Delivery pipettes

Amount of material required. It is convenient to employ an arbitrary ratio of 0 10 g. of solid or 0 20 ml. of liquid for 3 0 ml. of solvent. Weigh out 0 10 g. of the finely-powdered solid to the nearest 0 01 g. after some experience, subsequent tests with the same compound may be estimated by eye. Measure out 0-20 ml. of the liquid either with a calibrated dropper (Fig. 11,27, 1) or a small graduated pipette. Use either a calibrated dropper or a graduated pipette to deliver 3 0 ml. of solvent. Rinse the delivery pipette with alcohol, followed by ether each time that it is used. 

Pump pipette Delivery pipette with twin-bored stopper, glass elbow pipe and hand pump. (See Fig. Ill)... 

We now consider in somewhat more detail this typical procedure with occasional mention of possible modifications or alternatives. The first step is the weighing. Generally finely powdered rock samples of 10 to 100 mg provide adequate representation and sensitivity. Then comes addition of the spike. This is commonly measured by a standardized delivery pipette of a few ml volume or gravimetrically (e.g. Loubet et al., 1972a). Inasmuch as a number of lanthanides are to be determined, it is laborious to add spikes element by element. Hooker and co-workers (1975), for example, utilize two spike solutions La, Ce, Nd, Sm, Eu, and Gd Dy, Er, Yb, and Lu, Gast and co-workers (1970) used three La plus Ce, Nd, Sm, Eu, and Gd and Dy, Er, Yb, and Lu. We have found that a single composite spike solution provides eminently acceptable results over a wide... 

Standardisation of the mercuric nitrate solution. Measure out 2.0 ml of 0.025 M sodium chloride solution by means of a content pipette. Dilute to 15.0 ml with water and add 0.05 ml of bromophenol blue indicator solution. Add 0.1 N nitric acid until the yellow colour of the indicator appears and then add a further 0.5 ml of acid. After the addition of 100 ml of ethanol and 0.5 ml of diphenylcarbazone indicator solution, titrate the solution with the mercuric nitrate solution to the first appearance of a permanent violet colour. The solution should be stirred magnetically throughout the titration period. The use of a content pipette for measuring the sodium chloride solution is recommended, since it has been found that the reproducibility of repeated titrations is better than that obtained with, for example, a 5.0 ml delivery pipette, in conjunction with 0.01 M sodium chloride solution. The titration carried out as described must be corrected for the indicator blank value, obtained by the titration of 15.0 ml of water. This blank value is usually less than 0.05 ml of mercuric nitrate solution but much higher values have been obtained occasionally and these have been found to be due to the presence of chloride in the ethanol. In such instances, a suitable stock of ethanol may be mixed with a predetermined volume of the mercuric nitrate solution, sufficient to reduce the blank value to less than 0.05 ml. 

Into the conductivity vessel, fixed in the thermostat, introduce 20 C.C. of the acid solution with the delivery pipette, and after the solution has taken the temperature of the bath, determine the resistance of the solution, as described in the preceding experiment readings being taken, as before, with three different resistances in the box. 

Having taken a set of readings for the resistance of the solution, withdraw 10 c.c. of the solution with the withdrawal pipette, and introduce 10 c.c. of conductivity water with the delivery pipette mix the solution well by moving the electrodes up and down, but be careful not to deform the electrodes or to alter their relative positions, and also see that no air-bubbles... 

For dealing with smaller volumes of solution, micropipettes, often referred to as syringe pipettes, are employed. These can be of a push-button type, in which the syringe is operated by pressing a button on the top of the pipette the plunger travels between two fixed stops and so a remarkably constant volume of liquid is delivered. Such pipettes are fitted with disposable plastic tips (usually of polythene or polypropylene) which are not wetted by aqueous solutions, thus helping to ensure constancy of the volume of liquid delivered. The liquid is contained entirely within the plastic tip and so, by replacing the tip, the same pipette can be employed for different solutions. Such pipettes are available to deliver volumes of 1 to 1000 pL, and the delivery is reproducible to within about 1 per cent. 

Determination of C02.—Dilute 10 c.c. of the mash to 25 c.c. in a measuring flask and transfer 10 c.c. of the diluted liquid by means of a pipette to a small distilling flask which is directly connected to a nitrometer. To the solution add about 0-2 g. of yeast made into a cream with a little water and then at once displace the air by passing in carbon dioxide from above through a tube which does not dip into the liquid. Close the delivery tube by means of stop-cock or spring clip, fill the nitrometer with water saturated with carbon dioxide, and allow... 

The British Standards Institution (BSI) has laid down the permitted tolerances and delivery times for commonly used bulb transfer pipettes as shown in Table 2.5. 

Table 2.5 Tolerances and Delivery Times for One-Mark Pipettes ...

After about 5.0 ml has run into the pipette, turn A clockwise through 180°, so that solution now flows from the pipette to fill the delivery tube B. 

Suspensions can be introduced in a variety of ways. Some examples are to manually use syringes or pipettes, pour from a fared beaker, or automate delivery using calibrated pipettes. Each method has its own set of limitations, although automated methods may show less variability. Mixing of the suspension sample will generate air bubbles therefore, the mixing time of suspension samples must be strictly uniform to reduce erroneous or biased results. 

Spreadsheet 6.2. Calculation of the volume and measurement uncertainty of the delivery of a nominal 10-mL pipette under the scenarios given. These are graphed in figure 6.7. 

Cut off the delivery tube at a distance of about 1.5 cm. from the neck and seal on a tube B of thin glass 1.3 cm. in diameter and 50 cm. to act as an air condenser, bending the tube as shown in the figure. Make a tube C shaped like a pipette the wide part of which will just slip into the neck of the flask. The lower end is of very small tubing drawn to a capillary at the tip. When the tip is almost at the bottom of the flask, the upper part of the narrow tube should be just above the outlet into the condenser tube. The wide tube should extend about 3 cm. above the end of the neck of the flask and should then contract to a short, narrow tube over which a short piece of rubber tubing, provided with a pinch cock F, is slipped. 

It is essential that from the puncturing of the can or opening the sample through to the plating, extreme caution is to be exercised in aseptic technique. The mouth of each dilution bottle must be flamed prior to and after delivery of the sample. Caps on the bottles must be carefully removed and held between the fingers in such a position that the bottom or inside of the cap does not touch the fingers. If this happens in any way the bottle must not be used. This applies to pipettes as well. Pipettes can only be used once. 

Fig. 3.1. C02 delivery systems. On the left is a simple arrangement where air (from an air pump) may be mixed with C02 to produce 5% C02 in air for gassing bottles or feeding to an incubator. On the right is an arrangement for measuring out fixed volumes of C02 and delivering them through a three-way tap (at the bottom of the syringe) and a sterile Pasteur pipette to a bottle of cells.

In this experiment, three or four types of pipettes are selected to deliver water to a clean container. By weighing the delivered volumes, the accuracy of the different delivery methods is compared. The experiment also allows for the precision of pipette delivery to be observed. 

Cyclohexane should be introduced into the inner test tube from a weighing bottle (weighed before and after delivery) or from a pipette. Do not pipette cyclohexane by mouth use a rubber bulb. The quantity normally required is 15 mL. If a pipette is used, record the ambient temperature. 

Delivery of an aliquot through a pipette by positive displacement using a syringe or a micro pump that delivers precisely defined volume increments. 

Today s high potency drugs, intended for local and systemic treatments, depend on reliable delivery systems. As an alternative to squeeze bottles and pipettes, propellant-driven or mechanical-dispensing systems are often used. Aerosol systems are well known in inhalation therapy. They are ready to use and easy to handle. While new propellants will replace the old ones, the environmental and pharmacological discussions will continue. The switch to new propellants must be supported by sufficient clinical and toxicological data. In particular, compatibility problems must be addressed. Furthermore, attention must be paid to the surfactants not under dispute. 

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