Determination of sulfur dioxide content of grape skin extract and elderberry color by capillary electrophoresis

A rapid and simple method of determination of the sulfur dioxide content from residual sulfite in natural food color such as grape skin extract and elderberry color by capillary electrophoresis (CE) was developed. After distillation for 22 minutes under bubbling nitrogen gas by using a modified Rankine apparatus, the sulfite in samples was converted to sulfur dioxide. The sulfur dioxide was trapped in a 0.6% hydrogen peroxide solution as sulfuric acid. The sulfate ion was determined by CE using a 80.5 cm fused silica capillary column with a buffer for organic acid pH 5.6, with indirect UV detection at 240 nm against the reference at 200 nm. The recoveries of sulfur dioxide 25∼1,000 μg/g added to grape skin extracts and elderberry colors were 86∼104% and the quantitative limit was 15 μg/g. The proposed method was applied to 10 commercial food colors. Sulfur dioxide was detected in 5 grape skin extracts at levels of 38.4∼944 μg/g, but was not detected in 5 elderberry colors. The values determined by CE and colorimetry were in good agreement.