Direct coprecipitation method

Fig. 8.4. XRD patterns of borate>hydrotalcite-like LDHs prepared by (a) direct coprecipitation (method 3) (b) direct ion>exchange (method IB) (c) method lA, at 343 K, 6Sh (d) method 2, at 323 K, 7 days (e) method 2, at 363 K, 6h (f) same sample as (e), but with oriented sample for XRD.

Table 2 Chemical analysis of M2 Al/Cl (M = Ca, Zn) and the organic derivatives obtained by direct incorporation using the coprecipitation method. The basal spacing is displayed (Reprinted from [70] by permission of Elsevier)...

Polyoxometalate anions have also been incorporated by the direct coprecipitation of a ZnAl-LDH with a-(SiWn039)8 under mildly acidic conditions [83], and a ZnCr-LDH with V10O 8 at pH 4.5 [84]. The reconstruction method has also been used to incorporate such anions into MgAl- and NiAl-LDHs [5, 29, 85, 86]. 

The chemical coprecipitation with fast injection differs from conventional coprecipitation in the speed at pH of the reaction pH solution is increased in order to favor magnetite formation abruptly. Divalent and trivalent iron salt solutions have an initial pH of 0 to 1. On the conventional coprecipitation method, the pH of the solution is increased by the addition of an alkaline solution drop by drop, which is considered slow speed while on the rapid injection method, the pH of the solution is increased by adding the salt solution directly to ammonium hydroxide solution, speed to be considered rapid and explosive. The difference between both methods is schematically shown in figure 4. 

The determination of metals in water samples by neutron activation analysis (NAA) shows different sensitivities for different samples, including several cases where NAA sensitivity is better than all the analytical techniques. Several of the factors which can affect the sensitivity of the method are sample composition, neutron flux, irradiation time, decay time, coxmting time, and detector efficiency [328,329]. Different preconcentration methods have also been applied to NAA protocols for metal analysis. For instance, the use of coprecipitation method [330,331], chelating adsorbents [332], etc. One of the additional advantages of this methodology is that both the irradiation and neutral activation can be directly performed on the resin, without eluting the metals from the column. 

In the present work CcosZro 5O2 was prepared by the following method pine sawdust (wood biomass with the approximate size of 0.63-1.25 mm) was impregnated by solution of Ce and Zr nitrates in the ratio sawdust mixed oxide = 10 1 and the dried resultant system was calcined at 600°C during 4 hours to give, in a direct and simple manner, the material of desirable and predictable porosity, avoiding the use of additional chemicals in the process. The sample obtained with the help of sawdust is indicated as biomorphic. For comparison Ce-Zr oxide of the same composition was prepared by traditional coprecipitation method and calcined in the same conditions. 

Physical methods of gene transfer. Genes can often be transferred without the use of a cloning vehicle. This is especially important for certain plant cells, such as those of cereal grains, for which transfer of genes via the Ti plasmid has been difficult.167 If DNA, which may be in a plasmid, is coprecipitated with calcium phosphate, it can often be taken up directly either by animal cells or by plant protoplasts.168 169 Polycations also facilitate DNA uptake cationic liposomes seem to be especially effective.170 In the widely used electroporation technique a short electrical pulse of a few hundred volts / cm is applied to create transient pores in the plasma membrane through which the DNA can enter a cell.111 8,171 175 Chromosomes can be transferred by cell fusion and either... 

Drinking water Direct analysis or concentration by coprecipitation and solvent extraction fusion Fluorometry (total uranium) <20 pg/L (direct) 0.1 pg/L (cleaned) 104% (cleaned) Krieger and Whittaker 1980 (EPA Method 908.1)... 

In the analysis of high-purity substances, general matrix removal is often very important so as to pre-concentrate the elements to be determined. To this aim all separation techniques such as ion exchange, liquid-liquid extraction of a metal complex with organic solvents, fractionated crystallization, precipitation and coprecipitation as well as electrochemical methods may be used (for a systematic treatment, see Ref. [300]). These principles can also be applied in on-line systems, as is now possible with solid phase extraction. Here matrix elements or the analytes can be adsorbed as complexes onto the column and eluted for direct determination by AAS. 

To cope with matrix effects, and to achieve some enrichment, suitable separation methods can be applied, e.g. solvent extraction, coprecipitation, or volatilization directly from the inorganic solid sample (Heinrichs, 1979 Han et al., 1982 Sager, 1984). As the volatility of organic chelates is low, and the volatility of halogenides from organic solvents remains the same, organic phases obtained from solvent extractions have been put directly into the furnace. In this case, however, carry-over in the autosampler has to be prevented by an organic soivent, at ieast by an isopropanol/water mixture. 

Coprecipitation is a method for separation and preconcentration based on the formation of mixed crystals thanks to isomorphic exchange or adsorption of microcomponents on the surface of ionic crystals. Microelements in solutions in concentrations below ng/dm can hardly be isolated by direct precipitation, therefore different reagent carriers are used (Hoste et al., 1971 Das et al., 1983 Mizuike, 1983 Toelgyessy and Kyrs, 1989 Stoeppler, 1992 Nickson et al., 1995). The off-line approach... 

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