Bracketing procedures

In most routine applications, glass electrode cells are calibrated by the two-point or bracketing procedure, using two secondary (or primary) standards with values that bracket the range in which the unknown lies. 

Yap, W. T., Schaffer, R., Hertz, H. S., White, E. V., and Welch, M. J. (1983). On the difference between using linear and non-linear models in bracketing procedures in isotope dilution mass spectrometry. Biochem. Mass Spectrom. 10, 262-264. 

The gas-phase acidities (A//°acid) of the radicals C6H4X (X = H, F, Cl and CN)316 were determined in an FT-ICR investigation, with the bracketing procedure applied to the reaction of equation 43 in which HA is a reference acid of known acidity ... 

In the majority of practical applications, glass electrodes cells are calibrated by a two-point calibration, or bracketing, procedure using two standard buffer solutions, with pH values, pH(Sj ) and pH(S2), bracketing the unknown pH(X). Bracketing is often taken to mean that the pH(Si) and pHfSj) buffers selected from Table 2 should be those that are immediately above and below pH(X). This may not be appropriate in all situations and choice of a wider range may be better. 

Alternatively, a bracketing procedure may be adopted whereby two standard solutions are chosen whose pH values, pH(Sl), pH(S2) are on either side of pH(X). Then if the corresponding potential difference measurements are (S1), (S2), (X), then pH(X) is obtained from... 

Thienpont, L.M., Van Nieuwenhove, B., Stockl, D. and De Leenheer, A.P., Calibration for isotope dilution mass spectrometry - description of an alternative to the bracketing procedure, J. Mass Spectrom., 31, 1119-1125 (1996). 

To each of three different 13 x 100-mm test tubes, add 2 mL of distilled water and 1 drop of chlorophenol red indicator (color change from pH 5.2 to 6.8). Add 1 drop of 6 M aqueous eunmonia, NH3, solution to the first test tube and 1 drop of 3 M hydrochloric acid, HCl, solution to the third test tube so that the first and third test tubes will then serve as reference colors for the indicator. Bubble gas from your CO2 generator through the solution in the second test tube for a few minutes, (If CO2 generation is no longer strong, perform the bracketed procedure two paragraphs above.) Describe in TABLE 34.IB the colors of the three solutions. 

Normalization Standard bracketing procedure Zircon standard 91500... 

Preliminary measurements were made with a quadrupole-based system and reported (Gunther-Leopold et al. 2003), but after a multicollector ICPMS was installed in the hot laboratory, more precise isotope ratio measurements were made. The results were adjusted by use of internal correction (known isotope ratio of the same element) or by a bracketing procedure with certified reference materials (external correction). Additional measurements were made with a specially designed laser-ablation system that was coupled to the ICPMS instrument. The nuclear fuel burn-up assessment was based on measurement of the ratio between Nd isotope and the four main fissionable nuclides ( U, Pu, and " Pu) for UOj or MOX fuel. " Nd is formed... 

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