Graphene/poly(ethylene-co-vinyl acetate) composite electrode fabricated by melt compounding for capillary electrophoretic determination of flavones in Cacumen platycladi.

In this report, a graphene/poly(ethylene-co-vinyl acetate) composite electrode was fabricated by melt compounding for the amperometric detection of capillary electrophoresis. The composite electrode was fabricated by packing a mixture of graphene and melted poly(ethylene-co-vinyl acetate) in a piece of fused silica capillary under heat. The structure of the composite was investigated by scanning electron microscopy and Fourier transform infrared spectroscopy. The results indicated that graphene sheets were well dispersed in the composite to form an interconnected conducting network. The performance of this unique graphene-based detector has been demonstrated by separating and detecting rutin, quercitrin, kaempferol, and quercetin in Cacumen platycladi in combination with capillary electrophoresis. The four flavones have been well separated within 9 min in a 50-cm-long capillary at a separation voltage of 12 kV using a 50 mM sodium borate buffer (pH 9.2). The graphene-based detector offered significantly lower operating potentials, substantially enhanced signal-to-noise characteristics, lower expense of operation, high resistance to surface fouling, and enhanced stability. It showed long-term stability and repeatability with relative standard deviations of <5% for the peak current (n = 15).

Narrow mass extraction of time-of-flight data for quantitative analysis of proteins: determination of insulin-like growth factor-1.

Methods for quantitative analysis of proteins by mass spectrometry have progressed dramatically. While isotope-dilution approaches using selected reaction monitoring of tryptic peptides (also known as bottom up) have become common, the potential to use narrow mass extraction of high-resolution mass spectra provides a compelling alternative. We investigated the relationships between instrument performance and data processing with the aim of determining whether this approach can lead to robust bioanalytical assays for proteins. Our approach utilized off-line sample preparation combined with online sample extraction coupled to HPLC with the effluent from the analytical column directed to a high-resolution, high-mass accuracy quadrupole time-of-flight (qTOF) mass spectrometer operated in full scan mode. Narrow mass extraction of a single isotope from IGF-1 in the 7+ charge state (m/z 1093.5209) was used to generate extracted ion chromatograms. We found that with appropriate attention to instrument performance and data processing, quantitative protein assays with good sensitivity, high selectivity, and excellent analytical performance can be developed.

Expanding the mouse embryonic stem cell proteome: combining three proteomic approaches.

The current study used three different proteomic strategies, which differed by their extent of intact protein separation, to examine the proteome of a pluripotent mouse embryonic stem cell line, R1. Proteins from whole-cell lysates were subjected either to 2-D-LC, or 1-DE, or were unfractionated prior to enzymatic digestion and subsequent analysis by MS. The results yielded 1895 identified non-redundant proteins and, for 128 of these, the specific isoform could be determined based on detection of an isoform-specific peptide. When compared with two previously published proteomic studies that used the same cell line, the current study reveals 612 new proteins.

Determination of 5,7-dihydroxychromone and luteolin in peanut hulls by capillary electrophoresis with a multiwall carbon nanotube/poly(ethylene terephthalate) composite electrode.

A novel multiwall carbon nanotube/poly(ethylene terephthalate) (MWCNT/PET) composite electrode was developed for the determination of 5,7-dihydroxychromone and luteolin in peanut hulls in combination with capillary electrophoresis (CE). The electrode was fabricated by packing a mixture of MWCNTs and melted PET in a piece of fused-silica capillary under heat. Because of the simple composition of the phenolic constituents in peanut hulls, they were used to demonstrate the performance of the fabricated electrode. The results indicated that 5,7-dihydroxychromone and luteolin were well separated within 12 min in a 40 cm long capillary at a separation voltage of 12 kV using a 50mM borate buffer (pH 9.2). The MWCNT-based electrode exhibited significantly lower detection potentials, enhanced signal-to-noise characteristics, and higher resistance to surface fouling compared to graphite/PET composite electrode. It showed long-term stability and reproducibility with a relative standard deviation of 2.6% for the peak current (n = 15). The relation between peak current and analyte concentration was linear over about three orders of magnitude. The proposed method has been applied to determine the two bioactive constituents in real samples.

Facile assembly of graphene on anion exchange resin microspheres for electrochemical sensing and biosensing.

Graphene sheets were assembled on anion exchange resin (AER) microspheres based on the electrostatic interactions between graphene oxide and AER and subsequent chemical reduction. The prepared graphene-coated AER microspheres were characterized by scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. They were then embedded in the bores of pipette tips to fabricate disposable electrodes for electrochemical sensing. The workability and performance of the novel electrodes were examined by analyzing the electrochemical behavior of the electrodes for the sensing of ascorbic acid, dopamine, uric acid, acetaminophen, aniline, and glucose by cyclic voltammetry and amperometry. The advantages of the electrodes include ease of fabrication, low cost, pronounced electrocatalytic activity, and rapid response. Thus, they hold great promise for a wide range of applications.

Clinical utility of insulin-like growth factor 1 and 2; determination by high resolution mass spectrometry.

Measurement of insulin-like growth factor-1 (IGF-I) has utility for the diagnosis and management of growth disorders, but inter-assay comparison of results has been complicated by a multitude of reference standards, antibodies, detection methods, and pre-analytical preparation strategies. We developed a quantitative LC-MS method for intact IGF-I, which has advantages in throughput and complexity when compared to mass spectrometric approaches that rely on stable isotope dilution analysis of tryptic peptides. Since the method makes use of full-scan data, the assay was easily extended to provide quantitative measurement of IGF-II using the same assay protocol. The validated LC-MS assay for IGF-I and IGF-II provides accurate results across the pediatric and adult reference range and is suitable for clinical use.