Washing efficiency

The most efficient washing of the hydroxide was achieved applying a three-step process using an ammonium carbonate solution as the first step, followed by an ammonia solution, and water as the final step. This washing process brings about a ten-fold reduction in the concentration of fluorine compared with laboratory and industrial experience, in which a 2-4 fold reduction in the fluorine content of tantalum or niobium hydroxides following a one-step washing process was obtained. 

After the main filtrate has been removed for such treatment, the crystals on the filter pad should be washed to remove remaining traces of mother-liquor which, on drying, would contaminate the crystals. The wash liquid will normally be the same solvent or solvent mixture used for recrystallisation and must be used in the smallest amount compatible with efficient washing, in order to prevent appreciable loss of the solid. With the suction discontinued the crystals are treated with a small volume of the chilled solvent and cautiously stirred with a spatula or with a flattened glass rod (without loosening the filter paper) so that the solvent wets all the crystals. The suction is then applied again, and the crys-... 

Place the aqueous layer into a clean tube. The solution volume should be approximately 0.5 ml. Add 5 pi of 1 M MgCl2 and 1 ml of 2-propanol. Place on ice for 20 min, then pellet the DNA by centrifugation in a microcentrifuge for 30 min at 4°. Because relatively small quantities of DNA are being precipitated, the precipitation must be efficient. Wash the pellet with 1 ml of 70% (v/v) ethanol and centrifuge in a microcentrifuge at 4° for 5 min. Decant the ethanol and dry the pellet. 

Wash bottle This may consist of a 500 ml flat-bottomed flask, and the stopper carrying the two tubes should be preferably of rubber (cf. Fig. 11.1%). It is recommended that the wash bottle be kept ready for use filled with hot water as it is usual to wash precipitates with hot water this runs through the filter paper rapidly and has a greater solvent power than cold water, so that less is required for efficient washing. Asbestos string or cloth should be wound round the neck of the flask in order to protect the hand. 

Since the solids have a tendency to occlude significant amounts of the diol, efficient washing of the solids is essential to obtain good yields. Warm solvent can be employed to assist in removal of the product. 

Fig. 9. Rinsing of beads by immersion of device "A" into a water bath. The inverted, diagonal position is preferable. Alternate total removal and total submersion gives efficient washing. Alternatively, this washing step may be accomplished by serial transfer of beads from one Microtiter plate to another (the wells simply containing water), or by holding the beads under a moving stream of water.

Ethyl acetate may be used in a similar manner but the reaction is not as rapid or as complete as with methyl acetate and the methyl acetate therefore constitutes a preferred embodiment of the invention, particularly as the solvent power of methyl acetate for water is greater than that os ethyl acetate and it is therefore a more efficient washing medium thai ethyl acetate so that improved results are also obtained in the scconc step of the process. It will be apparent that the present inventior eliminates costly equipment for a troublesome fractional distillation oi for distillation of the acetamide itself and the reaction is not carried oir at high temperatures or under high pressures which further eliminate-the necessity for expensive apparatus. The expense and loss incident iv recrystallization which may be necessary in processes used hitherto, i-also avoided without any loss in purity of the acetamide. 

Reactants that are not transformed into urea are recycled to the reactor by means of an ejector. The plant is free from pollution problems. All vents are efficiently washed so that they are discharged to atmosphere practically free of ammonia and urea. Liquid discharge may have to be physically treated to meet local regulations or client requests. Also, discharge water can be reused as boiler feed water (BFW). 

Polystyrene containing 50% divinylbenzene provides a nonswelling, rigid support that possesses the attractive features of rapid reaction kinetics, efficient washing with organic solvents, and mechanical stability during oligonucleotide synthesis. This support has been derivatized to provide a primary amino functionality (Fig. 2) by the same procedure described for aminomethylated polystyrene resin (see Section II.A). 

The economy of wash liquid obtained by using several small quantities of liquid instead of one large one is important where the wash liquid is costly, as in the case of ether, or where the precipitate is appreciably soluble. Speedy washing with a minimum amount of liquid is desirable if the moist or impure precipitate is easily oxidized by air. Thus quick and efficient washing is needed in the preparation of cuprous chloride (Experiment 40) and is absolutely essential in the preparation of chromous acetate (Experiment 45). In the latter experiment the precipitate of chromous acetate separates from a mother liquor that is rich in sodium acetate and zinc chloride, and these salts must all be washed out of the precipitate before the latter can be dried. At the same time the precipitate is appreciably soluble in water and is very easily oxidized. Hence ice water that has been freed from air is used for washing. 

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