The pigments were extracted from a 2 g sample in
duplicate, to which 0.2 g magnesium carbonate had been
added, with 15 ml extraction solvent methanol:tetrahydrofuran
(1:1, v/v) (Hart and Scott, 1995), containing 0.1%
butyl hydroxytoluene (BHT), by homogenizing for 3 min at
2500 rpm using a Vortex homogenizer. The sample was
centrifuged for 3 min at 3000 rpm and the supernatant was
collected. The pellet was reextracted following the same
procedure until the supernatant was colorless. The
combined supernatants were reduced under a stream of
nitrogen. The residue was dissolved in acetonitrilemethanol-
ethyl acetate (60:20:20, v/v/v). The sample
solution was filtered through a 0.45 mm Nylon membrane
filter (Millipore) and 20 ml were injected into the liquid
chromatograph.
All extraction procedures were performed under subdued
light to avoid degradation loss of the pigments.