Nitrogen calibration

For simultaneous determinations of carbon and nitrogen, a calibration curve must also be computed for nitrogen, using acetanilide as the standard substance (Fig. 15-4). 

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Figure 2, Typical total inorganic fixed nitrogen calibration...

Refer the optical density (reagent blank solution in comparison cell), given by the sample solution to the nitrogen calibration graph and read off the number of micrograms of nitrogen present. Calculate the nitrogen content of the sample from... 

If air has been run at reduced pressure for oxygen or nitrogen calibration, or both, correct the equation for pressure as follows ... 

Schmidt S C, Schiferl D, Zinn A S, Ragan D D and Moore D S 1991 Calibration of the nitrogen vibron pressure scale for use at high temperatures and pressures J. Appi. Phys. 69 2793... 

When it is desired to evaluate the specific surfaces of a set of closely related samples of solid, however, only one of the samples needs to be calibrated against nitrogen (or argon), provided that all the isotherms of the alternative adsorptive can be shown to have indentical shape. A simple device for testing this identity, by use of the a,-plot, is described in Section 2.13 by means of the a,-plot it is also possible to proceed directly to calculation of the specific surface without having to assign a value to or to evaluate the BET monolayer capacity, of the alternative adsorptive. 

When other adsorptives, such as those detailed in Section 2.9, are employed for surface area determination, calibration against nitrogen or argon is strongly recommended, so long as the specific surface exceeds lm g . For areas below this figure the calibration becomes too inaccurate, and an alternative adsorptive, usually krypton, has to be used. 

As explained in Section 2.13, the use of iz,-plots makes it possible to avoid the involvement of either n or when an alternative adsorptive is being used for evaluating the surface areas of a set of related solids. It is then no longer necessary to exclude the use of isotherms having a low value of c, consequently the method is applicable even if the isotherm of the alternative adsorptive is of Type III (cf. Chapter 5). Calibration of one sample by nitrogen or argon adsorption is still required. 

Figure L Calibration plot for nitrosation potential showing amount of t -nitroso-thiomorpholine formed vs, the square of the nitrogen dioxide concentration. Standard conditions of 50%relative humidity, 25°C, and 1 L/min flow rate for 30 min...

S. A. Blagodatsky, I. V. Yevdokimov, A. A. Larionova, and J. Richter, Microbial growth in soil and nitrogen turnover model calibration with laboratory data. Soil Biol. Biochem. 50 1757 (1998). 

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