Determination of total vitamin C in fruit juices and related products by liquid chromatography: interlaboratory study.

A interlaboratory study was conducted to evaluate a liquid chromatographic (LC) procedure for the determination of total vitamin C in foods at levels of 5-60 mg/100 g. Emphasis was placed on fruit juices, although selected foods were also included in the study. Following dissolution of sample in water, endogenous dehydroascorbic acid was converted to ascorbic acid by precolumn reduction with dithiothreitol at neutral pH. Total ascorbate was determined by C18 reversed-phase LC with a phosphate eluent at pH 2.5, incorporating dithiothreitol to maintain vitamin C in the reduced form, and UV detection at 254 nm. Seven types of fruit juices and foods were tested by 19 collaborators in 7 countries. Three duplicate juices and foods met the criteria for Youden pairs and yielded repeatability relative standard deviation of 5.80-14.66%. Reproducibility relative standard deviation ranged from 6.36 to 35.54% (n = 10) with HORRAT values of 0.82-4.04. The LC method is suitable for routine use in fruit products and foods containing > 5 mg/100 g vitamin C and is recommended for further validation by AOAC INTERNATIONAL and International Fruit Juice Union.

Hplc detection of patulin in apple juice with GC/MS confirmation of patulin identity.

The official patulin LC procedure was further examined (AOAC 995.10). Juice or juice concentrate was extracted with ethyl acetate and cleaned up with sodium carbonate. Patulin in the dried extract was determined by reversed-phase LC with UV detection (280 nm) in 1% THF aqueous solution after evaporation of the ethyl acetate. An end-capped C18 column was required to separate patulin from hydroxymethylfurfural. Patulin was detected in approximately half of the >1000 extracts examined. Only ca 10% of the extracts contained patulin at levels greater than 50 microg/L (50 ppb). Some presumptive findings were confirmed by capillary gas chromatography/mass spectrometry as the trimethyl silyl derivative using electron ionization or as underivatized patulin using negative ion chemical ionization. Trifluoropropylmethyl polysiloxane capillary columns provided superior gas chromatography of underivatized patulin compared to phenyl/methyl polysiloxane and methyl polysiloxane columns.