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Application of different emulsifiers in preparation and stability of emulsion

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  • Save International Journal of M aterials and Chemistry 2013, 3(4): 69-74 DOI: 10.5923/j.ijmc.20130304.01 Utilization of Different Emulsifying Agents in the Preparation and Stabilization of Emulsions E. A. Kamba, A. U. Itodo*, E. Ogah Department of Chemical Sciences, Federal University Wukari Nigeria Abstract The ratio of emu lsify ing agents used to achieve stability is very important. In th is study effect of surfactant HLB and concentration on the emulsion stability were investigated. The time required for the two liquids to separate, creaming volume and microscopic observation were used to assess the emulsion stability. Emu lsifiers used in this study are based on their che mical structures and include synthetic, natural and fine ly dispersed solid partic les e mulsifie rs. It was observed that the optimal surfactant concentration for oil/ water emulsion long-term stability were 20% wt/vol. soap in the oil phase and 0.1% wt/vol. detergent in the continuous phase. Higher concentration of soap had a destructive effect on oil/water emu lsion stability wh ich correlated with the observation that interfacial film strength at the oil/water interface decreases as the detergent concentration increases. Methanol added to the inner aqueous phase exerted an osmotic pressure that caused diffusion of o il into aqueous phase and increased oil/water emulsion v iscosity through an increase in the volume fraction of the primary oil/water emu lsion. These types of viscosity increase impose a destabilization effect because of the likelihood of rupture of the outer and continuous phase droplets. Keywords Emu lsifiers, Surfactant, Soap, Detergent, Emu lsify ing Agents, Stabilization, Emu lsions 1. Introduction Emu lsions are used as a basis for a wide variety of both naturally occurring as well as manufactured materials in the industries such as food industries, pharmaceutical industries and cosmetic industries. Others include agrochemicals, petrochemicals and exp losives[1]. Stability in emu lsions is very important as it forms the basic approach for providing solution to problems in the manufacture of foods, drugs and cosmetics. The rheological, physicochemical and nutritional properties of some systems such as foods can be imp roved by regularly incorporating ingredients used in the process of emulsion preparation[2]. Stabilization of emu lsion becomes necessary in order to avoid loss of activity, degradation, and even reaction with some co mponents present in food systems of these ingredie nts which can lead to limitation in their bio -availab ility, or change theircolor or taste[2]. In general, emu lsions are by nature physically unstable, that is, they tend to separate into two distinct phases or layers over time. Any emulsion in which the globules do not retain their initia l character and do not remain uniformly distributed throughout the continuous phase is said to beunstable. Such emu lsion wou ld exh ib it d ifferent character other * Corresponding author: (A. U. Itodo) Published online at Copyright © 2013 Scientific & Academic Publishing. All Rights Reserved than the ideal behavior[2]. The types of instability in emu lsions include; Creaming , Breaking or Cracking andCo agulation or Flocculation. Although some pairs of liquids are immiscible, they can be forced together in an emu lsion. Instead of forming two separate layers with a clear boundary between them, small droplets of one liquid are spread throughout the other liquid. Th is is achieved by using an emu lsifying agent[3]. 1.1. Hydrophile-li pophile-balance (HLB) System A system was developed to assist in making systemic decisions about the amount and types of surfactants needed in stable products. The sys tem is called the HLB system and has an arbitrary scale of 1-18. HLB nu mbers are experiment ally determined for the different emulsifiers. If an emu lsifier has a low HLB nu mber, there are a low nu mber of hydrophilic groups on the molecule and it will have more of a lipophilic character. For instance, substances with low HLB nu mbers are generally o il soluble. As a result of their oil soluble character, they will cause the oil phase to predominate and form a water-in-o il emulsion. The higher HLB nu mbers would indicate that the emulsion has a large number of hydrophilic g roups on the molecule and therefore should be more hydrophilic in character. Substances with high HLB numbers are water-soluble. And because of their water soluble character, they will cause the water phase to predominate and form an o il-in-water emu lsion. Co mbinati on of emu lsifiers can produce more stable emulsions than using a single emulsifier with the same HLB number[4]. 70 E. A. Kamba et al.: Utilization of Different EmulsifyingA gents in the Preparation and Stabilization of Emulsions Although many works have been carried out aimed at testing the time required for two liquids to separate after being forced together by means of various emu lsifiers, different ways were fo llo wed to achieve this. Jim and Diane investigated the stability of water-in-water mu ltip le emu lsio ns by treating with span 83 and Tween 80. Rheological measurements were carried out using an AR 1000 Rheo meter. Rotational mapping was performed to eliminate possible small variat ions caused by the uneven surface of the shaft. A continuous ramping flow mode was used to measure viscosity under controlled shear stress ranging from 0.01 to 100 Pa. An Oscillation procedure at constant frequency of 1Hz was used to obtain information on storage and loss moduli. The informat ion regarding the mu ltip le droplet sizes was obtained by taking photomicrographs of the emulsion samples. The first step that is, the preparation of primary emu lsion was carried out in a high shear device to produce very fine droplets. The second emulsification step was carried out in a low-shear device to avoid rupturing the mu ltip le droplets[5]. Other methods of determin ing the emu lsion stability have been developed by researchers. These include; droplet size analyses[4], measuring physical properties of emu lsion[5], accelerated tests[6], and light s catterin g [7] . The objective of this study was to evaluate the long-term stability and creaming volu me o f o il/ water emu lsion with respect to the concentration, and HLBs of surfactants used. The objective of this study was to evaluate the long-term stability and creaming volume of oil/water emu lsion by measuring the concentration of emulsifiers, HLBs of surfactants used, and Turbidity. Evaluation of the effect of some formu lation variables like, the emulsifier type and oil phase content on emulsion stability was also carried out. 2. Experimental 2.1. Materials Lecithin, phospholipids derived fro m egg yolk and consisting primarily o f phosphatidylcholine,phosphatidyleth anolamine, and phosphatidylinositol, a product of M & B England, wasobtained as a solution. Cholesterol was also a product of M & B England. Analytical grade magnesium hydroxide,[Mg(OH)2] and alu miniu m hydro xide,[A l(OH)3] were products of BDH Chemicals Ltd. England. Methanol was manufactured by Merk Germany. Olive oil, soap and detergent which are products of MZM Continental Co mpany Nigeria and Unilever Nigeria Plc respectively, were obtained fro m local stores. Distilled water was used throughout while Starch, a product of Ficko Manufacturing Co mpany, FRN, was in powder form. Others reagents used include acetic ac id and NaN3. Routine laboratory apparatus were utilized viz: beakers, microscope(Nikon microscope Eclipse E400, Nikon Corporation, Japan), test tubes, micro-slides, grease pencil, cover-slips, stop watch, electronic balance (Accu-622, Fisher Scientific, Fair Lawn, New Jersey, USA), blender, measuring cylinder and mortar and piston. 2.2. Preparati on of Soap Sol ution 20g of soap was grounded and dissolved in 50cm3 of distilled water. 8 test-tubes were set. Each was marked with a grease pencil 3mm above the bottom curvature of the test-tubes. 50cm3 of olive oil was measured in a beaker[6]. 2.3. Preparati on of Lecithin Soluti on Emulsifier Buffer solution of acetic acid and NaN3was prepared by dispersing in a proportion of 100 mM and 0.02 wt% respectively in water and the pH was then adjusted to 3.0 by adding HCl. To prepare lecithin emulsifier, 2.0 wt% lecithin was dispersed into the buffer solution and was blended for 1 min at a frequency of 20 kHz, amp litude of 70%, and duty cycle of 0.5second to ensure complete dispersion of the emulsifier. The pH of the solution was maintained at 3.0 by addingHCl and then the solution was stirred for about 1 hour. 2.4. Preparati on of Emulsion Two sets of oil-in-water emu lsion were prepared; Emu lsion 1: 20g of starch powder was lev itated in a mortar, with 20c m3 oil until the powder was thoroughly wetted, then 10cm3of d istilled water was added all at once, and the mixtu re was vigorously and continually titrated for 3minutes until the primary emu lsion formed was creamy white and produced a “cracking” sound. Additional 20cm3 water was incorporated after the p rimary emu lsion was formed. 10 drops of soap solution was incorporated directly into the primary emu lsion, and addit ion of 10cm3 of methanol was next. When all the agents were incorporated, the emulsion was brought to final volu me in a measuring cylinder and then blended to ensure uniform distribution of ingredients[5]. The second form ofemu lsion (emu lsion 2) was prepared by homogenizing 20 wt% olive o il and 1.6 wt% o f the aqueous lecithin solution for several minutes using a stirring bar follo wed by blending. The emulsion was finally collected into a beaker and weighted on an electronic balance (Accu-622, Fisher Scientific, Fair Lawn, NJ, USA), connected to a personal computer to record t ime and mass data every 2 seconds using an installed data acquisition software (AccuSeries USB version 1.2, Fisher Scientific, Fair Lawn , NJ, USA); The experiments were carried out at 19.7℃. 2.5. Testing Emulsifying Strengths 2.5.1. Using Synthetic Emu lsifiers 3 test tubes were set, to one, 10cm3 of distilled water waspoured, 5cm3 of olive o il was added. 10 drops of soap solution were added. To the second test–tube 10cm3 of distilled water and 5cm3 of o live o il were shaken and 10 drops of detergent were added. To the third 10cm3 of distilled water was poured followed by 5c m3 of olive oil and International Journal of M aterials and Chemistry 2013, 3(4): 69-74 71 mixtu re of soap solution and detergent were added in drops (10). The final volu me of liquid in each test-tube was approximately the same. The test-tubes were shaken for 2 minutes and then left to stand. Time of separation of the liquids in each test-tube was noted[6]. 2.5.2. Using Natural Emu lsifiers 3 test-tubes were set; to each 10cm3 of d istilled water and 5cm3of olive o il were added. To the first 10 drops of cholesterol were added, to the second 10 drops of lecithin were added and to the third 10 drops of the mixture of cholesterol and lecithin were added. The 3 test-tubes were shaken and left to stand. Time of separation of the liquids in each test-tube was recorded[6]. at different times by gently agitating each emulsion in a test tube before analysis. A drop of each emulsion was placed on a microscope slide and thencovered with a cover slip. The microstructure of the emu lsion was then observed usingconventional optical microscopy (Nikon microscope Eclipse E400, Nikon Co rporation, Japan). The images were obtained using a CCD camera (CCD-300T-RC, DA GE-M T I,Mich igan City, IN) with Dig ital Image Processing Software (M icro VideoInstruments Inc., Avon, MA) installed on a computer. 3. Results and Discussion 2.5.3. Using Finely Dispersed Solid Particle Emu lsifiers In 2 test-tubes, 10cm3 ofdistilled water and 5cm3 of olive oil were poured. To the first, drops of magnesium hydro xide were added and to the second 10 drops of aluminum hydroxide were added. The test-tubes were shaken and time of separation in each was recorded[6]. 2.6. Effects of Surfactant HLB on Emulsion Stability 8 test-tubes were set to each 5cm3 of olive oil and 5cm3 of distilled water were added, drops of soap solution were added to the tubes as indicated in table 3. Drops of detergent were also added to the tubes as indicated in the same table. Each test-tube was shaken vigorously for 30-45 seconds. The time required for the interface to rise to the grease pencil mark was recorded. The tubes were ranked fro m 1-8 that is, fro m the longest to the shortest time of separation. The HLB value for the surfactant system in each test-tube was calculated using the relation below[7]. x (A) + y (B) HLB = (1) X + B x is Quantity of surfactant 1, A is HLB o f Surfactant 1, y is Quantity of surfactant 2 and B is HLB o f Surfactant 2. 2.7. Effect of Surfactant Concentration on Emulsion Stability The steps in 2.5 above were repeated but using 3 times the amounts of soap solution and detergent as indicated in table 4[7]. 15% 19% 14% 16% 19% 17% Soap Detergent Cholesterol Lecithin Mg(OH)2 Al(OH)3 Figure 1. Percent creaming volume foroil/water emulsion containing various emulsifiers Time (min) 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0 Soap Time (min) 3.3 Detergent Cholesterol Lecithin 4.2 2.1 1.3 Mg(OH)2 1.1 Al(OH)3 1.3 Emulsifiers 2.8. Creaming Volume Measurement The volumes of the creamed phase and the remain ing part of the emulsion were recorded. The following relation was used to calculatethe creaming volu me: Vmultiple emulsion − V x creamed phase 100% (2) Vmultiple emulsion This was achieved by pouring in a measuring cylinder[8]. 2.9. Microscopic Observation The effect of lecithin used in both emulsions was analyzed Figure 2. Separation time (min) for oil/water emulsion containing various emulsifiers Table 1. Separation time and creaming volume for oil/water emulsion containing single emulsifiers Te st-Tube 1 2 3 Emulsifier a b c Sep arat io n time (Min) 3.3 4.2 2.1 Creaming Vol. (%) 66.7 68.60 59.50 4 d 1.3 55.80 5 6 e f 1.1 1.3 51.90 55.10 Keys: a – Soap, b – Detergent, c – Cholesterol, d – Lecithin, e − Mg(OH)2,f −Al(OH)3 72 E. A. Kamba et al.: Utilization of Different EmulsifyingA gents in the Preparation and Stabilization of Emulsions Table 2. Separation time and creaming volume for oil/water emulsion containing mixed emulsifiers Te st-Tube Emulsifiers (drop) Separation time(Min) 1 Soap + Det ergent 5.2 2 Cholesterol + Lecithin 3.1 Creaming Vol. (%) 76.9 67.30 Table 3. Effect of surfactant HLB on emulsion stability Te st-tube 1 2 3 4 5 6 7 8 No. of Soap 5 4 4 2 2 1 0 0 det ergent 1 2 3 3 5 6 5 0 Calculated HLB 9.97 10.3 10.5 10.9 11.2 11.5 11.8 0 Sep.T ime 5.3 6.9 7.5 7.1 8.6 9.1 6.5 0.21 St ability Ranks 7 5 3 4 2 1 6 8 Sep − separation Table 4. Effect of surfactant concentration on emulsion stability Te st-tube 1 2 3 4 5 6 7 8 Drops Soap 15 12 12 6 6 3 0 0 Detergent 3 6 9 9 15 18 15 0 Calculated HLB 9.97 10.3 10.5 10.9 11.2 11.5 11.8 0 Sep. T ime 10.4 10.6 11.7 11.2 11.9 12.3 10.9 0.21 St ability Ranks 7 6 3 4 2 1 5 8 Sep − separation 3.1. Discussion The formulation of emu lsion 1 was well blended to ensure uniform distribution of ingredients. The methanol might reduce the physical stability of the emulsion, so it is added as near to the end of the process as possible to avoid breaking the emulsion by precipitating the starch powder. After 2 weeks, the emu lsion was observed to form 2 layers, one containing white substance which settled at the bottom of the container and the other containing a partially clear solution. This indicates that if the emulsion is left to stand for a long period of time, the partially clear solution may be clearer, that is more ingredients must have settled down. The soap solution that was added is believed to have broken down the oil mo lecules into smaller ones. Figure 1 is typical o f the Percent creaming vo lu me foroil/ water emu lsion containing various emulsifiers. Vo lu me recorded for soap and detergent is higher than those presented for other emu lsifying agents. This is an indication that they are better emu lsifiers. Figure 2 represents Separation time (min ) for oil/water emu lsion containing various emulsifiers. Here, the role of emu lsifying agents on separation time was observed. Detergents emulsion present high separation time of 3.3 minutes. This imp lied that detergent emulsion is more stable. The trend of stability followed the o rder; detergent (4.2 minutes) > Soap (3.3min ) > Cholesterol (2.1 min) >Lecithin (1.3 min )>A l(OH)3(1.3 min )>Mg(OH)2 (1.1 minutes). Table1 contains the proportions of water and olive o il in which soap and detergent were used as emulsifiers. Soap contains a sodium carboxy late salt (R-COO- Na+) which is highly ionic and usually quite water-soluble because of the strong attraction of water molecules to the charges on the ions. The R-group is a long hydrocarbon chain, as in the sodium stearate used. The structure is as follows [8]. CH3(CH2)n Where n is an interger >10 O CH3CH2CH2C ONa + Non polar hydrocarbon group (water insoluble). Ionic group (water Soluble) These diagrams symbolized the two impo rtant features of the structure. The circle represents the ionic carbo xy lates end of the molecule and the long time represents the non-polar hydrocarbon chain. The non-polar hydrocarbon group is not soluble in water, but water would be attracted to the ionic groups and hence tend to dissolve the mo lecules. As soon as the soap mo lecules are added, the hydrocarbon portions will not permit them to be exposed to water. Instead, they are attracted to each other, forming a cluster in wh ich they are literally dissolvedin each other. This grouping allows the ionic groups at the ends of the soap molecules to be attracted to the surrounding water molecules. The result is that the soap mo lecules are, in a sense, able to dissolve in the water. The agitation helps jar the o il fro m the surface and disperse it into tiny droplets. More and more soap molecules surround the oil, until it beco mes incorporated with in a soap micelle. An emulsion is achieved at this level. In table 1, it took soap 3.3mins to separate water and oil, while detergent took 3.2mins and their mixture 6.5mins this indicates that detergents are better emu lsifiers than soap and their mixture more better emulsifiers. Cholesterol proved better emu lsifying agents than lecithin and their mixtu re more stronger emulsifiers. Mg(OH)2 is a less powerful emu lsifying agent than Al(OH)3. Detergent on the other hand has molecules with features they share with soap. They are amphipathic and have a large non- polar hydrocarbon end that is oil soluble and a polar end that is H2O soluble. They act in essentially the same way as soap does[9]. Mixture of soap and detergent gave a more stable emu lsion, increasing the charges on the oil droplets this keeps them fro m coalescing[8]. Cholesterol and lec ithin have effect on interfacia l tension, but exert a proactive colloid e ffect reducing the potential for coalescence by providing a protective sheath around the droplets, impacting a charge to the dispersed droplets. Cholesterols give oil the capacity to absorb water; this is attributed to the little time of separation between the liquids. Lecithin on the other hand has a strong hydrophilic character[10]. When Cholesterol and lecithin were mixed, lycolecithin and cholersetyl ester were formed wh ich are the International Journal of M aterials and Chemistry 2013, 3(4): 69-74 73 real substances doing dissolution of oil in water[9]. When Mg(OH)2 was added it only took 1.1min fo r the layer between the molecu les to appear again, and when Al(OH)3 was added it took 1.8min to separate. This is an indication that the two emu lsifiers are poor in dissolution character. However A l(OH)3 is a better emulsifier than Mg(OH)2. Flocculation and resultant creaming represent potential steps towards complete coalescence of the dispersed phase. In addition the creaming volu me is indicat ive of the stability of internal aqueous droplets entrapped in the emulsifier droplet, since swelling or shrinkage of the internal aqueous drops directly affect the oil droplets size and hence thee creaming volu me[12]. Table 3 contains the result obtained when effect of surfactant HLB was tested. It can be seen from the table that the HLB values increas ed from tes t-tube 1-7. Test-tube 8 had a zero HLB because no surfactant was added. The time of separation elapsed before the first signs of phase separation was observed, and the stability was ranked fro m 1, (longest time) to 8, (shortest time). At low soap and detergent concentration, rapid coalescence among the inner and outer droplets to inner phase occurred, resulting in separation within a short period of t ime. In table 3, Test-tube number 6 took the longest time to separate the liquids thus the highest stabilized. As time of separation decreases the stability in creas es . used. A co mbination o f lecithin and cholesterol gave b igger globules than lecith in only (Figure 3). Similarly, combinatio n of soap and detergent formed s maller globules than soap only (Figures 4 & 5) In general, findings from this study is in good agreement with those reported in exist ing literatures[1 3,14,15,16]. Fi gure 4. globules from Soap Emulsion Figure 5. globules from Soap +Detergent Emulsion Fi gure 3. globules from Lecithin+ Cholest erol Emulsion Table 4, represents the effect of surfactant concentration on emu lsion stability. Effect of increasing the concentration of the surfactants was measured. It can be observed that the HLB va lues re mained the sa me while the time of separation increased. Hence, the ranking changed. Stability of emulsion can be tested for using other means. All these depend on the availability of materials[10]. As HLB value are scaled 1-8, soaps and detergents have 9.6 and 11.8 respectively. Their HLB values give them the ability or capacity to be both oil and water soluble. But their co mbination produced mo re stable emu lsion than using them singly; with the same HLB values[10]. However, HLB of 11.5 p roduces the most stable emu lsion of water and oil. On increasing the concentration of surfactants in table 4, the time of separation also increased, therefore, the mo re concentration of surfactant the mo re stable an emulsion is, also the longer the time it takes for separation of phase the more stable the emulsion is.When emu lsions are stable they tend to have smaller globules than unstable or less stable emulsions[17]. Figures 3-6 show globules formed when different types of emulsifiers were Fi gure 6. globules from Lecit hin emulsifier 4. Conclusions Emu lsions are very important mixtures, their stability study are still more important. In this study, the stability of emu lsions depends on the type and proportion of emulsifiers used. Findings fro m this analysis revealed that on increasing the concentration of surfactants, the time of separation also increased, therefore, the more concentration of surfactant the more stable the emulsion is. Also, the longer the time it takes for separation of phase the more stable the emu lsion is. Measure of synergistic effect proved that mixture of soap and detergent gave a more stable emulsion. The microscopic pictures of both emulsions indicate that lecithin used in emu lsion 2 (Figure 6) has greater stabilizing power than that 74 E. A. Kamba et al.: Utilization of Different EmulsifyingA gents in the Preparation and Stabilization of Emulsions used in emu lsion 1 (Figure 3). This can be seen in the sizes of emu lsion globules which tend to be bigger in emu lsion 1 (Figure 3). [8] J.GNairm. Solutions, Emulsions, Suspensions and Extracts, London University Press.Pg. 1509-1515, 2000. [9] J. Swarbrick. Course Dispersions.Bacon Inc. Boston. Pg. 282-290, 2002 REFERENCES [1] M . Shahin, S.A. Hady, M . Hammad and N. M ortadadevelop ment of stable O/W emulsions of three different oils. International Journal of Pharmaceutical Studies and Research Vol. II/ Issue II, 45-51, 2011 [2] J. Surha, Y.G. Jeongb and G.T. Vladisavljević On the preparation of lecithin-stabilized oil-in-water emulsions by multi-stage premix membrane emulsification [3] N.Akhtar1, M.Ahmad, H.M .S. Khan, J.Akram, Gulfishan,A. M ahmood and M .Uzairformulation and characterization of a multiple emulsioncontaining 1% l-ascorbic acid.Bull. Chem. Soc. Ethiop. 2010, 24(1), 1-10. [4] F.Donsì, M . Annunziata, G. Ferrari M icrobial inactivation by high pressure homogenization: Effect of the disruption valve geometry Journal of Food Engineering 115 (2013) 362–370 [5] I.A. M ersah, G.G M ichael, T. fabian, M . Osuogi. A Level Chemistry, West African Publishers. Afran Publications, Ghana Ltd, Pg. 186-196, 1993. [6] K.K Sharma, L.K Sharma. A Text Book of Physical Chemistry, Vikab Publishing House PVT Ltd. Pg. 545-546, 2002 [7] A.L Williams, H.D Embree, H.J De Bey. Introduction to Chemistry, Addison-Wesley Publishing Company London. Pg. 170-173, 1968 [10] W.J Reilly. Pharmaceutical Necessities, Oxford University Press, Richard Clay Ltd. Bungay Suffolk. Pg. 1395-1399, 1992. [11] W. How, K.D. Papadopoulos.Physiocochemical and Engineer ing Aspects. Washington pg. 181-187, 1997. [12] J. Jiao and D.J Burgess.Rheology and Stability of Water-in-oil-in-water M ultiple Emulsions (http://www.phar , 2003. [13] M . M ooney ,The Viscosity of a Concentrated Suspension of Spherical Particles. London University Press. Pg. 162-170, 1951 [14] G.LZubay, W. W Parson, D. E Vance. Principles of Biochemistry Wm. C. Brown Publishers Inc. united States. Pg. 465-476, 1995 [15] C. Donald, G. Allyn. Non Aqueous Solvents.M acmillan Publishers, New York. Pg. 122-125, 1992 [16] P. Walstra, Dekker. Encyclopaedia of Emulsion Technology. Vol. 4.P g 1-56, 1996. [17] S.B. Daniela, A.P.Tatiana, R.M Naira,B. Josiane,., S.V.Gisely, C.O.Gustavo and A. R. Pedro, Formation and stability of oil-in-water nanoemulsions containing rice bran oil: in vitro and in vivo assessments . 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