Page 231 - Tandem Techniques

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A 100 ml sample of hand squeezed, clarified fruit juice was extracted with two portions of 100 ml of
ether and the extracts discarded. The aqueous phase was then extracted with 4 portions of 100 ml of
ethyl acetate and the combined extracts evaporated to dryness in vacuo at 35-40°C. The residue was
taken up in 10 ml of ethanol, and 5 ml of 5% HCl added to a 3 ml portion of the solution, and the
mixture heated to 100ºC for two hours on an oil bath. The solution was extracted with three 10 ml
portions of ethyl acetate, the extracts were combined, dried over anhydrous sodium sulfate and
evaporated to dryness. The residue was dissolved in 0.2 ml of pyridine, 0.2 ml of hexamethyldisilazane
and 0.1 ml of trimethylchlorosilane added, and the mixture heated overnight at 60°C. The prepared
sample was separated on a Varian 3400 gas chromatograph which was directly interfaced with a
Finnigan MAT ion trap mass spectrometer. The capillary column was 50 m long, 250 µm I.D. and
carried a film of RSL 200 BP 0.2 µm thick. The oven was held at 130°C for 0.5 min, heated to 235 at
30°C/min and from 235 to 290°C at l°/min. The transfer line was maintained at temperature of 280°C
and the ion trap at 150°C. An example of the results obtained are shown in figure 5.30. In the
chromatogram of the standards, each peak represented between 1 and 2 µg/ml of flavanone in the
original juice. It is seen that the components are well separated and the technique is very effective for
assaying flavanones in juices. It is interesting to note that the grape juice gave no indication of the
presence of flavanones which occurred only in the citrus fruit juices.

McCalley and Torres-Grifol [41] investigated a head-space sampling technique for monitoring the
condition of oranges by GC/MS analysis. The aim of the work was to provide a simple and rapid test to
distinguish between good, damaged and diseased fruit. The technique was developed using Navel
oranges of low and medium ripeness and of approximately 200 g in mass. The oranges were placed in a
reaction vessel, 1.25 1 in capacity, which incorporated a GC septum to allow the removal of a sample of
the head space. The samples were taken at room temperature one hour after the fruit had been placed in
the flask. Although trapping techniques would give greater sensitivity, the head space sampling offered
a simpler procedure and a shorter overall analysis time. Retention of solutes on the syringe walls, while
sampling the head space, was reduced