Iron-content measurement

For elements such as silicon, alumina and sodium, there is a fairly good agreement between atomic absorption (AA) determination and EDS data for the parent Mg-rectorite. However, there are differences with respect to other elements, as shown in Table 6-1. This is not unexpected, since AA determination reports bulk analysis, whereas EDS reports the composition of the individual clay ciystal surface. The iron content measured by EDS is much higher than reported by AA analysis indicating that Fe is preferentially concentrated on the clay platelets surface, and that FejOj-containing phase impurities are negligible. The magnesium distribution is similar to that observed for Fe. 

The CD -ferrocene complexes were characterized by elemental analysis, IR, UV, and H-NMR spectra. Stoichiometries were determined by elemental analysis, and especially the iron content measured by atomic absorption analysis and from the H-NMR spectra, which show all the complexes obtained here are stoichiometric compounds and have definite ratios of CD/guest depending on the combinations of host and guest. Table I shows the results of the preparation of inclusion compounds of CDs with ferrocene. 3 CD formed 1 1 inclusion compounds with ferrocene. 

The molecular absoi ption spectra, registered at a lower temperature (e.g. 700 °C for iodide or chloride of potassium or sodium), enable one to find the absorbance ratio for any pair of wavelengths in the measurement range. These ratios can be used as a correction factor for analytical signal in atomic absoi ption analysis (at atomization temperatures above 2000 °C). The proposed method was tested by determination of beforehand known silicon and iron content in potassium chloride and sodium iodide respectively. The results ai e subject to random error only. 

Very thick absorbers may be required for applied-field measurements to achieve reasonable absorption depths and measuring times because the Mossbauer spectra are usually split into several hyperfine components. Here the iron content may be as large as 100 pg Fe per cm (1.75 pmol Fe per cm ), which would correspond to t 1 for a two-line spectrum. For smdies of frozen solutions, Fe concentrations of 1 mM are desirable for each nonequivalent iron site [35]. 

The determination of iron at trace levels can be accomplished by the spectrophotometric measurement of its complex with the reagent o-phenanthroline. The sensitivity of a particular method is 53 ppm per unit absorbance and the standard deviation of the blank estimated from 25 measurements is 0.002 of an absorbance unit. The practical detection limit is therefore 1.64aB or 0.0033 of an absorbance unit which corresponds to 0.17 ppm, and the theoretical detection limit is 3.28aB or 0.0066 of an absorbance unit which corresponds to 0.35 ppm. (The value of pB in this case is assumed to be zero.) Hence if a result is less than 0.17 ppm, the conclusion is that iron is not detected. If the value lies between 0.17 ppm and 0.35 ppm, the iron content should be reported as less than 0.35 ppm. ... 

If the analysis of a sample for iron content yields a mean result of 35.40% with a standard deviation of 0.30%, the size of the confidence interval will vary inversely with the number of measurements made. For two measurements, the confidence interval (90%) is... 

The calculations in Section 6.2 indicate that the root system as a whole can sustain considerable rates of O2 loss to the rhizosphere without compromising their internal O2 requirements. The standard O2 flux in the calculations in Section 6.2 was 0.5 nmol dm (root) s for the parts releasing O2. For rice roots grown in soil, Begg etal. (1994) obtained values of 0.1-1.2nmol dm (root) s from rates of Fe + oxidation and Fe(III) accumulation near planar layers of rice roots in anaerobic soil, and Kirk and Bajita (1995) obtained 0.1-0.2 nmol dm (root) s with the same experimental system but a soil with a smaller ferrous iron content. These values probably underestimate the total O2 release because they did not allow for O2 consumed by soil microbes. Revsbech et al. (1999) obtained values of 1-3 nmol dm (root) s from measurements of O2 gradients made with a microelectrode near rice roots in the soil used by Kirk and Bajita (1995). These values are in the middle of the range described above. 

A student repeatedly measures the iron content in a mineral and finds that the mean of five measurements is 5.62%. The student repeats the measurements again in groups of five and obtains means of 5.61%, 5.62%, and 5.61%. On the basis of this information, what can be said about the student s accuracy (or inaccuracy) ... 

For all these techniques, the general qualitative correlation between the measured parameter and the iron concentration was established. However, the measurements are too sensitive to the parameters of the experimental procedures and to physiological data beyond the iron content to allow for routine use in hospitals (43). Indeed, the relaxivity of ferritin is different in solutions, in the liver, in the spleen, in the brain, etc., which implies that MRI quantification protocols must be developed separately for each organ. 

Among these, iron is relatively easy to measure and serves as a reference, as a metallicity index, and thus as an indicator of the degree of evolution. Indeed, it is common practice in astronomy to treat the terms iron content (Fe/H) and metallicity (Z) as synonymous. Solar metallicity is denoted Zq. 

In irradiated potatoes, especially in some varieties and as a function of cultivating conditions of the raw material, after-cooking darkening may occur. This discoloration is attributed to formation of ferric-phenolic complexes. This phenomenon depends on the iron content, and is related to increased polyphenol formation and reduced citric acid levels, which are influenced by agronomic and climatic factors. Various technological measures have been developed to prevent this after-cooking darkening [23]. 

Distribution of iron on the lunar surface, as measured by the Clementine spacecraft, compared with the average iron contents (arrows) of Apollo highlands crustal rocks and lunar highlands meteorites. The meteorites, which presumably come from the nearside and farside, more closely match the global iron peak. The compositional ranges for various lunar rock types are shown as horizontal bars. 

A solution of the iron-transport protein, transferrin (Figure 7-4), can be titrated with iron to measure the transferrin content. Transferrin without iron, called apotransferrin, is colorless. Each molecule, with a molecular mass of 81 000, binds two Fe3+ ions. When iron binds to the protein, a red color with an absorbance maximum at a wavelength of 465 nm develops The absorbance is proportional to the concentration of iron bound to the protein. Therefore, the absorbance may be used to follow the course of a titration of an unknown amount of apotransferrin with a standard solution of Fe3+. 

The Hornsey (1956) procedure and its modifications have received widespread acceptance as relatively rapid measures of the adequacy of cure development in processed meats. The Hornsey procedure is also an accurate method for nutritional assessment of heme and heme iron content of meats (Carpenter and Clark, 1995), where ppm heme iron = ppm total heme/11.7. However, one caveat should be noted. The total heme pigment measurement is higher in cured meats than in similar uncured samples. Roasted turkey breast meat, for example, was reported by Ahn and Maurer (1989a) to have 23,26,34, and 34 ppm total pigment in samples formulated with 0, 1, 10, and 50 ppm nitrite, respectively. This effect should be considered to avoid overestimation of the heme iron content of cured meats. 

Thirteen specimens of 90/10 Cu-Ni alloys, each with a specific iron content, were tested in a corrosion-wheel setup. The wheel was rotated in salt sea water at 30 ft/sec for 60 days. The corrosion was measured in weight loss in milligrams/square decimeter/day, MDD. The following data were collected ... 

Lines of best fit for D2 of calculated vs. measured iron content computed from regression analysis at the... 

In pigeonites, X-ray diffraction (e.g., Clark et al., 1971 Brown et al., 1972 Takeda et al., 1974) and Mossbauer spectral measurements (Bancroft and Bums, 1967b) of samples from lunar and volcanic rocks demonstrate that there is a strong enrichment of Fe2+ ions in the M2 sites, but the enrichments are slightly smaller than those in metamorphic orthopyroxenes with similar iron contents due, in part, to the higher Ca contents of pigeonites. 

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