Partition coefficient log p (scientific lab report) - Essay Example

Thru partition, coefficient was expressed with the concentration in the non-aqueous or lipophilic phase as the numerator. This was expressed in a formula “P = Coil / Cwater.” In that context, the drug’s absorption can be predicted using the partition coefficient. In logarithmic partition, coefficient values are calculated to determine the solute’s hydrophocity, lipophilicity and it’s anent absorbability. Since body membranes are usually impermeable to foreign ionic species, only un-ionized drug molecules can partition into the membrane.

Hence, the lipophilicity correlates with the state of the drug including its acidity or pH level. Note that pH levels vary in all part of the body which implies that drugs partitioned in a specific part will also have diverse un-ionized states. “Partition coefficient’ also determines the acid dissociation constant or Ka. This can be calculated using the equation of Henderson-Hasselbalch where the “product of hydrogen ion ([H+]) and ionized acid ([A-]) concentrations” is divided by the “concentration of unionized acid ([HA]).

This formula is expressed with the following: Ka = [H+][A-] / [HA]  This experiment aims to determine the different pHs and degree of ionization affected the partition coefficient of salicylic acid. . The combination such three equations would result to  1/P’ = 1/P + Ka/[H+]P  of which P is partition coefficient  Ka is dissociation constant  CO is total concentration in oil phase; and CW is total concentration in aqueous phase. Researchers will also obtain the “absorbance values” using different concentration of salicylic acid because this is relevant in setting a calibration curve and a graph to reflect the concentration in the aqueous phase.

Moreover, a graph plotting 1/P’ against the reciprocal of hydrogen ion concentration (1/[H+]) yielded a line with an intercept of 1/P and a slope of Ka/P. Using the partition coefficient and the dissociation constant, the pKa was calculated.  Methodology This experiment comprised of two parts: (a) determination of salicylate concentration to produce a calibration curve and (b) salicylate concentration measured in solutions of four different pHs. a. Salicylate Concentration Determination to Produce a Calibration Curve  It aims to resolve the absorbance of salicylate solution at different concentrations to produce a calibration curve.

 As part of the method, researcher will use five test tubes. Test Tube 1 will contain 6mL of water which will be used as the blank solution to keep the calorimeter at zero. Other test tubes will contain 5mL of water which is added to 2mL of ferric nitrate solution. Further, 1mL of different concentrations of salicylate was added to test tube 1; 0.00125M for test tube 2; 0.0025M for test tube 3; 0.00375M for test tube 4; and 0.005M for test tube 5. With calorimeter set at a wavelength of 624nm, the absorbance of each test tube of salicylate solution was determined by pouring solution in cuvettes and inserting them into the calorimeter. Data