Study On The Determination Of Ultra-trace Phosphate In Seawater By Microfluidic Chip-based Liquid-liquid Extraction Technique

This paper mainly studied the microfluidic chip based on microfluidic liquid-liquid extraction method for the determination of ultra-trace phosphate in seawater,which lays the technical foundation for real-time monitoring of ultra-trace phosphate.The principle of reaction and detection is phosphomolybdenum blue spectrophotometric method.Through experiments,the reagents preservation method in the phosphomolybdenum blue spectrophotometric method was improved,the microfluidic reaction chip and microfluidic extraction chip were designed and the parameters of the chips were determined.Finally,the feasibility of the method was preliminarily verified through sample detection.The molybdate mixed solution can be preserved in darkness over half a year within 4?~25? ranges.The validity of ascorbic acid solution is shortened as the temperature rises;in per 100 mL of 0.1 g/mL ascorbic acid solution,adding 1 g of EDTA and 2 mL of glacial acetic acid as a complexing agents,removing oxygen by means of high purity nitrogen,followed by filtration sterilization reduces the effect of bacteria,and seal preserved in darkness can prolong the validity of the ascorbic acid solution to over 2.7~5 times within 4?~25? ranges.The main purpose of the microfluidic reaction chip is to generate phosphomolybdenum blue solution through the reaction in the chip,so as to detect the constant phosphate in seawater and provide samples for continuous extraction.The chip material is PDMS with cross injection channel and continuous semicircular reaction channel.The channel width is 250 ?m,the depth is 100 ?m,and the total length is 2000 mm.The outlet of the channel is taken over by the circular liquid storage tank after the reaction.The radius of the liquid storage tank is 2.52 mm and the depth is 2 mm.Flow ratio is sample: molybdate mixed solution: ascorbic acid solution =5:1:1.A stable two-phase liquid-liquid extraction system was formed by thephosphomolybdenum blue solution and the extractant in the microfluidic liquid-liquid extraction chip.The extraction reaction channel is 250 ?m wide,100?m deep and 1000 mm long,with a guide structure of 50 ?m in height.Except the extraction channel,the width of other channels is 125 ?m,the depth is 100 ?m.The peristaltic pump and three-way valve were used to design the cycle extraction process.The chip material was PDMS,the extractant was n-hexanol,the flow rate of the sample and extractant was 100 ?L/min,and the concentration of sample 10 times needed 2.5 minutes.The microfluidic reaction chip and microfluidic liquid-liquid extraction chip were used in series to verify that the microfluidic liquid-liquid extraction method has good reproducibility,high accuracy,good linear relationship,low reagent consumption and short reaction time in the detection of phosphate at ?mol and nmol/L levels.The detection limit of the method was 3.92 nmol/L,which also showed good performance in the actual detection of seawater samples.