Cation Removal

On-target washing presents a single but very effective approach to reduce the alkali ion content of MALDI sample preparations [123,124], For this purpose, 2-5 pi of alkali ion-free water containing 0.1-1% formic or trifluoroacetic acid is placed on top of the crystalline layer and removed after a few seconds by a microliter pipette or by blowing it off with a stream of pressurized air. The acidification avoids dissolution of the crystals in case of carboxylic acid matrix preparations. 

Cation exchange resins can be added prior to preparation to substitute alkali ions for ammonium (Fig. 11.13) [27]. To take full effect, it is important to keep the cation exchange beads even on the target in order to capture the alkali ion contamination of the metal surface, too. No useful signals are obtained when the laser hits the cation exchange beads. Furthermore, there is a risk of ion source contamination as beads may occasionally fall off the surface, even as a result of laser shots. 

Another approach is to use tips of microliter pipettes as miniature columns by filling them with size exclusion chromatography (SEC) stationary phase material or standard Cig reversed phase material [125,126]. Such tips are also commercially available as ZipTips [122]. There is a risk of sample absorption on the 

Finally, it is advantageous to add a surfactant blend (Invitrosol-MALDI protein solubilizer B, IMB) prior to preparation (Fig. 11.14) [127]. 

Equally, sodium dodecyl sulfate contaminations should be removed from 2D gel electrophoresis before subjecting samples to MALDI-MS [128]. 

---

Humic acids are alkaH-extractable materials and total humic acid content is a term that refers to the humic acid content of coal that has had its carboxylate cations removed with sodium pyrophosphate. Values for some typical AustraHan brown coals range from 24—92% (13). Treatment of lignitic coals with mineral acid to release the alkaH and alkaline cations may dissolve up to 20% of the coal. The naturally moist coals are slightly acidic and have a pH of 3.5—6.5. 

To predict the electron configuration of a monatomic cation, remove outermost electrons in the order np, ns, and (n — l)d fora monatomic anion, add electrons until the next noble-gas configuration has been reached. The transfer of electrons results in the formation of an octet (or duplet) of electrons in the valence shell on each of the atoms metals achieve an octet (or duplet) by electron loss and nonmetals achieve it by electron gain. 

Increasing the reducing agent/W ratio and using Na-naphthalenide led to the isolation of the two-electron-reduced, diamagnetic compound 19. The C2v symmetry of the h NMR spectrum and the X-ray analysis are in agreement with the cen-trosymmetric structure sketched in Scheme 2 for 19 [W = W, 2.614(1) A]. The six-coordination of the metal and the inclusion of the alkali metal cation removes the planarity ofthe 04 core and the cone conformation of the calix[4]arene. The sodium cation within the calix[4]arene cavity is r 3-bonded to two opposite arene rings. 

The need for invoking high rates of cation removal via reverse weathering was eliminated in the late 1970s when marine chemists realized that hydrothermal uptake and... 

The dissolved solids, such as calcium carbonates, are removed by hot-lime softening or demineralization.1 Demineralized water (also called deionized water) typically has essentially all anions and cations removed by ion-exchange resin. Demineralized water is preferable to hot-lime-softened water as boiler feedwater for several reasons. 

All the non-expanded 2 1 and 2 1 1 layer silicates can have their interlayer cations removed. Water and organic molecules can then penetrate between these layers to form expanded layer minerals. 

Many ionic compounds of AX2 stoichiometry possess the CaF2 (fluorite), or Na20 (antifluorite) structures shown in Figure 3.15. Fluorite is similar to CsCl, but with every other eight coordinate cation removed. Each fluoride anion is tetrahedrally coordinated by calcium ions. This structure is adopted by several fluorides and oxides. In the antifluorite structure, the coordination numbers are the inverse. Most oxides and other chalcogenides of the alkali metals (e.g. Na2Se, K2Se) possess the antifluorite structure, but so do some more covalent compounds, such as the silicides of Mg, Ge, Sn, and Pb. 

Removal of one electron should make no difference to the relative stabilities of polyene molecule ions or even electron polyene fragments as compared to their neutral counterparts, e.g. butadiene and the allyl radical should have the same relative stabihties as the butadiene molecule ion, and the allyl cation. Removal of one electron will, however, alter the stabihties, and thus the reactivities of cychc polyenes. The molecule ions of aromatic hydrocarbons will be substantially less aromatic then their neutral counterparts. Correspondingly the molecule ions of antiaromatic hydrocarbons will not be as antiaromatic as their neutral analogs, e.g. cyclobutadiene + should be relatively more stable than cyclobutadiene. The largest charge effects in hydrocarbons will be observed in nonaltemant ) monocychc hydrocarbons. The cyclopropenium ion 7 and the tropillium ion 2 are both strongly aromatic as compared to their neutral analogs. Consequently CsHs is a very common ion in the mass spectra of hydrocarbons while cyclopropene is not a common product of hydrocarbon pyrolysis or photo-... 

Another technique to identify the surface cations in MgO is connected to the use of the O2 superoxide anion and the EPR spectroscopy [92,93]. 02 can form at the surface of MgO by interaction of O2 with electron-rich centers see 3.4.7). The electric field at the surface created by the Mg cation removes the degeneracy of the Ttg orbitals giving rise to an EPR spectrum with three components of the g-tensor, gxx, gyy, and gzz- Depending on the cation where the superoxide anion is adsorbed, the splitting A between the Tigx and Kgy... 

To eliminate the problems associated with the washing step, Okazaki, Smith, and Moodie proposed a CEC procedure in which salts are not removed between the index cation saturation and extraction steps. Rather, the anion of the salt providing the index cation is analyzed in the final extract. In accordance with electrical neutrality, the CEC is then equal to the total quantity of index cations removed during extraction minus the quantity of index anions removed simultaneously. The main potential source of error from this procedure arises from anion repulsion, if the quantity of index salt remaining after saturation is merely calculated from the weight of solution retained and its initial (or average) concentration. This error minimized if the index solution is lowered to approximately 0.1 M during the final two saturation washes. The error is eliminated if the quantities of index salt are analytically determined instead. 

---