Evaluation of multi-solvent size exclusion chromatography columns packed with sub-2 µm particles for the characterization of synthetic polymers.

With the recent development of small particle stationary-phases and dedicated instrumentation, the combination of size-exclusion chromatography (SEC) with ultra-high performance liquid chromatography (UHPLC) technology has been realized. It opened up a new polymer analysis technique called UHP-SEC. Although high resolution and fast analysis can be achieved, the multi-solvent suitability for a given column was limited to either organic or aqueous eluents. In this work, the capability of novel SEC columns (AdvanceBio SEC columns) packed with 1.9 µm particles for the characterization of synthetic polymers in organic solvents as well as the multi-solvent compatibility for organic and aqueous eluents have been demonstrated. About six times faster separation for both polystyrene (PS) and polyethylene glycol (PEG) with good peak shape and repeatability were achieved in comparison with standard SEC columns at comparable resolution. Especially for PEG, in contrast to other SEC columns, this column could provide close-to-accurate determination of molecular weights with tetrahydrofuran (THF) as mobile phase. Good reproducibility was obtained after switching several times from water to THF and vice versa with RSD% in retention times less than 0.5 %. Different samples such as polyols, isocyanates and additives can also be analyzed for molecular weight and distribution or composition determination. Volume overload, especially with injection volumes higher than 10 µL needs to be considered. This new column offers a powerful choice for oligomer and polymer analysis with both aqueous and organic mobile phase. Ultimately, hyphenating SEC columns to various detectors can enable more information regarding chemical composition, molecular weight, concentration, and structure.

Magnetization of 3-dimentional homochiral metal-organic frameworks for efficient and highly selective capture of phosphopeptides.

Enrichment of phosphopeptides based on various affinity probes prior to mass spectrometry detection is usually required due to the low abundance and low ionization efficiency of phosphopeptides. In this work, a 3-dimentional homochiral metal-organic frameworks (MOFs) was modified with magnetic nanoparticles using a facile method and then utilized for phosphopeptides capture with high efficiency and specificity. Based on magnetic solid phase extraction, a rapid and efficient method was developed and the whole enrichment procedure could be easily finished within 10min. Efficient and highly selective capture of phosphopeptides from tryptic digests and human serum was achieved. This affinity probe showed satisfactory reproducibility of the particle synthesis and could be recycled for at least seven times. With all the advantages mentioned above, this strategy is of great potential for routine application in phosphoproteomes.

Metabolomics Approach Reveals Integrated Metabolic Network Associated with Serotonin Deficiency.

Serotonin is an important neurotransmitter that broadly participates in various biological processes. While serotonin deficiency has been associated with multiple pathological conditions such as depression, schizophrenia, Alzheimer's disease and Parkinson's disease, the serotonin-dependent mechanisms remain poorly understood. This study therefore aimed to identify novel biomarkers and metabolic pathways perturbed by serotonin deficiency using metabolomics approach in order to gain new metabolic insights into the serotonin deficiency-related molecular mechanisms. Serotonin deficiency was achieved through pharmacological inhibition of tryptophan hydroxylase (Tph) using p-chlorophenylalanine (pCPA) or genetic knockout of the neuronal specific Tph2 isoform. This dual approach improved specificity for the serotonin deficiency-associated biomarkers while minimizing nonspecific effects of pCPA treatment or Tph2 knockout (Tph2-/-). Non-targeted metabolic profiling and a targeted pCPA dose-response study identified 21 biomarkers in the pCPA-treated mice while 17 metabolites in the Tph2-/- mice were found to be significantly altered compared with the control mice. These newly identified biomarkers were associated with amino acid, energy, purine, lipid and gut microflora metabolisms. Oxidative stress was also found to be significantly increased in the serotonin deficient mice. These new biomarkers and the overall metabolic pathways may provide new understanding for the serotonin deficiency-associated mechanisms under multiple pathological states.

Facile synthesis of magnetic homochiral metal-organic frameworks for "enantioselective fishing".

Magnetic functionalized homochiral metal-organic frameworks (MOFs) were prepared and applied to efficient enantioselective fishing of chiral drug intermediates. Under optimized conditions, the enantiomeric excess (ee) value as high as 85.2% was achieved for methyl phenyl sulfoxide (MPS) within 3 min.

[Analysis of tartrazine aluminum lake and sunset yellow aluminum lake in foods by capillary zone electrophoresis].

A novel analytical method for tartrazine aluminum lake and sunset yellow aluminum lake using capillary zone electrophoresis (CZE) was studied. The pigments contained in the color lakes were successfully separated from the aluminum matrix in the pre-treatment process, which included the following steps: dissolve the color lakes in 0.1 mol/L H2SO4, adjust the pH of the solution to 5.0, then mix it with the solution of EDTA x 2Na and heat it in a water bath, then use polyamide powder as the stationary phase of solid phase extraction to separate the pigments from the solution, and finally elute the pigments with 0.1 mol/L NaOH. The CZE conditions systematically optimized for tartrazine aluminum lake were: 48.50 cm of a fused silica capillary with 40.00 cm effective length and 50 microm i. d., the temperature controlled at 20.0 degrees C, 29.0 kV applied, HPO4(2-)-PO4(3-) (0.015 mol/L, pH 11.45) solution as running buffer, detection at 263 nm. The conditions for sunset yellow aluminum lake were: the same capillary and temperature, 25.0 kV applied, HPO4(2-)-PO4(3-) (0.025 mol/L, pH 11.45) solution as running buffer, detection at 240 nm. The limits of detection were 0.26 mg/L and 0.27 mg/L, and the linear ranges were 0.53-1.3 x 10(2) mg/L and 0.54-1.4 x 10(2) mg/L for tartrazine aluminum lake and sunset yellow aluminum lake, respectively. The RSDs were 4.3% and 5.7% (run to run, n = 6), 5.6% and 6.0% (day to day, n = 6) for tartrazine aluminum lake and sunset yellow aluminum lake, respectively. Further developments for this method could make it a routinely used method analyzing color lakes in foods.

Solid-phase extraction with the metal-organic framework MIL-101(Cr) combined with direct analysis in real time mass spectrometry for the fast analysis of triazine herbicides.

MIL-101(Cr) is an excellent metal-organic framework with high surface area and nanoscale cavities, making it promising in solid-phase extraction. Herein, we used MIL-101(Cr) as a solid-phase extraction packing material combined with fast detection of direct analysis in real time mass spectrometry (DART-MS) for the analysis of triazine herbicides. After systematic optimization of the operation parameters, including the gas temperature of DART, the moving speed of the 1D platform, solvent for desorption, amount of MIL-101(Cr) extraction time, eluent volume and salt concentration, this method can realize the simultaneous detection of five kinds of triazine herbicides. The limits of detection were 0.1∼0.2 ng/mL and the linear ranges covered more than two orders of magnitude with the quantitation limits of 0.5∼1 ng/mL. Moreover, the developed method has been applied for the analysis of lake water samples and the recoveries for spiked analytes were in the range of 85∼110%. These results showed that solid-phase extraction with metal-organic frameworks is an efficient sample preparation approach for DART-MS analysis and could find more applications in environmental analysis.

Applications of homochiral metal-organic frameworks in enantioselective adsorption and chromatography separation.

Chiral separation is of great importance for drug development, pharmacology, and biology. Chiral metal-organic frameworks (MOFs) is a new class of porous solid materials with high surface area, large pore size, high chemical stability, uniformly structured cavities, and the availability of modification. The excellent properties of MOFs have attracted intense interest to explore their performance and mechanism in chiral separation. This review summarizes three synthetic strategies of chiral MOFs and their applications in enantioselective adsorption and chromatographic separation. All the experimental and molecular simulation results demonstrated that high enantioselectivity was strongly correlated with a close match between the size of the pore and chiral molecules.

Combination of dynamic pH junction with capillary electrophoresis-mass spectrometry for the determination of systemins in plant samples.

Systemin is an important group of plant peptide hormones participating in the regulation of plant defensive responses. An improved method, based on dynamic pH junction and capillary electrophoresis-quadrupole time-of-flight mass spectrometry, was developed for online enrichment and sensitive determination of trace systemins in plants. After optimization, the online enrichment factors for six target systemins ranged from 90- to 127-fold. The detection limits reached lower than 0.5 nM, which were comparable with the sensitivity of LC-MS method. Satisfactory quantitative results were obtained in terms of linearity (R(2) ≥ 0.993), dynamic range (3-120 ng/mL), and reproducibility (≤6.7%). For the analysis of real plant samples, a rapid sample preparation method was developed, using two steps of SPE purification with different retention and separation mechanisms. Finally, this method realized the successful detection of tomato systemin and tobacco hydroxyproline-rich systemin I from plant leaves with shorter analysis time.

Ambient mass spectrometry imaging: plasma assisted laser desorption ionization mass spectrometry imaging and its applications.

Mass spectrometry imaging (MSI) has been widely used in many research areas for the advantages of providing informative molecular distribution with high specificity. Among the recent progress, ambient MSI has attracted increasing interests owing to its characteristics of ambient, in situ, and nonpretreatment analysis. Here, we are presenting the ambient MSI for traditional Chinese medicines (TCMs) and authentication of work of art and documents using plasma assisted laser desorption ionization mass spectrometry (PALDI-MS). Compared with current ambient MSI methods, an excellent average resolution of 60 µm × 60 µm pixel size was achieved using this system. The feasibility of PALDI-based MSI was confirmed by seal imaging, and its authentication applications were demonstrated by imaging of printed Chinese characters. Imaging of the Radix Scutellariae slice showed that the two active components, baicalein and wogonin, mainly were distributed in the epidermis of the root, which proposed an approach for distinguishing TCMs' origins and the distribution of active components of TCMs and exploring the environmental effects of plant growth. PALDI-MS imaging provides a strong complement for the MSI strategy with the enhanced spatial resolution, which is promising in many research fields, such as artwork identification, TCMs' and botanic research, pharmaceutical applications, etc.

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.

Automated and sensitive analysis of 28-epihomobrassinolide in Arabidopsis thaliana by on-line polymer monolith microextraction coupled to liquid chromatography-mass spectrometry.

By on-line solid phase microextraction with polymer monolith coupled to liquid chromatography-mass spectrometry (SPME-LC-MS), an automated and sensitive method for analysis of the endogenous 28-epihomobrassinolide (28-epihomoBR) in Arabidopsis thaliana was developed in this work. Firstly, a poly(methacrylic acid-co-ethylene dimethacrylate) (poly(MAA-co-EDMA)) monolith was prepared in the capillary and applied in in-tube SPME. Polyethylene glycol (PEG) was used as porogen to adjust the specific surface area and hydrophobicity of the target monolith to get satisfactory permeability, high mechanical strength and good stability. The optimized monolith was then served as extraction medium for analysis of the derivatized 28-epihomoBR in plant samples with the cleanup of matrix and enrichment of desired analyte at the same time. Good linearity was obtained in the linear range of 5-500 ng/L with the coefficient of determination (R(2)) of 0.9996. The limit of detection (S/N=3) of 28-epihomoBR was found to be 2.0 ng/L and the limit of quantification (S/N=10) was 5.0 ng/L. Using this method, the endogenous 0.101 ng/g (FW) 28-epihomoBR was successfully detected from only 400mg A. thaliana samples with satisfactory recovery (80.3-92.1%) and reproducibility (RSD 6.8-9.6%). Comparing with other sample pretreatment methods, this automated on-line SPME-LC-MS method is rapid, sensitive, reproducible and laborsaving.

Applications of ambient mass spectrometry in high-throughput screening.

The development of rapid screening and identification techniques is of great importance for drug discovery, doping control, forensic identification, food safety and quality control. Ambient mass spectrometry (AMS) allows rapid and direct analysis of various samples in open air with little sample preparation. Recently, its applications in high-throughput screening have been in rapid progress. During the past decade, various ambient ionization techniques have been developed and applied in high-throughput screening. This review discusses typical applications of AMS, including DESI (desorption electrospray ionization), DART (direct analysis in real time), EESI (extractive electrospray ionization), etc., in high-throughput screening (HTS).

Online coupling of capillary electrophoresis with direct analysis in real time mass spectrometry.

The online coupling of capillary electrophoresis with ambient direct analysis in real time mass spectrometry (DART-MS) was realized by a coaxial tip interface. The analytes eluted from capillary electrophoresis (CE) were directly ionized by the metastable helium flux produced by DART and transferred into MS for the detection, with which the online separation and simultaneous detection were achieved. The CE-DART-MS can tolerate higher concentrations of detergents and salts than traditional CE-electrospray ionization (ESI)-MS and avoided the difficulties of collecting CE effluent and cleaning the interface, which simplified the experimental procedures and shortened the analysis time. The performance of the technique was successfully verified by capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC) using a mixture of 4-aminoantipyrine, zolmitriptan, and quinine. This online technique showed good repeatability with the relative standard deviations (RSDs; n = 5) of 0.56-1.23% for the retention times and 2.01-7.41% for the peak areas. The quantitative analysis of 4-aminoantipyrine was accomplished in the range of 0.01-0.50 mg/mL with the linear correlation coefficient of 0.9995 and limit of detection of 14.7 fmol. Compared with CE-ESI-MS, the ion suppression effects of nonvolatile salts and detergents were efficiently minimized. The signal intensity remained constant when the concentrations reached 100 mM for sodium borate and 30 mM for SDS (in 30 mM sodium borate buffer). In addition, the proposed method was successfully applied to the detection of the endogenous caffeine in Chinese white tea.

Normal phase LC coupled with direct analysis in real time MS for the chiral analysis of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol and jasmonic acid.

Normal phase chiral LC (NPLC) has been proved to be powerful and efficient for chiral separation. However, the combination of NPLC with ESI or atmospheric pressure chemical ionization MS is restricted by the poor ionization efficiency and thermal fragmentations of analytes to some extent. Direct analysis in real time MS (DART-MS) is an ambient ionization technique that shows high ionization efficiency of the analytes in the normal phase mobile phase. In this work, we coupled chiral NPLC to DART-MS for the chiral qualitative and quantitative analysis of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol and jasmonic acid enantiomers. Satisfactory results for the enantiomers of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol operating in the positive mode were obtained in terms of linearity (2.5-250 µg/mL, R(2) , 0.999-1.000) and repeatability (25 µg/mL, RSDs, 4.7-5.6%). Moreover, chiral NPLC-DART-MS resulted in the simultaneous chiral separation and detection of jasmonic acid enantiomers, which are very difficult to be analyzed by NPLC-ESI-MS and NPLC-APCI-MS. Compared with the coupled techniques of NPLC-ESI-MS and NPLC-APCI-MS, NPLC-DART-MS showed advantages in increasing the ionization efficiency and reducing the in-source thermal fragmentation of analytes.