262 IRON 



method (Fe-2, Fe-3). An aliquot of the ash sohition is titrated against 

 methyl red with NH4OH, and this same amount of NH4OH added to 

 another alicjuot (about 0.1 mg iron) to be used for the determination. A 

 pinch of cevitamic acid is added and then 15 ml of a sodium acetate- 

 acetic acid buffer solution (pH 5.4). The a-a-dipyridil reagent is added 

 to produce a color which is evaluated photometrically. 



Methods have been described for estimation of iron in blood plasma or 

 serum without the need of digestion (Fe-4, Fe-5). It is often necessary 

 to electroplate the iron to minimize self-absorption effects, and a satis- 

 factory method has been described as follows (Fe-6) : The samples are 

 placed in a pyrex dish or beaker, and carrier iron as the nitrate is added, 

 if necessary, to give 2 to 4 mg; 1 or 2 ml concentrated HNO3 is added for 

 each 5 g of sample. The sample is evaporated to dryness at 100 to 110°C 

 and placed in a cool muffle furnace, and the temperature raised to 500°C 

 for overnight ashing. If there is any residual carbon, the ash is moistened 

 with concentrated HNO3, dried, and returned to the muffle for about 

 30 min. The ash is dissolved in concentrated HCl, and the free acid 

 removed by evaporation, care being taken not to heat beyond the point 

 of dryness. The chloride residue is dissolved in saturated aqueous ammo- 

 nium oxalate and transferred to the electrolysis cell. If the ash is high in 

 phosphorus and calcium, the chloride residue is dissolved in 8 N HCl and 

 extracted with isopropyl ether, and the iron then extracted from the ether 

 with saturated ac^ueous ammonium oxalate, which is filtered into the elec- 

 trolysis cell. The iron is plated onto a copper disk at a potential of 

 8 volts and a current density of 6 amp/100 cm'^ for about 3.5 hr. The 

 solution can be tested with o-phenanthroline to check the completeness of 

 plating. 



Typical Methods. Ferric citrate or iron ammonium citrate labeled 

 wdth Fe^° was administered to rats in amounts of 0.05 mg Fe and 1 to 

 5 /iC (Fe-7). Because of the high concentration of iron in the blood, it was 

 necessary to viviperfuse the animals to obtain reliable tissue analyses; 

 this was done with a modified Tyrode's solution. Individual tissues were 

 wet-ashed in concentrated HNO3 plus Superoxol, and whole carcasses 

 were dry-ashed. Alicjuots of the ash solution were electroplated onto a 

 metal ointment capsule in a simple apparatus from a citrate solution 

 (Fe-3) for counting with a thin-mica-window tube. 



In another study with rats (Fe-8) the irradiated metal unit containing 

 Pe55,59 ^g^g dissolved in HCl and diluted just before use so that a 0.5-ml 

 dose contained about 2 mg iron and about 1.5 X 10^ counts/min. The 

 animals were dosed orally every other day for 10 days. Each carcass 

 was placed in a 1000-ml beaker, and 100 ml concentrated HNO3 plus 25 

 to 30 ml distilled H2() was added. The beaker was kept at 37°C until 

 the rat had dissolved, the solution then evaporated to about 125 ml and 



