Emulsion Technology - Lab Report Example

EMULSION TECHNOLOGY by of of PART I + PART II This lab report explores the idea of designing a formulation of a stabilized emulsion and identifying the best preservative for the preservation of an emulsion. The lab report discusses the Hydrophile-lipophile balance method to find out the HLB requirement of the oil phase in order to create a stable emulsion. The report discusses the effect of surfactants and also investigates the idea of blending two surfactants, Span 80 and Tween 80. Furthermore the report also covers the spectrophotometric analysis to determine the preservative actions of benzoic acid, methyl parabens and propyl parabens and also the supportive action of propylene glycol as a preservative. Finally better methods are suggested to negate and minimize the random and systemic errors during the experiment in order to achieve the best possible stabilized emulsion. Keywords: Hydrophile-lipophile Balance, Span 80, Tween 80, Spectrophotometric analysis, propylene glycol PART - I INTRODUCTION An emulsion is a setup of two immiscible liquid phases with one of them dispersed throughout the other in form of tiny and fine droplets. The phase consisting of tiny droplets is defined as the internal or disperse phase whereas the suspension phase is classified as the external or continuous phase. Water and oil are the two major constituents of pharmaceutical emulsions. An aqueous continuous phase will render the emulsion as oil-in-water (o/w) whereas an oily continuous phase will make a water-in-oil (w/o) emulsion. The stability of an emulsion is dependent on the characteristics of the interfacial film. Addition of an emulsifying agent lowers the interfacial tension and increases the stability of the emulsion. A wide variety of these substances are available: e.g. egg yolk, cetearyl alcohol, polysorbate 20, ceteareth 20 etc. In the past emulsions have been used to impart paraffin oil and other oily substances in a more palatable form (Aulton 1988, p. 93). Nowadays emulsions are very common in foods, cosmetics, personal hygiene and especially pharmaceuticals. Creams, ointments, liniments, pastes and films are some examples of pharmaceutical emulsions. They are classified according to the oil and water content in each of the preparation and also on their routes of administration (Troy, Remington & Beringer 2006, p. 886-887). To achieve the production of a stabilized emulsion this experimented was conducted in order to formulate a scientific method of emulsion design. MATERIALS & METHOD A condensed film consisting of an oil soluble component (OSC) and a water soluble component (WSC) in a ratio of 9:1 for the required o/w emulsion is needed at the interface between oil and water in order to achieve the best result. The Hydrophile – liphophile balance method (HLB) was designed in order to calculate the perfect HLB requirement of the oil. According to the method, a HLB number is allotted to each and every surfactant depending upon the extent of hydrophilicity and lipophilicity of the molecule. A surfactant expressing only hydrophilic properties is given the maximum number of 20, with sodium lauryl sulphate being the only exception having a HLB number of 40. MATERIALS Liquid Paraffin, Tween 80 (polyoxyethylene 20 sorbitan mono-oleate, Span 80 (sorbitan mono-oleate) Span 80 is selected as the OSC while Tween 80 is selected as the WSC at total blend concentration of 2% w/v. Both compartments are then administered into screw capped sample vials via a burette and then labeled. The vials are agitated by inversion and then emulsified by drawing into and expelling from a syringe three times. Six different formulations were prepared with varying ratios of Span 80 and Tween 80. The HLB of each formulation was calculated from the equation given below, so as to determine the required HLB of the oil. HLB [formula] = f [OSC] . HLB [OSC] + (1-f) [WSC] . HLB [WSC] The vials were left for 15 minutes and their stability was observed in terms of cracking, whiteness and creaming. The best emulsion was chosen considering the parameters and fine tuning was done and two new vials were prepared with similar HLBs on either side of the chosen emulsion. Another vial was prepared by replacing Tween 80 with Sodium lauryl sulphate. RESULTS The HLB values for the first six formulations (labeled E1 – E6) are tabulated below along with their respective surfactant quantities. Also the HLB values of two vials as a result of fine tuning are also tabulated below (labeled E7 & E8). Emulsion Liquid paraffin + 2% Span 80 (ml) Liquid paraffin (ml) Water + 2% Tween 80 (ml) Water (ml) HLB E1 10 0 0 10 4.3 E2 8 2 2 8 6.44 E3 6 4 4 6 8.58 E4 4 6 6 4 10.72 E5 2 8 8 2 12.86 E6 0 10 10 0 15 E7 7 3 3 7 7.51 E8 5 5 5 5 9.65 DISCUSSION Formulation of a stabilized emulsion is a very difficult job. A blend of two surfactants producing a condensed film was seen to have produced the best result. Formation of micelle is an important aspect of surfactant working. Normally in an aqueous solution it has a hydrophilic head which isolates an number of hydrophobic tails. When surfactants overcome the CMC (Critical Micelle Concentration) they are able to act as emulsifiers. Span 80 and Tween 80 were selected as the two components. By selecting surfactants with a wide difference in HLBs it allows us to use them in varying ratios to get a range of HLBs. As a result insoluble compound species are integrated into the micelle core allowing the insoluble substance to dissolve. As a result the stability can be assessed at each HLB number to achieve the best emulsion. Cracking, creaming and whiteness are the three characteristics through which the stability of an emulsion can be evaluated. Cracking can be defined as the partitioning of the emulsion into its constituent phases. Temperature, bacterial growth and addition of a chemical incompatible with the surfactant might lead to this. Creaming occurs whenever there is major difference in density of the two phases resulting in either sinking or rising of the disperse phase. Globule size and viscosity of the continuous phase also plays a part in creaming. To achieve a stabilized emulsion avoidance of creaming and cracking are kept at high priority. On the other hand whiteness indicates the extent of dispersion which is very necessary for a good emulsion. Considering these parameters vial E3 was designated as the best emulsion among the initial six formulations. Fine tuning was conducted and two new vials with a different proportion of surfactants than E3 were prepared. After finding out the required HLB value of 9.65 for the emulsion only Tween 80 was replaced by sodium lauryl sulphate and another emulsion is prepared keeping the rest of specification same. Sodium lauryl sulphate being an anionic surfactant has a much greater emulsifying ability than Tween 80 in an o/w emulsion. Also keeping in mind the production of emulsions at a higher scale, sodium lauryl sulphate is a better choice as it is easily available and cost effective. Errors are a part of any experiment. Random errors can occur during measurement of the required quantity of oil and surfactants. Human errors are also quite possible while evaluating the stability of emulsion. It is difficult to observe cracking and creaming as even a stable emulsion might cream which can be negated through shaking. A better method for assessing emulsion stability which can reduce chances of error is to follow globule size distribution with time. CONCLUSION We have gleamed from the above experiment that a combination of surfactants can be used to work out the required HLB value which works best for a particular oil phase and produces a stable emulsion. Also the mean particle size is at minimum when HLB value is close to optimim keeping the emulsion system stable. PART – II INTRODUCTION Preservation is an important aspect of any pharmaceutical preparation. Compliance with the preservative efficacy test is very essential. With emulsion, this task becomes a lot harder. An o/w emulsion has two phases, the internal oily phase and the external aqueous phase. It is the aqueous phase which offers the micro-organisms a place to grow and populate (Brocklehurst & Wilson 2000, p. 67). An o/w emulsion is more exposed to microbial contamination than a w/o emulsion because the external oily phase of the latter emulsion offers a protection (Aulton 1988, p. 335) Due to this contamination, the physical and chemical characteristics of an emulsion are spoiled resulting in odour and colour changes, pH changes, and causes gas production and hydrolysis of fats (Aulton 1988, p. 355). The reason behind difficult preservation of emulsion is the fact that any preservative which is added to an emulsion partitions into the oily phase. As the oily phase is devoid of any microbial growth, this partitioning renders the preservative useless. An increase in the concentration of preservative to overcome this effect can result in increased toxicological hazards. To study the partitioning behavior of three common preservatives namely benzoic acid, methyl parabens and propyl parabens this experiment was designed and conducted. METHOD MATERIALS Liquid Paraffin, Benzoic Acid. Methyl parabens. Propyl parabens. Propylene glycol Three formulations were prepared with three different preservatives. Another three formulations were prepared with the same specifications but with an addition of propylene glycol. 20 ml samples were prepared. The table below gives the formulation detail of every sample labeled (E1 – E3) and also those samples with an addition of propylene glycol labeled (E1P – E3P). Component % E1 E1P E2 E2P E3 E3P Liquid Paraffin 10 10 10 10 10 10 Propylene glycol - 1 - 1 - 1 Benzoic acid 0.02 0.02 - - - - Methyl parabens - - 0.02 0.02 - - Propyl parabens - - - - 0.004 0.004 Water (to 20) 9.98 8.98 9.98 8.98 9.996 8.996 The formulations were then shaken till dissolution and then left for 10 minutes in order for partitioning to take place. After 10 minutes the oil layer was aspirated and the aqueous phase after subsequent serial dilution was subjected to spectrophotometric analysis and the absorbance was calculated. RESULTS The absorbance reading of three vials was calculated as mentioned below Abs (230) Abs (257) Abs (255) E1 1.032 0.931 0.891 E1P 2.117 1.915 1.282 E2 2.234 1.526 1.372 E2P 2.451 1.661 1.950 E3 2.517 2.700 2.681 E3P 2.782 1.821 2.779 DISCUSSION Preservation of emulsion against different micro-organisms namely Pseudomonas, Aspergillus, Penicillium and Rhizopus is very important to maintain the physico-chemical characteristics of emulsion. The absorbance reading is affected by the concentration of aqueous phase. The greater the aqueous phase the more light will be transmitted and the emulsion will be less preserved as the aqueous phase provides the medium for microbial growth. Observing the calculations of absorbance, propyl parabens can be regarded as the best preservative compared to benzoic acid and methyl parabens as it has the highest absorbance of 2.779 compared to 1.032 and 1.526 of the former two at their respective wavelength. However the addition of propylene glycol draws a new observation as it increases the absorbance level of every vial, E1 from 1.032 to 2.117, E2 from 1.526 to 1.661 and E3 from 2.681 to 2.779. This is due to two reasons. Firstly propylene glycol is categorized as an antiseptic against different molds defining its preservative action against microbes. Secondly the marked increase in absorbance of E1 to E1P is due to dissolving action of propylene glycol on phenols like benzoic acid enhancing their preservative action. The little increase in E2 and E3 with the addition of propylene glycol is because it prevents the interactions between Tween 80 and parabens and thus increasing preservation. To minimize error in this experiment a much better testing method, the Preservative efficacy tests can be opted. CONCLUSION Theoretically it is not feasible and probable of selecting the best preservative for the emulsion system. The above spectrophotometric analysis though gives an idea regarding the concentration of bacteria and molds and enables us to choose the best preservative amongst the three available. REFERENCES Aulton, ME 1988, Pharmaceutics: The Science of Dosage Form Design, 2nd edn, Churcill Livingstone, Leicester, UK. Brocklehurst, TF & Wilson, PDG 2000, ‘The role of lipids in controlling microbial growth’, Grasas V Aceites, vol. 51, pp. 66-73, viewed 23 October 2011. Troy, DA, Remington, JP & Beringer, P 2006, Remington: The Science and Practice of Pharmacy, 21st edn, Lippincott Williams & Wilkins, Philadelphia Read More