Buffering materials

Accuracy and Interpretation of Measured pH Values. The acidity function which is the experimental basis for the assignment of pH, is reproducible within about 0.003 pH unit from 10 to 40°C. If the ionic strength is known, the assignment of numerical values to the activity coefficient of chloride ion does not add to the uncertainty. However, errors in the standard potential of the cell, in the composition of the buffer materials, and ia the preparatioa of the solutioas may raise the uacertaiaty to 0.005 pH unit. 

Isolation of radioactive wastes for long periods to allow adequate decay is sought by the use of multiple barriers. These include the waste form itself, the primary containers made of resistant materials, overpacks as secondary layers, buffer materials, concrete vaults, and finally the host rock or sod. Barriers limit water access to the waste and minimize contamination of water suppHes. The length of time wastes must remain secure is dependent on the regulatory limit of the maximum radiation exposure of individuals in the vicinity of the disposal site. 

Buffering materials To afford acidic, basic or neutral layers,... 

The isolation and safety functions of HLNW deep geological repositories are based upon the multibarrier concept, where a number of containment and isolation barriers are put in place. A schematic view of the multibarrier HLNW concept is given in Fig. 1. The main barriers of the system are the waste matrix itself a metallic container (either corrosion resistant like Cu or Ti, or based upon stainless steel) a buffer material (normally bentonite) and finally the host rock itself (essentially granite or clay, although salt domes are also being considered). 

Final adjustment with HC1 may be needed if the pH is more than one unit away from a pfCa value. When two buffering materials are present, the composition should be calculated independently for each. The measurement of pH should always be done with great care because it is easy to make errors. Everything depends upon the reliability of the standard buffers used to calibrate the pH meter.7 Often, especially during isolation of small compounds, it is desirable to work in the neutral pH region with volatile buffers, e.g., trimethylamine and C02 or ammonium bicarbonate,... 

Separation of salicylic acid and indomethacin was accomplished by packing 6 gms. of kieslguhr ground with citrate buffer on top of 2 gms. of kieslguhr mixed with pH 7.0 phosphate buffer. Material was eluted with heptane(42). 

The pH reference materials were selected also to cause small liquid junction potential < 0.01 in pH if the pH of the buffer solution prepared from this material is measured in cells with transference [12]. The molality of the primary buffer solutions are kept at < 0.1 mol kg-1 for the same reason [13]. Furthermore, the primary buffers have a long-time stability of stored solid material (>3 years), except solid borax buffer material. Borax buffer (0.1 mol kg-1) has a restricted stability of about 2 years only [14]. 

Buffer material that does not fulfil all the criteria for primary pH reference materials but to which pH values can be assigned using cell I are considered to be pH(SSs). 

The use of organic liquids, such as hexane (H5), heptane (D15), toluene (M24), chlorobenzene (C3), carbon tetrachloride (C4, S4) in direct contact with the paper was less successful because interaction between the organic solvent and the buffer material under investigation cannot be avoided. 

Many metal analyses are carried out using atomic spectroscopic methods such as flame or graphite furnace atomic absorption or inductively coupled plasma atomic emission spectroscopy (ICP-AES). These methods commonly require the sample to be presented as a dilute aqueous solution, usually in acid. ICP-mass spectrometry requires similar preparation. Other samples may be analyzed in solid form. For x-ray fluorescence, the solid sample may require dilution with a solid buffer material to produce less variation between samples and standards, reducing matrix effects. A solid sample is also preferred for neutron activation analyses and may be obtained from dilute aqueous samples by precipitation methods. 

Sometimes a plastic buffer material (usually white granulated polyethylene) is mixed with the shot to help prevent distortion during discharge. The buffer material may be found in the wound channel in close range shootings. Another innovation to prevent distortion is the use of a shot cup that encloses the shot as it travels through the barrel, with the shot cup falling away when it exits the muzzle. 

Also packaged SPC only bum and do not detonate when they are on fire. Safely packaged SPC are separated by buffering materials between the SPC boxes so that fire will not propagate from one to the other once initiated. As these examples illustrate, there are many ways to make explosives safer by segregating small portions by effective packaging. 

Effect of buffer materials in the gap sensitivity in VPC tubes under sand... 

For the gap sensitivity test of explosives, the effect of buffer materials was evaluated by using the explosion test under sand. The... 

Over the range of the test, sand is the best buffer material, but bubbling styrol and glass microspere are not as effective as air. 

Buffer materials to ease the effects of shock waves and the safest distance between units to prevent the propagation of explosion. 

The effect of buffer materials is to soften shock waves. The safety wrapping technique for paper percussion cups which are commonly used to start sports events was tested by exposure to a weak shock wave. The small gap test (II) (Sec.5.2.3 in this book) was used. A propagated explosion test using a strong shock wave was also tried in sand (Sec.3.8.3). As a result of these tests, it was found that river sand was a practical materia] that could be used to soften shock waves. 

Kozai, N., Y. Adachi, S. Kawamura, K. Inada, T. Kozaki, S. Sato, H. Ohashi, T. Ohnuki, and T. Banba. 2001. Characterization of Fe-montmorillonite A simulant of buffer materials accommodating overpack corrosion product. J. Nucl. Sci. Technol. 38 1141-1143. 

This case is typical of a buffered solution in that the initial and equilibrium concentrations of buffering materials are essentially the same. 

The pH of the buffered solution is determined by the ratio of the concentrations of the weak base and weak acid. As long as this ratio remains virtually constant, the pH will remain virtually constant. This will be the case as long as the concentrations of the buffering materials (HA and A or B and BH+) are large compared with the amounts of H+ or OH- added. 

In this case, water does not have to be explicitly taken into account. Notice that the rigorous equation produces a different result from the normal procedure only when the buffering materials are very dilute (on the order of 10 6 M or smaller). For buffered solutions with normal concentrations of HA and A-, the simple approach used in this text to treat buffers will suffice. However, the rigorous equation always gives the correct answer and has the advantage of emphasizing explicitly the approximations being made in the simpler approach. 

A new area of research is the control of pH for nonaqueous enzyme reactions using organic pH buffers. - These buffer materials, which are soluble in nonaqueous media, strongly control the effect of pH on the reaction, and are able to override the pH memory of the enzyme before lyophilization or immobilization from an aqueous solution. - Typically, buffer salts employed are oppositely charged (e.g., / -COOH and / -COONa+, where R is hydrophobic in nature). It is the ratio of these two forms that controls the enzymatic rate. The buffers are believed to function by displacing hydrogen atoms of carboxylic acid groups on the surface of the enzyme, . - ... 

Figure 11 compares the low-temperature modulus characteristics of representative fiber-coating (buffer) materials of the three types described earlier. The figure depicts the dynamic tensile modulus as a function of frequency at -40 °C. The data were obtained on films of the materials by using a Rheometrics rotational dynamic spectrometer operated over the frequency range from 10 to 10 rad/s. Curves obtained at different temperatures were shifted both horizontally and vertically in accord with established linear... 

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