IRON 277 



analysis, but Ramsay succeeded in circumventing this difficulty 

 by a selective extraction of the iron. As described, the method may 

 be used for the determination of 10-200 ng. iron. When applied to 

 analysis of 0.2 ml. portions of blood, the coefficient of variation was 

 0.45%. A bother characteristic of the titanometric method is that 

 frequent standardization is required and the titration must be carried 

 out in a manner which will prevent access of oxygen to the solution; 

 furthermore, the standard solution must be protected from oxygen 

 at all times. Ramsay employed a horizontal burette arranged as 

 shown in Figure 93. The standard solution is kept in contact with 

 an atmosphere of hydrogen, and a stream of carbon dioxide bubbles 

 is used for stirring. 



With the development of microcuvettes, the application of the 

 colornnetric methods for iron, e.g., the a,a'-dipyridyl or thiocyanate 

 reactions, to the small quantities considered in histochemical work 

 may be expected to offer more sensitive analyses, and possibly by 

 simpler jiroccdures. 



Kirk and Bentley Method for Iron 



SPECIAL REAGENTS 



5% Sulfuric Acid (iron free). 



3% Cadmium Amalgam.. Dissolve 3 g. pure cadmium in 100 g. 



mercury and store in a well-stoppered, deep, narrow vessel to 



minimize air oxidation. 

 0.01 N Ceric Sidfate. 



0.01 N Ferrous Ammonium Sulfate. Store as indicated on page 275. 

 0.025 M Phenarifhroline Ferrous Sulfate. Dilute ten times before 



using (page 275). 



PROCEDURE 



1. If the sample requires ashing, place in a platinum crucible (8 

 mm. deep, 12 mm. top diameter) and heat for 10 min. just below 

 visible redness. The small muffle furnace described on page 180 is 

 very well suited to tne purpose. Heating at too high a temperature or 

 for too long may cause formation of insoluble ferric oxide. The iron 

 concentration in blood is so high that a five fold dilution is necessary 

 to obtain a convenient sample (3-15 /^g. iron) . Addition of some iron- 

 free sodium hypochlorite soln. to the water used in the dilution 

 serves to dissolve clot fragments and assist in the ashing. Drive off 



