Aspirator tube

In the early days of flame spectrometry, some very elaborate accessories were designed to give reproducible discrete sample nebulization.16,17 However, as the technique became more widely employed, the devices used became progressively simpler, often taking the form of small funnels with a capillary bore outlet connected directly to the nebulizer capillary.17 Even this is not really necessary, because all that is required is a small (1-2 ml capacity) beaker with a conical depression in the bottom. Conventional Auto Analyser sample cups work very well. The end of the flexible nebulizer aspiration tube is simply dipped into the droplet of solution in the cone. This is especially useful if, for example, such sample cups have been used for evaporative pre-concentration of water samples in a vacuum desiccator.19... 

Contamination risk - wipe tlie outside of the aspirator tube with a clean tissue in between sarnples. standards to prevent... 

FIG. 5 Aspirator tube in use. A boiling stick may be necessary to promote even boiling. 

To recrystallize the caffeine dissolve it in 5 mL of hot acetone, transfer it with a Pasteur pipette to a small Erlenmeyer flask, and, while it is hot, add ligroin to the solution until afaint cloudiness appears. Set the flask aside and allow it to cool slowly to room temperature. This mixed solvent method of recrystallization depends on the fact that caffeine is much more soluble in acetone than ligroin, so a combination of the two solvents can be found where the solution is saturated in caffeine (the cloud point). Cool the solution containing the crystals and remove them by vacuum filtration, employing the Hirsch funnel or a very small Buchner funnel. Use a few drops of ligroin to transfer the crystals and wash the crystals. If you wish to obtain a second crop of crystals, collect the filtrate in a test tube, concentrate it to the cloud point using the aspirator tube (Fig. 5 in Chapter 3), and repeat the crystallization process. 

Remove the ether by simple distillation or by evaporation on the steam bath under an aspirator tube. See Fig. 5 in Chapter 5 or Fig. 9 in Chapter 3 or use a rotary evaporator (Fig. 7 in Chapter 10). When evaporation ceases, add 2-3 g of anhydrous sodium sulfate to the residual oil and heat for about 5 min longer. Then decant the methyl benzoate into a 50-mL round-bottomed flask, attach a stillhead, dry out the ordinary condenser and use it without water circulating in the jacket, and distill. The boiling point of the ester is so high (199°C) that a water-cooled condenser is liable to crack. Use a tared 25-mL Erlenmeyer as the receiver and collect material boiling above 190°C. A typical student yield is about 7 g. See Chapter 36 for the nitration of methyl benzoate. 

Heat a mixture of 4 g of benzoin and 14 mL of concentrated nitric acid on the steam bath for 11 min. Carry out the reaction under a hood or use an aspirator tube near the top of the flask to remove nitrogen oxides. Add 75 mL of water to the reaction mixture, cool to room temperature, and swirl for a minute or two to coagulate the precipitated product collect and wash the yellow solid on a Hirsch funnel, pressing the solid well on the filter to squeeze out the water. This crude product (dry weight 3.7-3.9 g) need not be dried but can be crystallized at once from ethanol. Dissolve the product in 10 mL of hot ethanol, add water dropwise to the cloud point, and set aside to crystallize. Record the yield, crystalline form, color, and mp of the purified benzil. 

The crude carotenoid is to be chromatographed on a 12-cm column of acid-washed alumina (Merck), prepared with petroleum ether (37-53°C) as solvent. Run out excess solvent, or remove it from the top of the chromatography column with a suction tube, dissolve the crude carotenoid in afew milliliters of toluene, and then transfer the solution onto the chromatographic column with a Pasteur pipette. Elute the column with petroleum ether, discard the initial colorless eluate, and collect all yellow or orange eluates together in a 50-mL Erlenmeyer flask. Place a drop of solution on a microscope slide and evaporate the rest to dryness (rotary evaporator or aspirator tube). Examination of the material spotted on the slide may reveal crystallinity. Then put a drop of concentrated sulfuric acid beside the spot and mix with a stirring rod. Compare the color of your test with that of a test on the other carotenoid. 

The basic components of the system are a liquid driver with only one carrier stream, a multi-port selection valve and a detector (Fig. 2.9). The valve is the heart of the sequential injection system and normally comprises 6—10 peripheral ports and a central port in a multi-position valve configuration. The central port is linked to a holding coil and the peripheral ports are connected to different solution aspiration tubes and transmission lines that are linked to different manifold components, e.g., detector and mixing chamber. Only one peripheral port is connected to the central port at any one time. Stream management inside the holding coil is accomplished by a bi-directional piston (or peristaltic) pump. The analyser is fully computer controlled and the injection volumes, residence times, delivery of solutions and analytical path lengths are selected based on a valve timing sequence and related flow rates. 

To this end, loop-based injection is preferred and the sample aspiration tube (Fig. 6.9) behaves as a sampling probe, as demonstrated in the landmark work of Thomsen et al. who determined reactive silicate in coastal waters during a cruise from Monterey Bay to San Francisco Bay in the USA [3]. The sample was continuously aspirated from a water layer about 2 m below the sea surface and a situation of "infinite sample volume" was attained in the main channel of a shipboard reagent injection (reversed flow) flow injection system. A reagent aliquot was injected into the flowing sample every 45 s and the resulting coloured zone was quantified by spectrophotometry. The height of the recorded peak was directly related to the reactive silicate concentration at the specified location and depth. 

After establishing the flame, insert the aspirator tube into distilled water, Allow the flame to stabilize for up to 1 minute by aspirating distilled water, prior to analysis. 

Fig. 9.6 Different mechanisms for placement of the final analytical solution in the measuring instrument. Indirectly, via the instrument autosampler, which can receive either a vial (A) or a sample aliquot to be held in cups (B). Directly, by means of a sensor (C) or by aspiration (D) at a fixed point where the tube is taken or with the aid of a moving aspiration tube, which is inserted by the robot arm (RA) in each tube in the rack in turn.

Baczkiewicz J, Michalski M. (1988) Oxygen transfer during mixing of acetic acid fermentation medium with self aspirating tube agitator. In Proceedings of Sixth European Conference on Mixing, Pavia, Italy, May 24-26, BHRA, Cranfield, UK. 

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