Extraction and determination of synthetic food dyes using tetraalkylammonium based liquid-liquid extraction

Tetraalkylammonium based liquid-liquid biphasic systems (employing room-temperature ionic liquids tetraoctylammonium N-lauroylsarcosinate, TOALS, and tetrahexylammonium dihexylsulfosuccinate, THADHSS, as well as tetrahexylammonium bromide, THABr) were used for liquid-liquid extraction of synthetic food dyes followed by spectrophotometric determination. Dyes studied are Allura Red AC, Red 2G, Azorubine, and Fast Green FCF (all anionic). Both extraction to pre-synthesized ILs and to ILs formed in situ was studied. The effects of pH, ionic liquid volume, dye concentration, time of extraction/centrifugation and other factors were investigated and optimum conditions were established. Dispersive liquid-liquid microextraction (DLLME) in situ is based on a metathesis between two salts which are suppliers of cations and anions of IL. It was found that efficiency of in situ DLLME with the studied ILs strongly depends on the ratio between cation and anion suppliers (THABr and NaDHSS/ NaLS, resp.) and drops sharply if an excess of anion supplier is used. Liquid-liquid extraction system using THABr was found to be superior for preconcentration and spectrophotometric determination of Allura Red AC and Azorubine in food samples. Under optimal conditions, recovery of all analytes was nearly 100%. Linear calibration curves in the range of 0.05-4.95 mg L-1 for Allura Red AC and 0.05-2.00 mg L-1 for Azorubine were obtained. Detection limits based on 3Sb were 0.004 and 0.006 mg L-1 for Allura Red and Azorubine, respectively. The proposed method was applied to determination of Allura Red and Azorubine in beverage and Easter egg coloring set.