Sodium isotopes, mobility

A decrease with rising temperature has also been observed for the relative differences of the external mobilities (250°-350°C.) of the lithium isotopes in eutectic NaNOs-KNOs mixtures (2). On the other hand the relative differences of the external mobilities of the sodium isotopes Na and Na in LiNOs (305°-359°C.) and in eutectic NaNOa-KNOs mixtures (255°-374°C.) rise with rising temperature (in the latter case the increase is followed by a decrease in the range 374°-434°C.) (70). 

Water samples are amended with isotopically labeled internal standards, acidifled, and purified/concentrated by Cig SPE. The extracts are evaporated to dryness, reconstituted with mobile phase and analyzed by LC/MS/MS. This method determines water residues of flucarbazone-sodium, sulfonic acid, sulfonamide and NODT with an LOQ of 50 ngkg for each analyte. 

Unfortunately, for the majority of small molecule LC-MS/MS analyses, stable isotope labelled internal standards are not available so far. In such cases, compounds with a very similar molecular structure typically serve as internal standard ( homologues or analogues ). Since the ionization properties are substantially determined by functional groups of a molecule, ionization behaviour may differ significantly—even between compounds with very similar over-all molecular structure. Differential clustering, e.g. with sodium, ammonium or formate ions often present in mobile phases may as well impact the parity of ionization yield between analyte and internal standard. Hence the availability of an appropriate homologue is crucial and critical for the development of reliable LC-MS/MS methods in TDM [51]. 

Three Au/u values for anions have been reported in the literature. Madorsky and Straus (54) found a difference in mobilities of " Cl and Cl of 0.0021 in a NaCl-solution. Wagener and Bilal (67) measured in a capillary separation tube a difference between formate and formate of 0.011 in sodium formate. Lamotte (39) gives a Au/u value of 0.022 for B02"- B02". It has been shown that this difference depends strongly upon the pH value of the solution. Therefore, it was concluded that the actual difference in mobility is negligible the effect has almost completely to be attributed to an isotope effect in the dissociation equilibrium B02 + BO2H i B02 + 11BO2H. 

Figure 18.1 Isocratic separation of 17 amino acids, the early appearing ones being insufficiently resolved and the last one not eluted (reproduced by permission of A. Serban, Isotope Department, Weizmann Institute of Science, Rehovot). Conditions sample, 50 ixl containing 5 nmol of each amino acid column, 15 cm x 4 mm i.d. stationary phase. Amino Pac Na-2 (cation exchanger) 7 im mobile phase, 0.4 ml min sodium citrate 0.2 N pH 3.15-sodium phosphate 1 N pH 7.4 (1 1) temperature, BB C VIS detector 520nm after derivatization with ninhydrine.

In theory, diffusion coefficients can be measured for any ion. In practice, however, most studies of ionic diffusion in glasses have been restricted to highly mobile ions which have a convenient radioactive isotope for use in tracer measurements. As a result, a majority of the data for ionic diffusion deals with sodium, with lesser amounts of data for potassium, rubidium, and cesium. Studies of lithium are very limited due to the lack of a radioactive isotope of lithium, while studies of divalent and other, more highly charged, ions are restrieted by the very low mobilities of these ions as compared to those of the monovalent ions. 

The electrophoretic mobilities of C-labeled cholic, deoxycholic, and chenodeoxycholic acid and their corresponding taurine and glycine conjugates were determined by Norman (42). The paper electrophoresis was performed in barbiturate buffer of ionic strength 0.1, pH 8.6, in an electric field of 7.5 V/cm for 3 hr. When 1 pg of each acid, as the sodium salt dissolved in 25 pi of water, was applied to the paper strips, the isotope determination after electrophoresis showed broad peaks all with a mean mobility similar to that of albumin or slightly lower. The electrophoretic mobilities of all of the bile acids were influenced by the concentration in the solution applied and presented difficulties in identifying bile acids in natural extracts. The migration of bile salt-lecithin micelles on paper electrophoresis has been reported by Shimura (43). The micelles were prepared by addition of lecithin to mixed bile salts, which may have also contained cholesterol. 

By using isotopic enrichment, the contributions of Li" " and Na mobility to the total conductivity have been decoupled. " Despite the difference in cation size and typical coordination environments lithium and sodium show similar activation energies of ca 0.64 eV and make similar contributions to the overall conductivity of the phase. This observation is incompatible with the simple view of a positive cation migrating through a static window and indeed it has been shown that the sulfate anions in LiNaS04 are dynamic in the P phase. There is an energy barrier to anion... 

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