The inhomogeneous re-crystallization process of matrix materials is the major concerns associated with matrix assisted laser desorption/ionization (MALDI) analysis. We describe here the approach termed compressed matrix thin film (CMTF) in order to make a uniform matrix deposition. In this approach, solid matrix particles are compressed under 10 MPa of pressure by a compressor that is regularly used in infrared spectroscopic analysis. Then aqueous samples can be deposited on the surface of the matrix film. Major advantages of the CMTF approach are summarized as follows. (1) Reproducible sample preparation procedure. Size and thickness of matrix thin films can be controlled by using a fixed mold.force and known amount of matrix materials. (2) Significantly decreased shot-to-shot variations and enhanced reproducibility. (3) Tolerance for in situ salt washing. Because matrix materials are hydrophobic, salts can be washed away while proteins or peptides are retained on the surface of matrix thin films through hydrophobic interactions. (4) Improved sensitivity. The hydrophobic coating of MALDI sample plate by matrix thin films prevents the spreading of samples across the plate and confines analytes to a small area, leading to increased local concentration. (5) A new means for tissue analysis. Tissue sections can be directly transferred to the uniform surface of matrix materials for reproducible and quantitative comparison of different molecules in different localization. The proposed CMTF should be an enabling technique for mass spectrometric analysis with improved correlations between signal intensities and sample quantities. 相似文献
Tunable polymerization of ionic liquid on the surfaces of multi-walled carbon nanotubes (MWCNTs) was achieved by a mild thermal-initiation-free radical reaction of 3-ethy-1-vinylimidazolium tetrafluoroborate in the presence of MWCNTs. Successful modification of polymeric ionic liquid (PIL) on MWCNTs surfaces (PIL-MWCNTs) was demonstrated by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis and X-ray photoelectron spectroscopy. The resulting PIL-MWCNTs possessed unique features of high dispersity in aqueous solution and tunable thickness of PIL layer, due to positive imidazole groups along PIL chains and controllable ionic liquid polymerization by tuning the ratio of precursor. Based on cation-π interaction between the positive imidazole groups on PIL-MWCNTs surface and hydroquinone (HQ) or catechol (CC), excellent discrimination ability toward HQ and CC and improved simultaneous detection performance were achieved. The linear range for HQ and CC were 1.0 × 10−6 to 5.0 × 10−4 M and 1.0 × 10−6 to 4.0 × 10−4 M, respectively. The detection limit for HQ was 4.0 × 10−7 M and for CC 1.7 × 10−7 M (S/N = 3), correspondingly. 相似文献
A rhodamine spirolactam derivative (1) was developed as a colormetric and fluorescent chemosensor for adenosine-5′-triphosphate (ATP) via hydrogen bonds interaction. As far as we know, this is the first case to explore ATP-induced ring-opening of spirolactam in rhodamine derivatives. It exhibited a highly sensitive “turn-on” fluorescent response toward ATP with a 47-fold fluorescence intensity enhancement under 20 equiv. of ATP added. The chemosensor can be applied to the quantification of ATP with a linear range covering from 1.0 × 10−7 to 2.0 × 10−4 M and a detection limit of 2.5 × 10−8 M. The experiment results show that the response behavior of 1 toward ATP is pH independent in medium condition (pH 6.0–8.0). Most importantly, the novel chemosensor has well solved the problem of serious interferences from other nucleoside polyphosphates such as ADP and AMP generally met by previously reported typical fluorescent chemosensors for ATP. Moreover, the response of the chemosensor toward ATP is fast (response time less than 3 min). In addition, the chemosensor can be used for the fluorescence assay for protein kinase activity with satisfactory results. The chemosensor for ATP based on hydrogen bonds interaction provided a novel strategy for the design of colormetric and ratiometric fluorescent probes for other target anions with high sensitivity and selectivity. 相似文献
The qualitative and quantitative capability of the ion trap mass analyzer could be greatly affected by the accumulation time. However, the importance of the accumulation time has not so far been thoroughly explored. Here, the influence of ion accumulation time on qualitative and quantitative analysis of complicated components was systematically investigated based on the case study of 40 ophiopogonins in Ophiopogon extract by hybrid ion trap time-of-flight mass spectrometry (LCMS-IT-TOF). In this process, the accumulation time was set at 10, 25, 50, 100, and 200 ms, respectively. The effect of accumulation time on qualitative analysis of ophiopogonins was studied by comparing the total ion current (TIC) of MS1, TIC of MS2, and the number and signal of fragmental ions. The results demonstrated that the signal could be greatly influenced by varying the accumulation time. The number and signal of the fragmental ions were increased significantly with a longer accumulation time in the range of 10–100 ms. Also, the effect of accumulation time on quantitative analysis of ophiopogonins was investigated by comparing the linearity, accuracy, and precision measured on LCMS-IT-TOF. Importantly, quantitative parameters could all be significantly improved by choosing an appropriate accumulation time.
A simple and novel flow‐injection chemiluminescence (FI‐CL) method was established for the determination of 2‐Methoxyestradiol (2‐ME) in pharmaceutical preparations and biological fluids. The method was based on the significant enhancement of the CL from the KMnO4‐Na2SO3 reaction by 2‐ME in acidic medium. Under optimized conditions, the CL intensity was correlated linearly with concentration of 2‐ME in the range of 5.0 × 10?8‐5.0 × 10?6 M (r = 0.9995). The detection limit (3σ) of 2‐ME was 7.5 × 10?9 M and the relative standard deviation was 0.8% at 5.0 × 10?7 M 2‐ME (n = 8). The proposed method was successfully applied for the flow‐injection CL determination of 2‐ME in pharmaceutical preparations and biological fluids with the recoveries from 92.4 to 106.8%. The possible CL reaction mechanism was also discussed briefly. 相似文献
β‐Ionone was oxidized with O2 under solvent‐free conditions catalyzed by an N‐hydroxyphthalimide/Co(acac)2 system in mild conditions with high conversion and excellent selectivity to oxo‐β‐ionone or 5,6‐epoxy‐β‐ionone in different reaction conditions, respectively. 相似文献
α,β-Unsaturated aldimines were specifically oxidized to amides with Oxone in the presence of AlCl3 as a Lewis acid in CH2Cl2. No migration of aryl group occurred in the rearrangement reaction. 相似文献
A practical copper-catalyzed alkylarylation of activated alkenes with azobisisobutyronitrile (AIBN) and beyond has been developed, in which incorporation of 3o nitrile moiety into an oxindole scaffold proceeded smoothly through cascade radical addition/C(sp2)-H cyclization. The use of readily available AIBN as radical source and inexpensive CuI as catalyst, as well as broad substrate scope and the simplicity of operation and handling, make this protocol a highly attractive approach to oxindoles bearing 3o nitrile moiety. 相似文献