Buffer solutions standard reference

Buffer solutions, NMR reference standard Buffer solutions Buffer solutions Phosphate bead test for metals Dessicant Fusion matrix... 

Table 8.14 National Bureau of Standards (U.S.) Reference pH Buffer Solutions 8.105...

Details for the preparation of the solutions referred to in the table are as follows (note that concentrations are expressed in molalities) all reagents must be of the highest purity. Freshly distilled water protected from carbon dioxide during cooling, having a pH of 6.7-7.3, should be used, and is essential for basic standards. De-ionised water is also suitable. Standard buffer solutions may be stored in well-closed Pyrex or polythene bottles. If the formation of mould or sediment is visible the solution must be discarded. 

It has become fairly common to adopt the manufacture of combinations of internal reference electrode and its inner electrolyte such that the (inner) potential at the glass electrode lead matches the (outer) potential at the external reference electrode if the glass electrode has been placed in an aqueous solution of pH 7. In fact, each pH glass electrode (single or combined) has its own iso-pH value or isotherm intersection point ideally it equals 0 mV at pH 7 0.5 according to a DIN standard, as is shown in Fig. 2.11 the asymmetry potential can be easily eliminated by calibration with a pH 7.00 0.02 (at 25° C) buffer solution. 

To construct a standard curve of various biotin concentrations, first zero a spectrophotometer at an absorbance setting of 500 nm with sample and reference cuvettes filled with 0.05M sodium phosphate, 0.15M NaCl, pH 6.0. Remove the buffer solution from the sample cuvette and add 3 ml of the (strept)avidin solution plus 75 pi of the HABA-dye solution. Mix well and measure the absorbance of the solution at 500nm. Next add 2 pi aliquots of the biotin solution to this (strept)avidin-HABA solution, mix well after each addition, and measure and record the resultant absorbance change at 500 nm. With each addition of biotin, the absorbance of the (strept)avidin-HABA complex at 500 nm decreases. The absorbance readings are plotted against the amount of biotin added to construct the standard curve. 

The ultraviolet chemical assay for erythromycin remains largely unchanged from that described by Kuzel et al.9 in 1954. This procedure is essentially as follows. The reference standard, alkali reagent, and buffer solutions are prepared prior to the assay. 

Reference buffer solutions, 14 25-26 Reference data, standard, 15 747 Reference dose (RfD), 25 238, 239 Reference electrodes, 9 571-574 ... 

For example, to prepare a pH = 9 buffer solution, one would prepare a solution of ammonium chloride (refer to Table 5.1), and then add a solution of sodium hydroxide while stirring and monitoring the pH with a pH meter. The preparation is complete when the pH reaches 9. The required conjugate acid-base pair would be NH3 - NHj. Recipes for standard buffer solutions can be useful. Table 5.2 gives specific directions for preparing some popular buffer solutions. 

The pH meter is standardized (calibrated) with the use of buffer solutions. Usually, two buffer solutions are used for maximum accuracy. The pH values for these solutions should bracket the pH value expected for the sample. For example, if the pH of a sample to be measured is expected to be 9.0, buffers of pH = 7.0 and pH = 10.0 should be used. Buffers with pH values of 4.0,7.0, and 10.0 are available commercially specifically for pH meter standardization. Alternatively, of course, homemade buffer solutions (see Chapter 5) may be used. In either case, when the pH electrode and reference electrode are immersed in the buffer solution being measured and the electrode leads are connected to the pH meter, the meter reading is electronically adjusted (refer to manufacturer s literature for specifics) to read the pH of this soluiton. The electrodes can then be immersed into the solution being tested and the pH directly determined. 

Obtain the continuous spectrum of the purified a-lactalbumin sample from 240 to 340 nm. Do this by placing a cuvette containing Tris buffer in the reference beam and a-lactalbumin in the sample beam. Record the UV spectrum. Dilute the solution with a known amount of buffer if the recorder runs off scale. Record the spectrum with standard a-lactalbumin. 

Accuracy and Interpretation of Measured pH Values. To define the pH scale and pertnil the calibration of pH measurement systems, a scries of reference buffer solutions have been certified hy the U.S. National Institute of Standards and Technology iNIST). The acidity function which is the experimental basis for the assignment of pH. is reproducible within about O.IKl.I pH unit from It) to 40T. However, errors in the standard potential of the cell, in the composition of the buffer materials, and in the preparation of the solutions may raise the uncertainty to 0 005 pH unit. The accuracy of ihe practical scale may he furthei reduced to (I.Ot)X-(l.(ll pH unit as a result of variations in the liquid-junction potential. 

Standard Reference System. A volume of 20 ml. 0.03M aqueous solution of complex metal cyanides was added to 200 ml. of the described N/15 Sprensen buffer system (apparent pH 7.45). 

TABLE 8.5 National Institute of Standards and Technology (formerly National Bureau of Standards U.S). Reference PH Buffer Solutions. 

The buffer value for the National Institute of Standards and technology (U.S.) reference pH buffer solutions is given below ... 

Commercial gel-filled pH probes were inserted into the soil column at 3 cm intervals, located between the anode and cathode (Figure 1). These were inserted through butyl rubber septa placed into holes drilled into the sides of the column. The pH probes were calibrated using standard buffer solutions before insertion into the soil column. Readings were taken daily for the duration of the experiment, by placing a reference electrode into a well at the top of the column, and connecting the reference and in-situ pH probes to an Orion Model EA 940 Expandable Ion Analyzer. All pH measurements were temperature compensated to 25 °C. 

The pH meter used for pH measurement consists of these glass and reference electrodes and a potentiometer for measuring electrode potential. The pH meter must be daily calibrated against the standard buffer solutions of pH 4, 7, and 10. pH measurements are affected by temperature and the presence of very high concentrations of suspended matter. 

As a liquid junction potential is avoided, the cell potential consists merely of the electrode potentials of the hydrogen and the silver/silver chloride reference electrode. Chloride at known concentrations, mcl, must be added to the (chloride-free) buffer solution to use the silver-silver chloride electrode in cells without transference as a reference. This is different from silver/silver chloride reference systems with fixed potentials used for example as standard references in single-rod glass electrodes. 

If the soil suspension were instead an aqueous solution, a scale of activity values for Na+ could be defined in terms of emf data obtained for standard reference solutions of prescribed (Na+), in exactly the same way as the scale of (H) values (the operational pH scale) is defined (arbitrarily) in terms of emf data for standard buffer solutions.39,40 However, the success of this extrathermo-dynamic calibration technique depends entirely on the extent to which E, and B in the standard reference solutions are the same as E, and B in the solution of interest. For the case of a soil suspension, the presence of colloidal material may cause these two parameters to differ very much from what they would be in a reference aqueous solution. If the difference is indeed large, the value of (Na+), m, or any other ionic activity estimated with the help of standard solutions and an equation like Eq. s2.23 would be of no chemical significance. 

Electrode Calibration Pipet 50 mL of the Buffer Solution into a plastic beaker. Place the fluoride ion and reference electrodes (or a combination fluoride electrode) into the plastic beaker and stir. At 5-min intervals, add 100 pL and 1000 pi. of the 1000 mg/kg Fluoride Standard and read the potential, in millivolts, after each addition. The difference between the two readings is the slope of the fluoride electrode and should typically be in the range of 54 to 60 mV at 25°. If the difference in potential is not within this range, check, and, if necessary, replace the electrode, instmment, or solutions. 

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