[Determination of eight organic residues in ion exchange resins by headspace gas chromatography]

An analytical method based on headspace gas chromatography was developed for the determination of eight organic residues in ion exchange resins, methyl isopropyl ketone, methyl butyrate, 3-pentanone, 1,3-diethyl benzene, 1,4-diethyl benzene, dichloroethane, 1,3-dichlorobenzene, and methyl methacrylate. The organic residues in different types of resins were studied to provide a basis for the safe use of ion-exchange resins in food and medicine. The main factors (chromatographic column, equilibrium temperature, equilibrium time, flow rate, etc.) that affect the accuracy and sensitivity of the eight organic residues were investigated during instrument analysis. The extraction solvent and chromatographic conditions for the samples were optimized. According to the extraction efficiencies of methyl benzene, methyl alcohol and dimethyl sulfoxide, 2.0 g of the sample was extracted with dimethyl sulfoxide under ultrasonic conditions at 20 ℃. A DB-23 chromatographic column (60 m×0.32 mm×0.25 μm) and hydrogen flame ionization detector (FID) were selected for the GC method, and good separation and quantitative results were obtained for the eight organic residues. The process and conditions are summarized as follows. The equilibration time of the headspace sampler was 30 min, and the equilibrium temperature was 80 ℃. The temperature of the sampler was 240 ℃, while that of the FID detector was 300 ℃, with nitrogen being used as the carrier gas. The programmed temperature of the column was maintained at 60 ℃ for 16 min, then increased to 200 ℃ at a heating rate of 20 ℃/min, and maintained at this level for 2 min. The flow rate was 1.2 mL/min for detection. The external standard method was utilized for quantitative analysis. Good linear relationships were observed for the eight organic residues, and the correlation coefficients (R²) were all above 0.999 in the mass concentration range of 0.02-200 mg/L. The limits of detection (LODs) were 0.0050-0.0375 ng/g. The average recoveries for the eight organic residues were in the range of 82.3% to 109.2% at three spiked levels, and the relative standard deviation (RSD, n=6) was 1.06% to 4.16%. Eleven types of resin samples were detected by this method, and a certain amount of organic compounds were observed in the resin samples. The methyl methacrylate content in the methacrylate resin XAD761 was 414.4 μg/g, while that in the styrene resin LX-69B was as high as 470.8 μg/g. As opposed to traditional analytical methods, the present method has high sensitivity, good accuracy, and precision, with simple operation without derivatization or the need for acid-base treatment of the sample to reduce contamination. This method can be used to simultaneously detect a variety of organic residues in ion-exchange resins, so that the detection efficiency is significantly improved.