The water-soluble fraction of total magnesium in olives
was also determined. A definite amount (4.0 g) of wet olive
sample was weighed, 100 ml of distilled water was added
and the mixture was stirred at 25 ◦C for 24 h. The mixture
was filtered through a filter paper and then through a 0.45 m
polymeric filter and the filtrate diluted. The magnesium content
of the extract was determined by FAAS. Four fractions
were determined in the olive–water extract: particulate magnesium
(the fraction that can pass through the blue ribbon
filter paper and not through the 0.45 m polymeric filter),
polyphenol-bound magnesium, polysaccharide-bound magnesium
and cationic magnesium. Amberlite XAD-4 and
Dowex 50Wx8-40 resins were used for the determination
of polyphenol-bound magnesium and cationic magnesium,
respectively. A known amount (5.0 g) of cation exchange
resin filled a column of 25 cm length and 0.8 cm diameter.
The optimised flow rate of sample through the column was
3mlmin−1. Two grams of Amberlite XAD-4 resin was used
in a polyethylene microcolumn at pH 5.5 (average pH of
the sample). The resin was blocked with In3+ before use to
protect of resin from attack by cations. The sorption resin
was cleaned with pH 5.5 buffer for preconditioning. Firstly,
resorcinol solution was loaded into the column as a model
solution of polyphenols. A decrease of the UV absorbance of
resorcinol at 250–300 nm was observed after passing
through the column. Polysaccharides included in the
olive–water extract were precipitated by adding ethanol.
After centrifugation and decantation, the precipitate was dissolved in 0.2M HCl (including 2500 gml−1) Sr for
AAS determinations
The water-soluble fraction of total magnesium in oliveswas also determined. A definite amount (4.0 g) of wet olivesample was weighed, 100 ml of distilled water was addedand the mixture was stirred at 25 ◦C for 24 h. The mixturewas filtered through a filter paper and then through a 0.45 mpolymeric filter and the filtrate diluted. The magnesium contentof the extract was determined by FAAS. Four fractionswere determined in the olive–water extract: particulate magnesium(the fraction that can pass through the blue ribbonfilter paper and not through the 0.45 m polymeric filter),polyphenol-bound magnesium, polysaccharide-bound magnesiumand cationic magnesium. Amberlite XAD-4 andDowex 50Wx8-40 resins were used for the determinationof polyphenol-bound magnesium and cationic magnesium,respectively. A known amount (5.0 g) of cation exchangeresin filled a column of 25 cm length and 0.8 cm diameter.The optimised flow rate of sample through the column was3mlmin−1. Two grams of Amberlite XAD-4 resin was usedin a polyethylene microcolumn at pH 5.5 (average pH ofthe sample). The resin was blocked with In3+ before use toprotect of resin from attack by cations. The sorption resinwas cleaned with pH 5.5 buffer for preconditioning. Firstly,resorcinol solution was loaded into the column as a modelsolution of polyphenols. A decrease of the UV absorbance ofresorcinol at 250–300 nm was observed after passingthrough the column. Polysaccharides included in theolive–water extract were precipitated by adding ethanol.After centrifugation and decantation, the precipitate was dissolved in 0.2M HCl (including 2500 gml−1) Sr forAAS determinations
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