Iron absorption method

Results from some recent studies (19-36) on the effects of fiber are summarized in Table I. For the most part, the results are from multi-day balance studies. However, Turnland et al. (36) used the stable isotope fecal monitoring method to assess zinc utilization and Simpson et al. (24) measured iron absorption from a single test meal. 

We have investigated the picosecond photodissociation of the 2 and CO forms of a number of synthetic and natural heme complexes that differ in the geometry and strain associated with the imidazole-iron (porphyrin) interaction using the standard Nd 61ass laser pump-probe absorption method. Our results indicate that it takes some picoseconds for these complexes to dissociate and further suggest that a pseudo four coordinate complex may be present as a photointermediate in the synthetic compounds with the strained imidazole geometry. 

Atomic absorption analysis made available to the routine laboratory an analytical technique which initially was intended to produce considerable simplification of procedures for the analysis of aqueous, acidic or basic solutions, and thereby contribute to a reduction in costs. Numerous reviews show the worldwide application of this technique [15, 40, 77, 126—129, 137]. Nevertheless, some 10 years passed before atomic absorption became part of the international standardisation of analytical methods. At present, there are many standard methods being developed on the basis of atomic absorption [35, 67], Some, dealing with the determination of metals in lubricating oils, are already in use [35, 66], although the overwhelming majority, for example those dealing with the analysis of iron ores [67], are still being developed. The first indication of standardisation of atomic absorption methods for iron and steel analysis was seen in 1973 [8]. 

The meals were extrinsically labelled by added 65 Zn. The rationale for this method is that a complete isotope exchange takes place between the added radioactive zinc isotope and the zinc present in the meal. Measurements of the uptake of radioactive iron isotopes in blood or in the whole body have been used for many years in studies of iron absorption. (12, 13, 14). The absorption in the present study is determined from measurement of the whole body retention of the radioisotope. However, this can not be done until the non-absorbed fraction of the isotope has left the body. During this periode of time some of the initially absorbed has been extrected. A correction of retention data... 

International Organization for Standardization ISO 8294, Animal and Vegetable Fats and Oils - Determination of Copper, Iron and Nickel Contents - Graphite Furnace Atomic Absorption Method (1994)... 

To determine iron absorption with tracers, a known amount of an iron tracer is given orally either by itself or with a meal. The appearance of the tracer, either in the feces or in whole blood, is monitored. In the fecal monitoring method, the feces are collected quantitatively. The collection period may last from as few as 3 (5) to as long as H days (6). Iron absorption is then estimated from the difference between the total amounts of tracer ingested and excreted. Probably, the most common and serious error in this method is introduced by incomplete fecal collection. 

Variability in Absorption Estimates In this study, the occurrence of a negative absorption value for one subject and the absence of a significant vitamin C effect raise some questions about the accuracy of the method However, the expected changes in absorption due to dietary treatments may be masked by the analytical variations associated with absorption measurements and biological variabilities of iron absorption Analytical variations can be introduced at several stages of the analytical procedures incomplete fecal collection, inhomogeneous samples, iron contamination, incomplete colorimetric reaction, non-quantitative recovery after chemical ashing, and variations in isotopic measurements due to ion statistics, memory effects, instrument drift, etc Some of these are not as serious as others, for example, contamination with natural iron woiold not affect the estimate of tracer concentrations provided it occurs before the total iron content is measured ... 

Precision The precision of the absorption value depends upon tfe precision of P, and E measurements This method for isotopic enrichment measurements by mass spectrometry has a precision of 2% as does the measurement of F by atomic absorption This precision is adequate for absorption and bioavailability studies with zinc and copper (Table I) since zinc and copper absorption are in the range of 30-70% Only fairly large changes in iron absorption can be discerned because non-heme iron absorption is typically less than 10% This may not be a serious problem in bioavailability studies since it is doubtful that very small changes in iron absorption from single foods are biologically significant ... 

Iron deficiency anemia occurs mainly in infants, children, and fertile women. For this reason, a variety of foods, including infant formula and infant cereals, is fortified with iron. Ferrous sulfate is a form of iron that is most readily absorbed by the gut, but when added to dry cereals it can promote their spoilage and rancidity. For this reason, dry cereals are fortified with elemental iron particles, ferric pyrophosphate, or ferrous fumarate (Davidsson et ah, 1997). Ascorbic add may also be added to the cereal to enhance iron absorption. To view some of the numbers, infant cereals may contain 75 mg iron/kg cereal (1.3 mmol iron/kg), 1 mmol phytic acid/kg, and 2.6 mmol ascorbic acid/kg (Davidsson et cd., 1997). Although phytic acid impairs iron absorption, the added ascorbate serves to prevent this effect. An alternate method for preventing phytate from impairing iron absorption is to treat the food with the enzyme phytase. A parent interested in enhancing a child s iron absorption can easily feed a child some orange juice, but it would not be practical to pretreat the child s cereal with phytase. A typical availability of ferrous sulfate in infants is about 3-5% (with no ascorbate), and 6-10% (with ascorbate). Ascorbate is effective when present in a twofold molar excess over the iron. 

The iron released may be measiu ed using a variety of methods based on two main techniques atomic absorption spectrometry (AAS) (flame or furnace) and ultraviolet (UV)-visible spectrophotometry. Flame AAS provides the reference method for determination of plasma iron. Protein precipitation with TCA is followed by centrifugation and measurement of iron in the supernatant by the absorption at 248.3 nm in an air-acetylene flame. While atomic absorption methods are routinely used for urine iron measurements, the need to remove protein and any hemoglobin contamination restricts the use of this technique in routine clinical chemistry for plasma iron. Electrothermal atomization AAS methods are typically used for determination of iron in tissues although inductively coupled plasma (ICP) is becoming more widely available. 

In view of all the complications inherent in these methods, it is not surprising that attempts were made to investigate the mechanism controlling iron absorption using the more reliable method of total body counting. Studies with humans revealed that in addition to iron loading or iron deficiency, the factors... 

Saarinen UM, Siimes MA, Dallman PR (1977) Iron absorption in infants High bioavailability of breast milk iron as indicated by the extrinsic tag method of iron absorption and by the concentration of serimi ferritin. J. Pediatr. 91 ... 

Bjdm-Rasmttssen, E., Hallberg, L., Isaksson, B., and Atvidsson, B. (1974) Food iron absorption in man. Applications of the two-pool extrinsic tag method to measure heme and nonheme iron absorption from the whole diet f Clin. Invest., 53,... 

Dubach, R., Moore, C.V., and Minnich, V. (1946) Studies in iron transportation and metabolism V. Utilization of intravenously injected radioactive iron for hemoglobin synthesis, and an evaluation of the radioactive iron method for studying iron absorption./. Lab. Clin. Med., 31, 1201-1222. 

Iron and molybdenum were determined by standard atomic absorption methods. Pore volume, densities and hardness values were determined by the usual methods used in catalysts characterizatiom Activities and selectivities of the catalysts in the conversion of methanol to formaldehyde were determined in a continuous flow pilot plant described by Karim and Hununadi [8]. Test conditions were reactor temperature 200 to 350°C (473-623 K) pressure, 10 atm (1013 kPa) flow rate, 15.858 cm /s methanol, 5.5% by volume in oxygen. 

Industrial Analysis UV/Vis molecular absorption is used for the analysis of a diverse array of industrial samples, including pharmaceuticals, food, paint, glass, and metals. In many cases the methods are similar to those described in Tables 10.6 and 10.7. For example, the iron content of food can be determined by bringing the iron into solution and analyzing using the o-phenanthroline method listed in Table 10.6. 

In general, siUca has proved to be a good material of constmetion for the burner. Cast iron, steel, or graphite was sometimes used. Gaseous HCl produced by this method is very pure and can be used to manufacture pure hydrochloric acid by the adiabatic absorption process (33) or falling film absorption process (34). 

Iron oxide yellows can also be produced by the direct hydrolysis of various ferric solutions with alkahes such as NaOH, Ca(OH)2, and NH. To make this process economical, ferric solutions are prepared by the oxidation of ferrous salts, eg, ferrous chloride and sulfate, that are available as waste from metallurgical operations. The produced precipitate is washed, separated by sedimentation, and dried at about 120°C. Pigments prepared by this method have lower coverage, and because of their high surface area have a high oil absorption. 

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