Microfluidics minimize the amounts of reagents and generate less waste. While microdevices are commonly single-sided, producing a substrate with microchannels on multiple surfaces would increase their usefulness. Herein, a polymethymethacrylate substrate incorporating microchannel structures on two sides was sandwiched between two polydimethylsiloxane sheets to create a multi-analysis device, which was used for the spectrophotometric analysis of the ferrous ion (Fe 2+ ) and the ferric ion (Fe 3+ ), by utilizing colorimetric detection. To monitor the signals from both channel networks, dual optical sensors were integrated into the system. The linear ranges for Fe 2+ and Fe 3+ analyses were 0.1 -20 mg L -1 (R 2 = 0.9988) and 1.0 -40 mg L -1 (R 2 = 0.9974), respectively. The detection limits for Fe 2+ and Fe 3+ were 0.1 and 0.5 mg L -1 , respectively. The percent recoveries of Fe 2+ and Fe 3+ were 93.5 -104.3 with an RSD < 8%. The microdevice demonstrated capabilities for simultaneous analysis, low waste generation (7.2 mL h -1 ), and high sample throughput (180 h -1 ), making it ideal for greener analytical chemistry applications.

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