## 2 Materials and Methods
### TP Experiment by LOC Device and Autoclave  
Before initiating the TP experiment, it was necessary to identify the relationship between the different concentrations of the PO4\({}^{3-}\)solution and their absorbance after staining using standard solutions (potassium phosphate monobasic, KH2 PO4). Thus, pre-prepared PO4\({}^{3-}\) solutions with different concentrations (0.0, 0.1, 0.5, 1, and 2 mg/1000 mL) were mixed with the coloring agent. The mixed liquid initially appear blue, and the color gradually darkened as the PO4\({}^{3-}\) concentration increased. The relationship between the PO4\({}^{3-}\) concentration and absorbance was determined using a UV-vis spectrophotometer to measure the absorbance of the blue mixture.  
The relationship between PO4\({}^{3-}\)concentration and absorbance was determined using a standard solution. Therefore, in the following TP experiment, sodium glycerophosphate (C3H2N2O6P) was selected as the original phosphorus solution. To assess the pretreatment effect of phosphorus-containing compounds under different photocatalytic reaction durations, phosphorus-containing compounds with a concentration of 1 mg/1000 mL were selected as analytes. The concentration of K2S2O8 (oxidizing agent) was 8 g/1000 mL. The prepared phosphorus-containing solution and oxidizing agent were added into a vial in a 1:1 ratio (total volume of 20 mL) and placed into the reaction chamber of the autoclave for 30 min to undergo pretreatment at a high temperature (121 \({}^{\circ}\)C) and high pressure (1.1 kg/cm\({}^{2}\)).  
The other analyte was pretreated using the LOC device with a 2 nm gold film through photocatalysis. The phosphorous solution and oxidizing agent were fed to the microchannel through micropump hoses, and the mixture produced by photocatalytic reaction was collected in a Petri dish at the output. The micropump flow rates were 11.10, 4.995, 3.885, 2.775, 2.220, and 1.665 mL/min, corresponding to photocatalytic reaction durations of 5, 10, 15, 20, 25, and 30 min, respectively. Throughout the experiments, UV light with a wavelength of 365 nm and power of 5 W was irradiated from the back. The inner diameter of the hose connecting the input to the test sample was 0.25 mm.  
According to the results of these photocatalytic degradation experiments with different photocatalytic reaction durations and a comparison with the autoclave results, the LOC device and autoclave yielded similar pretreatment effects when the photocatalytic time was 15 min. To assess the feasibility and accuracy of the experimental results, solutions containing phosphorus compounds with concentrations of 0 mg/1000 mL to 1 mg/1000 mL were photocatalyzed for 15 min, and the absorbance value obtained after dyeing was compared with that obtained by the autoclave.  
The PO4\({}^{3-}\)concentration in the experiment was distinguished using a colorant composed of ammonium molybdate (NH4)6 Mo7O24:4H2O), potassium antimony tartrate (KSbC4H4O7-1/2H2O), ascorbic acid (C6H8O6), and sulfuric acid (H2 SO4). The prepared colorant and the reagent containing PO4\({}^{3-}\) were mixed in a 1:1 (vol.) ratio, and the absorbance of the sample was measured by UV-vis spectrophotometry after standing for 15 min. The observed color depth varied with the PO4\({}^{3-}\) concentration.