Shift isobaric

Figure 13. Changes in 6 Fe values of HPS Fe standard as a function of contaminate elements Al, Mg, or La (12.5 to 75 ppb). All solutions were 400 2 ppb Fe. The Fe isotope compositions of the solutions are shifted from those in the pure Fe standard (6 Fe = +0.49 0.05%o) as a function of the impurity concentration. The magnitude of the this shift with impurity concentration is variable, as shown by data collected during three analytical sessions (parts A, B, and C). These impurity matrix elements do not produce molecular isobars, as evidenced by the fact that 5 Fe and 5 Fe values plot along a mass-dependent array (part D). Note that an important conclusion of these tests is that accuracy of Fe isotope measurements cannot be demonstrated by preservation of mass-dependent trends in Fe/ Fe and Fe/ Fe. Data were collected using the Univ. of Wisconsin-Madison Micromass IsoProbe.

FIG. 13.58 Data of Fig. 13.57 (isothermal) and others at different temperatures down to -15 °C (isobaric) reduced to 25 °C and 1 bar by shift factors oT,p whose magnitudes are indicated in the three-dimensional insert. From Fillers and Tschoegl (1977). Courtesy The American Institute of Physics. 

Shake, C.L., P.K.Weathersby, B.G.Caras, and J.Parker. 1995. Helium-Nitrogen-Oxygen Isobaric Shift and Saturation Decompression. NSMRL Report 1196. NTIS/ AD-A292 639/2. Groton, CT Naval Submarine Medical Research Laboratory. 

When the p-isotherms cross at a given pressure, (dup/d T)p changes its sign and this property is responsible for the above-mentioned minima. In addition, as the temperature increases, the minima are shifted to higher pressures. At higher temperatures, especially when approaching the critical temperature, the minimum becomes a shallow one. As an example for associated liquids, some selected Cp-isotherms and the pressure effects at different temperatures on the isobaric heat capacity of m-cresol are presented in Figures 2(al) and (a2), respectively. 

The C02 sorption isobar measurement at ambient pressure yielded a monotonic desorption curve with a saturation point at approximately -80 °C. (Fig. 3.4.12(a)) The saturated quantity of 3.0 molecules per Rh2 unit at -80 °C agrees well with the composition determined from the single-crystal X-ray diffraction data at -180 °C (Figs. 3.4.11 and 3.4.12). The DSC measurements repeatedly revealed exo- and endothermic phase transitions in a C02 atmosphere. (Fig. 3.4.12(b)) The temperatures where the sets of cyclic DSC peaks occur shift to lower values as the concentration of C02 (partial pressure) decreases, demonstrating that the observed crystal phase transition is gas-adsorption induced. The estimated value indicates that the a crystal can include no more than one C02 molecule under the current a-saturation condition and subsequently transforms to the inclusion crystal, which can include up to three C02 molecules per Rh2 unit in the channels (Fig. 3.4.12(c)). 

The beta-decay of the ground state between the isobars is superallowed. Application of the isobaric correction to the level system in general shows that the three lowest levels are at a definitely lower excitation than the analogous levels in G . The levels are however unbound, and have larger widths than their counterparts in Ci , particularly in the case of the lowest (s-wave) level. The dispersive level shift (Sect. 9) for this state is thus very marked and with the assumption of a suitable radius of interaction the relative displacement of the... 

Finally, it is assumed that the reactor system is operated under isobaric conditions, set at 5 atm. The water-gas shift and CH4 reforming reactions are assumed to be operated in the temperature range 700K[Pg.296]

In Fig. 5 the isobaric and isothermal pVT curves of P4SC are shown. Because of the very small changes in specific volume the first phase transition can hardly be seen in the isobaric experiment. The two transitions are resolved only in the heating runs. The phase transition temperature, Td, is shifted to higher values and a decrease in AVsp is observed for both phase transitions. The two transitions are separated by only about 7°C for all pressures investigated. In the isothermal experiment (Fig. 5, right) pressure-induced crystallization can be seen for temperatures above 120°C, concurrently with a decrease in Ksp. Crystallization experiments performed with different pressure cycles show no distinct changes in the phase behavior in particular, the pure J. phase could not be observed. 

Use of a collision cell. Another novel approach to eliminating isobaric spectral interferences is to nse a collision cell [21]. A collision cell approach is similar to the fragmentation scheme used in tandem mass spectrometry. An rf-only multipole collision ceU is positioned between the ion extraction optics and the mass analyzer and is filled with hydrogen or helium as a collision gas. Polyatomic interfering species, such as Ar", Ar 0", and ArH+, are converted to nentral species or noninterfering ionic species, and thns are shifted away from the m/z of the analyte. 

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