Thin layer chromatographic behaviour of dyes during microfluidic transport in functionalised calcium carbonate coatings

The applicability of highly porous functionalised calcium carbonate (FCC) as ab and adsorbent in thin layer chromatography (TLC) is investigated to provide functionality in printed microfluidics. Five different FCCs were prepared to illustrate effects of surface area and charge distribution. In its natural state, FCC displays anionicity within the particle pores and cationicity on the particle extremities (Lamminmäki et al., 2012 ). Two polymeric agents, cationic high molecular weight polyDADMAC and anionic sodium polyacrylate dispersant, were additionally used to control overall surface charge of the FCC particles. A silica gel TLC plate was used as reference. Three colorants, Sudan red, soluble in ethanol, and Gardenia blue and Amaranth red, each soluble in water, were chosen as optically traceable analytes. Ethanol and deionised water were subsequently applied, respectively, as eluents. The choice of the latter two dyes was specifically made to differentiate between an insoluble and soluble analyte in respect to mixture separation in the two wicking solvents. Eluent wicking time was fast within the higher surface area FCC coatings, and relatively low amounts of analyte could be used due to the high
separation resolution capabilities of FCC. Sudan red with ethanol eluent in FCC coatings displayed a higher in-solvent retention factor, Rf, than on the reference TLC plate, indicating that the dye shows no physisorption to FCC. Amaranth red and Gardenia blue remained strongly fixed against ethanol eluent.
With deionised water as eluent, the Sudan red remained fixed due to its insolubility, whereas the Amaranth red and Gardenia blue, being strongly polar, either became progressively adsorbed on FCC, undergoing charge attraction to cationised surface, or became fixed after a short distance, suggesting coagulation and subsequent size exclusion. By converting the surface to anionic charge, the anionic Amaranth red flowed freely with both the ethanol and aqueous solvents. The control properties support future microfluidic applications.