Analytical Chemistry Research最新文献

Chromatin contains valuable epigenetic information comprising of both DNA and post translational histone modifications. Traditionally, detection of epigenetic modifications on DNA and histone proteins requires different and elaborate preparation steps. In this study we report on a facile and unique approach for the simultaneous detection and quantification of epigenetic modifications on DNA and histone proteins in one sample preparation step. Our novel one-pot technique consists of a chromatin extraction step from whole blood using bi-functional carboxyl-functionalized magnetic nanoparticles as solid-phase absorbents. Leucocytes enrichment from blood and chromatin extracted from the leucocytes by lysis was achieved with the same carboxyl-functionalized magnetic nanoparticles. The isolated chromatin was then eluted from the magnetic nanoparticles with PBS 1×. Using the eluted chromatin as substrate, we developed a quantitative method for simultaneous detection of epigenetic modifications on DNA and histone proteins by a biotin–streptavidin mediated enzyme-based immunosorbent assay (two-step EIA) on a 96-well plate. The simultaneous detection of epigenetic modifications on DNA and histone was validated by DNA-based EIA and histone-based Western blotting analysis performed separately with conventional protocols. By coupling cell separation and chromatin purification with a simple detection module, the global epigenetic information could be evaluated in less than 8 h in leucocytes from blood. Our simplified cross-platform approach can be used by most laboratories for multiplex detection, uses non-hazardous materials and could be integrated with microfabrication methods for onchip analysis.

We have successfully observed the change in indium–gallium–zinc–oxide (IGZO) gas sensor sensitivity by controlling the light emitting diode (LED) power under the same gas concentrations. The light intensity dependence of sensor properties is discussed. Different LED intensities obviously affected the gas sensor sensitivity, which decays with increasing LED intensity. High LED intensity decreases not only gas sensor sensitivity but also the response time (T₉₀), response time constant (τ_res) and the absorption rate per second. Low intensity irradiated to sensor causes high sensitivity, but it needs larger response time. Similar results were also observed in other kinds of materials such as TiO₂. According to the results, the sensing properties of gas sensors can be modulated by controlling the light intensity.

Organosulphur compounds were determined in seawater samples by gas chromatography using a pulse flame detection method. The analytical method involved the use of octyl-diol mesoporous silica as a replacement for organic solvents in the extraction and pre-concentration of organosulphur compounds from seawater samples based on the solid phase dispersion extraction technique. The detection limits were in the range 0.6–2 ng S/L, while the repeatability and reproducibility were 7–12% and 13–16% respectively. Relative standard deviations (%) for recovery of n-ethanthiol (n-EtSH), di-n-ethyl sulphide (n-Et₂S) and di-n-ethyl disulphide (n-Et₂S₂) in spiked water samples were in the range 2.2–6.6% (at 0.5 μg/L level). Under the experimental conditions used, quantitative extraction of n-EtSH, n-Et₂S and n-Et₂S₂ was achieved with recoveries ranging from 93% to 99%. The procedure has been successfully applied to organosulphur determination in seawater samples collected from Jeddah beach (West of Saudi Arabia).

This paper describes two simple and novel analytical methods by using spectrophotometric technique for the determination of caroverine a spasmolytic drug in pharmaceutical formulations. The first (A) is a direct method in which analysis of the pure drug was carried out at its λ_max 304 nm in ethanol solvent. The method was linear from 0.5 to 18 μg/ml with correlation coefficient of 0.999 and molar absorptivity of 5.55 × 10⁴ L mole⁻¹ cm⁻¹. Limit of detection and limit of quantification were 0.44 and 1.47 μg/ml. While the second method (B) is based on the charge transfer reaction between caroverine as n-electron donor and 7,7,8,8-tetracyanoquinodimethane (TCNQ) as pi-acceptor resulting in highly colored stable complex, which showed maximum absorption band at wavelength of 525 nm. The thermodynamic parameters were calculated as association constant K_CT of 7.53 × 10⁴ mol⁻¹ and Gibbs free energy ΔG° of −6.72 kJ mol⁻¹. Different variables affecting the charge transfer reaction were carefully studied and optimized. At the optimum reaction conditions, Beer’s law was obeyed in a concentration range of 1–35 μg ml⁻¹ with molar absorptivity of 1.17 × 10⁴ L mole⁻¹ cm⁻¹ and correlation coefficient of 0.9999. The proposed methods were validated according to ICH guidelines.

The therapeutic benefit of phosphorothioate oligodeoxynucleotides (PS-ODN) containing immune stimulatory sequences has been demonstrated in animal models of cancer and infection. Several tools are available for the determination of these oligonucleotides in biological samples and pharmaceutical preparations, including UV spectroscopy, dye binding, isotopic tracing, capillary gel electrophoresis (CGE), hybridization-based enzyme-linked immunosorbent assay (ELISA), and chromatography techniques.

However, due to inter-assay variability and accuracy problems associated with the afore mentioned methods, we have developed and validated an isocratic high performance liquid chromatographic (HPLC) for analytical determination of PS-ODN containing unmethylated CpG motifs (CpG-ODN). Validation under Food and Drug Administration (FDA) guidelines of the analytical parameters include: linearity (r² 0.9996), LOD (0.86 μg/ml) and LOQ (6.25 μg/ml), intra (0.19–3.37%) and inter-day precision (0.63–3.75%) expressed as relative standard deviation (RSD), and robustness parameters (less than 2.80%). Using this method, recoveries ranging from 89.9% to 99.9% were obtained. Thus, this method provides a simple, sensitive, precise and reproducible examination which can be readily adapted for the assessment of CpG-ODN in different pharmaceutical preparations.

This study demonstrates the influence of the solvent when thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) is employed for the determination of elements of low volatility, taking magnesium (Mg) as leading case. Several organic solvents/water solutions of different characteristics (density, surface tension, viscosity, etc.) and proportions were employed for the TS-FF-AAS analytical determination. To this end, solutions containing methanol, ethanol and isopropanol in water were assayed. Measurements were performed at different acetylene/air ratios of the combustion flame and then, the corresponding response surfaces were obtained. Methanol/water 75% v/v as carrier and a fuel rich flame were found as the most sensitive alternative.

In the light of these findings and in order to explain the changes on the analytical signal, the influence of the solvent characteristics, the sample droplet size and the redox environment was studied. An estimation of the temperature of different zones of the heated flame furnace based on a modified signal ratio pyrometry method was analyzed for comparative purposes. A full discussion is provided throughout the paper.

Once obtained the best conditions for analysis, Mg was determined in samples of effervescent vitamin tablets comparing two different solvents. The tablets were dissolved in methanol/water 75% v/v and ethanol/water 75% v/v and then, directly introduced in the TS device. The methanol/water 75% v/v dissolution yielded a slightly higher sensitivity when compared to ethanol/water and thus, the latter was selected due to its lower toxicity. The obtained figures of merit are: LOD (3σb): 0.021 mg L⁻¹; LOQ (10σb): 0.068 mg L⁻¹, sensitivity: 0.086 L mg⁻¹; RSD%: 3.55, dynamic linear range 0.068–5 mg L⁻¹. Comparison of the results was performed by flame atomic absorption spectrometry (FAAS), showing a good agreement (95% confidence level, n = 5). Whilst the FAAS approach needed sample mineralization as no complete solubility was attained with both alcohol/water solvents, TS allowed direct introduction of the sample with an excellent recovery of the analyte after spiking. The whole TS procedure was more economic (lower amount of reagents and wastings, lower time of operation) and faster (60 h⁻¹ sampling throughput) than FAAS.

Nonetheless, the main objective of this work is to show that an analytical signal different from zero can be obtained for Mg via TS by simply choosing the adequate operational variables that allow an optimization of the mass transfer of the analyte into the atomizer and a favorable dynamics of desolvation/atomization.

This approach could broad TS analytical capabilities to other elements of lower volatility as it is shown here for the case of Mg.