title: Ultrasensitive, simple and solvent-free micro-assay for determining sulphite preservatives (E220-228) in foods by HS-SDME and UV-vis micro-spectrophotometry.
abstract: A new method based on headspace single-drop microextraction in combination with UV-vis micro-spectrophotometry has been developed for the ultrasensitive determination of banned sulphite preservatives (E220-228) in fruits and vegetables. Sample acidification was used for SO2 generation, which is collected onto a 5,5'-dithiobis-(2-nitrobenzoic acid) microdrop for spectrophotometric measurement. A careful study of this reaction was necessary, including conditions for SO2 generation from different sulphating salts, drop pH, 5,5'-dithiobis-(2-nitrobenzoic acid) concentration and potential interference effects. Variables influencing mass transfer (stirring, sample volume and addition of salt) and microextraction time were also studied. A simple sulphite extraction was carried out, and problems caused by oxidation during the extraction process were addressed. A high enrichment factor (380) allows the determination of low levels of free SO2 in fruits and vegetables (limit of detection 0.06 μg g(-1), limit of quantification 0.2 μg g(-1)) with an adequate precision (repeatability, relative standard deviation 5 %). In addition, the sulphiting process was studied through the monitoring of residual SO2 in a vegetal sample, thus showing the importance of a sensitive tool for SO2 detection at low levels.
authors.affiliation: Departamento de Química Analítica y Alimentaria, Área de Química Analítica, Facultad de Química, Universidad de Vigo, Campus As Lagoas-Marcosende s/n, 36310, Vigo, Spain.
authors.forename: E
authors.initials: E
authors.lastname: Gómez-Otero
authors.forename: M
authors.initials: M
authors.lastname: Costas
authors.forename: I
authors.initials: I
authors.lastname: Lavilla
authors.forename: C
authors.initials: C
authors.lastname: Bendicho
mesh_terms: D053000:Analytic Sample Preparation Methods / Q000379:methods*; D005506:Food Contamination / Q000032:analysis / Q000331:legislation & jurisprudence; D005520:Food Preservatives / Q000032:analysis*; D005638:Fruit / Q000737:chemistry*; D012680:Sensitivity and Specificity; D013053:Spectrophotometry / Q000379:methods*; D013447:Sulfites / Q000032:analysis*; D014675:Vegetables / Q000737:chemistry*; D014920:Wine / Q000032:analysis*
chemical_list: D005520:Food Preservatives; D013447:Sulfites