Symmetrical Peak Shapes Research Articles

Validation of a single liquid chromatography-tandem mass spectrometry approach for oxytetracycline determination in bull plasma, seminal plasma and urine.

Oxytetracycline is a broad‐spectrum antibiotic, which inhibits protein synthesis and is generally used for the treatment of pneumonia, shipping fever, leptospirosis and wound infections in cattle and swine. The present work proposes a novel liquid chromatography–tandem mass spectrometry (LC–MS/MS) method for oxytetracycline quantification in bull plasma, seminal plasma and urine, requiring limited sample treatment before analysis. Extraction with trichloroacetic acid followed by dilution of the supernatant in mobile phase proved to be effective in all three matrices, allowing to rapidly process large batches of samples. Sharp and symmetrical peak shape was obtained using a BEH C18 reversed‐phase column in a chromatographic run of just 3.5 min. The mass spectrometer operated in positive electrospray ionization mode and monitored specific transitions for oxytetracycline (461.1 → 425.8) and the internal standard demeclocycline (465.0 → 447.6). The method was validated over concentration ranges suitable for field concentrations of oxytetracycline found in each matrix, showing good linearity during each day of testing (R 2 always >0.99), as also confirmed by analysis of variance (ANOVA) and lack‐of‐fit tests. Excellent accuracy and precision were demonstrated by calculated bias always within ±15% and CV% below 10% at all quality control (QC) levels in the three matrices. Matrix effect and recovery were investigated for both analytes, which showed consistent and comparable behaviour in each matrix. To our knowledge, this is the first validated approach for mass spectrometric determination of oxytetracycline in seminal plasma and urine. The method was successfully applied to samples collected during a pharmacokinetic study in bulls, allowing to assess the oxytetracycline concentration–time profile in plasma, seminal plasma and urine.

Establishment of Holistic Quality Control Methods for Nelumbinis Folium Containing Alkaloids and Flavonoids with Simple HPLC Conditions.

In this study, a positive charged C18 column was used to explore its performance in analysis of herbal medicines containing alkaloids and flavonoids with Nelumbinis Folium (NF) as an example. A chromatographic fingerprint analysis method was established by high performance liquid chromatography-diode array detector with commonly used 0.1% formic acid as mobile phase additive and this method could simultaneously detect both alkaloids and flavonoids with good peak shape. It is noted that the HPLC conditions were directly applied in the HPLC-ESI-Orbitrap-MS/MS analysis, and 12 common peaks were identified. In the quantification method of nuciferine, compared with common C18 column, good performance was observed, including sharp and symmetric peak shape of nuciferine, and no obvious retention time shift in chromatogram. The fingerprint method and quantification method of nuciferine and quercetin-3-O-glucuronic acid could be readily utilized as quality control methods for NF and its related preparations.

STABILITY INDICATING RP-HPLC METHOD FOR SIMULTANEOUS DETERMINATION OF CEFTRIAXONE SODIUM AND SALBUTAMOL

An isocratic liquid chromatographic method with UV detection at 230 nm is described for simultaneous determination of ceftriaxone sodium and salbutamol in bulk. Chromatographic separation of the two drugs was achieved on an Inertsil ODS© C18 (250 × 4.6 mm, 5 μ) using a mobile phase consisting of 50 mM potassium dihydrogen orthophosphate and methanol (77:23 %V/V) adjusted to pH 7.0 with triethylamine at a fl ow rate of 1.0mL min-1. The optimum separation was achieved in less than 10 minutes. The developed liquid chromatographic method offers symmetric peak shape, good resolution and reasonable retention time for both drugs. The method was validated as per ICH guidelines.

Evaluation and application of a positively-charged phenylaminopropyl bonded stationary phase for separation of basic compounds

Silica-based positively-charged stationary phase bonding phenylaminopropyl (named PHN) was found to produce symmetrical peak shape and higher sample loading for basic compounds. In this work, firstly, surface charge property of the PHN was evaluated by ζ-potential and retention of NO3−. A considerable amount of pH-dependent positive charges was confirmed more than that on CSH Phenyl-Hexyl, a commercial positively-charged phenyl stationary phase. Then chromatographic evaluation of standard alkaloids revealed that PHN could offer better peak shape and higher column efficiency at lower pH, and it functioned well under a wide range of buffer ionic strength. The PHN also showed different selectivity for basic compounds compared to the CSH Phenyl-Hexyl. Furthermore, it provided superior peak shape for high sample mass, demonstrating potential applications of this stationary phase in a preparative scale. These results can be explained by the strong charge intensity of the PHN stationary phase. Finally, the PHN was applied to separate a fraction from rhizomes of Corydalis decumbens, and purify dehydrocorybulbine from Corydalis yanhusuo W.T. Wang. Our study indicated the advantages and potential applications of the phenylaminopropyl bonded PHN stationary phase for basic compound separation.

Re-Examining the Impact of Minimal Scans in Liquid Chromatography-Mass Spectrometry Analysis.

Liquid chromatography-mass spectrometry (LC-MS) is one of the most widely used analytical tools. High analysis volumes and sample complexity often demand more informative LC-MS acquisition schemes to improve efficiency and throughput without compromising data quality, and such a demand has been always hindered by the prerequisite that a minimum of 13-20 MS scans (data points) across an analyte peak are required for accurate quantitation. The current study systematically re-evaluated and compared the impact of different scan numbers on quantitation analysis using both triple quadrupoles mass spectrometry (TQMS) and high-resolution mass spectrometry (HRMS). Contrary to the 13-20 minimal scan prerequisite, the data obtained from a group of eight commercial drugs in the absence and presence of biological matrices suggest that 6 scans per analyte peak are sufficient to achieve highly comparable quantitation results compared to that obtained using 10 and 20 scans, respectively. The fewer minimal scan prerequisite is presumably attributed to an improved LC system and advanced column technology, better MS detector, and more intelligent peak detection and integration algorithms leading to a more symmetric peak shape and smaller peak standard deviation. As a result, more informative acquisition schemes can be broadly set up for higher throughput and more data-rich LC-MS/MS analysis as demonstrated in a hepatocyte clearance assay in which fewer MS scans executed on HRMS led to broader metabolite coverage without compromising data quality in hepatic clearance assessment. The demonstrated acquisition scheme would substantially increase the throughput, robustness, and richness of the nonregulatory analysis, which can be broadly applied in diverse fields including pharmaceutical, environmental, forensic, toxicological, and biotechnological.

A sensitive HPLC-FLD method for the quantitative determination of 3-chloro-1,2-propanediol by pre-column fluorescence derivatization with 9-(2-Hydroxypropyl)adenine

In this paper, a sensitive method for the determination of 3-chloro-1,2-propanediol (3-MCPD) by high performance liquid chromatography-fluorescence detection (HPLC-FLD) was established, in which 9-(2-Hydroxypropyl) adenine (HP-Ade) was selected as the fluorescent derivatization reagent because of its good water solubility and hydrophobicity. The principle of the method lies in the origination of chloroacetaldehyde with the periodate oxidation of 3-MCPD and its' fluorescence derivatization by HP-Ade to produce a strong fluorescent substance, name as 1-N6 -vinylidene-9-(2-hydroxypropyl)adenine (ε-HP-Ade), used for quantitative determination of 3-MCPD by HPLC-FLD. Some mobile phase conditions and incubation parameters related with the method features were studied and optimized. Under the optimal conditions, the method shows high sensitivity, good linearity (r 2 = 0.999) and good repeatability (RSD% between 1.04% and 2.55%), the detection limit (LOD) and quantification limit (LOQ) were 0.02 ng/mL and 0.06 ng/mL respectively. It has been successfully applied for the determination of various edible vegetable oil samples, the chromatogram shows symmetrical peak shape, perfect separation and very “clean” profiles. In comparison with gas chromatography-mass spectrum (GC-MS), the pretreatment process of the proposed method was totally operated in aqueous phase, the instrument requirements and cost are relatively lower, thus it will provide another choice for the routine analysis of 3-MCPD.

A discussion of approaches for fitting asymmetric signals in X‐ray photoelectron spectroscopy (XPS), noting the importance of Voigt‐like peak shapes

Although the fundamental, theoretical peak shape in X‐ray photoelectron spectroscopy (XPS) is Lorentzian, some Gaussian character is observed in most XPS signals. Additional complexity in the form of asymmetry is also found in many XPS signals, which requires more advanced peak shapes than the traditional, symmetric Voigt and Gaussian‐Lorentzian sum and product (pseudo‐Voigt) functions. Here, we discuss the merits and disadvantages of four approaches that have been used to introduce asymmetry into XPS peak shapes: addition of a decaying exponential tail to a symmetric peak shape, the Doniach‐Sunjic peak shape, the double‐Lorentzian, DL, function, and the LX peak shapes, which include the asymmetric Lorentzian (LA), finite Lorentzian (LF), and square Lorentzian (LS) functions. The Doniach‐Sunjic peak shape is the only asymmetric, synthetic peak that has a theoretical basis. However, it has an infinite integral, which makes it problematic in quantitative work. The mathematical bases for the LX and DL peak shapes are discussed, and practical examples of their use in peak fitting are presented. The case is made for the Voigt function being the most appropriate function for XPS peak fitting, in general, which suggests that a modified Voigt function may be the most reasonable for fitting asymmetric XPS signals. The LX and DL functions include convolution with a Guassian, which, with the exception of the LS function, makes them Voigt‐like functions. The sources of asymmetry and its complexity are discussed. It is emphasized that not every asymmetric spectrum should be fit with an asymmetric peak shape.

Determination of hydrazine in workplace air by gas chromatography with large bore capillary column

Objective: To determine hydrazine quantitatively in workplace air by gas chromatography with large bore capillary column. Methods: In October 2019, hydrazine in the air was adsorbed by acid silica gel tube sampling and desorped using sulfuric acid solution. After derivatization with furfural and extraction, the content of hydrazine was determined by DM-FFAP capillary column gas chromatography with flame ionization detector. Results: The linear regression equation was y=353.8x+21.2 (r=0.9998) between 0.1-2.0 μg/ml of target concentration. The detection limit was 0.030 μg/ml. The lower limit of quantification was 0.100 μg/ml. If 15 L air sample was collected, the minimum detection concentration was 0.004 mg/m(3) and the minimum quantitative concentration was 0.013 mg/m(3) respectively. The average desorption efficiency was 86.5%-89.4%. The recovery was 94.4%-97.1%. The relative standard deviation was 1.6%-4.9%. Hydrazine and furfural derivative was 2-furaldehyde hydrazine. Conclusion: The method has symmetrical peak shape of hydrazine derivatives chromatographic peaks, short analysis time, easy operation, and is suitable for the determination of the concentration of hydrazine in the air in the workplace.

Determination and Application of Nineteen Monoamines in the Gut Microbiota Targeting Phenylalanine, Tryptophan, and Glutamic Acid Metabolic Pathways.

It has been reported that monoamine neurotransmitters can be produced by gut microbiota, and that several related metabolites of amino acids in these pathways are associated with nervous system (NVS) diseases. Herein, we focused on three pathways, namely, phenylalanine (Phe), tryptophan (Trp), and glutamic acid (Glu), and established an underivatized liquid chromatography–tandem mass spectrometry (LC-MS/MS) method for the quantification of nineteen monoamine neurotransmitters and related metabolites in the gut microbiota. The neurotransmitters and related metabolites included Phe, tyrosine (Tyr), l-dopa (Dopa), dopamine (DA), 3-methoxytyramine, Trp, hydroxytryptophan, 5-hydroxytryptamine (5-HT), 5-hydroxyindole-3-acetic acid (5-HIAA), kynurenine (KN), kynurenic acid (KYNA), melatonin, tryptamine (TA), indole-3-lactic acid (ILA), indole-3-acetic acid (IAA), indolyl-3-propionic acid (IPA), Glu, gamma-aminobutyric acid (GABA), and acetylcholine (Ach). A fluoro-phenyl bonded column was used for separation, and the mobile phase consisted of methanol:acetonitrile (1:1) and water, with 0.2% formic acid in both phases. The compounds exhibited symmetric peak shapes and sufficient sensitivity under a total analysis time of 8.5 min. The method was fully validated with acceptable linearity, accuracy, precision, matrix effect, extraction recovery, and stability. The results showed that neurotransmitters, such as Dopa, DA, 5-HT, GABA, and Ach, were present in the gut microbiota. The metabolic pathway of Trp was disordered under depression, with lower levels of 5-HT, 5-HIAA, KN, KYNA, TA, ILA, IAA, IPA, and Glu, and a higher ratio of KYNA/KN. In addition, some first-line NVS drugs, such as sertraline, imipramine, and chlorpromazine, showed regulatory potential on these pathways in the gut microbiota.

Determination of Nateglinide in Tablet Formulation by HPLC Using a Pentafluorophenyl Core-Shell Column

Nateglinide is an insulin secretagogue which has been used for the treatment of Type 2 Diabetes mellitus. A simple analytical methodology for determination of nateglinide in tablet formulation is described. An isocratic reversed phase high performance liquid chromatographic (HPLC) method was developed using Kinetex pentafluorophenyl (PFP) (5μm particle size and 4.6 x 150 mm id) core-shell column as stationary phase and 0.05 M Na2HPO4 (pH=2.0) / methanol (30:70 v/v) mixture as mobile phase with the flow rate of 1.0 mL min-1 and diode-array detector at 215 nm. Column was termostated at 22°C. Under these conditions nateglinide was eluted with a symmetrical peak shape and the retention time was 4.779 minutes. The system suitability parameters such as tailing factor, capacity factor and theoretical plate were evaluted. The method was validated as per International Council on Harmonisation (ICH) guidelines. Linearity was obtained in the 2.54 - 40.70 μg mL-1 concentration range with equation y= 10.818x + 4.7048 (R2= 0.998). Limit of detection and limit of quantification were 1.07 and 2.54 μg mL-1. Accuracy of the method was tested by recovery studies which were in the range of 98.78 - 100.76 %. The intra-day and inter-day precision studies were carried out and the relative standard deviation values of peak areas were within ICH limits. The proposed method was successfully applied to the determination of nateglinide in tablet dosage form.

Determination of residual solvents in paclitaxel by headspace gas chromatography

BackgroundA simple and sensitive gas chromatographic method was developed and validated for the simultaneous determination of methanol, ethanol, acetone, isopropyl alcohol, dichloromethane, N-hexane, ethyl acetate, tetrahydrofuran, and N,N-diisopropyl ethyl amine in Paclitaxel. A chromatographic separation was done on DB-624 column, 30 m length × 0.53 mm ID, and film thickness 3 μm, using a flame ionization detector (FID) with gradient column oven temperature program. The injection was carried out in split mode, with a split ratio of 5:1. A mixture of N-methyl-2-pyrrolidinone (contains 1% piperazine) and water in the ratio of 80:20 (v/v) was selected as a diluent to obtain good sensitivity along with the recovery.ResultsThe developed gas chromatographic method offers symmetric peak shape, good resolution of more than 2.0 between the solvent peaks, and the relative standard deviation for replicate injections of all the solvents were found to be not more than 15.0% with reasonable retention time for all the solvents. The limit of detection for methanol, ethanol, acetone, isopropyl alcohol, dichloromethane, N-hexane, ethyl acetate, tetrahydrofuran, and N,N-diisopropyl ethyl amine was found to be 304.69 ppm, 497.98 ppm, 498.99 ppm, 504.49 ppm, 61.81 ppm, 30.07 ppm, 505 ppm, 73.05 ppm, and 2.09 ppm, respectively. Limit of quantitation of methanol, ethanol, acetone, isopropyl alcohol, dichloromethane, N-hexane, ethyl acetate, tetrahydrofuran, and N,N-diisopropyl ethyl amine was found to be 89.62 ppm, 146.47 ppm, 146.76 ppm, 148.38 ppm, 18.18 ppm, 8.84 ppm, 148.53 ppm, 21.49 ppm, and 0.62 ppm, respectively. Precision was found to be satisfactory. Linear in the range of LOQ to 150% level for all the solvents, and accuracy along with robustness, is performed, and acceptable results were obtained.ConclusionThe proposed method was demonstrated to be simple, sensitive, specific, linear, precise, accurate, and robust, hence can be used to determine the residual organic solvents in Paclitaxel drug substance and drug product.

In-situ and one-step preparation of protein film in capillary column for open tubular capillary electrochromatography enantioseparation

In this work, the phase-transitioned BSA (PTB) film using the mild and fast fabrication process adhered to the capillary inner wall uniformly, and the fabricated PTB film-coated capillary column was applied to realize open tubular capillary electrochromatography (OT-CEC) enantioseparation. The enantioseparation ability of PTB film-coated capillary was evaluated with eight pairs of chiral analytes including drugs and neurotransmitters, all achieving good resolution and symmetrical peak shape. For three consecutive runs, the relative standard deviations (RSD) of migration time for intra-day, inter-day, and column-to-column repeatability were in the range of 0.3%–3.5%, 0.2%–4.9% and 2.1%–7.7%, respectively. Moreover, the PTB film-coated capillary column ran continuously over 300 times with high separation efficiency. Therefore, the coating method based on BSA self-assembly supramolecular film can be extended to the preparation of other proteinaceous capillary columns.

Imidazolium ionic liquid bonded silica stationary phases: Part I: Hexadecylimidazolium stationary phase

In this first research report, the design of an ionic liquid (IL) silica based stationary phase is described and characterized chromatographically using standard solute probes and via physical measurements including Fourier transform infrared (FTIR) and thermogravimetric analysis (TGA). The stationary phase is hexadecylimidazolium bonded to silica microparticles for the retention of various small and large solutes primarily by reversed-phase retention mechanism and to some different extent via π-π interactions and electrostatic interactions. The hexadecylimidazolium functionalized silica stationary phase was obtained by first grafting the surface of 5 µm silica particles with 3-chloropropyltrimethoxysilane forming the so-called a primary sublayer followed by attaching a top layer of hexadecylimidazole, thus resulting in the formation of IL based reversed-phase column. The hexadecylimidazolium column thus obtained exhibited relatively symmetrical peak shapes and high separation efficiencies for the studied analytes with a wide array of functional groups including ionizable analytes. The observed unique retention characteristics and selectivity of the hexadecylimidazolium column can be attributed to its multi interactions with various solutes including hydrophobic, electrostatic, π–π and hydrogen bonding interactions. Abbreviations: ABs: alkylbenzenes; APKs:n-alkyl phenyl ketones; CPS: chloropropylsilyl-silica; CPTMS: chloropropyltrimethoxysilane; HILIC: hydrophilic interaction chromatography; ILs: ionic liquids; IPA: isopropyl alcohol; TFA: trifluoroacetic acid; TGA: thermogravimetric analysis; THF: tetrahydrofuran; PAHs: polyaromatic hydrocarbons

Development and Validation of an Automated Gas Chromatography Method for Determination of Dichloromethane in Ampicillin Sodium by Using Capillary Column Technology

Background: The main aim of the study was to develop an automated static headspace gas chromatography (SHS-GC) method for determination of dichloromethane (DCM) in ampicillin sodium by using a capillary column. Methods: SHS-GC also known as gas chromatography-headspace is the technique of choice due to its high sensitivity, excellent separation abilities, low limit of detection and simplicity of the instrumentation used for the technique. The headspace sampling method has more appropriate sensitivity than the direct injection method because it can clearly separate volatile analytes from the sample matrix and effectively concentrate them. Therefore, this method results in less complex sample preparation, decreased instrument contamination, and increased capillary column life. Results: The developed SHS-GC method showed symmetrical peak shape reasonable retention time for DCM. A linear relationship was obtained over the range of 2-240 μg mL-1 with a correlation coefficient (r2) of 0.993. The recovery, system precision and robustness of the method were within the acceptable values. The Limit of Detection (LOD) and Limit of Quantitation (LOQ) were 0.5 μg mL-1 and 2 μg mL-1 respectively. Conclusions: The results obtained in this study demonstrate that SHS-GC method is selective, precise, linear, accurate and robust for determination of dichloromethane in ampicillin sodium and its formulation (injection).

Reverse-phase High-Performance Liquid Chromatography Method Development and Validation for Estimation of Glimepiride in Bulk and Tablet Dosage Form

The present work demonstrates a simple, rapid, precise, specific, and sensitive reverse-phase high-performance liquid chromatography (RP-HPLC) method for analyzing glimepiride in pure and tablet forms. The present method was developed using a C18 column 150 × 4.6 mm, with 5 μm, and packing L1 maintained at a temperature of 30°C. The mobile phase was prepared by dissolving 0.5 gram of monobasic sodium phosphate in 500 mL of distilled water, pH of the solution adjusted to 2.1 to 2.7 with 10% phosphoric acid, and added 500 mL of acetonitrile. The mobile phase was pumped in the highperformance liquid chromatography (HPLC) system at a flow rate of 1 mL/min, and separation was carried out at 228 nm, using an ultraviolet (UV) detector. The chromatographic separation was achieved with peak retention time (RT) at about 9.30 minutes, and the method was found to be linear over a concentration range of 40 to 140 μg/mL. The specificity of the method represented no interference of the excipients during the analysis, and stability testing after 24 hours also showed that the method is suitable and specific. The accuracy was between 99.93 to 99.96%, with limit of detection (LOD) and limit of quantitation (LOQ) being 0.354 μg/mL, 1.18 μg/mL, respectively. Satisfactory results were found for precision and robustness parameters during the development and validation stage for the analytical method. The proposed method was also adopted for the analysis of glimepiride tablets to improve the overall quality control. Using this method, symmetric peak shape was obtained with reasonable retention time. The retention time of glimepiride for six repetitions is 9.3 ± 0.1 minutes; the run time is 21 minutes. The proposed RP-HPLC method is a modification of the United States Pharmacopeia (USP) method, and it was found to be valid for glimepiride within concentration ranges 40 to 140 μg/mL, using C18 analytical columns, and isocratic elution with UV detection, and at 1 mL/min of flow rate.

Penentuan Secara Serempak Kadar Minor Anion (F-, Cl-, NO2-, Br-, NO3-, SO42– dan PO43-) dalam Sampel Air Botol Kemasan dengan Teknik Kromatografi Ion Kinerja Tinggi

Analytical and separation conditions for the simultaneous determination of minor anions (F - , Cl - , NO 2 - , Br - , NO 3 - , SO 4 2– , and PO 4 3- ) using ion chromatography technique have been optimized. In this study, ion chromatography with a suppressed conductivity detection system was applied to determine the ionic species with high sensitivity. By these conditions, it has been targeted in the determination of the seven anions in bottled drinking water samples. With concentration of 6 mM Na 2 CO 3 and 1,2 mM NaHCO 3 were used as the eluent combination for all determinations. All the above anions could be completely determied and eluted were less than 30 min. All anions were displayed symmetrical peak shapes as in the chromatograms. The correlation coefficient ( r ) varies between 0.9995 and 1 for the above seven anions, whereas the detection limits calculated at S/N= 3 were 0.02–0.45 µg/L. The obtained optimum conditions were then applied to the simultaneous determination of minor anions in 6 bottled drinking water samples with different brands. From the overall drinking water samples which was collected commersially in North Maluku, there were no minor anions concentration exceeding the specified quality standards.

Separation Performance of Capillary Gas Chromatography Based on Monohydroxycucurbit[7]Uril Incorporated Into Sol-Gels as the Stationary Phase.

A novel monohydroxycucurbit[7]uril-based stationary phase for capillary gas chromatography (GC) has been produced. For this, a capillary column coating was made using a sol–gel technique, incorporating synthesized monohydroxycucurbit[7]uril [(OH)Q[7]] and hydroxy-terminated poly(dimethylsiloxane) (OH-PDMS) into the sol–gel network through hydrolysis and polycondensation and chemical sol–gel grafting to the inner wall of a fused-silica tube. The preparation method may produce a coating with greater integrity, which gives the prepared column a higher separation efficiency and better selectivity toward analytes than a reported stationary phase based on neat cucurbit[n]urils (Q[n]s). The prepared (OH)Q[7]/PDMS column had 3,225 theoretical plates per meter determined using naphthalene at 120°C and exhibited a weakly polar nature. The (OH)Q[7]/PDMS column has high resolution over a broad spectrum of analytes with symmetrical peak shapes and exhibited better separation performance than commercial capillary columns and reported columns based on neat Q[n]s that failed to resolve some critical analytes. Moreover, the column also showed good thermal stability up to 300°C and separation repeatability with relative standard deviation values in the range of 0.01–0.11% for intraday, 0.11–0.32% for interday and 0.29–0.58% for column-to-column. In addition, the energy effect on the retention of analytes on the (OH)Q[7]/PDMS stationary phase was investigated. The results indicated that retention on the column was determined mainly by the enthalpy change. As demonstrated, the proposed coating method can address some disadvantages that exist with the reported Q[n]s columns and combine the full advantages of (OH)Q[7] with the sol–gel coating method while achieving outstanding GC separation performance.

Unique Voltammetry of Silver Nanoparticles: From Single Particle to Aggregates

Understanding the electrooxidation process of metal nanoparticles (NPs) is very important because they have showed wide applications in electrocatalysis, sensing, and nanoelectronics. In this letter, we designed a strategy to investigate the anodic stripping voltammetry (ASV) of silver oxidation at single NP level and aggregation state by using gold single nanoelectrodes (SNEs) and ultramicroelectrodes. Results showed that the ASV peak potential and shape were significantly affected by the diameter and aggregation degree of the Ag NPs: symmetrical-peak shape, two-peak shape, and asymmetrical-peak shape appeared when Ag NPs changed from the single particle state to the large-aggregation state, and size-dependent ASVs for Ag NPs oxidation were also observed. These findings can help us deeply understand the metal NPs oxidation process and will benefit the related applications.

LC-MS/MS and LC-UV Determination of Moniliformin by Adding Lanthanide Ions to the Mobile Phase.

An innovative chromatographic analysis was developed for the determination of moniliformin (MON). Because of its ionic nature, MON is weakly retained in reversed-phase chromatography and the separation may be tricky. Nevertheless, this technique is normally used either with the formation of ion pairs or employing specific RP columns for polar compounds, or combining anion exchange and hydrophobic interactions. Hydrophilic interaction chromatography (HILIC) was also used, but a non-negligible peak tailing was observed. Besides its ionic nature, MON is a di-ketone and di-ketones, mainly β-di-ketones, can easily form complexes with lanthanide ions. Then, in this work the addition of lanthanide ions to the mobile phase was investigated, aiming at improving peak shape and MON separation. La3+, Tb3+ or Eu3+ aqueous solutions were used as mobile phase and MON was chromatographed using a LC-NH2 column. The probable formation of coordination complexes lanthanide-MON in the HPLC mobile phase allowed to obtain a symmetrical peak shape and a satisfactory chromatographic separation by both mass spectrometry (MS/MS) and UV detection. Finally, a suitable extraction and purification method for MON determination in cereal samples was developed.

Purification of tertiary and quaternary alkaloids from Rhizoma Corydalis using reversed-phase/weak cation-exchange mixed-mode class separation combined with preparative C18 and silica based strong cation-exchange chromatography

A new optimization strategy for purification of alkaloids from Rhizoma Corydalis using preparative liquid chromatography was developed, featuring a selective separation of different types of alkaloids into different parts by a reversed-phase/weak cation-exchange mixed-mode column (named C18WCX) at first. The total alkaloids of Rhizoma Corydalis were divided into four fractions with fraction III and IV corresponding to the tertiary type medium bases and the quaternary type strong bases, respectively. For fraction III, a conventional C18 column was used to isolate tertiary alkaloids using acetonitrile and 0.1% phosphoric acid (adjusted with triethylamine to pH 6.0) as mobile phases. High selectivity and symmetrical peak shapes of tertiary alkaloids were obtained, resulting in six main tertiary alkaloids isolated in a single run. As strong bases, quaternary alkaloids often suffer from serious peak tailing problem on conventional C18 columns. Therefore, a silica-based strong cation-exchange (SCX) column was used for purification of fraction IV. On the SCX column, good peak shapes in high sample loading were achieved. Five main quaternary alkaloids were isolated and identified from the fraction in one-step. The procedures presented effective for the preparative isolation and purification of alkaloids from Rhizoma Corydalis.