Curves precipitation curve

Figure 15. Illustration of possible variations in isotopic fractionation between Fe(III),q and ferric oxide/ hydroxide precipitate (Aje(,n),q.Fenicppt) and precipitation rate. Skulan et al. (2002) noted that the kinetic AF (ni)aq-Feiricppt fractionation produced during precipitation of hematite from Fe(III), was linearly related to precipitation rate, which is shown in the dashed curve (precipitation rate plotted on log scale). The most rapid precipitation rate measured by Skulan et al. (2002) is shown in the black circle. The equilibrium Fe(III),-hematite fractionation is near zero at 98°C, and this is plotted (black square) to the left of the break in scale for precipitation rate. Also shown for comparison is the calculated Fe(III),q-ferrihydrite fractionation from the experiments of Bullen et al. (2001) (grey diamond), as discussed in the previous chapter (Chapter lOA Beard and Johnson 2004). The average oxidation-precipitation rates for the APIO experiments of Croal et al. (2004) are also noted, where the overall process is limited by the rate constant ki. As discussed in the text, if the proportion of Fe(III),q is small relative to total aqueous Fe, the rate constant for the precipitation of ferrihydrite from Fe(III), (Ai) will be higher, assuming first-order rate laws, although its value is unknown.

The influence of neutral salts as well as of acids and bases on the swelling of gelatine which we have seen can be attributed to an apparent change in the solvation of the gel fibrils and may be interpreted in the light of Donnan s theory of the effect of a non-diffusible ion on the osmotic pressure differences between the two phases, is likewise to be noted in the alteration of the viscosity and alcohol precipitation values of protein solutions. From the considerations already advanced there should exist two well-defined maxima in the viscosity and alcohol precipitation curves when these properties are plotted as functions of the Ph, the maxima coinciding with the points of maximum dissociation of the salts... 

Before grafting, butadiene and acrylonitrile were diluted with benzene (0.25 part of benzene for one part of monomer). Other conditions were constant. The precipitation curve shown in Figure 7 is not very different from that of the standard graft polymer (without benzene). The PVC percentage in the first group of fractions is ca. 60-70%. The slope of the curve has two maxima which correspond to the two groups of fractions. The polymer is soluble at 20°C precipitation is continuous above n = 10-12 with a maximum value of the slope at n = 21-22. 

Both polymers are soluble at 20°C. For the sample with 1% mercaptan more than 50% of the polymer precipitates abruptly at n = 22. For 5% mercaptan the precipitation begins at n = 6 50% of the sample is recovered at n = 12 beyond that, the precipitation curve joins that obtained with a solution prepared at 70 °C. 

Figure 12. Effect of temperature of solubilization on precipitation curves...

An analogy of the shape of the precipitation curves of these samples and of mixtures of graft copolymers PVC should lead us to put forth the hypothesis of the presence of PVC homopolymer which would be solubilized by the graft copolymer. However, this quantity would be... 

Solutions Prepared at 70°C. Generally, precipitation curves may be divided in two types ... 

PVC homopolymer as small as 4% of total weight are sufficient to ensure modification of the precipitation curve. Thus, addition of PVC gives an abrupt precipitation about n = 6 and coprecipitation of the graft copolymer with the PVC. 

Experimental results show that at low grafting temperature (30°C) the solubility of grafted polymers is highly modified by butadiene-acrylonitrile chains. Precipitation curves look like those of polymers prepared using dichloroethane and therefore seem compatible with a less cross-linked BD-AN chain structure. At high grafting temperature (70°C), the precipitation curve resembles that obtained with DVB crosslinked copolymers. 

In addition to the effects of crystal lattice energy, choice of solvent other than n-paraffins can also be important. For example, Corbett and Swarbrick (10) have shown that a number of oxygenated compounds can precipitate asphaltenes from petroleum residua in quantities varying from 12 wt % to 100 wt % on resid. Clearly, the shape of the precipitation curves for the different solvents should be different from that for n-paraffins and from each other. However, the use of a solubility parameter type of polarity scale should permit rationalization of the results when considered along with the solubility parameter of the particular solvent. 

With certain horse antitoxins and antiprotein sera and in some patients with Hashimoto s thyroiditis who have antibodies to thyro-globulin, one finds a different type of quantitative precipitation curve, termed a flocculation curve.Precipitation occurs only over a narrow range, and soluble antigen-antibody complexes are formed in the region of antibody excess as well as of antigen excess. Flocculation curves have... 

Let a and b be our two precipitates. Under the pressure considered, the precipitate a has a solubility curve, the curve Ca (Fig. 67) in order that the solution be in equilibrium in contact with the substance a, it is necessary and sufficient that the representative point, which has the temperature for abscissa and the con-... 

FIGURE 22-1 pH-precipitation curves for 0.001 M divalent metal ions with 0.003 Af quinaldic acid. (From Flagg, p. 63.)... 

When the initial SPC concentration is increased, a change in the percent soluble protein as a function of pH is observed at 15 g/L a quasi-linear precipitation occurs whereas at 60 g/L the protein precipitation curve takes on a sigmoidal form. From initial pH to 7.0, no real difference is noted the percent soluble protein was about 100%. A high-protein concentration slows the electroacidification process as a result of the intrinsic buffering capacity of the protein [88,89]. However, the final percent soluble protein is not affected by an increase in the SPC concentration. 

The variation of precipitation as a function of pH is related to the different precipitation profiles of the two protein fractions, 7 S and 11 S [97]. According to Thanh and Shibasaki [97], protein concentrations (up to 4%) are favorable for the separation of the two globulin fractions. They noted that the 7 S fraction is not very sensitive to an increase in protein concentration, whereas the 11 S fraction started to precipitate earlier with a higher protein concentration. This correlates with the large change in soluble protein observed for pH 6, a point close to the isoelectric point of the 11 S fraction and the inflection point of the protein solubility curves. The electroacidification process influences the precipitation curve of the 11 S fraction the electroacidified 11 S fraction precipitation curve presents a slight shift in comparison with the chemical acidification curves (Figure 21.15a and 21.15b). The lower precipitation for the electroacidified proteins is the result of the lower extent of precipitation obtained for the 11 S fraction [88]. 

The shape of the precipitation curve obtained on gradual addition of ethanol to an aqueous solution of the polysaccharide material indicated heterogeneity. However, the five fractions collected showed no significant quantitative differences in component sugars. Another attempt to obtain fractionation of the polysaccharides by precipitation with ethanol from a solution in water or formamide was unsuccessful. Precipitation with hexadecyltrimethylammonium bromide likewise produced no clear separation. 2 Electrophoresis of some preparations showed them to be... 

In severely metal-polluted soils, hydrolysis and precipitation can remove hydrolysis-prone metals from solution as the pH approaches neutrality, so that experimental sorption curves, which include both chemisorption and precipitation, tend to be more abrupt than the one shown in Figure 4.5. For example, as the pH of the Cu/ A1(0H)3 system is adjusted upward, copper hydroxide can precipitate if insufficient adsorption has occurred to keep the (Cu )(OH ) activity product below the solubility product of Cu(OH)2. In the absence of adsorption, 10 10 and 10 Af Cu would begin to be removed from solution as Cu(OH)2 at pH 6.8, 6.3, and 5.8, respectively. This means that, in contrast to metal adsorption curves, metal hydroxide and oxide precipitation curves shift to lower pH as the total metal in the system increases. 

FIGURE 12.2 Solubility of noncharged homopolymers poly(NIPAM) andpoly(Af-isopropylmethacrylamide) (poly(NIPMAM) in 1 mM NaCl as a function of the temperature (precipitation curve) using optical density measurement. 

Figure 3.9 Determination of the critical temperature, Tc, from a cloud-point or precipitation curve.

Problem 3.17 Use the 1/ and 6 values obtained in Problem 3.16 to determine from theory the precipitation curves and the critical temperatures (Tc) for the four polystyrene fractions of Problem 3.16 in cyclohexane solution. 

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