Factors affecting solubilities of calcium and phosphate in neonatal total parenteral nutrient (TPN) solutions containing a new amino acid formulation were examined. Twelve TPN solutions containing various concentrations of TrophAmine, an amino acid formulation specific for infants and young children, were prepared in 10% dextrose injection. Some of the solutions also contained cysteine hydrochloride 40 mg/g of protein and either sodium bicarbonate or hydrochloric acid (lipid emulsion buffer) to buffer the solution pH to simulate that produced by simultaneously administering lipid emulsion through the i.v. line. Calcium gluconate and monobasic and dibasic potassium phosphate were added to 20-mL samples of the TPN solutions to achieve calcium concentrations of 10, 20, 30, 40, or 50 meq/L with phosphate concentrations of either 10, 20, 30, or 40 mmol/L; a total of 20 samples of each TPN solution was prepared. Samples were inspected visually for precipitation or crystallization after 18 hours at 25 degrees C and again after 30 minutes in a water bath at 37 degrees C. Clear samples at this time were also examined microscopically for evidence of microcrystallization. Solubility curves were prepared by plotting graphically the concentrations at which either visual or microscopic precipitation occurred. Temperature, amino acid concentration, and the addition of cysteine hydrochloride and lipid emulsion buffer each influenced the solubilities of calcium and phosphate in the TPN solutions. The use of TrophAmine as the amino acid source allowed slightly greater concentrations of phosphate to be solubilized as compared with older amino acid formulations.(ABSTRACT TRUNCATED AT 250 WORDS)