A simple,rapid and reliable liquid chromatography–mass spectrometry method for determination of methotrexate in human plasma and its application to therapeutic drug monitoring

A simple, rapid and reliable liquid chromatography–electrospray ionization tandem mass spectrometry method was established and validated for the determination of methotrexate in human plasma. After a straightforward protein precipitation by acetonitrile–water (70:30, v/v), methotrexate (MTX) and p‐aminoacetophenone (used as internal standard, IS) were separated on a Column C₁₈ column (50 × 2.1 mm, 3 µm; Column Technology, Fremont, CA, USA) using a gradient elution with mobile phase of acetonitrile and 0.03% acetic acid aqueous solution at a flow rate of 0.5 mL/min. The total chromatographic runtime was 5 min for each injection. Quantification detection was performed in a triple‐quadruple tandem mass spectrometer under positive mode monitoring the following mass transitions: m/z 455.3 → 308.3 for MTX and m/z 136.1 → 94.4 for IS. The calibration curve was linear over the range of 0.05–25.0 µmol/L with a lower limit of quantification of 0.05 µmol/L. The intra‐ and interday precisions were <5.2%, the accuracy varied from ?4.1 to 4.5%. The recovery was >94%. The LC‐MS/MS method showed an excellent agreement with the existing HPLC‐UV method using Passing–Bablok regression and Bland–Altman difference plot analysis. The validated LC‐MS/MS can be successfully applied to the routine therapeutic drug monitoring of MTX in clinical laboratories. Copyright © 2015 John Wiley & Sons, Ltd.     

Sustainable alternative in environmental monitoring using carbon nanoparticles as optical probes

Environmental monitoring is getting more important nowadays due to the greater stress faced by the natural environment in the era of urbanisation and industrialisation. To accomplish the task, rapid and reliable analytical probes are essentially needed to perform the monitoring at real time basis with high sensitivity and accuracy. In view of this, analytical probes developed using carbon nanoparticles are one of the latest alternatives that are proven with capability to detect various analytes of the environment. Carbon nanoparticles portray good fluorescence property that enables the integration onto optical sensing transducers. Further engineering via surface functionalization can be performed in the interest to improve the selectivity and sensitivity of the probes. There are several advantages of using carbon nanoparticles and the most significant benefit is the sustainability prospect as compared to other groups of fluorophores. Carbon nanoparticles can be synthesised with greener approach via simple pyrolysis or hydrolysis processes that involve minimum use of toxic or harmful starting precursors, besides able to tap on using renewable resources such as carbon rich agricultural wastes. The synthesis is often performed under mild condition and produces less or no side chemical products. Carbon nanoparticles by nature show low toxicity effect to the environment. This review focuses specifically of the sustainable significances, advantages and achievements in adopting carbon nanoparticles as an alternative for environmental monitoring.     

Strategies for differentiation of isobaric flavonoids using liquid chromatography coupled to electrospray ionization mass spectrometry

Flavonoids are a class of secondary plant metabolites existing in great variety in nature. Due to this variety, identification can be difficult, especially as overlapping compounds in both chromatographic separations and mass spectrometric detection are common. Methods for distinguishing isobaric flavonoids using MS² and MS³ have been developed. Chromatographic separation of various plant extracts was done with RP‐HPLC and detected with positive ESI‐MS operated in information‐dependent acquisition (IDA) mode. Two methods for the determination of flavonoid identity and substitution pattern, both featuring IDA criteria, were used together with the HPLC equipment. A third method where the collision energy was ramped utilized direct infusion. With the developed strategies, it is possible to differentiate between many isobaric flavonoids. Various classes of flavonoids were found in all of the plant extracts, in the red onion extract 45 components were detected and for 29 of them the aglycone was characterized, while the substituents were tentatively identified for 31 of them. For the strawberry extract, those numbers were 66, 30 and 60, and for the cherry extract 99, 56 and 71. The great variety of flavonoids, several of them isobaric, found in each of the extracts highlights the need for reliable methods for flavonoid characterization. Methods capable of differentiating between most of the isobars analyzed have been developed. Copyright © 2014 John Wiley & Sons, Ltd.     

Direct Measurement of Ammonia in Ambient Air

Abstract

A model is proposed which addresses the factors involved in the axial light attenuation of a coated waveguide (collector/sensor) whose polymer coating has been sensitized to ammonia. The experimental results appear to corroborate the model predictions of high sensitivity (ppb) and independence of sample flow on the collector/sensor. Concentration and relative humidity both determine the slopes of the transmission curves, the latter factor of which can be reduced to a second order effect by controlling the relative humidity in the sample holder.     

The assay of pterostilbene in spiked matrices by liquid chromatography tandem mass spectrometry and isotope dilution method

Pterostilbene (trans‐3,5‐dimethoxy‐4‐hydroxystilbene) is an active component found in several plant species, exhibiting important pharmacological properties. A new and reliable method of assaying this phyto compound in various matrices is presented; the assay is based on (1) the selectivity of liquid chromatography (LC) hyphenated with electrospray ionisation (ESI), (2) the specificity of a two‐step mass spectrometric analysis (MS/MS) and (3) the accuracy of the isotope dilution method. The labelled analogue may be conveniently synthesised in a few steps. The sensitivity of the method is confirmed by the very low limit of detection (LOD) and limit of quantitation (LOQ) values achieved in the assay of pterostilbene in two distinct fortified matrices, and is further supported by the observed accuracy values. Copyright © 2010 John Wiley & Sons, Ltd.     

A sensitive quantitative assay for the determination of propafenone and two metabolites, 5‐hydroxypropafenone and N‐depropylpropafenone,in human K2EDTA plasma using LC–MS/MS with ESI operated in positive mode

Propafenone is a potent antiarrhythmic agent; clinically propafenone has been used for a number of cardiac arrhythmias because it possesses multiple modes of action, via beta adrenergic receptor blockade and calcium antagonistic activity. Propafenone (PPF) exhibits extensive saturable presystemic biotransformation (first‐pass effect) resulting in two active metabolites: 5‐hydroxypropafenone (5‐OH PPF) formed by CYP2D6 and N‐ depropylpropafenone (NDP) formed by both CYP3A4 and CYP1A2 enzymes. A specific and sensitive LC–MS/MS method was developed and validated for quantitation of PPF, 5‐OH PPF and NDP using turboion spray in a positive ion mode. A solid‐phase extraction was employed for the extraction from human plasma. Chromatographic separation of analytes was achieved using an ACE‐5 C₈ (50 × 4.6 mm) column with a gradient mobile phase comprising ammonium acetate containing 0.01% TFA in purified water and acetonitrile. The retention times achieved were 1.36, 1.23, 1.24 min and 1.34 min for PPF, 5‐OH PPF, NDP and IS (carbamazepine), respectively. Quantitation was performed by monitoring multiple reaction monitoring transition pairs of m /z 342.30 to m /z 116.20, m /z 358.30 to m /z 116.20, m /z 300.30 to m /z 74.20 and m /z 237.20 to m /z 194.10, respectively. The developed method was validated for various parameters. The calibration curves of PPF and 5‐OH PPF showed linearity from 1 to 500 ng/mL, with a lower limit of quantitation of 1.0 ng/mL and for NDP linearity from 0.1 to 25 ng/mL with a lower limit of quantitation of 0.1 ng/mL. The bias and precision for intra‐ and‐inter batch assays were <10 and 5%, respectively. The developed assay was used to evaluate pharmacokinetic properties of propafenone and its major metabolites in healthy human subjects.     

On‐line process monitoring of coffee roasting by resonant laser ionisation time‐of‐flight mass spectrometry: bridging the gap from industrial batch roasting to flavour formation inside an individual coffee bean

Resonance‐enhanced multiphoton ionisation time‐of‐flight mass spectrometry (REMPI‐TOFMS) enables the fast and sensitive on‐line monitoring of volatile organic compounds (VOC) formed during coffee roasting. On the one hand, REMPI‐TOFMS was applied to monitor roasting gases of an industrial roaster (1500 kg/h capacity), with the aim of determining the roast degree in real‐time from the transient chemical signature of VOCs. On the other hand, a previously developed μ‐probe sampling device was used to analyse roasting gases from individual coffee beans. The aim was to explore fundamental processes at the individual bean level and link these to phenomena at the batch level. The pioneering single‐bean experiments were conducted in two configurations: (1) VOCs formed inside a bean were sampled in situ, i.e. via a drilled μ‐hole, from the interior, using a μ‐probe (inside). (2) VOCs were sampled on‐line in close vicinity of a single coffee bean's surface (outside). The focus was on VOCs originating from hydrolysis and pyrolytic degradation of chlorogenic acids, like feruloyl quinic acid and caffeoyl quinic acid. The single bean experiments revealed interesting phenomena. First, differences in time–intensity profiles between inside versus outside (time shift of maximum) were observed and tentatively linked to the permeability of the bean's cell walls material. Second, sharp bursts of some VOCs were observed, while others did exhibit smooth release curves. It is believed that these reflect a direct observation of bean popping during roasting. Finally, discrimination between Coffea arabica and Coffea canephora was demonstrated based on high‐mass volatile markers, exclusively present in spectra of Coffea arabica. Copyright © 2013 John Wiley & Sons, Ltd.     

电化学生物传感器在环境监测中的应用及发展前景

简要介绍了电化学生物传感器的工作原理,重点论述了电化学生物传感器在环境监测领域的应用及其研究进展,主要包括水环境污染物和大气污染物的监测,以及农药残留的监测等.同时,对电化学生物传感器的发展方向及前景进行了展望.     

重度原油注空气低温氧化过程研究(英文)

低温氧化反应对现场燃烧(ISC)技术点火的成功有十分重要的影响.采用高压氧化管,研究了不同温度压力下,新疆克拉玛依重度原油的低温氧化过程.结果表明,温度和压力的变化对低温氧化反应的放热程度、持续时间以及气体产物有明显影响.适合油样低温氧化反应的温度和压力分别为150℃和10MPa.此外,采用纯组分替代原油族组分进行低温氧化实验,研究低温氧化反应对原油族组分(饱和烃、芳香烃、胶质、沥青质)含量的影响.结果表明,原油所含族组分中,芳香烃组分最易被氧化,其含量由氧化前的19.17%减少到12.38%(150℃)和9.51%(250℃).随着低温氧化过程的进行,结构复杂的族组分(胶质、沥青质)的含量明显增加.实验数据对油藏实施注空气技术,以及该技术现场实施条件的确定有十分重要的指导意义.