Buffers and indicators

Notes. (1) Somewhat sharper end points may be obtained if the sample of water is first acidified with dilute hydrochloric acid, boiled for about a minute to drive off carbon dioxide, cooled, neutralised with sodium hydroxide solution, buffer and indicator solution added, and then titrated with EDTA as above. 

Sorensen is usually considered to be the first to have realized the importance of hydrogen ion concentration in cells and in the solutions in which the properties of cell components were to be studied. He is also credited with the introduction of the pH scale. Electrochemistry started at the end of the nineteenth century. By 1909, Sorensen had introduced a series of dyes whose color changes were related to the pH of the solution, which was determined by the H+ electrode. The dyes were salts of weak acids or weak bases. He also devised simple methods for preparing phosphate buffer solutions covering the pH range 6-8. Eventually buffers and indicators were provided covering virtually the whole pH range. 

Inorganic and physical chemistry Chemical equilibrium 6 Buffers and indicators... 

Y. Aoki, K. Akagi, Y. Tanaka, J. Kawai, M. Takahashi, Measurement of intratumor pH by pH indicator used in F MR spectroscopy. Invest. Radiol. 31 (1996) 680-689. R.Y. Tsien, A non-disruptive technique for loading calcium buffers and indicators into cells. Nature 290 (1981) 527-528. 

Tsien RY. A nondisruptive technique for loading calcium buffers and indicators into cells. Nature 1981 290 527-528. 

Figure 43. The competition between phosphate buffer and indicator for the pulse-emitted protons. 40 iA-f Bromo Cresol Green, 200pM (J-naphthol. The reaction was measured in water (O) or in micellar system (250 aM micellar concentration) (D).The results are normalized for HInmaJi measured in the absence of buffer.

Preliminary adjustments The speed of rotation of the magnet in the titrate was adjusted to provide a vortex just sufficient for proper mixing but not large enough to interfere with the light beam. Rate of titrant delivery was adjusted to approximately 600 il/min. A constant titrate volume was used by adding water to measured amounts of ammonium hydroxide, buffer, and indicator mixture. 

A measured amount of EDTA, buffer, and indicator was added to the titration vessel and the Y axis of the recorder was adjusted to give approximately 4 in. deflection. The titration was started and allowed to proceed past the end point in order to record a dynamic titration curve for this system. 

Many amphoterics behave as cationic surfactants at acid pH, allowing them to be determined by the standard two-phase titration method. The mixed indicator method for the analysis of ionic surfactants, as described by Reid, Longman, and Heinerth, is adequate, but emulsions form in the vicinity of the end point so that precise analysis is difficult (115). Sometimes these problems can be minimized by reversing the titration. For example, a solution of sodium lauryl sulfate, buffer, and indicator is titrated with an aqueous sample containing a quaternary or amphoteric surfactant. The same end point is observed as described under the titration of anionics (94,95). Further improvement can be made by carefully adjusting the amount of ethanol added to the titration flask, depending on the individual surfactant being analyzed (116). 

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