Inventing a method for accurately determining trace scale inhibitor in reverse osmosis (RO) concentrate is of great value for improving RO operation efficiency. In this regard, a module for detecting scale inhibitor polyepoxysuccinic acid (PESA) based on membrane enrichment was designed and a novel polythersulfone (PES) membrane modified by cationic polyacrylamide (CPAM) and pinacyanol chloride (PC) was developed. CPAM adsorption reduced the electronegativity of PES substrate and formed a prefiltering layer, which increased the rejection rate of PESA from 85% to 95%. Meanwhile, PC could complex with PESA to increase the PESA particle size and further improved the detection accuracy. The electrostatic force between the modified layer and PESA revealed that the electronics of CPAM and the complexity of PC can parallel promote the enrichment of PESA. Further, the extensive comparative study between membrane detection and conventional PC detection was performed. The PES-(CPAM/PC) membrane detection showed high sensitivity and the minimum detection concentration was 0.1 mg/L. Compared with PC detection, PES-(CPAM/PC) membrane detection improved durability by 33%. Simultaneously, the change rate of detection results in ionic interference is reduced by 15%. Finally, the practicability of the new module was verified by the PESA concentration detection in four RO concentrate. The enrichment detection method and mechanism provided in this study can provide technical guidance for scale inhibitor monitoring in water treatment.
Lei Wang,Peng Cao,Wei Li,Peijin Tong,Xiaofang Zhang,Yiping Du
Solid Phase Extraction Spectroscopy (SPES) developed in this paper is a technique to measure spectrum directly on the solid phase material where the analytes are concentrated in SPE process. Membrane enrichment and UV–Visible spectroscopy were utilized to fulfill SPES, and multivariate calibration method of partial least squares (PLS) was used to simultaneously detect the concentrations of trace cobalt (II) and zinc (II) in water samples. The proposed method is simple, sensitive and selective. The complexes of analyte ions were collected on the cellulose acetate membranes via membrane filtration after the complexation reaction with 1-2-pyridylazo 2-naphthol (PAN). The spectra of the membranes which contained the complexes of metal ions and PAN were measured directly without eluting. The analytical conditions including pH, reaction time, sample volume, the amount of PAN, and flow rates were optimized. Nonionic surfactant Brij-30 was absorbed on the membranes prior to SPES to modify the membranes for improving the enrichment and spectrum measurement. The interference from other ions to the determination was investigated. Under the optimal condition, the absorbance was linearly related to the concentration at the range of 0.1–3.0 μg/L and 0.1–2.0 μg/L, with the correlation coefficients (R 2 ) of 0.9977 and 0.9951 for Co (II) and Zn (II), respectively. The limits of detection were 0.066 μg/L for cobalt (II) and 0.104 μg/L for zinc (II). PLS regression with leave-one-out cross-validation was utilized to build models to detect cobalt (II) and zinc (II) in drinking water samples simultaneously. The correlation coefficient between ion concentration and spectrum of calibration set and independent prediction set were 1.0000 and 0.9974 for cobalt (II) and 1.0000 and 0.9956 for zinc (II). For cobalt (II) and zinc (II), the errors of the prediction set were in the range 0.0406–0.1353 μg/L and 0.0025–0.1884 μg/L.
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