Terms Of Peak Height Research Articles

Protein-assisted biomimetic synthesis of nanoscale gadolinium-integrated polypyrrole for synergetic and ultrasensitive electrochemical assays of nicardipine in biological samples

Electrically conductive polymer nanomaterials signify a promising class of sensing platforms in the field of electrochemistry, but their applications as electrocatalysts are commonly limited by their poor colloidal stability in aqueous media and large particle sizes. Inspired by biomineralization approaches for integrating nanoscale materials, herein, a gadolinium (Gd)-integrated polypyrrole (PPy) electrocatalyst (namely, BSA@PPy-Gd) was successfully prepared by choosing bovine serum albumin (BSA) as a stabilizer for biomimetic mineralization and polymerization in a “one-step” manner. BSA@PPy-Gd possesses outstanding water dispersibility, nanoscale morphology, and improved electrical conductivity. The electrocatalytic competency of the electrochemical (EC) sensing platform fabricated for the sensitive detection of nicardipine (NCD) was assessed. The synergy of remarkable conductivity, superior active surface area, and electrostatic interactions stimulated by the combination of BSA with the NH group of PPy on BSA@PPy-Gd and Gd increases the fast electron transfer at the analyte-electrode junction. The fabricated EC sensor, BSA@PPy-Gd/glassy carbon electrode (GCE), exhibits a current intensity greater than that of PPy/GCE, BSA/GCE, and bare GCE in terms of peak height at a pH of 7.0 in phosphate buffer solution. The newly fabricated EC sensing platform shows excellent electrocatalytic activities for the electroreduction of NCD in terms of a low detection limit (2 nM), good sensitivity, linear dynamic detection ranges (0.01–575 μM), operational stability, and repeatability and was also tested on rat and human serum specimens.

Formation efficiency of soil organic matter from plant litter is governed by clay mineral type more than plant litter quality

Plant litters incorporated in soils are decomposed by microorganisms and partially transformed into soil organic matter (SOM) through mineral-organic association and physical protection in soil aggregates. Few studies have linked the effects of clay mineralogy and plant litter quality on controlling the formation efficiency of SOM. Using model soils, the objectives of this study were (1) to determine the effects of clay mineral type and plant litter quality on soil respiration dynamics, and formation efficiency of SOM, physical fractions, and chemical and microbial compositions of SOM at the end of a 120-day incubation; (2) to unravel SOM protection mechanisms and extents by specific clay minerals; and (3) to understand the key role of clay minerals relative to plant litter quality in controlling SOM formation. The changes in X-ray diffraction peak intensity (in terms of peak height) of the clay minerals during incubation and after H2O2 treatment provided evidence for surface adsorption by vermiculite and pore entrapment by kaolinite and illite assemblages. The SOM protection extent parameter, defined based on accumulative soil respiration dynamics, explained well the variation of the formation efficiency of mineral associated SOM (MAOM) and, to a lesser extent, that of occluded particulate SOM (oPOM) in aggregates. 90–96% of plant litter-derived C was protected in the vermiculite material and 33–60% in the pure kaolinite and illite materials. The pure vermiculite material showed the greatest fractions of MAOM and oPOM, the highest relative abundances of O–alkyls and anomeric from carbohydrates in the MAOM fraction. < 1% of plant litter-derived C was transformed into microbial biomass and residues, and fungal residues only were associated with the pure vermiculite material. These results suggested that plant litter incorporated into the soil was decomposed mainly through the ex vivo modification pathway and transformed into SOM through both mineral-organic association and physical protection pathways. Plant litter-derived C was likely protected through mineral-organic association from the earlier stages of decomposition by vermiculite than kaolinite and illite, resulting in more plant carbohydrates associated with vermiculite. Therefore, clay minerals determined SOM formation pathways and played a greater role in controlling SOM formation efficiency than plant litter quality.

Field-amplified sample injection combined with CE for the enantiodetermination of cathinones in urine samples.

This work presents a capillary electrophoresis methodology for the enantiodetermination of cathinones in urine employing a liquid-liquid extraction sample pretreatment. The cathinones were enantioseparated by adding a mixture of 8mM 2-hydroxypropyl β-cyclodextrin and 5mM β-cyclodextrin to the background electrolyte, which consists of 70mM of monosodium phosphate aqueous solution at pH 2.5. Field-amplified sample injection was used as preconcentration strategy to improve the sensitivity. We studied various parameters that affect this stacking strategy, in particular, the sample solvent and its pH, the presence or absence of a low conductivity solvent plug introduced before the sample injection, the nature and volume of this plug, and the voltage and time of the electrokinetic injection of the sample. The optimum conditions were achieved by injecting a plug of isopropanol:H2 O 50/50 at 50mbar for 5s prior to the electrokinetic injection of the sample prepared in an aqueous solution of HCl 10-6 M. The sensitivity enhancement factors were from 562 to 601 in terms of peak area and from 444 to 472 in terms of peak height. The method was validated by analyzing spiked urine samples, obtaining a linear range of 25 to 1000ng/mL and limits of detection ranging from 15 to 45ng/mL.

Application of Differential Pulse Polarography for Detection of Riboflavin from Pharmaceutical Samples and Vegetables

AbstractRiboflavin (vitamin B2) plays an important role in living processes as a precursor of coenzymes. The core structure of riboflavin with isoalloxazine ring participates in enzyme‐catalyzed electron transfer processes of many important metabolites. Several methodologies have been developed for the determination of riboflavin, but those methods have disadvantages like long analysis time, consumption of a lot of reagents, and expensiveness. Hence, to overcome these problems, the DPP technique is proposed in this study. The DPP method is used for the quantitative analysis of riboflavin. The experimental conditions are optimized to obtain the best characterized peak in terms of peak height with analytical validation of the method. The proposed methods are applied for the analysis of riboflavin in pharmaceutical samples and vegetables. The riboflavin is found to adsorb and undergo irreversible reduction reaction at the working mercury electrode.

Overload Effects in Reversed Phase Protein Separations using Capillary-Channeled Polymer Fiber Columns.

In preparative chromatography, overloading effects are a fact of life. However, peak distortion is problematic in analytical scale chromatography, especially in the case of bio-macromolecule separations. Capillary-channeled polymer fibers have been employed for fast protein separations in reversed phase, ion exchange, and hydrophobic interaction liquid chromatography. Although the primary advantage of the phase is operation at high linear velocities (~100 mm s-1 ) without van Deemter C-term limitations, the limited specific surface area (<5 m2 g-1 ) suggests that a thorough understanding of overloading effects is needed. We evaluate important factors (injected mass and volume) affecting overload in terms of peak height, width and shape (asymmetry). Overload conditions readily apparent as the peak shape changes from a Gaussian distribution to a left-triangle with slight tailing; more-or-less classical overload behavior. Three methods were used to compute column efficiency in terms of plate counts (N), including the area height, half-height, and the Dorsey-Foley approaches. The half-height method is best-suited for describing column overload, accounting for peak distortion and achieving high levels of consistency. The limiting plate count (N0 ) and the column sample loading capacity (ω0.5 ) were key metrics to characterize overall column performance. Peak capacity (P) was used to assess gradient elution separation performance. Increased flow rates and column length result in enhanced loading capacity. pH mismatch between the sample matrix and the mobile phase, a common cause of protein overload with other phases, was not responsible for distorted peak shapes unless the solvent pH is close to the pI of protein samples.

The use of the M-Vac® wet-vacuum system as a method for DNA recovery

Collecting sufficient template DNA from a crime scene sample is often challenging, especially with low quantity samples such as touch DNA (tDNA). Traditional DNA collection methods such as double swabbing have limitations, in particular when used on certain substrates which can be found at crime scenes, thus a better collection method is advantageous. Here, the effectiveness of the M-Vac® Wet-Vacuum System is evaluated as a method for DNA recovery on tiles and bricks. It was found that the M-Vac® recovered 75% more DNA than double swabbing on bricks. However, double swabbing collected significantly more DNA than the M-Vac® on tiles. Additionally, it was found that cell-free DNA is lost in the filtration step of M-Vac® collection. In terms of peak height and number of true alleles detected, no significant difference was found between the DNA profiles obtained through M-Vac® collection versus double swabbing of tDNA depositions from 12 volunteers on bricks. The results demonstrate that the M-Vac® has potential for DNA collection from porous surfaces such as bricks, but that alterations to the filter apparatus would be beneficial to increase the amount of genetic material collected for subsequent DNA profiling. These results are anticipated to be a starting point to validate the M-Vac® as a DNA collection device, providing an alternative method when DNA is present on a difficult substrate, or if traditional DNA collection methods have failed.

A high-throughput UHPLC method for the analysis of 5-nitroimidazole residues in milk based on salting-out assisted liquid-liquid extraction.

A novel salting-out assisted liquid-liquid extraction (SALLE) method has been developed for the extraction of eight 5-NDZ antibiotics from milk samples prior to their analysis by UHPLC. An exhaustive study of the parameters involved in the SALLE procedure has been carried out, optimizing the extraction solvent volume, the amount of the salt agent, and the centrifugation and vortex timing by an experimental design. After sample treatment, the obtained extract was reconstituted in the mobile phase (6:94 (v/v) acetonitrile/water containing 0.1% (v/v) of formic acid) and analyzed by the proposed UHPLC-UV method. Separation was accomplished in a C18 Zorbax Eclipse Plus (50mm×2.1mm, 1.8μm) column at 45°C within 8min. Gradient mode was considered using a mobile phase consisting of 0.1% (v/v) formic acid aqueous solution and acetonitrile containing 0.1% (v/v) formic acid at a flow rate of 0.45mL/min. Analytical signals were monitored at 320nm. Matrix-matched calibration curves showed satisfactory linearity (R2≥0.996). LODs, ranging from 2 to 4μg/L, were achieved and precision studies showed RSDs lower than 12.8% in terms of peak height. Additionally, recoveries higher than 62.8% were obtained for all studied compounds in milk samples.

Comparative performance of AmpFLSTR® Identifiler® Plus PCR amplification kit and QIAGEN® Investigator® IDplex Plus kit

Many forensic STR kits are currently available in the market. The AmpFLSTR® Identifiler® Plus kit, which targets 15 STRs, is commonly used worldwide. The Thai forensic DNA community is built around it in terms of instrument, databases, and interpretation. QIAGEN's IDplex Plus kit targets the same loci, but the PCR cycling time is shorter by about 90min. A direct comparison that assesses forensic parameters and applicability to casework between the two kits has never been carried out. In this study, we performed a direct comparison between the two kits using serial dilutions of two control DNA samples and 60 randomly selected casework samples, including samples taken from improvised explosive devices and terrorist raids. We statistically compared the performance of the two kits in terms of peak height, number of allele detected (allelic drop-out), intra-locus balance, inter-locus balance, inhibitor tolerance, stutter ratio, concordance, and allelic drop-in. The results demonstrate that both kits are statistically similar in performance. IDplex Plus gave higher peak heights in sensitivity test and tolerated inhibitors better, but had slightly worse inter-locus balances and stutter ratios. However, these differences were not practically significant, as seen by the resulting profiles of the casework samples (p=0.601). The performance on low-template samples also was not different. In conclusion, laboratories looking to replace the aging Identifiler® Plus might consider the IDplex Plus as a faster, more robust alternative that fits right into their existing structure without further investment in instrument and DNA database. Having more kits available worldwide by different companies could help bring the technology to different forensic laboratories and the justice system as a whole.

Anionic microemulsion to solvent stacking for on‐line sample concentration of cationic analytes in capillary electrophoresis

The common SDS microemulsion (i.e. 3.3% SDS, 0.8% octane, and 6.6% butanol) and organic solvents were investigated for the stacking of cationic drugs in capillary zone electrophoresis using a low pH separation electrolyte. The sample was prepared in the acidic microemulsion and a high percentage of organic solvent was included in the electrolyte at anodic end of capillary. The stacking mechanism was similar to micelle to solvent stacking where the micelles were replaced by the microemulsion for the transport of analytes to the organic solvent rich boundary. This boundary is found between the microemulsion and anodic electrolyte. The effective electrophoretic mobility of the cations reversed from the direction of the anode in the microemulsion to the cathode in the boundary. Microemulsion to solvent stacking was successfully achieved with 40% ACN in the anodic electrolyte and hydrodynamic sample injection of 21 s at 1000 mbar (equivalent to 30% of the effective length). The sensitivity enhancement factors in terms of peak height and corrected peak area were 15 to 35 and 21 to 47, respectively. The linearity R(2) in terms of corrected peak area were >0.999. Interday precisions (%RSD, n = 6) were 3.3-4.0% for corrected peak area and 2.0-3.0% for migration time. Application to spiked real sample is also presented.

Novel, Calibration-Free Strategies for Supersaturation Control in Antisolvent Crystallization Processes

In-situ attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy and focused-beam reflectance measurement (FBRM) were used to monitor and control the antisolvent crystallization of paracetamol from an acetone–water mixture, which was conducted in a 150 mL flat bottom crystallizer with a Mettler Toledo Easymax Reactor system. Following the monitoring of a series of unseeded and seeded crystallization experiments using a constant addition rate of antisolvent, a simple calculation method for the set point of antisolvent addition rate, to maintain constant supersaturation via ATR-FTIR, was developed and implemented for feedback control of unseeded and seeded crystallizations. The implemented technique used a single peak in the ATR-FTIR spectral region without any calibration to effectively maintain supersaturation to a prespecified set point. By developing a solubility curve in terms of peak height and knowing key information of the process at any given time, the addition rate of antisol...

Intonational Means to Mark Verum Focus in German and French

German and French differ in a number of aspects. Regarding the prosody-pragmatics interface, German is said to have a direct focus-to-accent mapping, which is largely absent in French--owing to strong structural constraints. We used a semi-spontaneous dialogue setting to investigate the intonational marking of Verum Focus, a focus on the polarity of an utterance in the two languages (e.g. the child IS tearing the banknote as an opposite claim to the child is not tearing the banknote). When Verum Focus applies to auxiliaries, pragmatic aspects (i.e. highlighting the contrast) directly compete with structural constraints (e.g. avoiding an accent on phonologically weak elements such as monosyllabic function words). Intonational analyses showed that auxiliaries were predominantly accented in German, as expected. Interestingly, we found a high number of (as yet undocumented) focal accents on phrase-initial auxiliaries in French Verum Focus contexts. When French accent patterns were equally distributed across information structural contexts, relative prominence (in terms of peak height) between initial and final accents was shifted towards initial accents in Verum Focus compared to non-Verum Focus contexts. Our data hence suggest that French also may mark Verum Focus by focal accents but that this tendency is partly overridden by strong structural constraints.

On-line sample concentration and determination of cationic alkaloids in human plasma by micelle to solvent stacking in capillary zone electrophoresis

A sensitive method for the determination of three cationic alkaloids (berberine, palmatine and jatrorrhizine) from human plasma samples was developed by micelle to solvent stacking (MSS) in capillary zone electrophoresis (CZE). In MSS, the sample preconcentration mainly relies on the reversal in the effective electrophoretic mobility of the analytes at the boundary zone between the sample and CZE background solution (BGS). Under the optimized conditions, the sensitivity enhancement factors achieved in terms of corrected peak area were in the range from 47 to 53 for the alkaloids. The limits of detection (LODs) (S/N=3) for berberine, palmatine and jatrorrhizine were 0.01, 0.01 and 0.02μg/mL, respectively. The intraday (n=6) and interday repeatabilities (n=12) expressed as the relative standard deviations (RSDs) were less than 6.9% in terms of peak height and less than 7.3% in terms of corrected peak area, respectively. The recoveries of the method for the three alkaloids were in the range of 95.9–101.5% with peak height as the quantitative signal, and 92.6–103.6% with corrected peak area as the quantitative signal, respectively. The MSS-CZE method proved to be suitable for the analysis of the alkaloids in human plasma samples.

Extraction, Cleanup, and Chromatographic Determination of Imidacloprid Residues in Wheat

This study presents an improved method for quantitative analysis of imidacloprid residues in wheat grain using high performance liquid chromatography. The study used chromatographic response (in terms of peak height) as a quantitative tool for determination instead of peak area. The peak height of imidacloprid showed a very good linear correlation (R(2)=0.999) when compared with absolute values at six different concentrations. The limit of detection was found to be 0.01μg/mL. The recovery of imidacloprid residues in spiked wheat grain at three levels (0.03, 0.05, and 0.1μg/g) was in the range of 79%-88% with %RSD 5.72 at 0.05μg/g (w/w) and between 87% and 93% with %RSD 3.55 at 0.1μg/g (w/w). At 0.03μg/g (w/w) level, recovery was not within the recommended range of 70%-110%. Therefore, the lowest limit of quantification for this method was found to be 0.05μg/g.

Potential of long chain ionic liquids for on-line sample concentration techniques: Application to micelle to solvent stacking

The performance of micelle to solvent stacking (MSS) in capillary zone electrophoresis (CZE) was improved for anionic analytes using the long chain ionic liquid type cationic surfactant 1-dodecyl-3-methylimidazolium tetrafluoroborate (C 12-MIM-BF 4). The peak heights and corrected peak areas of the test profens and herbicides were enhanced up to 59 and 110-fold, respectively when compared to typical injection. These were up to 10 times better compared to the surfactant cetyltrimethyl ammonium bromide as MSS carrier. This performance was attributed to the properties of C 12-MIM-BF 4. MSS requires micelles in the sample for transport of bound analytes to a stacking boundary that contains an organic solvent for effective electrophoretic mobility reversal. The ionic liquid micelles provided better analyte transport properties that resulted from its hydrophobic and pi–pi interaction capabilities. The good solubility of the ionic liquid in high percentages of organic solvent also facilitated a more effective reversal of mobility. The LODs obtained for the test analytes were from 0.06 to 0.12 μg/mL. The linearity R 2 values in terms of peak height and corrected area were ≥0.99. The interday repeatabilities (%RSD, n = 10,) were 0.5–2.2% for retention time, 1.9–4.7% for corrected areas and 4.1–6.4% for peak heights.

High-sensitive protein analysis by FESI-CE-MALDI-MS

Capillary zone electrophoresis (CZE) and matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) are two techniques highly suitable for the separation and detection of intact proteins. Herein, based on the use of a recently introduced iontophoretic fraction collection interface for the coupling of CE and MALDI-MS, the potential of the combination of both techniques for the analysis of intact proteins is assessed. To further provide a bioanalytical platform with high-sensitivity capabilities, field-enhanced sample injection is integrated as on online preconcentration strategy upstream from the electrokinetic separation. Under optimized conditions, more than 3200- and 4800-fold improvement, respectively in terms of peak height and peak area, as well as LODs ranging from 5 to 10 nM, has been achieved.

Determination of aflatoxins B1 and B2 by adsorptive cathodic stripping voltammetry in groundnut

Abstract In this study, adsorptive stripping voltammetry was proposed for determination of aflatoxins B1 (AFB1) and B2 (AFB2) using hanging mercury drop electrode (HMDE) as the working electrode. Both aflatoxins were found to adsorb and undergo irreversible reduction reaction at the working mercury electrode. The experimental conditions were optimised by one-at-a time and experimental design to obtain the best characterised peak in terms of peak height with analytical validation of the method for each aflatoxin. The calibration curves for aflatoxins AFB1 and AFB2 were linear in the ranges of 0.4–40 ng ml −1 and 0.2–70 ng ml −1 with the limit of detections (LOD) 0.15 and 0.10 ng ml −1 , respectively. The proposed method was applied for the analysis of aflatoxins in groundnut samples and the results were compared with those obtained by the HPLC technique.

Determination of triazine herbicide residues in water samples by on-line sweeping concentration in micellar electrokinetic chromatography

A new method for the determination of atrazine, simazine and prometryn in water samples by on-line sweeping concentration technique in micellar electrokinetic chromatography (MEKC) was developed. Various parameters affecting sample enrichment and separation efficiency were systematically studied. Compared with the conventional MEKC method, up to 60–200-fold improvement in concentration sensitivity was achieved in terms of peak height by using this sweeping injection technique. The compound strychnine was used as the internal standard for the improvement of the experimental reproducibility. The limits of detection (S/N = 3:1) for atrazine, simazine and prometryn were 9, 10 and 0.5 ng mL −1, respectively. This method has been successfully applied to the analysis of atrazine, simazine and prometryn in lake, steam and ground water.

Comparison of two sample preconcentration strategies for the sensitivity enhancement of flavonoids found in Chinese herbal medicine in micellar electrokinetic chromatography with UV detection

Two on-column preconcentration techniques named stacking with reverse migrating micelles (SRMM) and anion selective electrokinetic injection and a water plug-sweeping with reverse migrating micelles (ASIW–sweep–RMM) were used and compared for concentration and separation of flavonoids in Chinese herbs using reverse migration micellar electrokinetic chromatography (RM-MEKC). The optimal background electrolyte (BGE) used for separation and preconcentration was a solution composed of 20mM phosphoric acid (H3PO4)–100mM sodium dodecyl sulfate (SDS)–20% (v/v) acetonitrile (ACN) buffer (pH 2.0), the applied voltage was −15kV. To achieve reasonable results of the two techniques, the conditions which affected preconcentration were examined. A comparison of used techniques with normal hydrodynamic injection (5s), concerning enhancement factors and limits of detection (LODs) was presented. Under the optimum stacking conditions, about 27–37- and 45–194-fold improvement in the detection sensitivity was obtained for SRMM and ASIW–sweep–RMM, respectively, compared to usual hydrodynamic sample injection (5s). The LODs (S/N=3) for SRMM and ASIW–sweep–RMM in terms of peak height, can reach down to 1.15×10−2μg/ml for hesperetin and 2.4×10−3μg/ml for nobiletin, respectively. Finally, the amounts of the six flavonoids in extract of Fructus aurantii Immaturus were successfully determined using ASIW–sweep–RMM. The six analytes were baseline separated with sample matrix under the optimum ASIW–sweep–RMM conditions and the experimental results showed that preconcentration was well achieved after the dilution of sample solutions.

Analyses of tobacco alkaloids by cation-selective exhaustive injection sweeping microemulsion electrokinetic chromatography

In this study, an on-line concentration method which coupled cation-selective exhaustive injection (CSEI) sweeping technology with microemulsion electrokinetic chromatography (MEEKC) was used to detect and analyze several tobacco alkaloids (nornicotine, anabasine, anatabine, nicotine, myosmine and cotinine) that are commonly found in various tobacco products. First, the effects of microemulsion compositions (oil, cosurfactant and solution pH) were examined in order to optimize the alkaloid separations in conventional MEEKC. The pH value and the injection length of basic plug were found to be the predominant influences on the alkaloid stacking. This optimal CSEI sweeping MEEKC method provided approximately 180- to 540-fold increase in detection sensitivity in terms of peak height without any loss in separation efficiency when compared to normal MEEKC separation. Furthermore, this proposed CSEI sweeping MEEKC method was applied successfully for the detection of the minor alkaloids nornicotine, anabasine and anatabine in tobacco products.

Analysis of Carbamazepine in Tablet and Human Serum by Sweeping‐Micellar Electrokinetic Chromatography Method

A sensitive and simple micellar electrokinetic chromatography (MEKC) method was developed for the determination of the antiepileptic drug carbamazepine (CBZ) using a sweeping on‐line concentration method with photodiode array detection. The effect of pH, concentration of the running buffer solution, organic modifier, applied voltage and injection time on the concentration efficiency and separation was investigated. An untreated fused‐silica capillary was used (50 cm; effective length, 40 cm, 75 µm i.d.) for the analysis. The background solution (BGS) was 50 mmol · L−1 NaH2PO4 (pH 3.0) containing 100 mmol · L−1 SDS and 20% acetonitrile (5.82 ms · cm−1) with an applied voltage of −20 kV at 25°C. Sample introduction was performed at 0.5 psi for 90 s with diode array detection at 214 nm. For the method, the calibration curve was linear over a range of 0.5–40 µg · mL−1 for CBZ with a correlation coefficient of 0.998. The detection limit (S/N=3∶1) of CBZ was 0.10 µg · mL−1. About 100‐fold improvement in concentration sensitivity was achieved in terms of peak height by the sweeping method compared to conventional injection method. The sweeping‐MEKC method has been successfully applied to the analysis of CBZ in tablet and human serum.