3.5.1 General Procedure
The general process of maceration on a small scale consists of placing the suitably crushed plant material, or a moderately coarse pow- der made from it, in a closed vessel and adding the selected solvent called menstruum. The system is allowed to stand for seven days, with occasional shaking. The liquid is then strained off and the solid residue, called marc,
is pressed to recover as much occluded solution as possible. The strained and expressed liquid thus obtained is mixed and clarifi ed by fi ltration. Plant material in fi ne powder form is never used, as it makes subsequent clarifi ca- tion of the extract diffi cult. In the case of vegetable drugs, suffi cient time is allowed for the menstruum to diffuse through the cell wall to solubilize the constituents within the cells and for the resulting solution to diffuse out. As the system is static, except for occasional shaking, the process of extraction works by molecular diffusion, which is very slow. Occasional shak- ing assists diffusion and also ensures dispersal of the concentrated solu- tion accumulating around the surface of the particles, thereby bringing fresh menstruum to the particle surface for further extraction. A closed vessel is used to prevent evaporation of the menstruum during the extraction period and thus avoids batch to batch variation.
At the end of the maceration process, when equilibrium has been reached, the solution is fi ltered through a cloth; the marc may be strained through a special press. The concentrations of active constitu- ents in the strained and expressed liquids, sometimes called miscella, are the same and hence they can be combined. The expressed liquid may be cloudy with colloidal and small particles, and suffi cient time (perhaps sev- eral weeks) is necessary for coagulation and settling. The settled matter is fi ltered through a fi lter press or any other suitable equipment.
3.5.2 Maceration Process for Organized and Unorganized Crude Drugs
Organized drugs have a defi ned cellular structure whereas un- organized drugs are non-cellular. Bark and roots are examples of organized crude drugs, while gum and resin are unorganized crude drugs. The proc- esses of maceration for organized and unorganized drugs are slightly differ- ent, as shown in Table 1.
Table 1: Four differentiating steps of the maceration process, for organized and unorganized crude drugs
Organized drugs Unorganized drugs
(i) Drug + entire volume of menstruum (i) Drug + four-fi fths of menstruum (in most cases) (ii) Shake occasionally for 7 days (ii) Shake occasionally on days 2
to 7, as specifi ed
(iii) Strain liquid, press the marc (iii) Decant the liquid. Marc is not pressed
(iv) Mix the liquids, clarify by subsidence for
fi ltration. Filtrate is not adjusted for volume (iv) Filter the liquid and add remaining menstruum through the fi lter
During maceration of organized drugs, the marc is pressed be- cause a considerable proportion of liquid adheres to it and cannot other- wise be separated. Moreover, the volume is not adjusted because a variable amount of liquid containing soluble matter is left in the marc. If the volume is adjusted, a weak product will result. Omitting adjustment, the volume of liquid expressed infl uences the product yield and the percentage of soluble matter, regardless of the effi ciency with which the marc is pressed in a hand press, screw press or hydraulic press; the strength of the product is not affected. Preparations made by this processes include vinegar of squill (Brit- ish Pharmaceutical Codex, BPC), oxymel of squill (BPC), tincture of orange (Indian Pharmacopoeia, IP), tincture of capsicum (BPC), compound tincture of gentian, tincture of lemon, and tincture of squill (BPC).
In maceration of unorganized drugs, the marc is not pressed because the desirable material is mostly dissolved and the remaining marc is gummy and slimy. Thus, it is neither practicable nor necessary to press it. Moreover, the volume is adjusted because the clear upper layer is easily separated by fi ltration from the lower layer. The solution contains practically all the soluble matter of the drug; the small amount adherent to the gummy matter is recovered when the marc is washed by menstruum in the fi lter.
Therefore, adjustment of volume leads to uniformity. Preparations made by this process include compound tincture of benzoin, tincture of myrrh (BPC), and tincture of tolu (BPC).
3.5.3 Modifi cations to the General Processes of Maceration
Repeated maceration may be more effi cient than a single mac- eration process, as described earlier, because an appreciable amount of active principle may be left behind in the fi rst pressing of the marc. Double maceration is used when the active constituents are particularly valuable and also when the concentrated infusions contain volatile oil. Where the marc cannot be pressed, a process of triple maceration is sometimes em- ployed. The total volume of solvent used is, however, large and the second and third macerates are usually mixed and evaporated before being added to the fi rst macerate.
3.5.4 Large-scale Extraction Procedures
For large-scale, industrial extraction, certain modifi cations are warranted. When the extraction vessel contains a small amount of solvent (500-1000 ml), occasional shaking is no problem. But, for industrial work where a large amount of solvent and huge vessels are involved, shaking the vessels is diffi cult. Obviously, there are alternative methods of agitation that are just as effective and much simpler to put into practice. In addition, eco- nomics become increasingly important and one of the most important objec- tives is to improve the effi ciency of extraction so that less solvent is needed
and evaporation requirements for concentrated products are reduced. Reduc- ing the cost of evaporation has the further advantage of minimizing the heat damage to thermolabile constituents. Some of the modifi ed maceration pro- cedures used for large-scale extraction are described in the next paragraphs.
3.5.4.1 Circulatory Extraction
The effi ciency of extraction in a maceration process can be improved by arranging the solvent to be continuously circulated through the drug, as indicated in the Figure 1. Solvent is pumped from the bottom of the vessel (through an outlet) and is distributed by spray nozzles over the sur- face of the drug. The movement of the solvent reduces boundary layers and the uniform distribution minimizes local concentration in a shorter time.
Figure 1: Circulatory extraction
3.5.4.2 Multistage Extraction
In the normal maceration process, extraction is incomplete, since mass transfer ceases when equilibrium is reached. This problem can be overcome using a multistage process. The equipment needed for this method is a vessel for the crude drug, a circulating pump, spray distributors and a number of tanks to receive the extracted solution. The extractor and tanks are connected with piping and valves as shown in Figure 2, so that any of the tanks may be connected to the extractor for transfer of the solution.
Each batch of drug is treated several times with solvent and, once a cycle is in process, the receivers contain solution with the strongest in receiver 1 and the weakest in receiver 3.
3.5.4.2.1 Advantages
The crude drug is extracted as many times as there are receiv- ers (in Figure 2 there are three receivers). If more extraction stages are required, it is only necessary to have more receivers. The last treatment of the drug – before it is discharged – is with fresh solvent, giving maximum extraction. The solution is in contact with fresh drug before removal for evaporation, giving the highest possible concentration.
3.5.4.2.2 Procedure
Fill the extractor with crude drug, add solvent and circulate.
Run off to receiver 1. Refi ll the extractor with solvent and circulate. Run off to receiver 2. Refi ll the extractor with solvent and circulate. Run off to re- ceiver 3. Remove drug from the extractor and recharge. Return solution from receiver 1 to the extractor. Remove for evaporation. Return solution from receiver 2 to the extractor and circulate. Run off to receiver 1. Return solu- tion from receiver 3 to the extractor and circulate. Run off to receiver 2. Add fresh solvent to the extractor and circulate. Run off to receiver 3. Remove drug from the extractor and recharge. Repeat cycle.
Figure 2: Multistage extraction
3.5.4.2.3 Extraction Battery
In the normal percolation process, the percolate is a very dilute solution, while the ideal situation is to obtain the maximum concentration possible. Continuous extraction devices of battery type are used when large amounts of a single material are handled. Such devices can be achieved by treating percolation as a multistage process. In an extraction battery proc- ess, a series of vessels is used and extraction is semicontinuous.
3.5.4.2.4 Equipment
An extraction battery consists of a number of vessels with in- terconnecting piping. Vessels are so arranged that solvent can be added to and the product taken from any vessel. These vessels can, therefore, be
made into a series with any of vessels as the fi rst of the series. The use of an extraction battery is illustrated in Figure 3, which shows the simplest arrangement of three vessels.
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