Transfer capillary pipette

Precipitations are usually carried out in micro centrifuge tubes. After centrifuging, the precipitate collects in the bottom of the tube. The supernatant liquid may be removed either by a capillary dropper (Fig. 2.13) or by means of a transfer capillary pipette. The latter consists of a thin glass tube (internal diameter about 2 mm this can be prepared from wider tubing) 20 to 25 cm in length with one end drawn out in a micro flame to a tip with a fine opening. The correct method of transferring the liquid to the... 

For the washing of precipitates the wash solution is added directly to the precipitate in the centrifuge tube and stirred thoroughly either by a platinum wire or by means of a micro stirrer, such as is shown in Fig. 2.34 the latter can readily be made from thin glass rod. The mixture is then centrifuged, and the clear solution removed by a transfer capillary pipette as already described. It may be necessary to repeat this operation two or three times to ensure complete washing. 

Table VI.12 Separation of Group I cations on the semimicro scale The residue may contain PbCl2, AgCl, and Hg2Cl2. Add 1 ml hot water to the ppt., place the tube in a boiling water bath for 1-2 minutes, and stir continuously. Centrifuge rapidly separate the solution from the residue with a capillary pipette and transfer the clear solution to a centrifuge tube.

The residue is dissolved in 2 ml of redistilled tetrahydrofuran (THF) containing 10 mg per 100 ml of coprostan-3 -ol (COP) as internal standard. (Blowout pipettes must not be used because moisture is detrimental to the formation of trimethyl silyl ethers.) The solution is transferred by capillary pipette to a 15-ml conical centrifuge tube, and the flask is rinsed out with 0.5 ml of fresh THF. Hexamethyldisilazane (0.3 ml) and trimethylchlorosilane (0.1 ml) are added. The tube is then stoppered, thoroughly mixed, and allowed to stand at room temperature overnight. 

Using a curved capillary pipette, pick up pieces and transfer to 10-ml Falcon plastic bottles with a drop of saline. Close bottles and place into 37°C incubator for 1-2 hr. 

Aspirate the supernatant and invert the centrifuge cone quickly over absorbent tissue. Drain 15 min. Slurry the precipitate with distilled water and transfer to a stainless steel planchet with a disposable capillary pipette. Dry the disk under an infrared lamp and flame the dried planchet to red heat. The a activity is then counted with a low-background proportional counter for 150 min. 

Since the mass-transfer coefficient at a micropipette is inversely proportional to its radius, the smaller the pipette the faster heterogeneous rate constants can be measured. Micrometer-sized pipettes are too large to probe rapid CT reactions at the ITIES. Such measurements require smaller (nm-sized) pipettes. Nanopipettes are also potentially useful as SECM tips (see Section IV.D) because they can greatly improve spatial resolution of that technique. The fabrication of nanopipettes was made possible by the use of a micro-processor-controlled laser pipette puller capable of puling quartz capillaries [26]. Using this technique, Wei et al. produced nanopipettes as small as 20 nm tip radius and employed them in amperometric experiments [9]. 

The advantages derived from the use of microscopic liquid-liquid interfaces have been highlighted in Sect. 5.5.3, and different approaches to support such small liquidlliquid interfaces in pores, pipettes, and capillaries have been addressed. The theoretical treatment of ion transfer through these interfaces needs to consider the asymmetry of the diffusion fields inside and outside the pore or pipette (i.e., diffusion can be approximated as linear in the inner phase, whereas radial diffusion is significant in the outer phase, especially for small sizes) [36, 40, 42-44]. 

Today, the company Affymetrix offers microarrays with >2,000,000 unique compounds. The fluidic system is quite simple. The sample is manually loaded with a pipette into the chip, and capillary forces transfer the sample to the incubation chamber. Incubation and mixing is enhanced by a moving air bubble actuated by slow rotation. 

Microscale Inverted Capillary Method. In microscale experiments, there often is too little product available to use the semimicroscale method just described. However, the method can be scaled down in the following manner. The liquid is placed in a 1-mm melting-point capillary tube to a depth of about 4-6 mm (see Figure 13.4B). Use a syringe or a Pasteur pipette that has had its tip drawn thinner to transfer the liquid into the capillary tube. It may be necessary to use a centrifuge to transfer the liquid to the bottom of fhe tube. Next, prepare an appropriately sized inverted capillary, or bell. 

P) in the capillary, such reactions can be carried out more systematically. Melting point capillaries (internal diameter 1—1.6 mm) are used, drawn out in the form of pipettes, and the desired amount of substance solution and of reagent solution are allowed to rise into two separate capillaries. The contents of one capillary are then transferred to the other by bringing the two pipette tips into suitable contact. Mixing is performed by tilting the capillary. Both ends of the capillary can now be sealed off and the contents warmed for a while if necessary. It is then cautiously opened at room temperature and the contents are directly applied to the layer. 

Using a Pasteur pipette, place a drop of the diluted or undiluted sample into the delivery ports (V-shaped groove) on each counting surface. Capillary action should draw the sample under the cover slip and uniformly fill the counting area. Alternatively, transfer a drop of the final... 

After 5 min transfer the contents of the tube with a polythene, capillary-ended Pasteur pipette to a prepared Sephadex G25 column, then wash in and elute with 0.5 ml aliquots of UB. 

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