Procedure
Proceed as directed for
Procedure under general chapter
345
, and calculate the quantity, in mg, of anhydrous citric acid (C
6H
8O
7) in the volume of Solution taken by the formula:
0.001(192.12/189.10)CS D(rU / rS)
in which 192.12 is the molecular weight of anhydrous citric acid; 189.10 is the molecular weight of citrate (C
6H
5O
7);
CS is the concentration, in µg per mL, of citrate in
Standard Preparation 2; D is the dilution factor; and
rU and
rS are the citrate peak areas obtained from the
Assay preparation for total citrate assay and
Standard Preparation 2, respectively.
Calculate the quantity, in mg, of phosphate, expressed as monobasic sodium phosphate monohydrate (NaH2PO4·H2O), in the volume of Solution taken by the formula:
0.001(137.99/94.97)CS D(rU / rS)
in which 137.99 is the molecular weight of monobasic sodium phosphate monohydrate; 94.97 is the molecular weight of phosphate (PO4); CS is the concentration, in µg per mL, of phosphate in Standard Preparation 2; D is the dilution factor; and rU and rS are the phosphate peak areas obtained from the Assay preparation for total phosphate assay and Standard Preparation 2, respectively.