Particle size stability of intralipid and mixed total parenteral nutrition mixtures.

The determination of the particle size of Intralipid fat emulsions by the non-perturbing method of photon correlation spectroscopy has been extended to include particle size determination using the Coulter counter and optical microscopy. Although little increase in particle size in 3-litre bags containing total parenteral nutrition mixtures was observed with the methods involving large dilutions, creaming was observed and optical microscopy showed aggregation and some coalescence to have taken place. The problem of re-dispersion upon dilution of aggregated (but not coalesced) fat emulsions makes direct optical observation essential in assessing the stability and safety of such fat emulsion mixtures. The effect of electrolytes (NaCl and CaCl2) on creaming, particle size and electrophoretic mobility showed both minimum stability and minimum zeta potential at 3 X 10(-3) mol dm-3 CaCl2 and at 2.5 X 10(-1) mol dm-3 NaCl. Thus, these maximum levels for electrolytes in total parenteral mixtures are indicated.