Traceability of pH measurements by glass electrode cells: performance characteristic of pH electrodes by multi-point calibration

Routine pH measurements are carried out with pH meter-glass electrode assemblies. In most cases the glass and reference electrodes are thereby fashioned into a single probe, the so-called 'combination electrode' or simply 'the pH electrode'. The use of these electrodes is subject to various effects, described below, producing uncertainties of unknown magnitude. Therefore, the measurement of pH of a sample requires a suitable calibration by certified standard buffer solutions (CRMs) traceable to primary pH standards. The procedures in use are based on calibrations at one point, at two points bracketing the sample pH and at a series of points, the so-called multi-point calibration. The multi-point calibration (MPC) is recommended if minimum uncertainty and maximum consistency are required over a wide range of unknown pH values. Details of uncertainty computations for the two-point and MPC procedure are given. Furthermore, the multi-point calibration is a useful tool to characterise the performance of pH electrodes. This is demonstrated with different commercial pH electrodes. ELECTRONIC SUPPLEMENTARY MATERIAL is available if you access this article at http://dx.doi.org/10.1007/s00216-002-1506-5. On that page (frame on the left side), a link takes you directly to the supplementary material.     

Collective excitations in solid hydrogen as observed by incoherent neutron scattering

Incoherent neutron scattering experiments are reported at a number of scattering angles for solid H₂ using the time-of-flight technique. The samples had an ortho concentration ofX0.91 and the temperatures were 4.2, 2.2 and 1.2 K. The recorded scattering functions exhibit the elastic line, the ortho-para conversion line, the phonon spectrum on the energy-gain side of the neutrons and finally the phonon spectrum on the energy-loss side. Analysis of the data shows multiple scattering to be very important especially at small scattering angles. Accordingly, the results of an extensive calculation are reported that include up to four-fold scattering. The phonon spectrum that brings calculation and experiment in agreement at all angles is presented. It is concluded from the comparison between the spectra at various temperatures that unexpectedly the samples have always remained in the hexagonal close-packed phase even below the usual transition temperature into the cubic phase. Comparison is made with the spectrum (also in thehcp phase) obtained from coherent neutron scattering. The high-energy phonon tail, to be expected for quantum crystals, is observed and is qualitatively consistent with that in a similar spectral density derived theoretically from ortho-para conversion data under pressure. No evidence of a libron spectrum atT=2.2 K for a sample withX=0.91 could be found, which is consistent with the absence of the cubic orientationally ordered phase in these experiments.Supported in this research by a grant from the National Science Foundation     

Two-dimensional condensation in camphor-10-sulphonic acid films at the mercury/electrolyte interface

The electrosorption properties of camphor-10-sulphonic acid (CS) in different electrolytes (Na₂SO₄, LiClO₄, KNO₃, KCl, KBr, KJ) were investigated experimentally by ac polarographic measurements at different temperatures. Depending on the type of electrolyte and on the temperature, film condensation was observed.The Frumkin interaction coefficient, determined from the critical degree of coverage, does not depend linearly on the reciprocal temperature as would be the case in correspondence to the temperature dependence of the pit width. This contradiction does not occur if the interaction coefficient is determined from the critical degree of coverage using the lattice gas model. The temperature dependence of the pit width of the differential capacity-potential curves, found in the experiment, can be theoretically described by both these models. The interaction coefficient in the models is inversely proportional to the temperature. Furthermore, the parameters of the standard free energy of adsorption, the interaction energy, the interaction coefficient of the Frumkin isotherm, the adsorption coefficient, and the maximal surface concentration of CS in the film were estimated and compared.     

Carbazole compounds as host materials for triplet emitters in organic light-emitting diodes: polymer hosts for high-efficiency light-emitting diodes

A carbazole homopolymer and carbazole copolymers based on 9,9'-dialkyl-[3,3']-bicarbazolyl, 2,5-diphenyl-[1,3,4]-oxadiazole and 9,9-bis(4-[3,7-dimethyloctyloxy]phenyl)fluorene were synthesized and their electrical and photophysical properties were characterized with respect to their application as host in phosphorescent polymer light-emitting diodes. It is shown that the triplet energy of a polymer depends on the specific connections between its building blocks. Without changing the composition of the polymer, its triplet energy can be increased from 2.3 to 2.6 eV by changing the way in which the different building blocks are coupled together. For poly(9-vinylcarbazole) (PVK), a carbazole polymer often used as host for high-energy triplet emitters in polymer light-emitting diodes, a large hole-injection barrier of about 1 eV exists due to the low-lying HOMO level of PVK. For all carbazole polymers presented here, the HOMO levels are much closer to the Fermi level of a commonly used anode such as ITO and/or a commonly used hole-injection layer such as PEDOT:PSS. This makes high current densities and consequently high luminance levels possible at moderate applied voltages in polymer light-emitting diodes. A double-layer polymer light-emitting diode is constructed comprising a PEDOT:PSS layer as hole-injection layer and a carbazole-oxadiazole copolymer doped with a green triplet emitter as emissive layer that shows an efficacy of 23 cd/A independent of current density and light output.     

Novel method for bulk resistance evaluation in conductivity measurement for high-purity water

A major issue with the electrolytic conductivity measurement for pure water is the lack of standard or reference methods. A primary method traceable to SI and suitable for pure-water conductivity measurement was developed at the Physikalisch-Technische Bundesanstalt (PTB), Germany, as the base for the calibration method for the conductivity measuring devices at the low conductivity level. This paper provides a novel method to calculate the bulk resistance of pure water using impedance measured at a single frequency, which is one of the key procedures for the primary methods.     

Electrocyclic ring opening reaction of a 1,3,4-oxadiazin-6-one into its azaketene tautomer

5-Methyl-2-phenyl-1,3,4-oxadiazin-6-one undergoes cycloaddition with 2-methylpropenylpyrrolidine. One of the cycloadducts is derived from the Diels-Alder reaction of a transient azaketene tautomer.     

Apparent molar heat capacities and volumes of silver nitrate and silver perchlorate in aqueous solution at 298 K

We have made calorimetric and density measurements leading to apparent molar heat capacities and volumes of dilute aqueous solutions of silver nitrate and silver perchlorate at 298 K. Resulting apparent molar properties at infinite dilution are the following: φ^o_c(AgNO₃) = ? 36.8 J K^?1 mol^?1, φ^o_v(AgNO₃) = 29.1 cm³ mol^?1, φ^o_c(AgClO₄) = 11.0 J K^?1 mol^?1, and φ^o_v(AgClO₄) = 43.5 cm³ mol^?1.     

A Novel Anti-Inflammatory d-Peptide Inhibits Disease Phenotype Progression in an ALS Mouse Model

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterised by selective neuronal death in the brain stem and spinal cord. The cause is unknown, but an increasing amount of evidence has firmly certified that neuroinflammation plays a key role in ALS pathogenesis. Neuroinflammation is a pathological hallmark of several neurodegenerative disorders and has been implicated as driver of disease progression. Here, we describe a treatment study demonstrating the therapeutic potential of a tandem version of the well-known all-d-peptide RD2 (RD2RD2) in a transgenic mouse model of ALS (SOD1*G93A). Mice were treated intraperitoneally for four weeks with RD2RD2 vs. placebo. SOD1*G93A mice were tested longitudinally during treatment in various behavioural and motor coordination tests. Brain and spinal cord samples were investigated immunohistochemically for gliosis and neurodegeneration. RD2RD2 treatment in SOD1*G93A mice resulted not only in a reduction of activated astrocytes and microglia in both the brain stem and lumbar spinal cord, but also in a rescue of neurons in the motor cortex. RD2RD2 treatment was able to slow progression of the disease phenotype, especially the motor deficits, to an extent that during the four weeks treatment duration, no significant progression was observed in any of the motor experiments. Based on the presented results, we conclude that RD2RD2 is a potential therapeutic candidate against ALS.     

Tandem Michael‐addition/cyclization synthesis and EGFR kinase inhibition activity of pyrido[2,3‐d]pyrimidin‐7(8H)‐ones

5‐Methoxy and 5‐anilinopyrido[2,3‐d]pyrimidin‐7(8H)‐ones 2a‐2f were obtained by a tandem Michael addition‐cyclization reaction of methanol and anilines with pyrimidinylpropynoate 5. Methoxy derivative 2a was obtained in 62% yield by treatment of 5 with methanol and potassium carbonate. Anilino derivatives 2b‐2f were prepared in 31–71% yields by reacting 5 with the corresponding anilines in refluxing methanol. This methodology accomplishes Michael‐addition and pyridopyrimidinone ring formation in one‐pot and affords the desired products in reasonable yield without chromatography. Propynoate 5 did not react with 4‐cyanoaniline under these conditions. Reaction of 5 with 2‐aminopyridine gave the unexpected arylpyrido[2,3‐d]pyrimidinone 8 in 58% yield and reaction of 5 with imidazole afforded Michael‐adduct 9 in 69% yield. Compounds 2a and 5 were submicromolar inhibitors of epidermal growth factor receptor (EGFR) tyrosine kinase.