Adjustment buffer

Another approach to matrix matching, which does not rely on knowing the exact composition of the sample s matrix, is to add a high concentration of inert electrolyte to all samples and standards. If the concentration of added electrolyte is sufficient, any difference between the sample s matrix and that of the standards becomes trivial, and the activity coefficient remains essentially constant. The solution of inert electrolyte added to the sample and standards is called a total ionic strength adjustment buffer (TISAB). 

The total ionic strength adjustment buffer serves several purposes in this procedure. Identify these purposes. 

Total Ionic Strength Adjustment Buffer (TISAB). Dissolve 57 mL acetic acid, 58 g sodium chloride and 4g cyclohexane diaminotetra-acetic acid (CDTA) in 500 mL of de-ionised water contained in a large beaker. Stand the beaker inside a water bath fitted with a constant-level device, and place a rubber tube connected to the cold water tap inside the bath. Allow water to flow slowly into the bath and discharge through the constant level this will ensure that in the... 

Ionic strength adjuster buffer 565, 570 Ionisation constants of indicators, 262, (T) 265 of acids and bases, (T) 832, 833, 834 see also Dissociation constants Ionisation suppressant 793 Iron(II), D. of by cerium(IV) ion, (cm) 546 by cerium(IV) sulphate, (ti) 382 by potassium dichromate, (ti) 376 by potassium permanganate, (ti) 368 see also under Iron... 

Keyboard sixteen push-buttons for entry of data and instructions for manual or automatic calibration, based on the three National Bureau of Standards (NBS) buffers of pH 4, 7 and 9, whose values as a function of temperature have been permanently and separately stored to three decimal places and at intervals of 0.1° C. Hence there is no need to enter pH values, as the electrode automatically identifies the buffer in use and the apparatus immediately retrieves and displays the temperature-adjusted buffer value the isopotential adjustment is defaulted to pH 7.000. 

Total ionic strength adjustment buffers TISABs) are used to equalize Ionic activity n different solutions. 

It is often more convenient to relate the potentiometer reading directly to concentration by adjusting the ionic strength and hence the activity of both the standards and samples to the same value with a large excess of an electrolyte solution which is inert as far as the electrode in use is concerned. Under these conditions the electrode potential is proportional to the concentration of the test ions. The use of such solutions, which are known as TISABs (total ionic strength adjustment buffers), also allows the control of pH and their composition has to be designed for each particular assay and the proportion of buffer to sample must be constant. 

To leam that the change of y with ionic strength is a major cause of error in electroanalytical measurements, and so it is advisable to buffer the ionic strength (preferably at a high value), e.g. with a total ionic strength adjustment buffer (TISAB). 

Often, the potentiometric determination of concentration requires a preferred pH range. If pH is also important, then the ionic strength adjuster can conveniently function additionally as a pH buffer. Such tablets are called total ionic strength adjustment buffers (or TISABs). ... 

The fluoride content of a sample of toothpaste is unknown. Accordingly, a sample of the toothpaste was digested in acid solution, filtered to remove the white gritlike solid and then buffered with a total ionic strength adjustment buffer (TISAB) to pH 6. A fluoride electrode is immersed in the clear solution and the emf recorded when the reading was steady. 

The activity a and concentration c are related by a = (c/c ) x y (equation (3.12)), where y is the mean ionic activity coefficient, itself a function of the ionic strength /. Approximate values of y can be calculated for solution-phase analytes by using the Debye-Huckel relationships (equations (3.14) and (3.15)). The change of y with ionic strength can be a major cause of error in electroanalytical measurements, so it is advisable to buffer the ionic strength (preferably at a high value), e.g. with a total ionic strength adjustment buffer (TISAB). 

TISAB total ionic strength adjustment buffer... 

Frant and Ross [108] recommended sample adjustment using TISAB buffer ( Total Ionic Strength Adjustment Buffer ), obtained by dissolving 57ml glacial acetic acid, 58 g NaCl and 4g 1,2-cyclohexanediaminetetraacetic acid (CDTA), adjustment of the solution pH with sodium hydroxide to 5 to 5.5 and dilution to 1 litre, all to maintain a constant ionic strength and pH between 5 and 5.5 and to complex ions such as Al or Fe that interfere in the determination. A detailed... 

The system can tolerate a high amount of water in the eluate and also organic acids or ammonia for pH adjustment. Buffered solvent systems will increase the noise level and can be used only in low amounts. Gradient elution is important for complex samples and will be tested in the near future. 

For dilute solutions, the Debeye-Huckel law (log 7 = —0.5zf/°5) indicates that 7 will be a constant for a given ionic strength /. Therefore, the same quantity of inert electrolyte, called the support electrolyte, must be added to the sample and to the series of standards to increase the concentration of external ions and stabilise the ionic strength. This addition of ISAB (Ionic Strength Adjustment Buffer) is intended to limit variation in 7. Under these conditions, the measured difference in potential only depends on the concentration of the ion to be analysed and is given by equation (18.3). 

There are many methods that allow the determination of the concentration q of an ionic species i in a sample. In the presence of an ionic strength adjuster (ISA) or a buffering solution that can fix the pH (TISAB, Total Ionic Strength Adjustment Buffer) all of these methods are based on application of equation (18.3). 

See if pH alone provides adequate separation. For acids, begin with 50 mM borate buffer, pH 9.3. For bases, try 50 mM phosphate, pH 2.5. If the separation is not adequate, try adjusting buffer pH close to the average pKa of the solutes. 

In addition to considering an adjusted buffering range in mixed solvent systems, the effects of dilution on the pH of the formulation should also be considered (Rubino, 1987). As formulations containing mixed solvent systems are diluted, the solvent effects onWIievjil decrease. For example, the a of the buffer acid will decrease as the formulation is diluted due to the dilution of the cosolvent. The consequences of the pqbWnges on the physicochemical stability of the active compounds should be carefully studied. 

Van Staden [4,5] employed flow injection analysis coupled with a coated tubular solid-state bromide-selective electrode for the determination of bromide in soils. Soil-extracted samples are injected into 10 mol/1 potassium nitrate carrier solution containing 1000 mg/1 chloride as an ionic strength adjustment buffer. The sample buffer zone formed is transported through the bromide selective electrode onto the reference electrode. The method is applicable in the range 10-50 000 mg/1 bromide. The coefficient of variation of this method is better than 1.6%. 

Raise the NaCl concentration in the DNA solution by adding volume of salt adjustment buffer [5 M NaCl, 100 mAf Tris-HCl (pH 7.4), 10 mM EDTA], Mix this solution, spin down briefly, and then add j volume of sterile 40% PEG and repeat the mixing. Incubate the mixture at 25° (room temperature) for about 2 hr. 

Salt adjustment buffer 5 M NaCl, 100 mAf Tris-HCl (pH 7.4), 10 mAf EDTA... 

Capillary zone electrophoresis is another technique which has been used to separate products such as organic acids.26 Separation is based on differences in the mobility of analytes exposed to an electric field. Resolution and separation time in such systems depends on factors including electroosmotic flow (EOF), and a number of approaches for adjusting the EOF have been examined. While some of the approaches (pretreatment of capillaries) are not useful as means of process control, adjusting buffer pH and the electric field27 seem to be possible handles for true feedback control of the separation, although closed-loop operation does not seem to have been attempted. 

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