Effect of pH on extraction

Generally, it has been found that the organic acids and bases do exist in aqueous solution as equilibrium mixtures of their respective neutral as well as ionic forms. Thus, these neutral and ionic forms may not have the same identical partition coefficients in a second solvent therefore, the quantity of a substance being extracted solely depends upon the position of the acid-base equilibrium and ultimately upon the pH of the resulting solution. Hence, extraction coefficient (E) may be defined as the ratio of the concentrations of the substance in all its forms in the two respective phases in the presence of equilibria and it can be expressed as follows  

In fact, the actual effect of the equilibrium on the extraction may be shown by determining the extraction coefficient for the system  

Therefore, for this particular system the efficiency coefficient E may be expressed as follows  

From Eq. (v) it is quite evident that E approaches Kp, A as K[H], becomes small and K AH as K[H] j becomes large. 

assuming that only A extracts (/. ., A being a neutral organic base and AH the conjugate acid), Eq. (v) may be expressed as  

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Gardner and Yates [26] developed a method for the determination of total dissolved cadmium and lead in estuarine waters. Factors leading to the choice of a method employing extraction by chelating resin, and analysis by carbon furnace atomic absorption spectrometry, are described. To ensure complete extraction of trace metals, inert complexes with humic-like material are decomposed by ozone [27]. The effect of pH on extraction by and elution from chelating resin is discussed, and details of the method were presented. These workers found that at pH 7 only 1-2 minutes treatment with ozone was needed to completely destroy complexing agents such as EDTA and humic acid in the samples. 

Fig. 5. Effect of pH on extraction of lactic acid (40 g/L) by Alamine 336 (30% [v/v] in 2-octanol) at 80 mL/min flow rate (A) time course of lactate concentration in base reservoir (B) extraction rate as affected by pH of feed solution.

Because of the formation of emulsions at phase boundaries for APE surfactants, EEE is limited to the degradation products APs, alkylphenol monoethoxylate to triethoxylate (APE(l-3)) and alkylphenol ethoxy carboxylate (APEC). Dichloromethane and hexane are the solvents commonly used in the extraction of APs and APE(l-3) from liquid samples.For phenolic compounds including BPA, OP, and NP, water samples are often acidified to pH < 4 with hydrochloric acid. Acidification of water samples suppresses the dissociation of phenols and prevents the ionization of the analytes, which increased the efficiency of the extraction. Del Olmo et al. " studied the effect of pH on extraction of BPA using sodium hydroxide and hydrochloric acid for adjustment. The result obtained showed that the extraction efficiency remains constant for pH values lower than 6.5, decreasing sharply for higher values. This behavior agrees with the weak acid nature of BPA. 

Selective extraction experiments were then performed to see transference of some transition elements (Cu ", Ni ", Co ", and Fe " ) from the aqueous phase to the organic phase by the synthesized polymeric calixarenes. Phase-transfer studies in water-chloroform confirmed that polymer 2b and 3b were Fe ion-selective as was its monomer (1). Extraction of Fe " cation with 2b and 3b was observed to be maximum at pH 5.4. Only trace amounts of other metal cations such as Cu, Ni ", and Co " were transferred from the aqueous to the organic phase (Table 3). Furthermore, the extracted quantities of these cations remained unaffected with increasing pH. The effect of pH on the extraction of 3b was lower and 56% extraction was accomplished even at pH 2.2. The extraction experiments were also performed with calix[4]arene (1) the ratio was 8.4% at pH 2.2. The polymeric calix[4]arenes were selective to extract Fe " from an aqueous solution, which contained Cu +, Ni, Co ", and Fe " cations, and it was observed that the... 

Effect of pH on the rate of silica extraction from vitreous silica powder at 80°C (after El-Shamy and Douglas, 1967)... 

An HPLC method was employed for the study of the effect of pH on cream particle formation and solid extraction yield of black tea. Broken black tea (60g) was brewed with 21 of boiling distilled water for lOmin then filtered. After cooling down, pH of aliquots of 45 ml were adjusted to 1.2, 2, 3, 7, 9, 11 and 13 with 3 M HC1 and NaOH, respectively. 

Y. Liang and Y. Xu, Effect of pH on cream particle formation and solids extraction yield of black tea. Food Chem. 74 (2001) 155-160. 

An understanding of partition coefficient and the effect of pH on partition coefficient is useful in relation to the extraction and chromatography of drugs. The partition coefficient for a compound (P) can be simply defined as follows ... 

Effects of pH on the Recovery of Mutagenic Activity. The effect of pH, characteristic of the modified EMSL method, was examined in the following experiment. Residue organics extracted from a sample of primary sludge first were isolated via the milling procedure and then recombined in proportions representative of the original sample. An aliquot (ALIQ-I) of this reconstituted sample was bioassayed. A second aliquot (ALIQ-II) was spiked into aqueous base of pH 11. Then, the... 

Figure 23-2 Effect of pH on the distribution coefficient for the extraction of a base into an organic solvent. In this example, K = 3.0 and pfCafor BH is9.00.

Chethan, S. and Malleshi, N. G. (2007a). Finger millet polyphenols Optimization of extraction and the effect of pH on their stability. Food Chem. 105, 862-870. 

Figure 12. Effect of pH on ether extractability of h -THC in vivo metabolites from unhydrolyzed Rhesus urine...

The dramatic effect of pH on K for the extraction of some antibiotics can be seen in Table 1. 

Effect of Derivatization pH on Aldehyde Recovery. Binding of aldehydes to other wine components (SOj, phenols, etc.) is highly pH dependent, therefore the effect of pH on derivatization efficiency was evaluated. Following addition of aqueous cysteamine to spiked wine samples, the pH was adjusted to 2, 8, or 10, and the solutions were allowed to react for 1 hour. The pH of all samples was then readjusted to 8.5, and the samples were extracted and analyzed as described above. Initial results indicated that no consistent differences in recovery at the different pH s were observed, however, overall variability appeared greater at pH 2. These results provide preliminary evidence that the total aldehyde concentration (free plus bound) is measured with this procedure. Further studies with model solutions containing added SO2 and phenols are needed to fully evaluate this result. 

Layers Lost Vs. Apparent Solubility Estimates. Figure 5 shows a summary data plot wherein the vertical axis gives the apparent number of layers removed or extracted of silica (0-6 week data set, dissolved silica concentration 1-5 yiM, pH range 7.5-8.5) and the horizontal axis gives our estimated "apparent" solubility values in dissolved silica. Each mineral is represented by a box because of the effect of pH on both the actual dissolution rate or surface flux and on our "cross-over" or "apparent" solubilities. This can also be seen in Figures 4a-z, wherein higher pH values usually result in higher dissolution rates and lower solubilities. 

FIG. 15-14 The effect of pH on the partition ratio for extraction of penicillin G (pK, = 275) from hioth using an oxygenated organic solvent The partition ratio is expressed in units of grams per/liter in the oigairic phase over that in the aqueous phase. [DatajhmiR L. Feder, M.S. thesis (Polytechnic Institute of Brooklyn, 1947).]... 

Figure 2 Effect of pH on the extraction of polygalacturonase from the cell wall fraction of tomato Reproduced with the permission of Reference 37 ...

Figure 2 The effect of pH on cell separation in mature green tomato pericarp tissue. Cell separation assays were carried out on pericarp fragments (5 to 10 cells) extracted with buffered phenol...

FIG. 9.3. Effect of pH on the extraction of some divalent metals from aqueous solution into chloroform by O.OIM 8-hydroxyquinoline (oxine). 

These complications provide an explanation for the lack of agreement obtained from many studies which have been carried out to assess the effect of pH on heavy metal availability, as well as the relative effectiveness of various reagents for the extraction of these metals from clays, soils, and sediments. The extractability or leachability of these metals should be viewed in terms of the Eh and pH of the system, soil plus extractant, as compared with that of the system soil plus pore water, and the solubilities of Fe(OH)3(a) and Mn02(a ), especially the latter, in the extractant utilized, [(a) indicates an x-ray amorphous solid as opposed to (c), a crystalline phase.]... 

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