Page 106 - Modern Derivatization Methods for Separation Sciences

Document Página 1 de 2

Page 45

followed by clean-up with an ion-exchange column [262]. A post-column fluorescent derivatization of
octyltin compounds, dodecyltin compounds and dibutyltin (DBT) in peanut oil and diet foods to form
the fluorescent complex (λex420 nm, λem495 nm) with molin reagent (2',3,4',5,7-pentahydroxyflavon)
was reported [263]. DBT and dioctyltin compounds in food containers and packings made of
polyvinylchloride were analysed following purification in the pre-column equipped with column-
switching, followed by post-column derivatization with molin reagent and fluorescent detection [264].

1.2.7.3—
Hydroperoxides

Lipid peroxidation has received much attention because of its toxicity, bitter taste and off-flavors. To
prevent lipid peroxidation of foods, some efforts have been made such as packing, adding antioxidation
reagents, and removing oxygen. Lipid peroxidation in vivo is also speculated to relate to some diseases
or aging. Therefore, it is necessary to measure lipid hydroperoxides.

The most widely used method for the study of lipid peroxidation in biological materials is the
thiobarbituric acid method. The use of the post-column HPLC method with luminol and isoluminol has
been popular [265-267]. Recently, post-column HPLC with diphenyl-1-pyrenylphosphine (DPPP) was
developed for the analysis of lipid peroxides in edible oil [268]. In this method, hydroperoxides in
vegetable oil, butter and margarine are dissolved in chloroform or extracted with chloroformmethanol
(2:1), separated on the reversed-phase HPLC and reacted with DPPP using the postcolumn method.
Hydroperoxides oxidize DPPP quantitatively to a strongly fluorescent oxide (λex352 nm, λem380 nm).
DPPP itself has almost no fluorescence but its oxidized product, DPPP oxide, has strong fluorescence.
DPPP was less reactive to dialkyl peroxides, and not reactive to unoxidized fatty acids, hydroxy acids
and their esters [269]. This method detected 2 pmol triacylglycerol monohydroperoxides.

1.2.7.4—
Isocyanate Monomers

Within the food packaging industry isocyanates are used in polyurethane polymers and adhesives.
During manufacture, residual unpolymerized isocyanate monomer can remain in the polymer and may
migrate into food that subsequently comes into contact with the polymer. Analytical methods for
isocyanate have been mainly employed for the analysis of air, using tryptamine [270] and 9-(N-
methylaminomethyl) anthracene (MAMA) as derivatizing reagents. The use of the precolumn method
with MAMA was reported for the analysis of polyurethane used for food containers and packaging and
isocyanate in laminate samples [271]. This method determines 10 kinds of isocyanate as MAMA
derivatives followed by separation on reversed-phase HPLC and fluorescent detection (λex254 nm,
λem412 nm). The detection limit is 0.03 ppm.

References

[1] Long, A.R., Hsieh, L.C., Malbrough, M.S., Short, C.R. and Barker, S.A. (1990) J. Assoc. Off. Anal.
Chem., 73, 868.

[2] Reimer, G.J. and Suarez, A. (1991) J. Chromotogr., 555, 315.

[3] Reimer, G.J. and Suarez, A. (1992) J. AOAC Int., 75, 979.

http://emedia.netlibrary.com/nlreader/nlreader.dll?bookid=17968&filename=Page_45.html 30/09/2003