Oxygen, determination precision

It is worthwhile to note that Cannizzaro s work led to approximate values of the relative atomic masses. His goal was not to determine highly precise values for atomic masses but rather to pin down the approximate values (for example, to show that oxygen s relative mass was 16 rather than 8). The most precise values for atomic masses were determined by quantitative experiments in which the combining masses of elements were carefully measured, such as in the work of Berzelius. 

A topic which has attracted an inordinately large research effort over the years is the determination of precise structure of heterocyclic molecules which are potentially tautomeric - the pyridinol/pyridone relationship (section 1.2.4) is one such situation. In principle, when an oxygen is located on a carbon a or 7 to nitrogen, two tautomeric forms can exist the same is true of amino groups. 

Relatively inexpensive portable colorimetric indicators are now commonly used to detect the presence of a variety of contaminant gases in the atmosphere. These are normally specific for one or perhaps a series of gases. For example, the NBS colorimetric detector uses an indicator tube that contains a 15-mm section of yellow palladous silico-molybdate gel the gel changes color when exposed to carbon monoxide at concentrations as low as 0.001 vol. % in air. Figure 52 shows one version of a commercial unit used for carbon monoxide as well as carbon dioxide, the unsaturated hydrocarbons, and a variety of other gases this unit can also be used to determine the approximate concentrations of contaminants in liquid oxygen. Precise determinations can be made with a variety of analytical tools, including infrared... 

Benedict, Francis Gano (1870-1957) American nutritionist (director of the nutrition institute in Boston) who developed a calorimeter and a spirometer used to determine oxygen consumption and measure metabolic rate know for his precise CO2 and O2 measurements. 

While it may be relatively easy to understand the interaction between O2 (a diradical in its fundamental state) and the 3dz orbital of the L4Fe catalytic site (see the Energy Scheme in Fig. 10.21), it is not so easy to understand the interaction mechanism and reaction path followed during the reduction reaction of O2 on N-doped carbons in acid medium. Several calculations were performed by various groups to determine the precise origin of the reduction capabilities and the oxygen reduction mechanism on these N-based catalysts. They will now be reviewed. 

As shown in a certification round organized within BCR, different methods can be used to determine oxygen in nickel with a precision and accuracy better than 10 % at the 10 Mg/g level (242). Table VII-28 summarizes the results obtained for oxygen in BCR-CRM No.99 (certified value ... 

The nuclear charge and the electrons it attracts primarily determine the ways in which atoms behave toward other atoms. Mass differences cause only minor chemical effects. Since the isotopes of an element have the same nuclear charge and the same number of electrons per neutral atom, they react in the same ways. Thus we can speak of the chemistry of oxygen without specifying which one of the three stable isotopes is reacting. Only the most precise measurements will indicate the very slight chemical differences among them. 

Accuracy. Precision and Conditions for Thermal and Fast NAA for Al. Cl Mn Determination of Pellet Weight and of the Copper/Oxygen Ratio to... 

Cluster 2 appears to be unique among Fe-S-containing proteins whose structures have so far been determined, emd it has been termed the hybrid cluster (6) because of its diverse chemical nature. Figure 14 is a schematic drawing of the cluster as interpreted from the final electron density synthesis and the structure refinement. The cluster contains both oxygen and sulfur bridges, and X represents a site whose precise nature has not been determined, but which may contain a partially occupied and/or disordered substrate molecule (see Section III,B,3,b). The environments of the four iron atoms can be described as follows. 

---