Measuring divider Coefficient
This Laboratory survey trades with the Analytic Procedure of the Measurement of Partition Coefficient. Partition Coefficient is a really of import standard for Organic substances. It finds usage in Pharmaceutical Industry, Pollution suspension systems, Agro Chemicals, and Chemical Industry. There are many methods available for finding the Partition Coefficient, particularly Instrument methods like, Chromatography, Electrophoresis etc. The method adopted here is a simple, dependable and various one, which utilizes basic rules of Chemical Analysis.
The method used was by measuring of pH and Colorimetric finding of the organic Ligand. The procedure used for breakdown was aˆ?Shaking Flask methodaˆ? . The given sample was diluted and buffered suitably and an aliquot was partitioned with an equal measure of the given oil. The pH of the aqueous stage was measured. The clear aqueous solution was farther diluted suitably and used for Colorimetric appraisal utilizing a Calibration graph prepared. These informations were used for calculation of evident Partition coefficient and so true Partition coefficient.
Measuring Partition Coefficient
Chemistry is a material Science, covering with the survey of Physical and Chemical belongingss of the affair found in the existence. There are many subjects in Chemistry covering with different stuffs and belongingss, like Inorganic Chemistry, Organic Chemistry, Physical Chemistry, Pharmaceutical Chemistry, Analytical Chemistry etc. The Analytic Chemistry is a particular subdivision of Chemistry covering with the finding of Chemicals, measure wise and quality wise. The Analytic Chemistry uses the cognition available in other subdivisions of Chemistry, like Inorganic Chemistry, Organic Chemistry, Physical Chemistry, and many rules of Physics.
The utilizations and applications of Analytic Chemistry are broad, and practically, in every facets of human life, analytical Chemistry is involved in some manner or other, say, in Clinical Chemistry, Pharmaceutical Chemistry, Forensic Chemistry, in commercialism, in Customs Department and so on. The measuring of Partition Coefficient is a typical analytical process utilizing many theoretical rules of assorted subdivisions of Chemistry. It denotes the differential sums of the substances found at equilibrium conditions in the organic stage and the aqueous stage for a set of conditions like Concentration, pH, Temperature etc.
This Lab survey purposes at and involves, in add-on to larning partitioning technique, Electro Chemical application – the pH measuring, colorimetric measuring, computational techniques, and Calculation processs. The divider coefficient survey assumes significance, because it finds usage in Pharmaceutical Chemistry for drug design, development, and bringing, Pesticide design, dirt Chemistry, designing of Chemical Plants by Chemical Engineers, and besides for Chemists and Scientists working on Liquid – Liquid Equilibrium informations.
Sample readying: Sodium salicylate solution of 0.2 gm mol per litre ( mol ) was taken for this survey. From this stock standard solution four Trial samples, named A to D, were prepared. 10 milliliter of 0.2 mol standard solution was pipetted into each of the four 100 milliliter volumetric flasks marked A to D and diluted to the grade with four buffer solutions of different pH, and assorted exhaustively. So the concentration of the end point diluted samples was 0.02 mol each.
Partitioning: Aliquots of 25 milliliter of the above diluted samples, 4 Nos, were taken in 4 separating funnels. Then, 25 milliliter of the given oil was added in each of the 4 separating funnels, marked A to D, and assorted exhaustively and gently by inverting and revolving for 10 proceedingss. Then the mixture in the separating funnels were allowed to settle exhaustively. After the aqueous and organic beds became clear, the aqueous beds of the four separating funnels were drained into four glass beakers marked A to D.
pH measuring of aqueous stage: The pH of the four partitioned aqueous samples were measured utilizing a pH metre.
Determination of Salicylate concentration in the Aqueous stage: For finding the Salicylate concentration, Colorimetric method was adopted where the optical density of the Iron- Salicylate composite was measured. The process adopted for developing the criterion and trial samples is given below.
Preparation of Standard colour Solutions: Four different Standard solutions of Sodium Salicylate, viz. , 0.00125mol, 0.0025 mol, 0.00375 mol and 0.005mol were prepared along with a space.
Five trial tubings were taken. The first 1 was marked as 1 ( Blank ) , and the others as 2,3,4, and 5.
To the space, 1 milliliter of H2O was added, and in the others, one milliliter each of the prepared criterions were added. Then 2 milliliter of the given Ferric Nitrate was added to all the trial tubing. Then 5 milliliters of H2O was added into all the five trial tubing. All the trial tubings were shaken gently to blend the contents exhaustively and waited for some clip for the complete development of the colour. The five solutions represented 0.0000 mol, 0.00125mol, 0.0025 mol, and 0.00375 mol and 0.005mol Salicylic acerb concentration severally.
Preparation of Calibration Graph: The Colorimeter ( Spectrophotometer ) was set at the moving ridge length of 624 nanometers. Placed the space in the cuvete in the tintometer and adjusted the optical density as nothing. Then the other standard solutions were placed one by one and noted the optical density readings. Calibration Graph was plotted, plotting concentration of salicylic acid in X axis and Absorbance at the Y axis.
Preparation of Test samples: 10 milliliter of each of the four Partitioned aqueous beds were diluted with H2O to 50 milliliters, therefore doing a diluted sample. From these, 1 ml solution each were placed in four trial tubings, marked A, B, C, & A ; D. Then, 2 milliliter ferrous Nitrate and 5 milliliters H2O were added in all the four trial tubings and treated similar to the Standard tubings.
Measurement of Salicylic acid concentration of the trial samples: The optical density of all the four trial samples were measured similar to the criterions. The Salicylic acerb concentration of the trial samples were arrived from the Calibration graph. The concentration arrived was of the diluted samples. So the concentration of the partitioned aqueous stage was multiplied 5 times to acquire the concentration of the salicylic acid. This gives the Cw, i.e. , the concentration of the salicylic acid in the partitioned aqueous solution.
Determination of CO: The Cw was subtracted from the concentration of the buffered solution, i.e. , 0.02 mol, to acquire the CO.
Determination of Hydrogen Ion concentration: From the pH of the four partitioned aqueous solutions, Hydrogen Ion concentrations were calculated.
Measure 1. Calculation of H+ and 1/H+ from the pH
Model computation for Experiment A ; pH = 2.35.
pH is the negative logarithm to establish 10 of Hydrogen ion concentration.
So Hydrogen ion concentration is the antilog of – 2.35= 0.00447
Reciprocal of Hydrogen ion concentration = 1/H+ =1/0.00447 = 223.9
Similarly H+ and 1/H+ are calculated for other experiments and tabulated below.
pH of the buffer added
[ H+ ]
1 / [ H+ ]
Measure 2a. Calculation of the concentration of salicylate added to each dividing funnel: The salicylic acerb concentration of the sample taken = 0.2 gram. mol/Liter. 10 milliliter of this solution was diluted with buffer to 100 milliliter. So the concentration of the diluted solutions, added to each
dividing funnel, taken for the Partition experiment were 0.2×10/100 = 0.02 gram mol/L each.
Measure 2b. Calculation of Cw and Co: The partitioned concentration of salicylic acid in H2O and oil, denoted by [ S ( aq ) ] and [ S ( org ) ] are Cw and Co in the expression severally.
25 milliliter of the Solution A ( 0.02 gram mol Sodium Salicylate, buffered with buffer of 2.0 pH ) was partitioned with 25 milliliter of oil. After separation of the stages, the pH was measured in the aqueous stage. Then the aqueous stage was diluted five crease for colorimetric appraisal. The optical density obtained for experiment A was 0.065 and the corresponding concentration obtained for experiment Angstrom from the standardization graph = 0.00054. So the concentration of this undiluted Partitioned aqueous solution, [ S ( aq ) ] , is five times of the value determined calorimetrically = 0.00054x 5 = 0.0027. This is CW
The concentration of salicylic acid in the organic stage is the concentration of the diluted solution taken for the Partition experiment, minus concentration of the undiluted Partitioned aqueous solution, i.e. CO = ( 0.02- CW ) = ( 0.02 -0.0027 ) = 0.0173gm mol/L.
Apparent divider coefficient P ‘ = CO / CW = 0.0173/0.0027 = 6.4
1/P ‘ = 1/6.4=0.156
CW, CO, P ‘ and 1/P ‘ for other experiments were besides calculated like wise and tabulated below.
The standardization graph of this survey is attached individually.
Salicylate Concentration in aqueous stage of the diluted aliquot, from standardization Graph
Salicylate Concentration in aqueous stage the undiluted aliquot, CW i.e. ( [ S ( aq ) ] )
Salicylate Concentration in Organic stage
CO i.e. ( [ S ( org ) ] ) =
0.02- S ( aq )
Calculation of P ‘ and 1/P ‘
[ S ( aq ) ] i.e. CW
[ S ( org ) ] i.e. CO
P ‘ = ( CO / CW )
Measure 3. Preparation of 1/H+ vs. 1/P ‘ Graph and Calculation of P and Ka: A graph was plotted with 1/H+ in X axis and 1/P ‘ in Y axis. The incline, Ka/P was estimated from the graph = 0.0001518. The intercept, 1/P, was at 0.13, and therefore, P = 1/0.13 = 7.69.
Ka = ( Ka/P ) x P = 0.0001518 x 7.69 = 0.001167 ; pKa = – log of 0.001167 = 2.93
The survey consequences show a definite tendency of higher immersion of the organic acid, i.e. , Salicylic acid, into the organic bed at a lower pH and frailty versa. This is in conformity with the theory, which implies, at a lower pH, the H+ ion concentration will be higher, which will in consequence enhance association of the ions, R- + H+ a†’ RH, to organize nonionized molecule that can come in the organic stage. So the nonionized acid will be preponderantly in the organic bed. At higher pH, the H+ ions will be low and there will be the inclination of the acid to ionise in the aqueous stage, RH a†’ R- + H+ , therefore forestalling the acid to come in the organic stage.
So the ionised acid ion will be preponderantly in the aqueous bed. This is established in this experiment ; CO, the concentration of salicylic acid in organic stage is highest, 0.0173mol, in Experiment A, where the pH is the lowest, 2.35 ; and lowest, 0.0075 mol, in Experiment D where the pH is the highest,4.02. Consequently the Apparent Partition coefficient P ‘ which is the ratio of CO / CW is highest in Experiment A and lowest in Experiment D. This shows, the pH of the solutions affect the breakdown.
The truth of the survey depends both on the truth of pH measuring and the measuring of optical density. The one-dimensionality of the graph- 1/H+ vs. 1/P ‘ depends on both the measurings. But the curve was non absolutely additive as expected.
The possible beginnings of mistakes. While transporting out the Chemical Analysis, one has to be cognizant of the possible beginnings of mistakes. Alexeyev ( p 48 ) classifies the mistakes in aˆ?Quantitative Analysisaˆ? as Systematic mistakes, random mistakes and errors. The systematic mistakes are: mistakes of the method, mistakes of setup & A ; reagents, and Operative mistakes. Random mistakes do go on during
any analysis and one has to be argus-eyed and careful to avoid them. Mistakes are rough mistakes caused by careless noting of the readings in the instruments, parallax mistake, improper labeling of the assorted trial samples stoping with confusion while tabling the readings etc.
The possible systematic mistakes in this survey are: mistakes of the method, say non unvarying pH among the four trial in the colorimetric appraisal. Lyalikov.Y ( p 40 ) warns, aˆ?many colored compounds are sensitive to Hydrogen Ion concentrationaˆ? . aˆ?Changes in pH non merely affects extinction, but change spectrophotometer curve of the substance as wellaˆ? , Lyalikov.Y ( 41 ) . The standardization curve obtained is non directly as expected, demoing the coloured composite did non obey Beer Lambert Law, which states, optical density is relative to molar extinction coefficient, Iµ , deepness of the solution bed, L, and concentration, C. ( A=Iµ x L x C ) . It was expected at least to be a smooth curve of a definite form. But the curve is non really smooth bespeaking some mistake, may be changing concluding pH of the coloured solutions.
Possible mistakes of setup: leaking dividing funnel. Possible mistakes of reagents: truth of the buffers.
Operative mistakes: Possible non unvarying commixture during breakdown, incorrect and non unvarying draining from pipettes. It was expected that the curves of Calibration graph and that of 1/H+ vs. 1/P ‘ to be consecutive lines. But they are non directly as expected. The ground may be due to some or a combination of the above cited mistakes.
Comparison of the consequence with Literature: The literature value for Ka of salicylic acid as given by Harris, Daniel. C. ( p 183 ) is Ka = 1.07 ten 10A?3. The consequence obtained in this Lab survey is 0.001167. This is higher than the value reported in aˆ?Quantitative Chemical Analysisaˆ? by approximately 9 %
The phenomenon of breakdown: The chemical substances exhibit different solubility in different dissolvers. Solvents may be classified into two groups, Aqueous and Non aqueous, in other words polar and non polar. Similarly the chemicals may be classified as Hydrophilic and Hydrophobic. Hydrophobic substances can besides be termed as Lipophilic. A hydrophilic substance will easy fade out in an aqueous dissolver and a hydrophobic ( Lipophilic ) substance will easy fade out in not aqueous ( Organic ) dissolver. If a substance is in contact with both the Hydrophilic and Hydrophobic Solvents, the substance will acquire distributed in both the dissolvers and the proportion of distribution will be harmonizing to the nature of the substance with regard to its Hydrophilic or hydrophobic nature and this belongings is termed as the Partition coefficient.
Partition coefficient finds application in Pharmaceutical industry, agrochemical Industry, Pollution surveies and for planing of Chemical Process by Chemical Engineers.
Drugs are meant to be ingressed into human organic structure. The divider coefficient finds use in drug design, as it is a step of the hydrophobicity of the drug concerned. If the divider coefficient is high, it denotes high hydrophobicity ( high lipophilicity ) and such a drug will easy come in the lipid parts of the variety meats and remain for longer clip and hence may turn out toxic. On the other manus a low Partition coefficient denotes a hydrophilic nature and therefore the drug will remain longer in the aqueous parts – blood watercourse and will non readily immersion into the tissues. So the soaking up, elimination and incursion of the drugs into the organic structure variety meats are related to the Log P value of a drug. An intermediate Partition coefficient is preferred while planing the drugs by the Pharmacologists. Earll. Mark enumerates the optimal Partition Coefficient, as Log P, for different types of drug applications.
Optimum CNS incursion around Log P = 2 +/- 0.7 ( Hansch )
Optimum Oral soaking up around Log P = 1.8
Optimum Intestinal soaking up Log P =1.35
Optimum Colonic soaking up Log P = 1.32
Optimum Sub linguistic soaking up Log P = 5.5
Optimum Percutaneous Log P = 2.6 ( & amp ; low mw )
The drug has to be designed consequently for each of the application. The Formulation and dosing signifiers, as given by Earll. Mark:
Low Log P ( below 0 ) Injectable
Medium ( 0-3 ) Oral
High ( 3-4 ) Transdermal
Very High ( 4-7 ) Toxic construct up in fatty tissues
The drug has to travel into human organic structure through different paths, say, mouth, skin, Blood etc all holding different pH. So the drug has to be designed taking into consideration of the consequence of pH. Mark Earll gives the pH of the assorted parts of the organic structure: Stomach 2, Kidneys 4.2 ( variable ) , Small Intestine: Fed 5.0 & A ; Fasted 6.8, Duodenal Mucus 5.5, Plasma 7.4.
Harmonizing to Chemie.DE information service GMBH, The Hydrophobic drugs are preferentially distributed to hydrophobic compartments such as lipid bilayers of cells while hydrophilic drugs preferentially are found in hydrophilic compartments such as blood serum. The Partition coefficient of the drug determines the Absorption. Distribution, Metabolism and elimination of the drugs. When a drug is admitted orally, it passes through the alimental canal and has to be absorbed through the lipid beds of the epithelial membrane of the little bowel. So the drug should be sufficiently Lipophilic as to go through through the lipid beds.
At the same clip it should non be excessively lipotropic, otherwise, it will remain for good in the epithelial calls and will non come in the blood watercourse for conveyance to the needed location. Similarly the drug has to be metabolized and excreted after its map is over. This besides depends on the Hydrophobicity. Similarly the other signifiers of drug disposal are besides need to be studied in this facet. So control of the Hydrophobicity ( lipophilicity ) while developing the drug is of import. Here is the usage of Partition coefficient measuring, which is a step of the hydrophobicity.
Partition coefficients find usage in planing pesticides. One has to plan the insect powder in such a manner it has got a really high divider coefficient, i.e. , holding high hydrophobicity, instead
high lipotropic inclination, so that the insecticide easy penetrates into the being and remain for good doing high toxicity, therefore turn outing its efficaciousness in killing the plagues. But, the inauspicious effect is, the pollution facet, vide Chemie.DE information service GMBH.
In divider surveies, Octanol/ H2O system is usually used. Earll. Mark provinces, aˆ?Octanol was chosen as a simple theoretical account of a phospholipid membrane ; nevertheless it has shown serious defects in foretelling Blood-brain barrier or tegument penetrationaˆ? .
aˆ?The most needful liquid- liquid divider coefficient is the octanol-water divider coefficient. Ko/w is accepted as a good mention parametric quantity for solute hydrophobicity. Indeed, Ko/w can be quickly estimated utilizing capillary cataphoresis with a micellar or micro emulsion solution and/or RPLCaˆ?
Leahy, Taylor and Wait of ICI have proposed, in add-on to octanol, trichloromethane, cyclohexane and propene ethanediol dipelargonate ( PGDP ) for patterning biological membranes, notes Earll. Mark.
For finding the Partition Coefficient, there are many other Instrumental methods, like, HPLC. Paper Chromatography, Thin bed chromatography and Electrophoresis. Berthod. A and Carda-Broch. S. enumerates the assorted analytical Techniques. They are: Shake-flask method, HPLC method, Micro emulsion electro kinetic capillary cataphoresis, Counter-current chromatography ( CCC ) , Co current CCC, Micellar electro kinetic capillary chromatography ( MEKC ) , Micro emulsion electro kinetic capillary chromatography ( MEEKC )
Alexeyev, V. ( 1969 ) . Quantitative Analysis. Moscow: Mir Publishers.
Berthod.A, Carda-Broch.S ( 2004 ) Determination of liquid-liquid divider coefficients by separation methods. Journal of Chromatography A, 1037 3-14
Chemie.DE information service. GMBH. Encyclopedia of Chemistry, Partition coefficient, Retrieved January 28, 2010, from hypertext transfer protocol: //www.chemie.de/lexikon/e/Partition_coefficient
Earll, Mark. A usher to Log P and pKa measurings and their usage. Retrieved January 28, 2010, from www.raell.demon.co.uk/chem/logp/logppka.htm
Harris, Daniel C. Quantitative Chemical Analysis. Google Books.
Lyalikov, Y. ( 1968 ) . Physicochemical Analysis. Moscow: Mir Publishers.