Liquid Liquid Extraction

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Liquid-Liquid Extraction:

Liquid-Liquid Extraction Dr. Archana Naik, SVB’s College of Pharmacy 1 S.Y.B. Pharm

Introduction:

Introduction Liquid-Liquid Extraction or solvent extraction is one of the separation technique and it is the most common method adopted in the field of analysis. Extraction is the process of transfer of constituent from one liquid phase to another liquid phase by contact. This process is also as called Partitioning or distribution . In p’ceutical field solvent extraction method is adopted in separation and isolation of various ingredients from their complex formulation. 2 Dr. Archana Naik , Saraswathi Vidya Bhavans College of Pharmacy

Solvent Extraction:

Solvent Extraction Generally one of the two methods are used for extraction purpose. 1. removal of interfering or unwanted substance from preparation by crystallization, filtration, sublimation or distillation method. 2. separation or isolation of active ingredient from preparation i.e. extraction technique. There are two types of extraction techniques 1. Solid phase extracton 2. Liquid Liquid extraction 3 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

liquid-liquid extraction :

liquid-liquid extraction liquid-liquid extraction has been employed predominantly and effectively not only for the pre-concentration and isolation of a ‘single’ chemical entity just before its actual estimation, but also for the extraction of classes of organic compounds or groups of metals, just prior to their usual estimation either by instrumental techniques. 4 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

theory:

theory The concept of “like dissolves like” works well in LLE. A hydrophobic molecules prefers an organic medium whereas an ionic compound prefers to remain in aqueous solution. When shaken, with two immiscible solvents, the compound will distribute itself between the two solvents. Normally one solvent is water and the other solvent is a water-immiscible organic solvent . 5 Dr. Archana Naik , Saraswathi Vidya Bhavans College of Pharmacy

Theory:

Theory Consider a single solute(A) distributed between two immiscible solvent then the resulting equilibrium can be written as A aq A org or Solute in lower phase Solute in upper phase At equilibrium the molecules naturally distribute themselves in the solvent where they are more soluble Distribution of solute in upper and lower phase is depending on the affinity of the drug towards solvents. 6 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Nernst distribution law:

Nernst distribution law Liquid liquid extraction method is based on nernst law which states that ‘ the ratio of activities of solute material in the two immiscible solvent at equilibrium is remain constant . Usually concentrations are substituted for activity, then distribution law is written as When solute in dissolved in two solvents which are immiscible in each other the solute distribute itself in both solvents and ratio of conc. of two solution remains constant and it is called as partition coefficient 7 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

distribution or partition coefficient(KD):

distribution or partition coefficient(KD) A quantitative measure of the how an organic compound will distribute between aqueous and organic phases is called the distribution or partition coefficient. It is denoted by equilibrium constant K It is the ratio of the concentrations of the solute in the two different solvents once the system reaches equilibrium. distribution or partition coefficient is also denoted as KD KD= (Note that K is independent of the actual amounts of the two solvents mixed but it is dependant on temperature.) If K D large , the solute will tend toward quantitative distribution in organic solvent 8 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

KD:

K D Benzoic acid is a weak acid in water with a particular ionisation constant Ka. The distribution constant is given by K D = [HBz]e eq 1 [HBz]a e is ether solvent and a represents the aqueous solvent.(note that benzoic acid in aqueous layer exist as Bz-, depending on magnitude of Ka and pH of the aqueous layer) 9 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Distribution ratio::

Distribution ratio: Distribution ratio: Is the ratio of concentrations of dissociated and undssociated form solute in 2 different solvents. We can derive the difference between D and K D from the equilibria involved. eq3 10 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Slide11:

The acidity constant of Ka for ionization of the acid in the aqueous phase is given by Hence From eqn 1 [ HBz ] e =K D [ HBz ] a Substitution of equation 5 and 6 in eqn3 gives eq4 eq5 eq6 eq7 eq8 Distribution ratio: 11 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Slide12:

Eq 3 put value of [ HBz ] o as K D [ HBz ] a ( calculated in eq 5) put value of [ Bz -] o as (calculated in eq 6) eq 7 12 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Distribution ratio:

Distribution ratio This equation predicts that when [H+]a >Ka, D is nearly equal to K D , and if K D is large the benzoic acid will be extracted into the ether layer; D is maximum under these condition. If on the other hand, [H+] < Ka, then D reduces to K D [H+]a/Ka, which will be small and the benzoic acid will remain in the aqueous layer. i.e. in alkaline solution the benzoic acid is ionized and cannot be extracted, while in acid solution it is largely undissociated. In solvent extraction the separation efficiency is usually independent of the concentration. 13 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Separation factor:

Separation factor The separation factor is one distribution ratio divided by another; it is a measure of the ability of the system to separate two solutes. For instance, if the distribution ratio for  nickel  (D Ni ) is 10 and the distribution ratio for  silver  (D Ag ) is 100, then the silver/nickel separation factor (SF Ag/Ni ) is equal to D Ag /D Ni  = SF Ag/Ni  = 10. 14 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Extraction of drug:

Extraction of drug The distribution ratio D is a constant independent of the volume ratio. However the fraction of the solute extracted will depend on the volume ratio of the two solvents. If larger volume of organic solvent is used, more solute must dissolve in this layer to keep the concentration ratio constant and to satisfy the distribution ratio. The fraction of the solute extracted is equal to the milimoles of the solute in the organic layer divided by the total no of milimoles of solute . 15 Dr. Archana Naik , Saraswathi Vidya Bhavans College of Pharmacy

Extraction:

Extraction If the partition coefficient for a solute between two solvents is known, it is possible to calculate the fraction of the solute that is present in each phase at equlibrium. Let P be the fraction of that solute in the upper phase and q is the fraction in the lower phase at equilibrium. The quantity p is defined by P= Amount of solute in upper phase Total amount of solute 16 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Extraction in upper(p) and lower phase(q):

Extraction in upper(p) and lower phase(q) Amount is express in terms of concentration C and volume V Amount of solute in upper phase=CuVu Total amount of solute=CuVu +C L V L Ratio of phase volume U=Vu/V L Eqn K=Cu/C L Cu=KC L 2 Eqn U=Vu/V L Vu=UV L 3 Therefore eq 1 becomes P= CuVu /CuVu +C L V L and P= KC L .UV L / KC L .UV L + C L V L P= C L V L KU/ C L V L (KU +1) P= KU/KU+1 and %P= (KU/KU+1) x100 17 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Slide18:

The equation relates the fraction of solute extracted into upper phase to the partition coefficient and ratio of phase volumes since P is the fraction extracted into phase volume , 100P is % extracted into upper phase. P+q =1, q=1-p, q=1- [KU/KU+1] q= 1/KU+1 q= (KU +1) –KU /KU+1 q = 1/KU+1 The larger the partition coefficient, large amount of solute will be the extracted in upper phase. Fraction of drug in lower phase 18 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

%P:

%P A solute is known to have a partition coefficient of 4 between water and ether. If 15 ml of an aqueous solution of the compound is extracted with one 20 ml portion of ether what % of original solute will be found I the ether K=4 U=20/15= 1.33 P=KU/KU+1= 4 x1.33/4x 1.33+ 1 =5.32/5.32+1= 0.842 In percentage it is 84.2% 19 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Multiple extraction:

Multiple extraction Unless K is extremely large, a significant portion of solute will not get in both phases after extraction. Therefore at that time we have to reextract the solute for maximum recovery. If very less amount of solute is extracted in 1 st extraction so to remove all the remaining solute we have to reextract with additional portion of fresh extractant. 20 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Slide21:

During every extraction calculate the fraction of solute extracted or calculate no of extraction required to achieve desired extent of extraction. State of extraction after one equilibrium is mention below. 1=p+q total fraction extracted (p) =1-q In multiple extraction p=1-q n Sr no Fraction of total extracted in nth extraction Total fraction extracted Fraction remaining 1 P p q [1-p] 2 Pq 1 p+pq q 2 [1-( p+pq )] 3 Pq 2 p+pq+pq 2 q 3 [1-( p+pq +p q 2 )] n pq (n-1) ∑ n n =1 pq (n-1) q n 21 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Percent efficiency:

Percent efficiency Consider K=4 in ether water system U=1 so no of extraction required for extraction of maximum drug can be calculated by using formula given above. (out of 1, [ku/ku+1 = 4/5]0.80 of the solute is extracted in the first step. In second extraction fraction extracted is 0.80 of remaining 0.20 [pq= 0.8x0.2=0.16] so total extraction is 0.8+.16= 0.96) No of extraction n Total extracted (%) 1 80.00 2 96.00 3 99.20 4 99.84 5 99.97 22 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Comparison of single and multiple extraction:

Comparison of single and multiple extraction Compare the efficiency of extraction of 10 ml aqueous solution of compound with a) one 40 ml portion of ether b) four 10 ml portions of ether if K is 4 in ether water system. Single extraction a) K=4, U= ether layer vol/aq layer vol= 40/10=4 P=KU/KU+1 =4x4/4x4+1=16/17=0.9412 =94.12% b) Multiple Extraction K=4,U=ether layer vol/aq layer vol= 10/10=1 (q =1/KU+1=1/4x1+1=0.2) So total fraction extracted in 4 th extraction= 1-q 4 = 1-(0.2)4 =1-0.0016=0.9984 in percentage it is 99.84% 23 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Comparison of single and multiple extraction:

Comparison of single and multiple extraction Results indicate that more efficient extraction is achieved with several extraction than single extraction utilizing same total volume of extractant. In multiple extraction Only 20 ml (2 portions of10-10 ml ) can extract more than 96% than that of 40 ml used in single extraction. 24 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Types of Liquid Liquid extraction: A. Single extraction (Batch):

Types of Liquid Liquid extraction: A. Single extraction (Batch) Batch extraction is carried out using set of separating funnel. A solution from which a substance is to be extracted and immiscible solvent are introduced into separating funnel. Two phases are mixed thoroughly in order to extract the substance from one phase to other phase. For more efficiency fresh extractant is added to raffinate and extraction is continued several times. Extraction by this method is carried out when partition coefficient of solute is high. Method is simple and quick. Hence widely used for extraction on small scale. For extraction on a large scale, a continuous extraction procedure is used. 25 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Single extraction (Batch):

Single extraction (Batch) 26 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

B.Continuous Extraction:

B.Continuous Extraction In some cases, it is difficult to efficiently remove a solute unless a large number of extractions are conducted. An alternate approach is a continuous extraction. With an appropriate setup, an efficient extraction can be conducted with a minimum of extracting solvent. Advantages Only uses a small amount of solvent Can remove a high percent of a solute Can work unattended for long periods 27 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Continuous Extraction:

Continuous Extraction The continuous extraction method is carried out when the partition coefficient of solutes is low . An immiscible extracting liquid is kept flowing continuously through the solution from which a solute is to be extracted. Although there is not enough time for the equilibrium to reach, a solute is extracted continuously in this extraction method. This method requires a special kind of extractor, depending on whether the solvent used for extraction is lighter or heavier than sample solution. 28 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

i) Extracting solvent lighter than the sample solution:

i) Extracting solvent lighter than the sample solution Apparatus used for this type of extraction is shown in fig It is similar to that of the Soxhlet apparatus but instead of one solvent , two solvents are used in this case. The extracting solvent (e.g. a non-aqueous solvent), which is lighter than the sample solution (e.g. an aqueous solution), is placed in a container (A). It is connected to a container (B) holding the Sample solution to half its capacity. A glass tube (C), having a funnel shaped opening at one end and a glass bulb with holes at another end, is placed inside container B. This body is then connected to a condenser (D), which is attached at the upper end of the container B. 29 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

i. The extracting solvent being lighter than sample solution:

i. The extracting solvent being lighter than sample solution when extracting solvent in the container (A) is heated. Vapor of the extracting solvent passes to the condenser where it get condense. The droplets of extracting liquids enter the glass tube C and then escape through the holes in the glass bulb . it passes through the sample solution and extract the solute and accumulated on the top of the sample solution. When sufficient quantity of extracting solution get collected in container B, it overflows in to the flask (A) from the side arm (S) the process is continued till the extraction is complete. 30 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

ii) Extracting solvent heavier than the sample solution:

ii) Extracting solvent heavier than the sample solution Apparatus used for this type of extraction is shown in fig The extracting solvent placed in RBF (A) and is heated. The sample solution to be extracted is present in a container (B). Vapor of the extracting solvent passes into the condenser and falls as droplets into the funnel type glass tube (C), and pass through the sample solution. In this process it extracts the solute and get accumulated at the bottom of the container B. When volume of extractant rises to sufficient height it overflows in to the flask (A) from the side arm (S) and the process is continued till the extraction is complete. Continuous extraction method is used when the material to be extracted has low partition coefficient for a pair of solvents. 31 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Continuous Extractor:

Continuous Extractor Extracting solvent lighter ii) Extracting solvent heavier than the than the sample solution sample solution 32 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

C. Countercurrent Distribution :

C. Countercurrent Distribution Generally for simple extraction separating funnel method is used but if sample solution contains 2 or more substances having similar distribution coefficients then their separation using single batch extraction is very poor. So by a technique of succesive extraction with fresh solvent, complex mixture with similar distribution coefficient may be separated. Eg counter currentextraction technique CCD is basic liquid liquid extraction that permits separation of sub with very similar partiton coefficient. 33 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Working of CCD:

Working of CCD Term countercurrent indicates that 2 phases move in apposite directions. In this one phase is stable and other phase is in moving state. The countercurrent distribution process involve train of tubes each containing two separate chamber within which the individual equilibrium occur. Chamber A in all tubes filled with solvent A (which is denser than extracting solvent 2) Tube one contain sample and extracting solvent (2) is introduced into first tube through inlet B 34 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Working of CCD:

Working of CCD After shaking back and forth and then allow the phase to separate. Then tube is tilted to 90 0 . The less dense solvent flow through tube C into chamber D then assembly is rotated to original position and solvent flows out through tube E into next tube leaving solvent 1 in chamber A of first tube. Fresh solvent 2(lighter solvent extractant) is added to first tube and process is repeated. 35 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Slide36:

Solute originally extracted into solvent 2 (extractant or less denser solvent)has been transferred to second tube containing solvent 1 (no sample) where it is redistributed. This procedure is repeated several times depending on separation efficiency or no of tubes. In this way transfer of solute in the direction of motion of upper phase (solvent 2) takes place. If sample contains 2 solutes with different partition coefficient they will pass through tube with different rate i.e. sub with larger partition coefficient will travel faster. Counter current is very efficient process for separation of closely related compounds. Working of CCD 36 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Diagram of CCD tube:

Diagram of CCD tube B A E D C 1 st position B A E C D 2 nd position CCD tube is rotated to 90 0 37 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

CCD:

CCD The greater the difference of the distribution ratio of various substances, the better the separation between each other. A much larger number of tubes is required to separate mixtures of substances with almost similar distribution ratios. 38 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Extraction of drug in CCD:

Extraction of drug in CCD 39 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Solid liquid extraction Soxhlet apparatus::

Solid liquid extraction Soxhlet apparatus: Continuous hot percolation process or Soxhlet extraction Apparatus. The apparatus consists of three parts- A flask: For boiling of solvent. A Soxhlet extractor: Having the drug in thimble, a side tube & siphon tube A reflux condenser: For condensation of vapors 40 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Soxhlet extraction:

Soxhlet extraction Typically soxhlet extraction is only required where the desired compound has limited solubility in a solvent. Extraction carried out by distillation and condensation of the solvent . Apparatus allows multiple extractions to be done repeatedly using same volume of solvent. Soxhlet extraction has been a standard method of extraction of solids from crude material Extraction of solid is imp step in preparation of many pharmaceuticals. 41 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Soxhlet extractor:

Soxhlet extractor Soxhlet extractor is used only for thermostable compounds A finely ground drug is held in a porous bag or thimble (made up of filter paper) is placed in chamber E Extracting solvent is placed in flask A and heated to boiling vapors rise through side arm B are condensed in condenser D . The condensed extractant drips into the thimble containing crude drug extracting it by contact. When level of exctractant in chamber E rises to top of siphon tube c , extractant come back to flask A and process is repeated several times to achieve max extraction of solute. 42 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Slide43:

43 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Slide44:

Separation of pair of substances is much influence by their distribution behavior. The feasibility of resoling two subs is explained in terms of separability factor α α =K1/K2 Where K is partition coefficient of two substances in LLE If value of α is unity means two subs can not separated by extraction. So greater the deviation of α from unity more feasible is the separation. In separation of two substances by LLE requires that one of the solute has small k, so other sub is extractable from raffinate. Factors affecting LLE 44 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Factors affecting LLE:

Factors affecting LLE Number of Factors affect distribution coefficient of solute which affect extraction and these can be utilized for effective separation. K can be increase by considering following points: Choice of solvent pH effect Salting out effect Control of hydrophobicity 45 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Conditions of a choice of solvent which is used as extractant::

Conditions of a choice of solvent which is used as extractant : Criteria for Selection of solvent : 1. The density of extractant should be difference from water density. 2. Low Boiling point 2. Should be selective. 3. High distribution coefficient 4. Should have the minimum viscosity. 6. Should be inexpensive and of low toxicity. 46 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Choice of solvent:

Choice of solvent The partition coefficient is influenced by chemical nature of the solvent So choice of solvent is important factor to achieve good recovery. Widely used extractant are diethylether, chloroform and hydrocarbons. Ex: separation of sodium benzoate(SB) and caffeine(C) Mixture of SB and C is dissolved in water both are soluble. Extraction is carried out with chloroform(C is quite soluble but SB is insoluble) Final result is total C is present in Chloroform layer and SB remains in water layer. Separated constituents is then quantitatively analyzed using spectrophotometric technique. 47 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Control of ionic strength: salting out effect:

Control of ionic strength: salting out effect If the salt concentration of an aqueous solution is made very high, the solubility of nonelectrolyte will be decreased. The reduction of solubility by an increase in ionic strength is called as salting out effect. This is because due to high salt conc. in water, availability of water molecule to act as solvent for non-electrolyte get reduced. The ions of the salt tying up much of water (through strong ion dipole force) so solute due to unavailability of water get extracted in to organic solvent. This helps to increase extraction efficiency of solute having greater solubility in water. 48 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

pH effect:

pH effect pH plays an important role in extraction process. Many comp encountered by pharmaceutical analyst are weak acids or bases. Solubility of these subs depends upon their ionic form. Generally ionized species are soluble in polar solvents and nonionoised in nonpolar solvents. These form can be Inter-converted by adjusting pH of medium . Hence pH control is most powerful means for influencing the value of partition coefficient. 49 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Effect of pH on separation of mixture of acid and base :

Effect of pH on separation of mixture of acid and base Acetylsalicylic acid (acid)and antihistamine(base) Both drugs are separated by dissolving in water. Then acidify the solution using HCl and extracting the Acetylsalicylic acid (unionized in HCl)completely with ether . Then antihistamine which is in its salt form(due to reaction of basis drug with HCL) in aqueous layer cab be extracted by adding base to release the drug in free form. Finally using other organic solvent extract antihistamine Pka of weak neutral acid =5 i.e at pH 5 equal amount of acid are present in the anion and neutral form At pH 6 about 10% remains in neutral form At pH 7 1% in neutral form and at pH8 0.1 % present as the acid. 50 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Control of hydrophobicity:

Control of hydrophobicity The partition coefficient of an ion can be altered by making the ion more hydrophobic. In two phase system (aq and org phase) ions are normally expected to partition almost completely to aq. Phase. If hydrophobic counter ions are added, so ion pair may be hydrophobic enough to partition into org. phase. Another way is use of macrocyclic sequestering agent such as crown ether. 51 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Slide52:

Ex benzene water system, KMnO4 partitions completely into aq layer and benzene layer is colorless. In presence of crown ether, benzene layer becomes colored indicating that some of KMnO4 have distributed in benzene layer. This is because permanganate ion is complexed within the cavity of the crown ether, which thus masks the high polarity of ion, presenting hydrophobic external surface. 52 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Slide53:

Emulsion : It may be defined as-a dispersed system containing at least two immiscible liquid phases’. The effective and meaningful extraction of an analyte is rendered almost impossible when one encounters an emulsion formation during an extraction process thereby the separation of the two phases becomes difficult. Actually, it offers a frequent and serious problem when dealing with the extraction of drugs from biological as well as pharmaceutical formulations. Emulsion formation problem 53 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Emulsion formation problem:

Emulsion formation problem Emulsion formation enhances the area of the interface between the two immiscible solvents and as a result also enhances the ‘free energy’ of the system, which may be designated by the following expression : Free energy = γ × Δ A where γ = Interfacial tension, and A = change in surface area resulting from emulsification. Obviously the ‘lowest free energy’ is given by the most stable state for a system at constant pressure and, therefore, in due course an emulsion shall ‘break’ spontaneously to the two-layered system. 54 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Slide55:

It has been observed that once an emulsion is formed it is very difficult to break it. Therefore, it is absolutely necessary to adhere to the following guidelines, as far as possible, in order to avoid forming emulsions in the course of an extraction process : (1) Always affect very cautious and gentle agitation besides employing a sufficiently large liquid liquid interface to obtain a reasonably good extraction. Especially when the two-liquid layers have a large contact surface in an extraction process, vigorous or thorough shaking of the two phases is not required at all, (2) The removal of any finely divided insoluble material(s) in a liquid phase must be done by filtration before carrying out the extraction process. Ways to minimize Emulsion formation problem 55 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Slide56:

(3) Always prefer and use such solvent pairs that have a large density difference and a high interfacial tension, for instance : water and hexane, as they are less prone to emulsion problems. In contrast, such solvent pairs as water and benzene should not be used in the extraction process. (4) When performing extraction from water always ensure not to work at pH extremes and particularly at high pH ranges to avoid emulsification. (5) In cases, of acute emulsion-problems substances like-anion exchangers alumina or silica gel are used specifically to resolve the problem by adsorption of the emulsifying agents. In fact, it would be advisable to employ the technique of column chromatography for the effective separation of the analyte as compared to an extraction process. Ways to minimize Emulsion formation problem 56 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Applications of extraction in the drug analysis:

Applications of extraction in the drug analysis Separation of elements Concentrating impurities Clearings of the basic component from impurities in the process of synthesis of substances of drugs Definition of the basic component from impurities in the process of synthesis of substances of drugs For identification and quantitative definition of chemical agent or substances-markers in the process of the analysis of phytogenesis drugs Increase of sensitivity and selectivity of reactions 57 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Slide58:

Studying of formation constant of complexs Studying of substance condition in a solution (a charge, polymerisation degree) Separation – controlled by pH which controls ionization and complex formation Clean up before analysis Preconcentration : Extract from a large aqueous volume into a much smaller organic volume. treatment of extracts, tinctures, antibiotics, preparations from a different biological material . Applications of extraction in the drug analysis 58 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Difference between continuous extraction and Multiple extraction:

Difference between continuous extraction and Multiple extraction Ex. Soxhlet apparatus Multiple extraction is one phase system i.e.Single solvent is used Not suitable for thermolabile compound Multiple extraction method can separate only one constituent at a time It is solid liquid extraction technique Technique is used when K value is quite differ. Same extracting solvent is used repeatedly for extraction Ex. Counter current distribution CCD is two phase system i.e. Two solvents are used suitable for thermolabile compound CCD method can separate two constituent at a time It is Liquid liquid extraction technique Technique is used when K values of 2 drugs in solvents are almost similar. Fresh extracting solvent is used every time for extraction. 59 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Difference between multiple extraction and single extraction:

Difference between multiple extraction and single extraction Single extraction (Batch) Used when partition coefficient of solute between two solvents is extremely large. Maximum recovery is not possible in single extraction. Extraction efficiency is less as compared to multiple extraction Suitable for thermolabile compound Total volume of extractant required in single extraction technique is more as compared to multiple extraction Ex. Separating funnel Multiple extraction Used when partition coefficient of solute between two solvents is almost same. Maximum recovery is possible in multiple extraction Extraction efficiency is more as compared to single extraction Not suitable for thermolabile comps Total volume of extractant required in multiple extraction technique is less as compared to single extraction Ex. Soxhlet apparatus 60 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

Slide61:

1. Practical Pharmaceutical Chemistry by Beckett, A H & Stenlake, J B , 2005, 4th edition, Part I and II, CBS Publishers and Distributors, India. 2. A Textbook of Pharmaceutical Analysis by Kenneth A Connors, 2002, 3rd edition, John Wiley and Sons, Canada. 4 Fundamentals of Analytical Chemistry by Douglas A. Skoog, Donald M. West, F. James Holler, 1991, 7th edition, Saunders College Publishing, USA. 5. Analytical Chemistry by Gary D. Christian, 6th edition, John Wiley & Sons, Singapore. References 61 Dr. Archana Naik, Saraswathi Vidya Bhavans College of Pharmacy

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