Standard solutions: Sudan I, Sudan II, Sudan Red B, Sudan Red 7B, Sudan Orange G and 4-dimethylaminoazobenzene were individually (10 mg) dissolved in 5 mL acetone, and Sudan III, Sudan IV, Sudan 7B, Para Red in 15 mL acetone. The solutions were filled up to 20 mL with methanol (stock solutions of 0.5 mg/mL each). The standard mix solution was prepared by mixing 200 µL each of the stock solutions and filling up to 10 mL with methanol (each dye: 10 ng/µL). The same 1:50 dilution was applied for the internal standard solution used for overspraying.

Sample extraction: to 1 g of homogenized spice sample 1 mL internal standard stock solution and 4 mL acetone was added. Sample was vortexed for 1 min followed by the addition of 6 mL methanol, manually shaken for another minute and centrifuged at 4000 rpm. Supernantant was directly used for HPTLC.

Sample application: bandwise with automatic TLC sampler ATS 4 (CAMAG, Switzerland), band length 7 mm, track distance 10 mm, distance from lower plate edge 8 mm, distance from left and right edges min. 15 mm

Applied volume: 1 - 20 µL for standard solutions, overspotted by 10 µL internal standard solution, 2 µL for sample extract

Development: in automatic developing chamber ADC 2 (CAMAG, Switzerland) with eluent iso-hexane - methyl ethyl ketone (5:1, v/v), tank saturation 10 min, migration distance 68 mm, humidity control by saturated potassium carbonate solution (45 % relative air humidity) for 4 min

Documentation: in documentation system DigiStore 2 (CAMAG, Switzerland) under white light illumination