ESSENTIAL METALLIC ELEMENTS 73 



Sugars are frequently highly contaminated with metallic compounds. 

 Steinberg (1937) has reported a sample of glucose to contain the following 

 elements: lithium, sodium, strontium, calcium, rubidium, potassium, 

 manganese, aluminum, iron, rhodium, nickel, silver, copper, magnesium, 

 tin, boron, and silicon. The metallic contamination of non-ionic com- 

 pounds such as the sugars can be sharply reduced by a variety of mild 

 procedures. Shu and Johnson (1948) give these details for an aluminum 

 hydroxide coprecipitation method: To 140 g. of glucose contained in 500 

 ml. of solution, 1.25 g. of Al2(S04)3'18H20 were added. Dilute ammo- 

 nium hydroxide was added until the pH rose to 9, and the precipitate of 

 A1(0H)3 Avith the adsorbed impurities was filtered off. This treatment 

 was repeated until the desired degree of purification was attained. Non- 

 ionic substances such as glucose and urea may be purified by treatment 

 with cation-exchange materials operating on the hydrogen cycle. Perl- 

 man (1945) used Zeo-karb H (Permutit Corporation) for this purpose. 

 Various ion-exchange materials are used to purify beet juice in the manu- 

 facture of sugar. Mulder (1939-1940) found the combination of ammo- 

 nium sulfide and Norit to be efficient in removing copper from media. 

 The sulfide ion forms insoluble heavy-metal sulfides while the activated 

 carbon serves as a "gatherer." 



Complex-forming reagents such as diphenylthiocarbazone (dithizone) 

 (Stout and Arnon, 1939), and 8-hydroxyquinoline (Waring and Werkman, 

 1943) are useful in removing heavy-metal ions from, or testing the purity 

 of, salts used in preparing media. These reagents and the metal com- 

 plexes they form are removed from solutions by extraction with chloro- 

 form or other organic solvents. The chemistry of complex formation 

 between organic compounds and ions is treated by Yoe and Sarver (1941). 

 Others have merely added such complex-forming reagents to the media, 

 in which the various metallic ions combine with the reagent to form non- 

 available compounds. The specificity of the reagent, concentrations of 

 reagent and the metallic ion or ions, the pH of the medium, as well as the 

 stability of the complex, enter into the success of this type of treatment. 

 Hickey (1945) found that 2,2'-bipyridine inactivated ferrous iron in media 

 treated with this reagent. It is better to remove metallic impurities from 

 the media by extraction than to depend upon complexing compounds to 

 hold these ions in non-ionic combination. 



Certain compounds used in making media such as the amino acids and 

 hydroxy acids form non-ionized complexes with various metallic ions. 

 Media containing these types of compounds are difficult to free from 

 metallic contamination. In addition, some fungi excrete hydroxy acids, 

 such as citric acid, which may modify the availability of the essential 

 micro elements. 



Media may be freed of essential micro elements by a biological process. 



