Micro-centrifuge tubes

A Pyrex micro filter (Fig. XII, 2, 18) of 8 ml. capacity and furnished with a sintered glass disc is useful for the filtration of hot or boihng hquids. The long cylindrical tube reduces evaporation. The filter may be inserted into a test-tube with side arm (Fig. XII, 2, 13) and the filtrate collected in a centrifuge tube or semimicro test-tube receiver. 

BioRad produces Bio-Spin disposable polypropylene chromatography columns (Catalog No. 732-6008) that can be packed with up to 1.2 ml gel filtration media. Their micro Bio-Spin columns hold 0.8 ml media. Both are autoclavable columns that have snap-off column tips, polyethylene media bed supports, and fit standard centrifuge tubes. 

Micro centrifuge tubes (Fig. 11.34) of 0-5-2 ml capacity replace test-tubes, beakers and flasks for most operations. Two types of centrifuge tubes are shown b is particularly useful when very small amounts of precipitate are being handled. Centrifuge tubes are conveniently supported in a rack consisting of a wooden block provided with 6 to 12 holes, evenly spaced, of 1-5 cm diameter and 1-3 cm deep. 

Solutions are separated from precipitates by centrifuging. Semimicro centrifuges (Section II.4.5), either hand-operated or electrically-driven, can be used. Adapters are provided inside the buckets (baskets) in order to accommodate micro centrifuge tubes with narrow pen ends. 

Precipitations are usually carried out in micro centrifuge tubes. After centrifuging, the precipitate collects in the bottom of the tube. The supernatant liquid... 

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. 11.37 the latter can... 

The heating of solutions in centrifuge tubes is best carried out by supporting them in a suitable stand (compare Figs. 11.22-23) and heating on a water bath. When higher temperatures are required, as for evaporation, the liquid is transferred to a micro beaker or micro crucible this is supported by means of a nichrome wire triangle as indicated in Fig. 11.38. Micro beakers may be heated... 

The passage of hydrogen sulphide into a solution in a micro centrifuge tube... 

Traces of turbidity and of colour are also readily distinguished in micro test-tubes (50 x 8 mm) or in micro centrifuge tubes. As a general rule, these vessels are employed in testing dilute solutions so as to obtain a sufficient depth of colour. The liquid in a micro centrifuge tube or in a test-tube may be warmed in a special stand immersed in a water bath (compare Figs. 11.22-23) or in the apparatus depicted in Fig. 11.47. The latter is constructed of thin aluminium or... 

The problem of separating solid and liquid phases either before or after taking a sample drop or two of the test solution frequently arises in spot test analysis. When there is a comparatively large volume of liquid and the solid matter is required, centrifugation in a micro centrifuge tube (Fig. 11.34) may be employed. Alternatively, a micro sintered glass filter tube (Fig. 11.49), placed in a test-tube... 

Micro distillation is sometimes required, e.g. in the chromyl chloride test for a chloride (see Section IV.14). The apparatus depicted in Fig. 11.59 is suitable for the distillation of very small quantities of a mixture. A micro crucible or a micro centrifuge tube may be employed as a receiver. 

Phosphoric and arsenic acids form compounds analogous to silicomolybdic acid which also react with benzidine with colour formation hence these acids should be removed before applying the test. In the presence of phosphoric acid, the test is carried out as follows. Mix a drop of the test solution with 2 drops of the molybdate reagent in a micro centrifuge tube and centrifuge the mixture. Transfer the supernatant liquid to a micro crucible by means of a capillary tube, warm gently, cool and add 2 drops 05m oxalic acid solution (the latter decomposes the small quantity of residual phosphomolybdate (NH4)3[PMo12O40] but has little action on the silicomolybdic acid complex), then introduce a drop... 

In the presence of anions which are precipitated by calcium chloride solution, proceed as follows. Precipitate the acetic acid test solution with calcium chloride solution, and collect the precipitate on a filter or in a centrifuge tube. Remove the water from the precipitate either by drying or by washing with alcohol and ether. Mix a small amount of the precipitate with diphenylamine in a dry micro test-tube, add a little concentrated phosphoric acid, and heat gently over a free flame. Calcium phosphate and free oxalic acid are formed, and the latter condenses with the diphenylamine to aniline blue and colours the hot phosphoric acid blue. The colour disappears on cooling. Dissolve the melt in alcohol, when a blue colouration appears. Pour the alcoholic solution into water thus precipitating the excess of diphenylamine, which is coloured light blue by the adsorption of the dyestuff. The dye may be extracted from aqueous solution by ether. 

The reagents in phosphate-buffered saline are added, in the order stated above, to 2 ml polypropylene micro (Eppendorf) centrifuge tubes. 

Procec/Mre. - - Determinations on a micro scale are performed in 3-ml conical Pyrex centrifuge tubes. A volume of antiserum (containing antibody or myeloma antibody or crude seed extract or purified lectin) previously centrifuged until it no longer deposits sediment and containing about 6-8 fig of antibody N (AbN) or lectin N in a volume of about 50-100 fil is added to tubes containing a suitable range of accurately mea-... 

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... 

The transfer of precipitates is comparatively rare in micro qualitative analysis. Most of the operations are usually so designed that it is only necessary to transfer solutions. However, if transfer of a precipitate should be essential and the precipitate is crystalline, the latter may be sucked up by a dry dropper pipette and transferred to the appropriate vessel. If the precipitate is gelatinous, it may be transferred with the aid of a narrow glass, nickel, monel metal, or platinum spatula. The centrifuge tube must be of type a (Fig. 2.31) if most of the precipitate is to be removed. 

Micro centrifuge tubes are cleaned with a feather, pipe cleaner or small test-tube brush (cf. Fig. 2.30). They are then filled with distilled water and emptied by suction as in Fig. 2.38. After suction has commenced and the liquid removed, the tube is filled several times with distilled water without removing the suction device. Dropper pipettes are cleaned by repeatedly filling and emptying them with distilled water, finally separating rubber bulb and glass tube, and rinsing both with distilled water from a wash... 

The following micro apparatus will be found useful micro porcelain, silica, and platinum crucibles of 0.5 to 2 ml capacity micro beakers (5 ml) and micro conical flasks (5 ml) micro centrifuge tubes (0.5, 1.0 and 2.0 ml) micro test-tubes (40-50 x 8 mm) micro volumetric flasks (1, 2, and 5 ml)... 

Spot tests may be performed in a number of ways on a spot plate, in a micro crucible, test tube, or centrifuge tube, or on filter paper. Gas reactions are carried out in special apparatus. 

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