Pipettes cotton plug

Dilute the dark green reaction mixture with 10 mL EtOAc and filter through a Pasteur pipette packed with a cotton plug and a layer of sand (and layer of Celite, optional). Direct the filtrate into a separating funnel charged with 1 M... 

Traditionally, pipettes were filled by sucking fluid into the tube with the mouth. This procedure, however, carries the risk of getting chemicals in the mouth. To protect the user, some pipette ends are designed to receive a cotton plug (see Fig. 2.20). 

There are three different styles of serological pipettes. Style I has a standard end piece. Style II has an end that can receive a cotton plug (see Fig. 2.20). Style III has the same type of end as Style II, but also has a larger tip opening to speed the emptying process. 

Using solid sodium aluminate powder, prepare a 4% (w/v) aqueous aluminate solution in an 8-mL vial, and shake vigorously until dissolved. Filter this solution into a clean 8-mL vial through a disposable pipette fitted with a cotton plug. 

Semimicroscale Columns. The procedure to fill a commercial semimicroscale column is essentially the same as that used to fill a Pasteur pipette (Section 19.6). The commercial column has the advantage that it is much easier to control the flow of solvent from the column during the filling process, because the stopcock can be adjusted appropriately. It is not necessary to use a cotton plug or to deposit a layer of sand before adding the adsorbent. The presence of the fritted disc at the base of the column acts to prevent adsorbent from escaping from the column. 

Filter a dilute solution of the requisite material in a suitable solvent, preferably the solvent from which you plan to crystallize the material, into a small pear-shaped flask or any round-bottom flask that can be attached to a rotary evaporator. To filter a small volume, it is convenient to use a very tight cotton plug in a disposable Pasteur pipette, or a syringe. 

Glassware is removed from the soaking baths and cotton wool plugs removed from pipettes (take care not to splash the caustic chloros). 

Gas Chromatography-Mass Spectrometry. Prepare methoxime derivatives by heating the extract from the thin-layer chromatographic plate with 100 xl of an 8% solution of methoxyamine hydrochloride in dry pyridine at 60° for 30 minutes, and evaporate in a rotary film evaporator. Silylate by dissolving the residue in 100 Lll of chloroform, adding 100 Lll of A,0-bis(trimethylsilyl)acetamide and 20 Lll of trimethylchlorosilane, then seal, and heat for 2 hours at 60°. When only 5a-estrane-3P,17a-diol is to be confirmed the methoxime formation can be omitted. Prepare a 2-cm column of Sephadex LH-20 in a Pasteur pipette with a cotton wool plug, using a... 

With this pipette the solution can not only be removed for weighing, but the volume can be determined at the same time. It consists of the wide tube a, to which the graduated capillary b, furnished with a cap Cj is attached. To the lower end of the pipette the tube e, with plug of cotton wool, can be fixed. After the pipette has been filled by sucking at the end of h, the stop-cock d is closed and the cap c placed on the capillary. The apparatus can then be weighed, and the volume of the solution be ascertained by means of the graduations. 

Sterilized pipettes, 1 ml capacity (if necessary plugged with cotton wool)... 

C. Flasks, test tubes, etc. are first closed with cotton wool or cellulose plugs or caps, and for bottles with glass stoppers the sterilizing strip is inserted and the stopper is loosely fitted. Pipettes are sterilized in sterilizing boxes made of tin. The ventilation holes must... 

Allow the solution to cool to room temperature and transfer the resin to the column with a pipette. Plug the top of the column with cotton and pass the remaining solution through the column. 

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