Measurement errors iron absorption

Effect of Heat Processing on Bioavailability of Added Iron. Several studies in Table III measured directly the effect of heat processing on added iron. These studies compared processed foods to a control group of identical unprocessed food. Studies in Table 111 utilizing unprocessed controls include 15, 19, and 23. Other studies did not employ an unprocessed control, but used a reference dose to enable comparisons from study to study. Reference doses of ferrous sulfate (most animal assays) or ferrous ascorbate (most human tests) were frequently used. Preparation of ferrous ascorbate, usually a 2 1 molar ascorbic acid iron solution, has been detailed by Layrisse et al. (25). These controls enabled measurement of variation in iron absorption from subject to subject, important in view of greater absorption of an iron deficient versus an iron replete subject. When a reference dose was fed as a radiolabeled salt (55Fe), and on alternate times the test diet was fed with a different radiolabel (59Fe), errors due to variation in subject absorption were eliminated, as each subject served as its own control. The different availabilities of various iron sources from baked enriched rolls were established in this manner (17). 

Since the weighing of such small sample quantities can influence the analytical error, it is desirable to avoid the need to weigh the sample. One channel is occupied by the reference absorption measurement, for example with pure iron or low-alloy steels an iron hollow-cathode lamp is used and the measurement takes place at 372 nm. In this case, only one further element can be determined. The carrying out of the method is simple (Fig. 6). Tests of this compact sample technique with standard materials, of which there are at present only a few containing certified trace elements, show satisfactory agreement (Fig. 7). As regards traces, the chips of standard materials are very homogeneous. 

Errors associated with iron quantification and abimdance measurements are common to both fecal monitoring and hemoglobin incorporation methods According to Janghorbani and Young (2 )> acceptable absorption estimates can be obtained if the precision of these measurements is kept below 5% The analytical procedures developed in this study are thus considered satisfactory since the relative standard deviation was 2 48% for total iron quantification and less than 2% for ion abimdance determinations ... 

Silicate is determined spectrophotometrically with ammonium molybdate and ammonium vanadate. The pH of the sample must be adjusted to 7-8. Potassium cyanide is added to prevent interference of heavy metals. Oxalic acid is added to destroy mo-lybdophosphate and vanadophosphate and to bind aluminum in a complex. As in all spectrophotometric determinations, high and variable optical absorption of the sample (due to color or turbidity) at the wavelengths of investigation causes errors tannin, iron, and sulfide also interfere. To avoid contamination, all contact surfaces should be of polyethene. It is also possible to determine silicate using FAAS, in which case nitrous acid and ethyne must be used as flame gases. As silicates are present in colloidal form, the sample must be introduced into the AAS equipment using an ultrasonic nebulizer. Such a nebulizer is also used when silicate is measured by ICP-AES. 

This view is supported by the inconsistency which has been discovered between the abundances of elements determined from photospheric absorption lines and those obtained from the intensity of coronal emission lines (Pottasch (1963, 1964)). As shown in Table 10.3,- discrepancies of at least a factor of ten exist for all of the elements in the iron group. In the case of iron this difficulty has now been resolved. Recent measurements of f-values of iron by the beam-foil technique have shown conclusively that previous f-values for iron obtained by the emission method contained serious systematic errors and there has been a consequent revision of the abundance of iron in the Sun toivards the coronal value. 

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