Batch equilibration method

Under this umbrella, a number of different applications lie, amongst others the batch equilibration and equilibrium soil solution methods. According to the USEPA (1999), the former represents the most common laboratory method for determining partition coefficients—normally defined as Kd—both for contaminated sites studies and for predictions of chemicals behaviour in soils (OECD, 2002). The batch equilibration method consists of mixing a soil with a known amount of liquid (background electrolyte), which is then shaken into a slurry and allowed to equilibrate for an adequate time. The solution will be separated from the solids by centrifuging the slurry, resulting in a supernatant and a separated solid phase. The supernatant will, therefore, be removed, filtered and analysed. 

These data are selected from sorption values measured by Williams et al (2.) to show the large difference in Kvalues obtained by the conventional batch equilibration method and by desorption of residual DBCP in field samples. Desorption Kd values are clearly several times larger than those obtained by batch equilibration. Although it might be expected that desorption equilibration times much longer that those used in these tests (3 hours) might have resulted in smaller differences, recent measurements using 24-hour sorption and desorption equilibrations also indicated a several-fold difference in Kd between sorption of DBCP from recently added DBCP solution and desorption of DBCP added to dry soil a few weeks earlier (30). 

Potentiometric titration and batch equilibration methods were employed to examine the above estimate of the chelating behavior of Dowex A-1 resin. 

NIST SRM diesel particulate matter flocculation-based batch equilibrium method with 59-d equilibration time, air-bridge equilibrium with 123-d equilibration time, Nguyen et al. 2004)... 

A review of the commonly used experimental methods for solubility determinations is presented in Table 1. Briefly, batch equilibration is the conventional method of preparing saturated solutions for solubility determinations, where an excess amount of solute chemical is added to water and equilibrium is achieved... 

In simple experiments, particulate silica-supported CSPs having various cin-chonan carbamate selectors immobilized to the surface were employed in an enantioselective liquid-solid batch extraction process for the enantioselective enrichment of the weak binding enantiomer of amino acid derivatives in the liquid phase (methanol-0.1M ammonium acetate buffer pH 6) and the stronger binding enantiomer in the solid phase [64]. For example, when a CSP with the 6>-9-(tcrt-butylcarbamoyl)-6 -neopentoxy-cinchonidine selector was employed at an about 10-fold molar excess as related to the DNB-Leu selectand which was dissolved as a racemate in the liquid phase specified earlier, an enantiomeric excess of 89% could be measured in the supernatant after a single extraction step (i.e., a single equilibration step). This corresponds to an enantioselectivity factor of 17.7 (a-value in HPLC amounted to 31.7). Such a batch extraction method could serve as enrichment technique in hybrid processes such as in combination with, for example, crystallization. In the presented study, it was however used for screening of the enantiomer separation power of a series of CSPs. 

Two general methods, the analytical method and the synthetic method (Grant and Brittain 1995), are available for determining solubility. In the analytical method, the temperature of equilibration is hxed, while the concentration of the solute in a saturated solution is determined at equilibrium by a suitable analytical procedure. The analytical method can be either the traditional, common batch agitation method, or the more recent flow column method. In the synthetic method, the composition of the solute-solvent system is hxed by appropriate addition and mixing of the solute and solvent, then the temperature at which the solid solute just dissolves or just crystallizes is carefully bracketed. 

The so-called batch equilibration technique is classified as pH". In this method the final (after long shaking) pH of dispersion is plotted as a function of the initial pH at constant pH and solid to liquid ratio and the plateau of the curve indicates the PZC provided that the oxide is free of soluble acids and bases. 

The terms batch equilibration [653], pH drift method [654], addition method [552], solid addition method [655], powder addition method (cited in [656] after [654]), potentiometric titration [234] ( sic —in the present book, the term potentiometric titration is reserved for a different method, described in Section 2.5), and salt addition [573] ( sic —in the present book, the term salt addition is reserved for a different method, described later in this section) refer to the same method, which is now described. A series of solutions of different pHs is prepared and their pHs are recorded. Then, the powder is added and the final pH is recorded. The addition of a solid induces a shift in the pH in the direction of the PZC. The pH at which the addition of powder does not induce a pH shift is taken to be the PZC. Alternatively, the PZC is determined as the plateau in the pHfln, (pH ,.,., .j) curve. The method assumes that the powder is absolutely pure (free of acid, base, or any other surface-active substance), which is seldom the case. Even with very pure powders, the above method is not recommended for materials that have a PZC at a nearly neutral pH. Namely, the method requires accurate values of the initial pH, which is the pH of an unbuffered solution. The display of a pH meter in unbuffered solutions in the nearly neutral pH range is very unstable, and the readings are not particularly reliable. The problem with pH measurements of solutions is less significant at strongly acidic or strongly basic pHs (see Section 1.10.3). The above method (under different names) became quite popular, and the results are referred to as pH in the Method columns in the tables in Chapter 3. The experimental conditions in the above method (solid-to-liquid ratio, time of equilibration, and nature and concentration of electrolyte) can vary, but little attention has been paid to the possible effects of the experimental conditions on the apparent PZC. The plateau in the pH, , (pH, ,, ) curve for apatite shifted by 2 pH units as the solid-to-liquid ratio increased from 1 500 to 1 100 [653]. Thus, the apparent PZC is a function of the solid-to-liquid ratio. 

DBCP Sorption on Soil and Saprolite. For the Kunia site, sorption values were measured on samples from several depths in Boreholes 2 and 3 as well as from three shallow depths near the well. The borehole sorption data, obtained by flow equilibration, are given in Table I. Batch equilibration gave results which were about 20% higher for samples with the highest sorption, but the batch method had inadequate precision when sorption was low, as for samples 2-1, 2-3 and 3-2. The precision of the flow-equilibration method for DBCP is limited only by the GC analysis. Zero values in Table I indicate sorption Kd < 0.01 ml/gm. Of the several borehole samples, only sample 3-1 showed substantial sorption of DBCP. In both boreholes there was little sorption below 1 meter. The diminished sorption of DBCP with increasing depth appears to be related principally to a decrease in organic carbon with depth. 

Complexation of metal ions with the carboxyl resin Complexation of the carboxyl resin was carried out towards Fe(II), Fe(III), Co(II), Ni(II) and Cu(II) ions by a batch equilibration technique. A quantity (100 mg) of the resin was stirred in an aqueous metal salt solution (0.05 mol L , 50 mL) for 24 h. The complexed resins were collected by filtration and washed with distilled water to remove uncomplexed metal ions. The concentrations of the metal salt solutions were estimated by UV spectrophotometric methods. 

To check the methods used in the sorption studies, activated charcoal ground to pass a 5-mm sieve was used as an adsorbent. In a batch equilibration study 50-mg quantities of charcoal were incubated 16 h with 2,500 ng benzene. It was found that 98% of the benzene was sorbed, thus indicating that the methods used for the batch equilibration provided sufficient opportunity for benzene to be sorbed. It was also found that benzene did not adsorp to the glass centrifuge tubes. 

Methods The measurements were carried out by batch equilibration, most by an isotope dilution technique. Samples of clay were pre-equilibrated several times with NaCl-CaCl2 solutions of fixed compositions, until successive equilibrations showed no change in concentration. To separate samples (separate because of he difficulty of discriminating between the gamma emission of Na and Ca radioisotopes) were added known amounts of Na and Ca tracers, and the solutions were allowed to equilibrate for 2-5 days. The solid was centrifuged down, and aliquots of the supernatant solutions were counted. By material balance, the fractions of the activity adsorbed were computed, and, from these, the distribution coefficients, D... 

The extent of adsorption of eommereial surfaetants developed for use in reservoir recovery proeesses ean vary from near zero to as high as 2.5 mg/g. Surfactant adsorption on rock surfaces is usually measured by either static (batch) or dynamic (coreflood) experiments. The static adsorption method, employing crushed rock samples, is essentially the classical method for determining adsorption isotherms at the aqueous solution/solid interface and involves batch equilibrations of particles in solutions of different initial surfactant concentration. The dynamic coreflood method is more involved but employs a greater solid to liquid ratio and is therefore more sensitive, see references [J69-J7J]. Temperature, brine salinity and hardness, solution pH, rock type, wettability, and the presence of a residual oil phase have all been found to influence the extent of adsorption of different surfactants [116,152,172],... 

Soil sorption coefficients are most often determined using a batch technique (Organization for Economic Cooperation and Development, 1983 American Society for Testing and Materials, 1993 2001), whereby a small quantity of the soil is agitated for a period of time (e.g., 18 hours) with an aqueous solution of the chemical under investigation the phases are then separated and the concentration of chemical measured in one or both of the phases. While in principle the method is simple, problems can arise due to, for example, incomplete phase separation, lack of time for equilibration, volatilization loss, and chemical instability. 

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