PHOSPHATE BUFFERS 



pH 5.8 - 8.0 



An alternate method of preparing phosphate buffers is to weigh out 

 the proper proportion of dibasic and monobasic phosphate salts and dissolve 

 to volume with distilled water. This procedure is of advantage under two 

 circumstances : 



a) When buffers in pyrex distilled water are desired, since this 

 avoids the time-consuming procedure of preparing standard 

 NaOH in pyrex distilled water. 



b) When pure potassium or pure sodium phosphate buffers are 

 desired, without the presence of the other ions. The advan- 

 tage of the solids method is that no new standard solutions need 

 be prepared. 



To make 1 liter of M/15 Phosphate Buffer, weigh accurately the amount 

 of monobasic phosphate (Na or K as desired) and the amount of dibasic phos- 

 phate (Na or K as desired) into a 1 liter volumetric flask, dissolve, and 

 dilute to the mark with distilled water. Since dissolution may be slow, 

 it is best, at first, to add 700 ml. of hot distilled water and shake until 

 dissolved, then cool to room temperature and dilute to volume. 



In each case, use Merck reagent grade salts of the formulas given 

 below. Freshly opened chemicals, kept in the dry room, may be used with- 

 out other drying. 



PHOSPHATE BUFFERS M/15 

 Reference: Recalculated from Sorenson, S.P.L. ; Ergeb. Physiol. 

 22_393 (1912) 

 Monobasic Salts Dibasic Salts 



KH2PO4 NaHgPO^'HjO pH K2HPO4 Na2HP04 



8.327g. 8.442g. 5.8 0.9580g. 0.7809g. 



7.942 8.051 6.0 1.452 1.183 



7.442 7.545 6.2 2.090 1.704 



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