop a mathematical model that predicts a signal enhancement at high field strengths, where the BSI signal is dominated by the voltage dependent mechanism. This is confirmed in both simulation and experiment, which show that the analyte peak area grows linearly with separation voltage at high field strengths. This effect can be exploited by adjusting the background electrolyte (BGE) to increase the conductivity difference between the BGE and analyte zones, which is shown to improve BSI performance. We also show that this approach has utility in small bore capillaries where larger separation fields can be applied before excess Joule heating degrades the separation. Unlike other optical detection methods that generally degrade as the optical pathlength is reduced, the BSI signal-to-noise can improve in small bore capillaries as the larger separation fields enhance the signal.

Multipurpose new gas chromatography column based on pillararenes functionalized with imidazolium ionic liquids

BackgroundGas chromatography is worldwide recognized as one of the most important analytical techniques, due to its high versatility and reliability. The heart of a gas chromatograph is the column, that allows analyte peak separations and, consequently, accurate qualitative and qualitative analyses. New and more efficient columns are always requested to satisfy new and challenging analytical needs. ResultsIn this work, imidazolium ionic liquids functionalized pillar [5] arenes have been used for the first time as gas chromatographic stationary phases, considering their highly symmetric pillar-shaped architecture with cavities rich in π-electrons. Four imidazolium ionic liquids functionalized pillar [5] arenes have been tested as stationary phases with numerous analytes and isomers. In particular, one of these showed superior performances if compared to commercial columns, enabling challenging isomeric separations of halogenated benzenes, aromatic aldehydes, and aromatic anilines. Significance and noveltyTo our knowledge, this is the first report on the use of the ionic liquid P[n]A as a stationary phase in chromatography, either in GC or liquid chromatography (LC) separations. This work demonstrates the promising potential of ionic liquid P[n]A stationary phases for chromatographic separations.

In vitro evaluation of tropolone absorption, metabolism, and clearance

Tropolone compounds can inhibit hepatitis B virus (HBV) replication at sub-micromolar levels and are synergistic upon co-treatment with nucleos(t)ide analog drugs. However, only a few compounds within this chemotype have been screened for their pharmacological properties. Here, we chose 36 structurally diverse tropolones from six subclasses to characterize their in vitro pharmacological parameters. All compounds were more soluble in pHs that reflect the gastrointestinal tract (pH 5 and 6.5) than plasma (pH 7.4). Those compounds that had solubility limits >100 μM were tested in a passive permeability assay, and there was no general trend in the compounds' passive permeability at any pH. Twenty-nine compounds with the best absorption parameters were tested in HEK293 cells to assess potential cytotoxicity; measured toxicities were similar to those in the hepatic HepDES19 cells used for screening (R2 = 0.55). Sixteen representative compounds were tested against five major CYP450 isoforms and there was no substantial inhibition by any compound against any of the enzymes tested (<50%). The t1/2 values of 15 compounds were determined in the microsome stability assay and 12 compounds were evaluated in plasma protein binding assays to assess factors affecting their rate of clearance. All compounds with detectable analyte peaks had t1/2 > 30 min, and while 4 of 12 had statistically significant decreased potency in conditions with increased albumin concentrations, only one compound's potency was biologically significant. These data indicate that the tropolones have pharmacological characteristics that reflect approved drugs and inform future structure activity relationships during drug design.

Determination of Nifedipine by Validated RP-HPLC Method in Bulk and Pharmaceutical Dosage Form

The present paper deals with the development and validation of reverse phase HPLC method for the determination of Nifedipine on Nucleosil 100, 5 μm, C8, 250 x 4.0 mm column. A mobile phase consisting of 40 ml 2-propanol: 60 ml phosphoric acid 0.85% was employed in this study. The flow rate was kept at 0.8 ml/min and the injection volume was 10 µl. The separation was performed at 40°C. Eluents were monitored by UV detector set at 237 nm. The developed method was statistically validated for the linearity, precision, robustness, specificity and solution stability. The specificity of the method was ascertained by force degradation studies by acid and alkali hydrolysis, oxidation, heat and photo degradation. The degraded products were well resolved from the analyte peak with significant differences in their retention time values.