Analysis of Azithromycin in Human Plasma by LC–MS–MS

A simple sensitive and selective liquid chromatographic–tandem mass spectrometric method was developed and validated for the quantification of azithromycin in human plasma. Roxithromycin was used as the internal standard. The chromatographic separation was performed on a SunFire C18, 50 mm × 2.1, 3.5 μm column at 30 °C with mobile phase consisted of 1.54 g ammonium acetate, 250 mL water, 570 mL acetonitrile, 180 mL methanol and 0.6 mL glacial acetic acid. Flow rate was 0.2 mL min⁻¹. The work-up procedure involved a liquid–liquid extraction of the compounds. Mass spectrometric data were acquired in single ion monitoring. MRM mode of the ions 749.58 > 591.6 and 837.64 > 158.2 for azithromycin and roxithromycin, respectively. The method was validated in the concentration range of 2–1,000 ng mL⁻¹. Absolute recovery of azithromycin was 81.97%. Retention time for azithromycin was 0.9 and 1.1 min for roxithromycin. The run time was 2 min. This method was found suitable to analyse human plasma samples for application in pharmacokinetic, pharmacodynamic, bioavailability/bioequivalance studies.

     

A comparison of electron ionization mass spectra obtained at 70 eV,low electron energies,and with cold EI and their NIST library identification probabilities

Electron ionization (EI) mass spectra of 46 compounds from several different compound classes were measured. Their molecular ion abundances were compared as obtained with 70‐eV EI, with low eV EI (such as 14 eV), and with EI mass spectra of vibrationally cold molecules in supersonic molecular beams (Cold EI). We further compared these mass spectra in their National Institute of Standards and Technology (NIST) library identification probabilities. We found that

1. Low eV EI is not a soft ionization method, and it has little or no influence on the molecular ion relative abundances for large molecules and those with weak or no molecular ions.
2. Low eV EI for compounds with abundant or dominant molecular ions in their 70 eV mass spectra results in the reduction of low mass fragment ions abundances thereby reducing their NIST library identification probabilities thus rarely justifies its use in real‐world applications.
3. Cold EI significantly enhances the relative abundance of the molecular ions particularly for large compounds; yet, it retains the low mass fragment ions; hence, Cold EI mass spectra can be effectively identified by the NIST library.
4. Different standard EI ion sources provide different 70 eV EI mass spectra. Among the Agilent technologies ion sources, the “Extractor” exhibits relatively abundant molecular ions compared with the “Inert” ion source, while the “High efficiency source” (HES) provides mass spectra with depleted molecular ions compared with the “Inert” ion source or NIST library mass spectra.

These conclusions are demonstrated and supported by experimental data in nine figures and two tables.     

A Comment on Change of Nusselt Number Sign in a Channel Flow Filled by a Fluid-Saturated Porous Medium with Constant Heat Flux Boundary Conditions

The aim of this Letter is to show that, the Nusselt number sign might be changed without changing of heat transfer direction at the wall of channels, even for flows without viscous dissipation.     

Bargaining over a climate deal: deadline and delay

Assuming that a North-South transfer is the key to effective climate cooperation, we ask when and how much the North should offer to the South in return for a commitment to reduce deforestation and forest degradation. In light of the risk of irreversible damage over time, we examine a negotiation with a deadline. In this case, the North threatens the South over a negotiation dead-end in case an agreement is not reached rapidly. We assess the conditions for an agreement to be immediate or delayed, and discuss those situations likely to result in negotiation failure. Despite the risk of irreversible damage over time, we show that cooperation is likely to be delayed and we identify situations wherein the North and South do not reach an agreement within the deadline. Although Pareto-improving, cooperation may collapse because of inefficiencies related to incomplete information. What’s more, we show that in negotiations with a deadline, uncertainty about the benefits deriving from cooperation and the irreversibility of the damage that will be caused if cooperation is delayed are the two key components affecting choice.     

Hybrid Materials Based on Conducting Polymers for Nitrite Sensing: A Mini Review

Well-known as a hazardous compound, nitrite constitute a real threat to the public health. So, there is a pressing need to detect and quantify them in different matrix. Even though conventional analytical methods can be used to address this issue, electrochemistry allows a fast, sensitive, and efficient analysis. Conducting polymers continue to raise great interest among scientific communities due to their properties. Moreover, their combination with carbon nanomaterials, or metallic nanoparticles improves their properties, and provides great results. In this paper, we will focus on some revealing works devoted to the electrochemical detection of nitrite using this kind of materials.     

Controllability results for the two-dimensional heat equation with mixed boundary conditions using Carleman inequalities: a linear and a semilinear case

In this paper, we prove controllability results for a two-dimensional semilinear heat equation with mixed boundary conditions. It is well-known that mixed boundary conditions can present a singular behaviour of the solution. First, we will prove global Carleman estimates then we will use these inequalities to obtain controllability results.     

Electron Ionization Mass Spectra of Organophosphorus Compounds. Part III: Mass Spectrometric Fragmentation of Diethyl Spiro[Pyrimidino[5,3′][1,2]Oxazole] Phosphonate,Diethyl (Oxazolo[5,4-D]Pyrimidine-4,6-Dione)Phosphonate,and Diethyl (Pyrimidino[4,5-B][1,4]Oxazine)Phosphonate Derivatives

Abstract

Fragmentation pathways of 14 organophosphorus compounds derived from diethyl spiro[pyrimidino[5,3][1,2]oxazole] phosphonates, diethyl (oxazolo[5,4-d]pyrimidine-4,6-dione)phosphonates, and diethyl (pyrimidino[4,5-b][1,4] oxazine)phosphonates were investigated by electron impact mass spectrometry (EI-MS). The intensity of the recorded molecular ion peaks showed various values depending on the nature of the compounds. Characteristic fragment ions were formed by successive loss of simple functional groups followed by decomposition of heterocycles connected to pyrimidine rings.     

Synthesis of C 2-Symmetric Chiral Amino Alcohols: Their Usage as Organocatalysts for Enantioselective Opening of Epoxide Ring

A series of β-amino alcohols derivatives were synthesized from (R)-2-amino-1-butanol and (S)-1,2-propanediol, and they have been used as organocatalaysts in the racemic ring opening of epoxide in good yields with high enantiomeric excess (up to 97%).