There has been a growing requirement among manufacturers of
infant formulations and raw material suppliers to declare levels of
inositol in their products. Although not a vitamin, inositol has
nutritional purpose in infantnutritionandrequires reliable analytical
procedures.Whereas various advanced forms of chromatography are
being developed based upon liquid chromatography, there remains a
place for gas-chromatographic techniques for those laboratories that
have this instrumentation. GLC has several manipulative limitations
because of the need for prior silylation, but it also has a benefit if total
inositol is required. The rigorous sample preparation converts
phosphatidylinositol and inositol phosphates to free inositol, thereby
losing identification of inositol speciation if this were required. The
fact that inositol can survive at high temperature in a strongly acidic
environment allows a reliable determination of its silylated ether,
free from other interferences, by simple GC separations. Figures of
merit for the procedure were sufficiently good to permit the
described method to be used for routine product compliance.
In the case of samples containing plant proteins, such as soybased
infant formulations, there are difficulties with interpretation
of results if phytic acid is totally excluded as a nutritional
source of inositol in humans. At the minimum hydrolysis period of
4 h required for full recovery of inositol-containing phospholipid in
milk-based products, the described GC method, when applied to
soy-based products, includes approximately 20% of the phytic acid
present, which potentially yields a bias compared to alternative
methods where IP6 is excluded. Most manufacturers add enough
free inositol to meet their label expectations thereby alleviating
potential interpretation difficulties from various methodologies.