Accumulator acetonitrile

A reaction of dinitrogen tetroxide with acetonitrile in the presence of indium was carried out. The technician wanted to accelerate the process by stirring the medium, causing ils detonation. This accident was put down to the vioient oxidation of the acetonitrile accumulated, by nitrogen oxide catalysed by indium. 

Fig. 2.56 Dependence of the net peak current of probucol on the accumulation time. The amount of acetonitrile in the supporting electrolyte is 0 (i), 3 (2) and 6% (v/v) (3). The other experimental conditions are the same as for Fig. 2.55 (with permission from [85])...

As expected from Alder s endo rule, and justified by consideration of maximum accumulation of unsaturation in the transition state, secondary orbital interactions and dispersion forces, furan reacts with maleic anhydride in acetonitrile at 40 °C (78JOC518) to give initially... 

Two features need to be noted. Firstly, platinum-195 chemical shifts are quite sensitive to temperature, and in order to obtain acceptably narrow lines the solution temperature should be kept constant over the data accumulation time. Secondly, solvent effects need to be considered. A study of cis- and fraraj-PtCl2(PBu )2 in 14 solvents shows a change in A<5(P) of only 0.83p.p.m., but a change in Av(PtP) of 84.2Hz between n-hexane and acetonitrile.1355 Further work on temperature, solvent, substituent, oxidation state and stereochemical effects on 31P and 195Pt NMR chemical shifts and complexes is needed, and further efforts to collect and correlate data will be very useful.1356-1358... 

For flavones in citrus peel oils, separations were accomplished with isocratic mobile phases of 38% and 40% acetonitrile in H20 (1). The extracts of peel and cold-pressed peel oils were diluted in ethanol and analyzed by reversed-phase on various C18 columns with good results. For the dilute citrus oils, gradient elution was preferred, to prevent the accumulation of terpenes on the column. With normal-phase chromatography, the elution order is reversed terpenes elute with the solvent front and are not a problem. 

Fig. 22 The positive ion and linear mode MALDI-MS spectrum of 39 in ACCA (15 mg/mL 1 1 water-acetonitrile) MALDI matrix using nitrogen laser accumulating 50 shots. Inset spectrum shows expanded mass region of 39 [47]...

The direct coupling of liquid chromatography with proton NMR has been attempted numerous times. Early experiments of coupled HPLC- H-NMR were conducted in a stop-flow mode or with very low flow rates [193-195]. This was necessary to accumulate a sufficient number of spectra per sample volume in order to improve the signal-to-noise ratio. Other problems associated with the implementation of on-line HPLC-NMR have included the need for deuterated solvents. However, with the exception of deuterium oxide, the use of deuterated eluents is too expensive for routine analysis. Therefore, proton-containing solvents, such as acetonitrile or methanol, must be used. To get rid of the solvent signals in the spectra, the proton NMR signals of the solvents have to be suppressed. 

Fuchigami and his coworkers employed [EMIM][OTf] for the electropolymeri-zation. They found that the polymerization of pyrrole in the ionic liquid proceeds much faster than that in conventional media like aqueous and acetonitrile solutions containing 0.1 M [EMIM][OTf] as a supporting electrolyte, as shown in Figure 8.7. It is known that in the radical-radical coupling, further oxidation of oligomers and polymer deposition in the electrooxidative polymerization are favorably affected because the reaction products are accumulated in the vicinity of the electrode surface under slow diffusion conditions, and consequently the polymerization rate is increased. It is reasonable to assume that the polymerization rate in [EMIM][OTf] is higher than that in the conventional media, since neat [EMIM][OTf] (viscosity ... 

This plot represents the variation of an excessively adsorbed amount of acetonitrile with the variation of the equilibrium concentration of acetonitrile in the bulk solution. In the adsorption system the influence of adsorption forces exerted by the adsorbent surface are limited in their distance consequently, we should have limited volume where adsorbed analyte accumulates. It is also assumed that liquid is uncompressible and that molar volumes of both components do not change under the influence of adsorption forces. This leads to the displacement adsorption mechanism. 

This suggests that there is no actual penetration of the eluent and also the analyte molecules between the bonded ligands, but rather the accumulation (adsorption) of them on the surface. This was also confirmed by the study of the viscosity of bonded chains [32], which shows that the viscosity of bonded C18-type alkyl chains is at least two orders of magnitude higher than the viscosity of corresponding free alkanes (note that free octadecane is solid at room temperature, and it is almost insoluble in acetonitrile). 

In a binary eluent system (acetonitrile-water), an adsorbed organic phase with finite thickness and composition different from the bulk mobile phase is preferentially accumulated near the surface of the bonded phase. The organic layer accumulated near the bonded ligands could behave as a liquid stationary phase in reversed-phase HPLC, and it contributes to the overall analyte retention process. 

The multilayered character of acetonitrile adsorption creates a pseudo-stationary phase of significant volume on the surface, which acts as a suitable phase for the ion accumulation. In the low organic concentration region (from 0 to 20 v/v% of acetonitrile), studied ions show significant deviation from the ideal retention behavior (decrease in ion retention with increase in acetonitrile composition) due to the formation of the acetonitrile layer, and significant adsorption of the chaotropic anions was observed. This creates an electrostatic potential on the surface in which there is an adsorbed acetonitrile layer, which provides an additional retentive force for the enhancement of the retention of protonated basic analytes. When the dielectric constant is lower than 42 [167], this favors the probability of ion pair formation in this organic enriched layer on top of the bonded phase. 

Dendrimer 30 contains ten Ru-based units. The six peripheral Ru ions are easier to oxidize than the inner ones, because the terminal bpy ligands are better electron donors than the 2,3-dpp bridging ligands. As a result, a single six-electron wave is observed on oxidation, indicating the equivalence of the peripheral metal units. Oxidation of inner units was not observed up to -1-2.0 V in acetonitrile, presumably because of the large positive charge accumulated on the periphery [78]. 

MALDI TOP (7) mass spectra were recorded on a Bruker Reflex instrument (Billerica, MA). The rp-HPLC fractions containing PMP labeled oligosaccharides were dried in a SpeedVac concentrator (Farmingdale, NY) and redissolved in water/acetonitrile (75/25, v/v). 2,5-Dihydroxybenzoic acid (DHB) was used as a matrix. Normally, 0.3 uL of a half-saturated solution of DHB in water/acetonitrile/trifluoroacetic acid (70/30/0.1, v/v) was mixed on the sample dish with 0.3 pL of the sample solution. Desorption and ionization was done with a nitrogen laser (337 nm) adjusted to minimum laser attenuation. Mass spectra (10 to 20) were accumulated in linear negative ionization mode with an acceleration voltage of 25 kV. Calibration was done externally with bovine insulin and angiotensin I. 

The TE column is equilibrated with a minimum of two solvent combinations. The first solvent is strong, to wash the TE column free of impurities it may have accumulated from a previous sample (remember, this column is used over and over, so this step is critical so there is no sample carryover). This solvent is probably pure methanol or acetonitrile if using a reversed-phase filled TE column. The second solvent is not strong it is used to bring the TE column to equilibrium to accept the sample components of in-... 

The Helmholtz capacity of a metal electrode is typically on the order of 10 laF/cm, " " which is much greater than the value for a silicon electrode. " It has been reported that the Hehnholtz layer capacitance of silicon in 0.1 M JMFe(CN)6 + 0.5 M KCl aqueous solution is about 3pF/cm. ln 0.1 M tetrabutylammonium perchlorate (TBAP) in acetonitrile it is found to be about 1.5 aF/cm. " A larger Ch value, 22 p,F/cm, has been found for deep accumulation of a silicon in acetonitrile and the value varies with the accumulated charge. " ... 

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