124 MICROSCOPIC TECHNIQUES 



Methods 

 Phosphorus 



By means of his microscopic photometric technique (page 120) 

 Norberg ( 1942 ) developed a method for the estimation of phos- 

 phorus in quantities down to 0.5 nijug. with an error not greater than 

 about 20% for single analyses. Naturally the error is less with larger 

 samples and greater accuracy is obtained by averaging the results 

 of several determinations. For amounts of phosphorus under 1 m/^g., 

 Deniges' stannous chloride method is recommended, while for 1 m/^g. 

 and more it is preferable to employ Fiske and Subbarow's amino- 

 naphtholsulfonic acid method, which is technically easier. 



Norberg Method for Phosphorus 



SPECIAL REAGENTS 



0.005 N Calcium Acetate. 



1 N Hydrochloric Acid. 



Deniges Reagents, (a) 0.01 M sodium molybdate in 0.6 .V sulfuric 

 acid; (b) 0.2 N stannous chloride in concentrated hydrochloric 

 acid, approximately 2.5% SnC^-HoO. 



Fiske and Subbaroiv Reagents, (a) 0.022 M sodium or ammonium 

 molybdate in 0.75 N sulfuric acid; (6) dissolve 12 g. sodium meta- 

 bisulfite in 80 ml. water, stir in 0.2 g. 1,2,4-aminonaphtholsulfonic 

 acid (some commercial preparations of this compound are not 

 suitable, that of British Drug Houses Ltd. proved to be good) and 

 add 2 ml. 20% crystallized sodium sulfite. Let stand overnight 

 and filter off the undissolved aminonaptholsulfonic acid. Store in 

 a dark bottle. 



PROCEDURE 



1. Obtain the sample on the tip of a quartz needle (page 123). If 

 the sample is liquid, pipette 1 /il. 0.005 N calcium acetate onto the 

 needle tip with the sample and allow to dry in the air. If the sample 

 is solid, the calcium acetate is placed on the tip and allowed to dry 

 before taking on the sample. The excess calcium is required to pre- 

 vent loss of phosphorus during the incineration. 



