Separation of Bases

However, two points should be kept in mind. One is that an increasing fraction of carbonic acid is ionized as the solution becomes more dilute ( 6.8% in 0.1 mM carbonic acid, for example). A second point is that the high concentration of on the exchange column ( 4.2 M) pushes the ion-exchange equilibrium to the right. For 0.1 mM carbonic acid, it can be calculated that only a few theoretical plates would be needed for complete conversion of H2CO3 to and HCO3 . 

A second enhancement column, placed just after the first enhancement column, provides stiU more sensitive detection. This is an anion-exchange column in the hydroxide form that converts K HC03 (equivalent conductance = 118) to K OH (equivalent conductance = 272). 

Haddad et al. measured retention volumes for a variety of bases on a quaternary ammonium functionabzed PS-DVB stationary phase using dilute aqueous sodium hydroxide as the eluent [20]. Values for the retention volumes and distribution coefficients of selected bases are given in Table 8.5. Strong bases, which are fuUy ionized at the eluent pH, elute at the column void volume and have a JQ value of 1.0. Solutes intermediate between these two extremes are partly ionized and generally can be separated by an ion-exclusion mechanism. 

Higher aliphatic amines (bulylamine, pentylamine, diethylamine, etc.) had larger retention volumes and values well above 1.0. A mixed retention mechanism involving hydrophobic adsorption and steric effects was observed for these compounds. Aromatic amines were found to be retained almost solely by a reversed-phase mechanism involving interaction of the solute with the unfunctionalized regions of the stationary phase. Retention of these solutes could be manipulated most easily by addition of acetonitrile to the eluent 

Very weak bases can be determined by I EC, but the sensitivity of conductivity detection is not very good. Tanaka et al. [21] separated ammonium from other common cations in biological nitrification-denitrification process water by I EC with ion-exchange enhancement of conductivity. More recently, Mori et al. [22] used a similar procedure to determine hydrazine (N2H4, or N2H5OH in aqueous solution). Trace levels of hydrazine in boiled water need to be monitored. 

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Figure 12 Gradient separation of bases, nucleosides and nucleoside mono- and polyphosphates. Column 0.6 x 45 cm. Aminex A-14 (20 3 p) in the chloride form. Eluent 0.1 M 2-methyl-2-amino-l-propanol delivered in a gradient from pH 9.9-100 mM NaCl to pH 10.0-400 mM NaCl. Flow rate 100 ml/hr. Temperature 55°C. Detection UV at 254 nm. Abbreviations (Cyt) cytosine, (Cyd) cytidine, (Ado) adenosine, (Urd) uridine, (Thyd) thymidine, (Ura) uracil, (CMP) cytidine monophosphate, (Gua) guanine, (Guo) guanosine, (Xan) xanthine, (Hyp) hypoxanthine, (Ino) inosine, (Ade) adenosine, (UMP) uridine monophosphate, (CDP) cytidine diphosphate, (AMP) adenosine monophosphate, (GMP) guanosine monophosphate, (IMP) inosine monophosphate, (CTP) cytidine triphosphate, (ADP) adenosine diphosphate, (UDP) uridine monophosphate, (GDP) guanosine diphosphate, (UTP) uridine triphosphate, (ATP) adenosine triphosphate, (GTP), guanosine triphosphate. (Reproduced with permission of Elsevier Science from Floridi, A., Palmerini, C. A., and Fini, C., /. Chromatogr., 138, 203, 1977.)...

FIGURE 14.17 Ultrahigh resolution nano LC-MS separation of base peak chromatogram of 2351 peptides identified in trypsin digest of mouse brain lysate P2 fraction using Micro-Tech XtremeSimple nano-LC and Thermo Electron LTQ. Column 100 cm x 75 fim C18 column, 3 /mi, 8000 psi column head pressure. Solvent composition time 350 min gradient, 5 to 35% B. Solvent A 2% acetonitrile, 0.1% formic acid. Solvent B 95% acetonitrile, 0.1% formic acid. Data analysis Sequest, PeptideProphet, and Protein Prophet. 

Distinctions between water-soluble fractions of mixed hydrocarbons may be made by using solvent extraction of the water-soluble base/neutral and acid fractions with methylene chloride (EPA 1991c Thomas and Delfino 1991a). This separation of base/neutral and acid fractions will permit the GC resolution of the type of water soluble hydrocarbons present in the aqueous phase. Hexane has also been used as a solvent (DellAcqua and Bush 1973), as has pentane (Coleman et al. 1984). 

Real space algorithms (section 4) allow for mappings between present day computer programs and strict molecular quantum mechanics [10,11]. It is the separability of base molecular states that permits characterizing molecular states in electronic Hilbert space and molecular species in real space. This feature eliminates one of the shortcomings of the standard BO scheme [6,7,12]. Confining and asymptotic GED states are introduced. In section 5 the concept of conformation states in electronic Hilbert space is qualitatively presented. 

Analogous considerations hold for the separation of bases, as shown in Table 5-2. Generally, for the separation of ionic compounds, the pH is kept in the range of 2 to 8, to optimize the useful life of the column/system. 

For reversed-phase ion-pair chromatography a non-polar surface (e.g. Cg or C- g) is used as a stationary phase and an ionic alkyl compound is added to the aqueous mobile phase as a modifier. For the separation of acids, an organic base (e.g. tetrabutylammonium phosphate) is added to the eluent for the separation of bases, an organic acid (e.g. octane sulphonate) is used. Reversed-phase ion pairing is presently the most popular approach because of the simpler technical requirements and very high column performance. It is however essential to operate the system only after equilibrium of the mobile phase and the stationary phase has occurred in order to obtain reproducible analyses. 

Cohen AS, Terabe S, Smith JA, Karger BL (1987) High-performance capillary electrophoretic separation of bases, nucleosides, and oligonucleotides Retention manipulation via micellar solutions and metal additives. Anal Chem 59 1021-1027. 

For separation of bases the pH of the mobile phase is about 1-3.5, for separation of acidic samples about 7-9. 

Silica tends to dissolve above pH 8, and crosslinked polymeric particles, for example, polystyrene or polymethacrylates, are used for separation of bases. These can withstand strongly basic mobile phases but exhibit somewhat lower efficiency. 

Chemisorption leads to a number of undesirable effects in chromatographic separation, and systems which are prone to chetnisorption should be avoided. The separations of bases on silica or of certain acids on alumina may require special precautions, such as addition of acid or base to the solvent or adsorbent. Florisil should be used only after the sample of interest has been tested for chemisorption on Florisil,... 

The following procedure, modified from Gilchrist s method, is intended for the recovery of platinum from residues containing base metals and noble metals (other than those of the platinum group) as well as strong com-plexing agents. A preliminary separation of base metals as hydrated oxides considerably reduces the time required to obtain pme platinum by the precipitation of ammonium hexachloroplatinate(IV). The authors have tested the procedure both with actual laboratory residues and with syn-... 

For the separation of bases, the residual silanol groups can be blocked by addition of triethylamine or octylamine in %o amounts. For the separation of acidic components, the addition of 0.5-1 % acetate, phosphoric acid or... 

RPIP chromatography uses a hydrocarbonaceous stationary phase and either an aqueous or aqueous-organic mobile phase which also contains the counter-ion. The stationary phase is usually an octadecyl bonded phase and the mobile phase is usually an aqueous buffer with either methanol or acetonitrile as an organic modifier. The choice of counter-ions depends on the solutes to be separated, but generally for the separation of acids a hydrophobic organic base is added to the mobile phase, while for the separation of bases a hydrophobic organic acid is added. Separations of other compounds are similarly obtained by the addition of an appropriate counter-ion. 

Among these chemicals are silver nitrate - added to allow separation of cisitrans isomers, particularly for lipid analyses potassium oxalate - added to allow discrimination of polyphosphoinositides magnesium acetate - added to help in the separation of phospholipids ammonimn sulfate - added so that the plate is self-charring (after heating) carbomer -added for the analysis of mannitol/sorbitol and sodium hydroxide - added to improve the separation of bases and organometallics. 

Zirconium-containing raw is a promising scandium source [19-23]. It was established that Sc is accumulated in carbon-containing residue after chlorination [21] and in manifold after separation of base zirconium sulfate [22-23], The extraction technology used for Sc recovery is based on leach neutralization, sludge separation, sludge leaching by nitric or hydrochloric acid, and scandium extraction by TBP solution in kerosene. The treated solution free of Sc is a valuable source of Zr and Hf. 

The intramolecular energies of DNA base pairs interaction, AG, at the stage of unwinding are all positive, which is a residt of separation of base pairs upon formation of the intercalation cavity. The energies of the solvation of the intercalation site, AG flp are all negative and result from hydration of the intercalation cavity upon DNA unwinding. 

Figure 4 Structures and MP2/6-31G (0.25) interaction energies (kcal mol" ) for 10 stacked ba.se pairs. The structure has been optimized by the MP2-fitted empirical potential under the as.sumptions that the bases are coplanar and the vertical separation of bases is constant (3.3 or 3,4 A). The value.s in parentheses are the Hartree-Fock interaction energie,s...

Figure 1.13 vs F2 plot showing the separation of bases into the families of the fit treatment ... 

Table II shows the PRT-ase activities of the various mutants expressed as percent of wild-type activity. The hpt mutant is primarily affected in its IMP activity. The remaining activity is due to G-PRT and can be completely inhibited by the addition of guanine to the reaction mixture (data not shown). The gpt mutant is deficient in GMP and XMP activity with only minimal decrease in IMP activity. The residual activity for XMP in all gpt strains is an artifact imposed by the rapid assay using DE-81 Whatman discs to capture the nucleotide. The bases are usually washed off by NH4HCO3 and water, but this washing does not allow complete removal of the Cl4 xanthine substrate. In a more tedious method involving separation of base and nucleotide by thin layer chromatography, XMP activity in the gpt strains is virtually undetectable.

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