Comment on "First principles electrochemistry: electrons and protons reacting as independent ions" [J. Chem. Phys. 117, 10193 (2002)

The entropy of the electron gas used by Llano and Eriksson (LE) in the definition they used for an absolute half-cell potential (AHCP) is indeterminate. This AHCP is therefore not based on a thermodynamically well-defined process and cannot easily be extended to other thermodynamic functions such as entropy. An alternative approach to the AHCP avoids these difficulties. The present comment also corrects statements and concepts presented by LE about the temperature coefficient of the Fermi level and surface charge of the electrolyte solution.     

A novel high-performance fourier transform ion cyclotron resonance cell for improved biopolymer characterization

A new trapped ion cell design for use with Fourier transform ion cyclotron resonance mass spectrometry is described. The design employs 15 cylindrical ring electrodes to generate trapping potential wells and 32 separately assignable rod electrodes for excitation and detection. The rod electrodes are positioned internal to the ring electrodes and provide excitation fields that are thereby linearized along the magnetic field over the entire trapped ion volume. The new design also affords flexibility in the shaping of the trapping field using the 15 ring electrodes. Many different trapping well shapes can be generated by applying different voltages to the individual ring electrodes, ranging from quadratic to linearly ramped along the magnetic field axis, to a shape that is nearly flat over the entire trap volume, but rises very steeply near the ends of the trap. This feature should be useful for trapping larger ion populations and extension of the useful range of ion manipulation and dissociation experiments since the number of stages of ion manipulation or dissociation is limited in practice by the initial trapped ion population size. Predicted trapping well shapes for two different ring electrode configurations are presented, and these and several other possible configurations are discussed, as are the predicted excitation fields based on the use of rod electrodes internal to the trapping ring electrodes. Initial results are presented from an implementation of the design using a 3.5 T superconducting magnet. It was found that ions can be successfully trapped and detected with this cell design and that selected ion accumulation can be performed with the utilization of four rods for quadrupolar excitation. The initial results presented here illustrate the feasibility of this cell design and demonstrate differences in observed performance based upon different trapping well shapes.     

Simultaneous high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS-MS) analysis of cyanide and thiocyanate from swine plasma

An analytical procedure for the simultaneous determination of cyanide and thiocyanate in swine plasma was developed and validated. Cyanide and thiocyanate were simultaneously analyzed by high-performance liquid chromatography tandem mass spectrometry in negative ionization mode after rapid and simple sample preparation. Isotopically labeled internal standards, Na¹³C¹⁵N and NaS¹³C¹⁵N, were mixed with swine plasma (spiked and nonspiked), proteins were precipitated with acetone, the samples were centrifuged, and the supernatant was removed and dried. The dried samples were reconstituted in 10 mM ammonium formate. Cyanide was reacted with naphthalene-2,3-dicarboxaldehyde and taurine to form N-substituted 1-cyano[f]benzoisoindole, while thiocyanate was chemically modified with monobromobimane to form an SCN-bimane product. The method produced dynamic ranges of 0.1–50 and 0.2–50 μM for cyanide and thiocyanate, respectively, with limits of detection of 10 nM for cyanide and 50 nM for thiocyanate. For quality control standards, the precision, as measured by percent relative standard deviation, was below 8 %, and the accuracy was within ±10 % of the nominal concentration. Following validation, the analytical procedure successfully detected cyanide and thiocyanate simultaneously from the plasma of cyanide-exposed swine.     

Mass Spectral Peak Distortion Due to Fourier Transform Signal Processing

Distortions of peaks can occur when one uses the standard method of signal processing of data from the Orbitrap and other FT-based methods of mass spectrometry. These distortions arise because the standard method of signal processing is not a linear process. If one adds two or more functions, such as time-dependent signals from a Fourier transform mass spectrometer and performs a linear operation on the sum, the result is the same as if the operation was performed on separate functions and the results added. If this relationship is not valid, the operation is non-linear and can produce unexpected and/or distorted results. Although the Fourier transform itself is a linear operator, the standard algorithm for processing spectra in Fourier transform-based methods include non-linear mathematical operators such that spectra processed by the standard algorithm may become distorted. The most serious consequence is that apparent abundances of the peaks in the spectrum may be incorrect. In light of these considerations, we performed theoretical modeling studies to illustrate several distortion effects that can be observed, including abundance distortions. In addition, we discuss experimental systems where these effects may manifest, including suggested systems for study that should demonstrate these peak distortions. Finally, we point to several examples in the literature where peak distortions may be rationalized by the phenomena presented here. Graphical Abstract

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Aspect-ratio dependent oscillatory thermocapillary convection in the floating half zone

The dependency of the critical Marangoni number on the geometrical aspect ratio of the floating half zone is essential to predict the onset of oscillatory thermocapillary convection.The experimental studies in the microgravity conditions on floating half zones of several centimeters in diameter have predicted that the critical Marangoni number increases with the increasing aspect ratio,and the terrestrial experimental studies have predicted the contradictory conclusion for floating half zones of several mil...     

Non-Gravitational Effects with Density-Matching in Evaluating the Influence of Sedimentation on Colloidal Coagulation

The method of density matching between the solid and liquid phases is often adopted to effectively eliminate the effect of sedimentation of suspensions in studies on dynamic behaviour of a colloidal system. However, the associated changes in the solvent composition may bring side effects to the properties investigated and therefore might lead to a faulty conclusion if the relevant correction is not made. To illustrate the importance of this side effect, we present an example of the sedimentation influence on the coagulation rate of suspensions of 2μm （diameter） polystyrene. The liquid mixtures, in the proper proportions of water （H2O）, deuterium oxide （D2O） and methanol （MeOH） as the liquid phase, density-matched and unmatched experiments are performed. Besides the influence of viscosity, the presence of methanol in solvent media, used to enhance the sedimentation effect, causes significant changes （reduction） in rapid coagulation rates compared to that in pure water. Without the relevant corrections for those non-gravitational factors it seems that gravitational sedimentation would retard the coagulation. The magnitude of the contribution from the non-gravitational factor is quantitatively determined, making the relevant correction possible. After necessary the influence of the sedimentation on coagulation rates at corrections for all factors, our experiments show that the initial stage of the coagulation is not observable.