Burettes automatic

The success of this preparation depends upon the use of the apparatus (1) depicted in Fig.///, 57, 1, which permits of the automatic separation of the water produced in the reaction this will be termed a water-separator tube. Convenient dimensions for students preparations are indicated in the diagram. Determine the volume v of the tube up to the neck, i.e., between A and B, by adding water from a burette. The quantity of water which should be eliminated, assuming a quantitative conversion of the alcohol into the ether, may be computed from the equation ... 

In piston burettes, the delivery of the liquid is controlled by movement of a tightly fitting plunger within a graduated tube of uniform bore. They are particularly useful when the piston is coupled to a motor drive, and in this form serve as the basis of automatic titrators. These instruments can provide automatic plotting of titration curves, and provision is made for a variable rate of delivery as the end point is approached so that there is no danger of overshooting the end point. 

A titrimetric method involves the controlled reaction of a standard reagent in known amounts with a solution of the analyte, in order that the stoichiometric or equivalence point for the reaction between the reagent and the analyte may be located. If the details of the reaction are known and the stoichiometric point is located accurately and precisely, the amount of analyte present may be calculated from the known quantity of standard reagent consumed in the reaction. In most cases a standard reagent solution is prepared and added manually or automatically from a burette an alternative procedure is coulometric generation of the reagent in situ. The stoichiometric point may be detected by use of a visual indicator or by an electrochemical method (Chapter 6). 

Potentiometric titrations are readily automated by using a motor-driven syringe or an automatic burette coupled to a chart recorder or digital printout system. This is described in more detail in Chapter 12. A micro-processor-controlled titrator is discussed in Chapter 13. 

One area of analytical chemistry which is currently developing rapidly is the automation of methods. Some degree of automation has been used for a number of years in instruments such as automatic burettes coupled to absorptiometric or electrometric end-point detectors, and in data output devices which provide continuous pen recording or signal integration facilities. The major features of recent developments include the scope for instrumental improvements provided by solid-state electronic circuits and the increasing application of digital computers (Chapter 13). 

Sets of parameters such as burette volume, reagent strength, increment size and time interval, end-point potential, format of results, etc., can be stored and recalled from memory as standard methods for routine analyses. An alphanumeric keyboard is used to enter or change the parameters, to take individual pX or mV readings and to control the rinsing and the refilling of the automatic burette. Raw titration data and computed analytical results can be printed out as a permanent record, and titration curves can be produced on a chart recorder or VDU. 

The resulting reagent solution is then transferred into a suitable reservoir fitted with an automatic burette (protected from the atmosphere with a Drierite tube) and refrigerated. If kept dry, the reagent will be good for a month or two even though it will turn yellow and then orange in color. 

Titrations can be automated and controlled by a microprocessor. The titrant is delivered via an automatic burette and the end-point is detected potentiometrically... 

Adiabatic Dewar calorimeters are usually used in the closed mode. However, it is possible to incorporate a vent line to either an external containment vessel or to a burette for measuring the permanent gas evolution rate. This vent line contains an automatic valve to simulate the operation of the pressure relief system. 

Open the stopcock of the burette, inject from a syringe through the inlet port 0.5 mol of the compound to be hydrogenated as a liquid or as an ethanolic solution when hydrogenation will proceed automatically as in the external hydrogenation technique. 

In the iodimetric titration procedure, the combustion gases are bubbled through a diluent solution containing pyridine, methanol, and water. This solution is titrated with a titrant containing iodine in a pyridine, methanol, and water solution. In automated systems, the titrant is delivered automatically from a calibrated burette syringe and the endpoint detected amperometrically. The method is empirical, and standard reference materials with sulfur percentages in the range of the samples to be analyzed should be used to calibrate the instrument before use. Alternative formulations for the diluent and titrant may be used in this method to the extent that they can be demonstrated to yield equivalent results. 

An automatic or manual titration apparatus may be used. In the latter case, the burette is graduated in U.U05-mL increments and the pH meter is provided with a wide reaching scale and glass-calomel electrodes. After each test the reaction vessel is evacuated by suction and washed several times with water, the washings being removed each time by suction,... 

Automatic titration device with a 25 0.02 mL burette and a pH meter giving a reading to 0.01 are suitable (or manual titration burette (25 0.02 mL... 

Die pH electrodes and die tip of the burette ace immersed in die solution die pH Is adjusted to 6.7 with 0.02 NaOH and to pH 7.0 with 0.02 N NaOH. Hie automatic burette is zeroed. Now. exactly 5 mL of die enzyme reference solution 3 are added simultaneously a stopwatch is started the pH is maintained at 7.0 by automatic titration. After exactly 10 minutes, the pH is abruptly brought up to 9.0 by manual addition of titiant. This must be completed within 30 seconds. The burette volume is read and the volume of 0.02 N NaOH consumed is recorded (Nri). The blank solution is handled in the same way, however, the addition of enzyme is immediately followed by titration to pH 9.0. The volume is read again and recorded (Nr2). 

A related form of an automatic potentiometric titrator is instrumentation that permits the maintenance of the acidity or basicity of a solution over a period of time. Such devices are known as pH-stats, and find application in kinetic studies of hydrolysis reactions. The general approach is (by either manual or automatic means) to add either acid or base such that the pH in the solution is maintained constant over a period of time. Normally the amount of acid or base added as a function of time is sought in order that kinetic measurements may be made for the system. In its simplest form the acidity of the solution is monitored with a pH meter and controlled at a preselected value by the addition of acid or base from a burette the quantity delivered as a function of time is recorded in a notebook. Obviously for the fast reactions this becomes difficult and dependent on the dexterity of the individual. 

Unless a burette is automatic and one wishes to fill to the 0.00 mL mark, overfill the burette about 10 mm past the zero line. Let the liquid settle a minute, then release some of the liquid into a beaker or some other receptacle by slightly opening the stopcock. Let the fluid lower to the zero line. Wait another minute to allow the fluid to settle to the new level, and re-check the level of the meniscus at the zero line. Release or add more liquid as necessary. 

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