Yiping Liao

CE‐MS analysis of heroin and its basic impurities using a charged polymer‐protected gold nanoparticle‐coated capillary

The first application of charged polymer‐protected gold nanoparticles (Au NPs) as semi‐permanent capillary coating in CE‐MS was presented. Poly(diallyldimethylammonium chloride) (PDDA) was the only reducing and stabilizing agent for Au NPs preparation. Stable and repeatable coating with good tolerance to 0.1 M HCl, methanol, and ACN was obtained via a simple rinsing procedure. Au NPs enhanced the coating stability toward flushing by methanol, improved the run‐to‐run and capillary‐to‐capillary repeatabilities, and improved the separation efficiency of heroin and its basic impurities for tracing geographical origins of illicit samples. Baseline resolution of eight heroin‐related alkaloids was achieved on the PDDA‐protected Au NPs‐coated capillary under the optimum conditions: 120 mM ammonium acetate (pH 5.2) with addition of 13% methanol, separation temperature 20°C, applied voltage −20 kV, and capillary effective length 60.0 cm. CE‐MS analysis with run‐to‐run RSDs (n=5) of migration time in the range of 0.43–0.62% and RSDs (n=5) of peak area in the range of 1.49–4.68% was obtained. The established CE‐MS method would offer sensitive detection and confident identification of heroin and related compounds and provide an alternative to LC‐MS and GC‐MS for illicit drug control.

Nanoparticle: is it promising in capillary electrophoresis?

Separation sciences progress with size. On the one hand, extensive efforts devoted to miniaturization of analytical instruments have significantly promoted the development of this field. On the other hand, wide applications of novel materials with size at the sub-micron level as separation media have offered more and more opportunities for solving separation puzzles. The potential of nanostructured materials, e.g., nanoparticles (NPs), in chromatographic and electrophoretic techniques has gradually been discovered in recent years. NPs usually refer to a kind of nanomaterial with a spherical-like appearance measured in nanometers, sometimes up to 1500 nm, with a large surface-to-volume ratio and other fascinating properties derived from the “quantum size effect”. Existing NPs comprise the following [1–3]: fullerene NPs, silica NPs, precious metal NPs, metal oxide NPs, semiconductor quantum dots, and polymer-based NPs (i.e., polymer NPs, molecular micelles, molecularly imprinted polymers, and dendrimers). Surface modification with functional groups and/or molecules is a key procedure to prevent the prepared NPs from aggregation and to control the particle size, and also provide extra selectivity when the NPs are used as separation media. NPs are mostly stabilized by steric exclusion and electrostatic repulsion. A great breakthrough giving deep insight into the structure of nanometersized gold particles protected by p-mercaptobenzoic acid (p-MBA) has been achieved recently [4]. The prepared NP comprises 102 gold atoms and 44 p-MBAs (Fig. 1). The central gold atoms are packed in a Marks decahedron, surrounded by additional layers of gold atoms in unexpected geometries. The p-MBAs interact not only with the gold but also with one another, forming a rigid surface layer. It is interesting that particle aggregation can be utilized in sensitive detection of particular molecules, which can induce NP aggregation indicated by solution color change and monitored by electron microscopy [5].

Fragmentation study and analysis of benzoylurea insecticides and their analogs by liquid chromatography-electrospray ionization-mass spectrometry

Two insecticides, diflubenzuron and hexaflumuron, and their analogs have been separated by liquid chromatography (LC) and their fragmentation mechanisms were studied by electrospray ionization-ion trap mass spectrometry (ESI-MS(n)) in both positive- and negative-ion modes. Sequential product ion fragmentation experiments were performed in order to explain the degradation pathways and identify their predominant fragment ions. It was indicated that the characteristic fragmentations are the loss of neutral molecules such as HF, HNO(2), and HCl to form stable ring structure or the cleavage of the acyl amine to form conjugated structure. Furthermore, the separation and determination of two benzoylurea (BU) insecticides and their analogs in the water samples from Weiming Lake have been described by LC-ESI-MS in negative mode. By the use of deprotonated molecule for quantitative analysis at low capillary exit voltage, low detection limits, good linearity and reproducibility for standard solutions were presented.

Fragmentation pathways of heroin‐related alkaloids revealed by ion trap and quadrupole time‐of‐flight tandem mass spectrometry

The electrospray ionization (ESI) ion trap and quadrupole time-of-flight (QqToF) mass spectra of heroin and seven related alkaloids, i.e., morphine, codeine, O-6-monoacetylmorphine (6-MAM), thebaine, acetylcodeine, papaverine and narcotine, have been extensively investigated in this work. The ESI mass spectrometric fragmentation pathways of protonated 6-MAM, heroin, acetylcodeine, and thebaine were comprehensively elucidated for the first time with the aid of high-resolution mass spectrometry. It was found that cleavage of the piperidine ring was the featured fragmentation route of six of the compounds, although not of papaverine and narcotine. In addition, a simple high-performance liquid chromatography (HPLC)-based separation method gave baseline resolution of all eight components. This study could play an important role in the screening for these alkaloids in different matrices by HPLC coupled to tandem mass spectrometry (MS/MS).

Determination of dissociation constants of aristolochic acid I and II by capillary electrophoresis with carboxymethyl chitosan-coated capillary

Aristolochic acid-I and aristolochic acid-II have been proved to be the main bioactive and toxic component in Aristolochia plants. As a result, the determination of their dissociation constants, which are important property parameters for weak acids, is highly desired for related pharmacological and toxicological studies. In this work, the dissociation constant values of aristolochic acid-I and aristolochic acid-II were determined by capillary electrophoresis using carboxymethyl chitosan-coated capillary, based on their electrophoretic mobilities by using nonlinear regression as well as linear regression, showing that the two models give comparable results. The data were also compared with those obtained by capillary electrophoresis with polybrene-coated capillary, and no conspicuous difference was observed. The correlation coefficients were all higher than 0.998 for both linear and nonlinear regression model. The pKa values were found to be 3.3±0.1 for aristolochic acid-I and 3.2±0.1 for aristolochic acid-II.

Graphene matrix for signal enhancement in ambient plasma assisted laser desorption ionization mass spectrometry.

In this work, the signal intensity of ambient plasma assisted laser desorption ionization mass spectrometry (PALDI-MS) was significantly increased with graphene as matrix. The graphene functions as a substrate to trap analytes, absorb energy from the visible laser irradiation and transfer energy to the analytes to facilitate the laser desorption process. The desorbed analytes are further ionized by helium plasma and analyzed by MS. Compared with a traditional organic matrix, α-cyano-4-hydroxycinnamic acid (CHCA), graphene exhibited much higher desorption efficiency for most of the compounds benefitting from the strong optical absorption at 532nm. The performance has been confirmed by the facile analysis of more than forty compounds with various structures. Additionally, this method was successfully applied to distinguish three kinds of Chinese tea leaves by detecting the endogenous caffeine and theanine, which proved the utility, facility and convenience of this method for rapid screening of main components in real samples.

Membrane-Based Continuous Remover of Trifluoroacetic Acid in Mobile Phase for LC-ESI-MS Analysis of Small Molecules and Proteins

We developed a “continuous” trifluoroacetic acid (TFA) remover based on electrodialysis with bipolar membrane for online coupling of liquid chromatography (LC) and electrospray ionization mass spectrometry (ESI-MS) using TFA containing mobile phase. With the TFA remover as an interface, the TFA anion in the mobile phase was removed based on electrodialysis mechanism, and meanwhile, the anion exchange membrane was self-regenerated by the hydroxide ions produced by the bipolar membrane. So the remover could continuously work without any additional regeneration process. The established LC-TFA remover-MS system has been successfully applied for the qualitative and quantitative analysis of small molecules as well as proteins.

Separation and Sensitive Detection of α-Lactalbumin and β-Lactoglobulin by Capillary Zone Electrophoresis

α-lactalbumin and β-lactoglobulin are main impurities in the lactose products extracted from whey,which may cause allergy.Therefore,the separation and detection of race α-lactalbumin and β-lactoglobulin are of great importance to food and pharmaceutical industry.In this work,a simple,fast,sensitive and reproducible capillary zone electrophoresis(CZE) method has been developed for this purpose.After simple sample preparation procedure,α-lactalbumin and β-lactoglobulin can be baseline separated within 2 minutes under following conditions:25 mM phosphate buffer at pH 7.0,+ 30 kV applied voltage,25 ℃ capillary temperature,205 nm UV detection,and sample injection at 50 mbar for 10 s。The limit of detection(LOD) at 3 times of S/N is 3.0 and 12 mg/L for α-lactalbumin and β-lactoglobulin,respectively.The repeatability(RSD,n=6) is below 1% for migration time and below 6% for peak area.These data qualified the method to the analysis of real lactose samples.The proposed method also shows a great potential in other fields of food and pharmaceutical industry.