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The aim of this work was to study the optimal conditions for anthocyanin extraction from natural plant materials in order to develop a pH test kit. The plant materials used were butterfly pea flower (BPF), roselle red flower (RRF) and dragon fruit peel (DFP). The solvents used in this study were distilled water, 1% HCl/95% ethanol (HE), 0.1 N acetic acid, 0.5% vinegar and 20% white liquor. A plant materialto- solvent ratio of 5: 50 (w/v) and an extraction time of 2 h were employed. The result shows that BPF could produce the highest average yield of anthocyanins, and that HE was the optimal solvent. Anthocyanins from the BPF+HE extract yielded the best properties for buffers in various pH, produced easily classifiable pH ranges, and were the most suitable to develop a pH test kit. In conclusion, the pH test kit developed by this method can be used for effluent measurement and will provide results similar in term of accuracy to those produced by a commercial pH test kit and a field pH meter.
Key words: Effluent, extraction of anthocyanin, pH test kit, water-soluble colorant.