Extraction factor, partitioning calculation

A sample contains a weak acid analyte, HA, and a weak acid interferent, HB. The acid dissociation constants and partition coefficients for the weak acids are as follows Ra.HA = 1.0 X 10 Ra HB = 1.0 X f0 , RpjHA D,HB 500. (a) Calculate the extraction efficiency for HA and HB when 50.0 mF of sampk buffered to a pH of 7.0, is extracted with 50.0 mF of the organic solvent, (b) Which phase is enriched in the analyte (c) What are the recoveries for the analyte and interferent in this phase (d) What is the separation factor (e) A quantitative analysis is conducted on the contents of the phase enriched in analyte. What is the expected relative erroi if the selectivity coefficient, Rha.hb> is 0.500 and the initial ratio ofHB/HA was lO.O ... 

In all cases, the selective solvents (entrainers) have the task of altering the partition coefficients in a way that high separation factors and selectivities for the different phase equilibria (extractive distillation vapor-liquid equilibrium (VLE), extraction liquid-liquid equilibrium (LLE), absorption gas-liquid equilibrium (GLE)) are achieved, resulting in a separation of compounds. The required partition coefficients, separation factors and selectivities can be calculated with the help of thermodynamic models (g -models, equations of state). 

By substitution of known values into this expression, the concentration is found to be 9 X 10 M. Thus, one extraction stage as described decreases the benzoic acid concentration in the effluent to just under one-half the original value. Similarly, by substituting this concentration value and Kp into Eq. 10.36, the concentration of benzoic acid obtained in the benzene extract is found to be 0.04 M, a ratio corresponding to the benzoic acid partition factor between these two liquids. The same equation may also be used to calculate the single-stage extraction parameters for any other solute of interest, provided that Kp for the system is known, or is determined experimentally. 

As was noted above, most aroma compounds tend to be lipophilic. Log P values for a range of aroma compounds found in foods are presented in Table 3.1. (Log P as defined here is the logarithm of the oikwater partition coefficient and relates to an octanoliwater systan. The values presented are calculated as opposed to experimentally determined.) If one considers the Log P values presented in Table 3.1, one notices that the vast majority of these aroma compounds will partition into the oil phase (i.e., the organic solvent in an extraction). Thus, solvent extraction of a food can be a very effective means of preparing an aroma isolate for study. The weaknesses of this method include the obvious factor that different aroma compounds have different partition coefficients and thus, will be extracted to varying extents in the extraction process. Certainly, the more water-soluble components such as diacetyl... 

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