Failure to verify high levels of pyrroloquinoline quinone in eggs and skim milk.

The levels of pyrroloquinoline quinone (PQQ) in eggs, skim milk and milk was re-examined by the use of gas chromatography/mass spectrometry. PQQ was extracted from the samples, after addition of [U-13C]PQQ as internal standard, with n-butanol and Sep-Pak C18 cartridges. After derivatization of PQQ with phenyltrimethylammonium hydroxide, molecular peaks at m/z 448 and 462 were used for detection of PQQ and [U-13C]PQQ, respectively, by selected ion monitoring. PQQ could be detected in eggs, skim milk and milk, but their levels were very low (e.g., egg yolk: 7.0 ng/ml; skim milk: 2.5 ng/g dry weight). Our data for eggs and skim milk are far below those measured by the redox cycling method of Gallop's group.