Analyte fully protonated

The methyl, hydroxy, methoxy, chloro, cyano, and nitro derivatives of A -methyl-A -nitrosoaniline were separated on a Cjg column (A = 290 nm) using a 30/70 acetonitrile/water (lOmM phosphate buffer at pH 5.6) mobile phase [948]. The methyl and chloro derivative peaks were noticably fronted. Elution was complete in 30 min. The same separation was achieved in <15 min with excellent peak shapes, when the mobile phase was changed to acetonitrile/methanol/water/80% H3PO4 (at pH 3.2). A mobile phase pH low enough to keep the amine analytes fully protonated seems to be necessary to prevoit unfavorable analyte interaction with the silica support. Plots of log k versus percent acetonitrile (from 20% to 50%) were nonlinear. The detection limits were reported as 3 x 10 M. Linear ranges were found to cover the range 5 x 10" to 2 x lO"" M. 

This means that the effective mobility will depend on their pK in relation to the pH of the BGE. For weak bases, the analyte will be practically fully protonated (BH ) at pHpartially protonated at pipHpIweak acid which will be practically non-ionized at pHpartially ionized at p A—2pipi[Pg.327]

In some textbooks, the C02 dissolved in water is represented by H2C03 this notation is chemically incorrect - H2C03 is fully protonated carbonic acid. Another notation that you might encounter is H2C03, which is the analytical sum of true H2C03 and dissolved C02 at 25°C, dissolved C02 is 99.85% of this sum, so we will just use [C02]. Notice in this expression that the concentration of dissolved C02 is given in moles per liter (M) and the partial pressure is in atmospheres. We know that the atmospheric partial pressure of C02 is 380 ppm, which is 380 x 10-6 atm. Hence,... 

A. Fully protonated analyte (cationic form), which shows the lowest retention. The analyte is in the most hydrophilic form. Its interactions with the hydrophobic stationary phase are suppressed. A compound in its ionic form is more hydrophilic, so it tends to have less interaction with hydrophobic stationary phase and also tends to be more solvated... 

Spectrophotometric pJCa values. .. were determined. .. using 1 cm cuvettes at 25 0.5 °C. The experimental results showed that tire three analytes were fully protonated and deprotonated at about pH... 

A Fully protonated analyte (cationic form), low retention. The analyte is in the most hydrophilic form. Its interactions with the hydrophobic stationary phase are suppressed. 

In summary, HPLC analysis of basic analytes is more beneficial in a low pH region where these components are fully protonated and the problems associated with running with very high pHs in the mobile phase may be avoided. The elution of acidic and hydrophobic neutral components may be achieved by employing a gradient after basic components have been separated at low pH values. 

At pH 2. compound C1 and compound B2 are fully protonated and the perchloric acid is in its fully ionized (anionic) form. The increase in retention in the pH range from 2 to 2.5 is governed by ion association, between protonated basic analyte and negatively charged perchlorate ion. This ion association causes a desolvation of water molecules around the protonated basic analyte. Once the protonated basic analyte is less solvated by water it has a more hydrophobic nature, and for this reason the retention on the reversed-phase packing is increased. 

Yes, other acidic modifiers have shown the same effect. It was found that the highest effect on the retention of fully protonated analytes was obtained by the employment of perchloric acid, use of trifluoroacetic acid yielded results to a lesser extent and in some cases, phosphoric acid also had shown some effects. Also, other acids such as nitric acid, formic acid, acetic acid, propanoic acid, may also show similar effects. 

The retention of phenylethylamine increased by approximately 1.5 min with an increase in counteranion concentration from 10 mM (pH 1.84) to 25 mM (pH 1.58). At pH 1.84, phenyethylamine is fully protonated. As the counteranion concentration was increased, the ion association occurred, causing decrease of solvation of the phenylethylamine analyte and making it more hydrophobic. The phenyethylamine... 

Normal a-PET fluorescent chemosensors are not effective in the acidic pH region because of the fluorescent switch unit, usually a nitrogen atom in an alkylamino moiety, can be fully protonated. As a result, the fluorescence is already fully switched on by protonation. Adding analytes and the binding of the analytes will not result in further fluorescence enhancement. Based on the anthracene-a-methylbenzylamine chiral molecular profile, a bulkier chirogenic centre was introduced into the boronic acid (Figure 6.10). ... 

The virial methods differ conceptually from other techniques in that they take little or no explicit account of the distribution of species in solution. In their simplest form, the equations recognize only free ions, as though each salt has fully dissociated in solution. The molality m/ of the Na+ ion, then, is taken to be the analytical concentration of sodium. All of the calcium in solution is represented by Ca++, the chlorine by Cl-, the sulfate by SO4-, and so on. In many chemical systems, however, it is desirable to include some complex species in the virial formulation. Species that protonate and deprotonate with pH, such as those in the series COg -HCOJ-C02(aq) and A1+++-A10H++-A1(0H), typically need to be included, and incorporating strong ion pairs such as CaSO aq) may improve the model s accuracy at high temperatures. Weare (1987, pp. 148-153) discusses the criteria for selecting complex species to include in a virial formulation. 

In the case of an unknown chemical, or where resonance overlap occurs, it may be necessary to call upon the full arsenal of NMR methods. To confirm a heteronuclear coupling, the normal H NMR spectrum is compared with 1H 19F and/or XH 31 P NMR spectra. After this, and, in particular, where a strong background is present, the various 2-D NMR spectra are recorded. Homonuclear chemical shift correlation experiments such as COSY and TOCSY (or some of their variants) provide information on coupled protons, even networks of protons (1), while the inverse detected heteronuclear correlation experiments such as HMQC and HMQC/TOCSY provide similar information but only for protons coupling to heteronuclei, for example, the pairs 1H-31P and - C. Although interpretation of these data provides abundant information on the molecular structure, the results obtained with other analytical or spectrometric techniques must be taken into account as well. The various methods of MS and gas chromatography/Fourier transform infrared (GC/FTIR) spectroscopy supply complementary information to fully resolve or confirm the structure. Unambiguous identification of an unknown chemical requires consistent results from all spectrometric techniques employed. 

In MALDI, the sample is deposited on a target and co-ciystallized with a solid matrix [14-15]. The target is transferred to vacuum and bombarded by photon pulses from a laser, in most cases a nitrogen laser (337 nm) nowadays. The ionization results from efficient electronic excitation of the matrix and subsequent transfer of the energy to the dissolved analyte molecules, which are desorbed and analysed as protonated or cationized molecules [7]. The ionization process is not fully understood. Extremely high molecular-mass compounds, e.g., in excess of 200 kDa, can be analysed using the MALDI, if performed on a time-of-flight mass spectrometer (Ch. 2.4.3). 

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