Stability of ascorbic acid in a standard total parenteral nutrition mixture

We investigated the stability of ascorbic acid (AA) and the sum of AA plus dehydroascorbic acid (TAA) in a total parenteral nutrition (TPN) mixture that contained 1000 ml Vamin 14, 1000 ml glucose 30%, 500 ml Intralipid 20%, potassium phosphate, a multivitamin preparation (Cernevit) and trace elements. We used a spectrophotometer to measure AA and TAA. AA decreased from 42.2 (+/-0.9) mug/ml to 6.8 (+/-0.2) mug/ml in 7 days. Over the same time the concentration of TAA decreased from 42.2 (+/-0.5) mug/ml to 35.9 (+/-0.6) mug/ml, i.e. 63.3 (+/-1.2)% of the original concentration. When the solution was stored in glass bottles and saturated with nitrogen or when trace elements were omitted, the concentration decreased by only 25.2 (+/-0.2)% and 23.8 (+/-1.6)% respectively over 7 days. The influence of oxygen, lipids, trace elements and underfilling the bag was also investigated. We conclude that it is acceptable to prepare these bags in advance and to store them for 7 days at 2-4 degrees C.