Total ionic strength buffer

Fluoride was determined mainly by using an Orion fluoride electrode (model 90-01) with a Coming model 10 expanded pH meter. The procedures described earlier (9,11,12) were modified as follows. To a 10 ml sample of water in a plastic beaker was added 40 ml of stock seawater (30%o), followed by 10 ml of total ionic strength buffer (TISB, pH = 5.5, ionic strength 1.9) (13). Initial reading (=Ex) was recorded after... 

These are indirect methods based around computational procedures, using estimates of the monomeric inorganic aluminium fraction and free and total fluoride concentrations. Normally, free fluoride is determined by direct measurement with an ion-selective electrode. The total fluoride concentration is determined using the same ion-selective electrode technique, but after the addition of a total ionic strength buffer (TISAB). LaZerte [177]... 

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. 

Fluoride. A fluoride concentration of ca 1 mg/L is helpful in preventing dental caries. Eluoride is deterrnined potentiometrically with an ion-selective electrode. A buffer solution of high total ionic strength is added to the solution to eliminate variations in sample ionic strength and to maintain the sample at pH 5—8, the optimum range for measurement. (Cyclohexylenedinitrilo)tetraacetic acid (CDTA) is usually added to the buffer solution to complex aluminum and thereby prevent its interference. If fluoroborate ion is present, the sample should be distilled from a concentrated sulfuric acid solution to hydrolyze the fluoroborate to free fluoride prior to the electrode measurement (26,27). 

Direct analysis with the fluoride lon-selective electrode requires addition of total ionic strength adjustor buffer solution (TISAB) to the standard and to unknown samples Some advantages of this addition are that it provides a constant background ion strength, ties up interfenng cations such as aluminum or iron, which form a complex with fluoride ions, and maintains the pH between 5 0 and 5 5 According to the manufacturer s claim, reproducibility of direct electrode measurement IS 2 0%, and the accuracy for fluonde ion measurement is 0 2% [27]... 

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... 

Ke and Regier [71] have described a direct potentiometric determination of fluoride in seawater after extraction with 8-hydroxyquinoline. This procedure was applied to samples of seawater, fluoridated tap-water, well-water, and effluent from a phosphate reduction plant. Interfering metals, e.g., calcium, magnesium, iron, and aluminium were removed by extraction into a solution of 8-hydroxyquinoline in 2-butoxyethanol-chloroform after addition of glycine-sodium hydroxide buffer solution (pH 10.5 to 10.8). A buffer solution (sodium nitrate-l,2-diamino-cyclohexane-N,N,N. AT-tetra-acetic acid-acetic acid pH 5.5) was then added to adjust the total ionic strength and the fluoride ions were determined by means of a solid membrane fluoride-selective electrode (Orion, model 94-09). Results were in close agreement with and more reproducible than those obtained after distillation [72]. Omission of the extraction led to lower results. Four determinations can be made in one hour. 

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. 

FIGURE 1.6 Effect of organic modifier (methanol) percentage in the elnent on the retention factors (a) and observed enantioselectivities (b) of Af-(2,4-dinitrophenyl)-a-(2-chlorobenzyl)-proline employing an 0-9-[(2,6-diisopropylphenyl)carbamoyl]quinine-based CSP. Experimental conditions Elnent, ammonium acetate buffer-methanol (total ionic strength = 25 mM pHj, = 6.5), methanol content varied between 60 and 90%, while ionic strength and apparent pH were kept constant temperature, 40 C flow rate, 0.8 mLmin . (Reproduced from A. Peter et al., J. Sep. ScL, 26 1125 (2003). With permission.)... 

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... 

Ge (2000) carefully designed a universal protein array (UFA) system based on the use of various transcription factors, their activators, and cofactors as probes. A total of 48 different, highly purified factors were used to create the UFA on nitrocellulose filters. Frotein-protein interactions of various binding affinities could be assessed using different ionic strength buffers (e.g., 100 mM KCl vs. 1000 mM KCl). The relative binding of radiolabeled ( T) GST-K-p52 proteins to various transcription factors was studied. 

Total ionic strengths of solutions in the cells were varied from about 0.005M to ca. 0.02Af. The concentrations of solutions in cell C were made so that the buffer ratio in Equation 15 always had a value between 0.4 and 0.6. The nonaqueous cosolvents used in this study were Reagent Grade or better, and they were tested to be sure that they were free from significant quantities of potentially interfering substances such as halide ions, acids, and bases. Densities of tetra-hydrofuran-water mixtures were determined pycnometrically at 15° C and at 35°C. 

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). 

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