A Validated Quantification of Sudan Red Dyes in Spicery using TLC and a 16-bit Flatbed Scanner.

Abstract

We present a video-densitometric quantification method for Sudan red dyes in spices and spice mixtures, separated by TLC. Application was done band-wise in small dots using a 5μL glass pipette. For separation, the RP-18 plates (20 × 20cm with fluorescent dye; Merck, Germany, 1.05559) were developed in a vertical developing chamber without vapor saturation from the starting point to a distance of 70mm by using acetonitrile, methanol, and aqueous ammonia solution (25%; 8 + 1.8 + 0.2, v/v) as mobile phase. The quantification is based on direct measurements using an inexpensive 16-bit flatbed scanner for color measurements (in red, green, and blue). Evaluation of only the green channel makes the measurements very specific. For linearization, an extended Kubelka-Munk expression for data transformation was used. The range of linearity covers more than two magnitudes and lies between 20 and 500ng. The extraction from a 2g sample with acetonitrile, evaporation, and reconstitution to 200μL with methanol and the band-wise application (7mm) of a 10μL sample allows a statistically defined LOD of less than 500ppb of Sudan red dyes. To perform the analysis, a separation chamber, RP-18 plates, 5μL glass pipettes, and a 16-bit flatbed scanner for 105 € are needed; therefore, the separation method is inexpensive, fast, and reliable.