Acid dissociation constant buffers

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 ... 

The situation is more interesting when the solution is buffered with a weak acid, say HA. Then, if = (H )[A ]/[HA] is the apparent acid dissociation constant, we have... 

Apparent partition coefficient (logZ)) at an ionic strength of / = 0.02M, log P value of the neutral microspecies and the acidic dissociation constant of 5 was calculated (97ANC4143). The distribution coefficient of 5 was determined between 1-octanol and universal buffer in the pH range 3-10 at a... 

APPENDIX 4 SATURATED SOLUTIONS OF SOME REAGENTS AT 20°C 829 APPENDIX 5 SOURCES OF ANALYSED SAMPLES 830 APPENDIX 6 BUFFER SOLUTIONS AND SECONDARY pH STANDARDS 830 APPENDIX 7a DISSOCIATION CONSTANTS OF SOME ACIDS IN WATER AT 25°C 832 APPENDIX 7b ACIDIC DISSOCIATION CONSTANTS OF SOME BASES IN WATER AT 25°C 833... 

Allen RI, Box KJ, Comer J et al. (1998) Multiwavelength spec-trophotometric determination of acid dissociation constants of ionizable drugs. 17(4-5) 699-712 Avdeef A, Bucher JJ (1978) Accurate measurements of the concentration of hydrogen ions with a glass electrode calibrations using the Prideaux and other universal buffer solutions and a computer-controlled automatic titrator. Anal Chem 50 2137-2142... 

Calorimetric measurements on a reaction like the hydrolysis of ATP yields Ar // ° at the experimental T, pH, and ionic strength. The calorimetric heat of reaction Aj/Zc must be corrected for the heat effect of the hydrogen ions produced by the enzyme-catalyzed reaction on the acid dissociation of the buffer, as described in Chapter 15. If Zf is measured at several temperatures and the acid dissociation constants of all the reactants are known at these temperature, the equilibrium constant K for the reference reaction can be calculated at each temperature. Plotting InAT versus 1/Tyields, which is given by... 

The ocular bioavailability of a topically applied drug (i.e. the percentage of effective drug available at the ocular surface or in the anterior segment) depends upon a number of factors. The acidic dissociation constant (pRa) of the drug and the pH of the vehicle determine the differential solubility of the drug on the ocular surface and its intraocular bioavailability. Increasing the concentration of buffer in ophthalmic solutions extends the time taken for the tear film to return... 

Consider a glycosyl donor, GlyZ, reacting exclusively with the anions of two potential acceptors, HX and HY, whose acid dissociation constants are and Ky. For simplicity we consider the solution to be buffered at a pH well below the lower of pXx or pXy. We can then write... 

The acid dissociation constants were determined according to the mediod outlined in [6] using a a concentration of ketobemidone and norketobemidone of 2 x 10 M. A portion of 10.00 ml of the aminophenol solution is mixed with 5.00 ml of buffer. The pH and the absorbance at 300 nm were recorded using as reference solution a mixture of 5.00 ml of 0.1 M HCl and 10.00ml of the aminophenol solution with the absorbance, A cid. The maximum absorbance, Amax/ was obtained in a solution of 5.00 ml of 0.3 M NaOH and 10.00 ml of the aminophenol solution. 

The four microscopic acid dissociation constants of pentazocine were determined according to [4,5] at 20 °C using sodium carbonate-bicarbonate buffer solutions of ionic strength 0.1. 

From a practical point of view, the octanol-water partition coefficient of benzoic acid is 74 (log = 1.87), its acid dissociation constant is 6.3 x 10 (pAia = 4.2), and its dimerization constant, k2, is about 0.04. At physiological pH of 7.4, benzoic acid is exclusively in the benzoate anion form. Eq. 4 gives a Dq/w value of 0.05 whatever be the benzoic acid concentration injected (the buffer capacity is assumed to be high). When 1 Mbenzoic acid is injected in a pH 1 buffered aqueous phase, the measured Dq/w value will be 77. A 0.1 M injection at pH 1 would produce a Dq/w value of 74.3. In all cases, the Pq/w coefficient is 74. The peak position of benzoic acid in the CCC chromatogram critically depends on the aqueous phase pH and marginally on the injected concentration. 

Figure 9-2 shows the calculated response of a buffer to small additions of H" or OH . The buffer is a mixture of HA (with acid dissociation constant = 10... 

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